The first three weeks of May offers an excellent opportunity for observes at Northern Hemisphere and tropical latitudes to spot elusive Mercury. During this apparition the planet is visible just after sunset low down above the west-north-western horizon. Peak altitude occurs on May 7th when greatest eastern elongation is reached. On this day, Mercury will be 21 degrees from our star and visible as a magnitude +0.2 point of light 10 or so degrees above the horizon, 45 minutes after sunset.
Due to the angle of the ecliptic, an apparition of Mercury is often better seen from one particular hemisphere. For this apparition, the Northern Hemisphere wins and this also happens to be the their most favourable evening apparition of the year.
Mercury remains an early evening object for observers located at tropical and Northern Hemisphere latitudes during the first three weeks of May. The planet is located in Taurus and is visible after sunset towards the west-northwest as soon as it's dark enough.
Mercury climbs higher in the sky each evening until it peaks on May 7th, the date of greatest eastern elongation. For example, from 52N (e.g. London, England) the fast moving planet (mag. +0.2) is positioned 11 degrees above the horizon, 45 minutes after sunset. Afterwards its altitude decreases until it's finally lost to the bright twilight sometime during the third week of the month. It should be noted that Mercury is at its brightest before elongation - it fades from magnitude -0.4 to +1.5 during the first half of May. Located a few degrees northeast of Mercury is much more brilliant Venus (mag. -4.3).
The chart below shows positions of Mercury and Venus from latitude 52N (e.g. London, England). The view will be similar from other northern temperate locations.
On May 12th, Mercury (mag. +1.0) passes 8 degrees north of orange giant star Aldebaran (α Tau - mag. +0.9) the brightest star in Taurus. The fast moving planet then reaches a stationary point on May 19th. Retrograde motion follows pulling Mercury back towards the Sun with it arriving at inferior conjunction on May 30th.
From the Southern Hemisphere the planet is not well placed for observation but may be glimpsed extremely low down above the west-northwestern horizon just after sunset at the start of the month.
Venus continues as a blazing evening object as it heads towards greatest eastern elongation of 45 degrees on June 6th. The planet is so bright that it can't be mistaken and can be spotted even before the Sun dips below the horizon. During May it brightens from magnitude -4.2 to -4.4 with its apparent size increasing from 17 to 22 arc seconds. The phase of the planet decreases from 67 to 54 degrees during the same period.
The period of visibility of Venus varies considerably depending on location. From northern temperate latitudes the planet sets almost 3.5 hours after the Sun at the start of the month, increasing to 4 hours by months end. However, much further south the planet can be seen for as little as 2 hours. On May 21st the waxing crescent Moon passes 8 degrees south of Venus and at the end of the month, Venus passes 4 degrees south of the Gemini twins, Castor (α Gem - mag. +1.6) and Pollux (β Gem - mag. +1.1).
Mars has now just a few weeks to go before reaching solar conjunction on June 14th. The "Red planet" spends the first few days of May in Aries before moving into Taurus where it remains for the rest of the month. With an apparent magnitude of only +1.5 it's not bright easily lost to the evening twilight and unlikely to be seen this month.
Jupiter is now 3 months past opposition but despite fading in brightness the planet remains a brilliant object in Cancer. The gas giant is moving direct and positioned 7 degrees southeast of beautiful binocular and small telescope open cluster M44 "The Praesepe".
Jupiter is visible as soon as it's dark enough. At the end of the month, it sets just after midnight from northern temperate latitudes but visibility is somewhat shorter for those living in the tropics and further south. The planets magnitude decreases from -2.1 to -1.9 during May with the apparent size diminishing from 38 to 35 arc seconds over the same time period.
On May 24th, the waxing crescent Moon passes 5 degrees south of Jupiter.
Saturn reaches opposition on May 23rd and is therefore visible all night as it continues its slow retrograde motion, starting the month in Scorpius before moving into faint Libra on May 12th. The favourite planet of many astronomers is now at it's stunning best with the rings wide open at a tilt of 24.4 degrees and an apparent diameter of 18.5 arc seconds. Including the rings it spans some 42 arc seconds across. The current southerly declination of Saturn means it's much better placed for Southern Hemisphere or tropical based observers.
Through telescopes, Saturn's rings are a wonderful sight and visible even in the smallest of instruments along with Titan, the largest and brightest moon of Saturn. Larger telescopes reveal subtle planet details and many of the planets other moons.
At opposition, Saturn shines at magnitude +0.1 and is positioned 8.967 AU or approximately 1341 million kilometres (833.5 million miles) from Earth. The full Moon passes 2 degrees north of Saturn on May 5th.
Uranus at magnitude +5.9 is currently located in Pisces. For the first half of May from northern temperate latitudes the planet is too down low to be seen against the bright morning twilight. However, the situation quickly improves and by months end Uranus rises over 2 hours before the Sun, therefore visible through binoculars and telescopes against the darker backdrop. Observers located further south have it even better with Uranus well placed in the early morning sky throughout the month. At the start of the May, the planet rises 2 hours before the Sun with the visibility period more than doubling by May 31st.
The waning crescent Moon passes 0.2 degrees north of Uranus on May 15th and an occultation is visible from central South America, west and central Africa (11:55 UT).
Neptune is a morning object amongst the faint stars of Aquarius, the Water Bearer or Water Carrier. The planet is better placed from tropical and southern latitudes, rising in the east some four hours before the Sun at the beginning of the month. By months end it can be seen around midnight. From Northern temperate latitudes Neptune is better seen towards the end of the month when it rises 3 hours or so before the Sun.
At magnitude +7.9, the Solar System's most distant planet is never bright enough to be visible to the naked eye but can be spotted with binoculars and small telescopes. Telescopes at medium to high magnifications reveal a featureless small blue disk that spans just 2.3 arc seconds across.
The last quarter Moon passes 4 degrees north of Neptune on May 12th.
The annual Eta Aquariids (or Eta Aquarids) meteor shower peaks on May 6, 2015. Sadly this year's event will be adversely impacted due to the presence of the nearby almost full Moon.
The parent body for the Eta Aquariids shower is Halley's comet (1P/Halley). This isn't the only annual meteor shower associated with the famous comet; the stronger October Orionids also originate from Halley. Although Halley has now left the inner Solar System and won't return until 2061, it's worth remembering that all Eta Aquariids meteors are actually a small part of the famous comet burning up in the Earth's atmosphere!
The radiant of the Eta Aquariids is located in northern part of the zodiac constellation of Aquarius, close to its border with Pegasus and Pisces. The radiant is positioned only 1 degree south of the Celestial Equator and therefore visible from practically all of Earth's surface, exception being the North Pole.
Despite it's global presence the Eta Aquariids meteor shower favours certain locations. The radiant is very well placed from equatorial latitudes, rising in the east after midnight and high in the sky before sunrise. From Southern Hemisphere latitudes it's also well seen but not so good from northern temperate locations. For example, from London, England (51.5N) the radiant rises just before dawn and therefore all but the brightest shooting stars are lost to the morning twilight.
There are at least 6,000 stars in the sky that are bright enough to be visible with the naked eye. Of these we could expect 3,000 or so to be seen at any one time under dark skies (since one half of the Earth is in daylight). However, none can rival the glory of the brightest night-time star of all, Sirius.
Located in the constellation of Canis Major "the Great Dog", Sirius shines with an apparent magnitude of -1.46. It's easily brighter than its nearest rival Canopus (α Car mag. -0.72) and four times more brilliant than Arcturus, the brightest star in the northern section of sky. Sirius is also known as the "Dog Star" and what's immediately noticeable is it twinkles! The star flashes through many colours of the rainbow - especially when close to the horizon - but of course this has nothing to do with Sirius itself; it's a pure white star and the colour variations are solely caused by the Earth's unsteady atmosphere. In practice all stars do twinkle, also to a lesser extent the planets, but the effect is most obvious with Sirius.
To the naked eye Sirius appears as a single star but it's actually a binary system. The primary component is a white main-sequence star of spectral type A1V termed Sirius A. This star - the one we see with the naked eye - has a radius of 1.7 times that of the Sun and is 25 times more luminous than our star. However, the secondary component is much fainter.
In 1844, German astronomer Friedrich Bessel noticed that Sirius "weaved" its way through the sky instead of moving in a straight line. He deduced that there must be an unseen companion at least as massive as the Sun and with an orbital period of 50 years. Bessel worked out where the companion should be but despite extensive observations he couldn't find it.
It was on January 31, 1862 when American telescope-maker and astronomer Alvan Graham Clark finally discovered the companion, now named Sirius B or the "Pup". The reason why it took so long was because it's a white dwarf star, 10,000 dimmer than its neighbour. Clark discovered Sirius B with an 18.5-inch (470 mm) aperture refractor telescope, which happened to be the largest refracting telescope in the World at that time. At magnitude +8.6, Sirius B isn't particularly faint and if located on it's own, it would even be visible with binoculars.
Today, Sirius B can be spotted with a much small sized scope than Clark's. The separation between the two stars varies between 3 and 11.5 arc seconds. It's even possible to glimpse the Pup with a good quality 100mm (4-inch) refractor on nights of excellent seeing when close to maximum separation. When at minimum separation the B star is incredibly difficult to observe.
In 2005, using the Hubble Space Telescope, astronomers determined that Sirius B has a diameter of 12,000 kilometres (7,500 miles) almost equal to that of the Earth and a mass 98% that of the Sun. The star system is close to Earth at 8.6 light-years distant. Perhaps surprising, Sirius is one of the least powerful first magnitude stars, its brilliance is simply due to its proximity.
Naturally Sirius has its place in ancient history. It's name has Greek origins which is unusual as most other named stars are Arabic based. The Greek translation is "sparkling" or "scorching" and along with the Romans they regarded it as an unlucky omen. The Egyptians placed much significance on Sirius. It was worshipped as Sothis or the "Nile Star" and it's first appearance in the dawn sky marked the important annual flooding of the Nile River.
With a declination of 16S, Sirius is visible from almost the entire World. The exceptions are latitudes 74N or greater where the star never rises above the southern horizon. However, from cities just inside the Artic Circle such as Murmansk in Russia, Tromsø in Norway and Barrow in Alaska it can be seen, though admittedly not for very long.
Finding Sirius is easy but in case of uncertainty it's located along an imaginary line extending from the three stars of Orion's belt southwards.
There is an old mystery surrounding the colour of Sirius. It was often described in ancient times as red or orange although today it's clearly pure white. Around AD 150, the great astronomer of his time Ptolemy described Sirius as reddish along with five other stars, Betelgeuse, Antares, Aldebaran, Arcturus and Pollux. Some astronomers agreed with Ptolemy's observations but others noticed only a white star. However, it all seems very strange.
Changes to Sirius A or B over a period of 2,000 years can be rejected as the timescale is too short and there is no sign of nebulosity in the system that would be expected had such a change taken place. Sir John Herschel suggest that a space cloud may have passed between us and Sirius therefore reddening the light as seen from our perspective but this seems unlikely as we would almost certainly be able to still detect such a cloud today. It also seems unlikely that the twinkling of Sirius would have fooled Ptolemy as any red colour is never permanent and the star was relatively high in the sky from his location and above the thicker layers of the atmosphere.
Most likely there was no change in the colour of the star but this remains a curious mystery even today!
Newly found comet MASTER (C/2015 G2) is currently brightening sufficiently that it should reach naked eye brightness from southern and equatorial latitudes soon. When discovered on April 7th by astronomers using the MASTER-SAAO telescope at the South African Astronomical Observatory near Sutherland it shone at magnitude +10.7. The following week it had already brightened to 9th magnitude and is now on course to reach magnitude +5 during the middle of May.
Location and star chart
Comet MASTER spends most of April moving through Aquarius on a south-easterly trajectory. On April 20th it passes 0.5 degrees north of planetary nebula NGC 7293, the Helix Nebula. At magnitude +7.3, the Helix isn't visible to the naked eye but is still the sky's brightest planetary nebula. However, it's a large object with a low surface brightness and therefore not as easy to spot as it's magnitude suggests. For example, the Dumbbell Nebula (M27), a slightly fainter but more compact planetary is much easier to see.
The comet then cuts through a corner of Piscis Austrinus on April 27th when it's located 5 degrees north and slightly east of the constellations stand out star, Fomalhaut (α PsA - mag. +1.2). After spending only a few hours in Piscis Austrinus it then moves into faint Sculptor where it remains for the rest of the month.
At the end of April, MASTER is predicted to have brightened to magnitude +6.8. On May 13th it reaches closest point to Earth at 70 million kilometres or 44 million miles distant. The comet should continue to brighten before peaking at magnitude +4.9 on May 15th. It then reaches perihelion on May 23rd when it's located 115 million kilometres (72 million miles) from the Sun.
From southern and equatorial latitudes, MASTER is currently well placed for observation and is visible towards the east before sunrise during April. From northern temperate locations the comet is not observable until September when it will be extremely faint. Of course, comets are unpredictable and anything could happen, so keep watching!
The finder chart below shows the positions of comet MASTER from April 17 to May 5, 2015.
Arcturus, mag. -0.04, is an orange giant that's usually regarded as the fourth brightest star in the night sky. However, it does have justifiable claims for third position since it's marginally brighter than both main components of the Alpha Centauri system. What's clear is that Arcturus is the brightest star in the northern section of the celestial hemisphere.
Arcturus is the stand out star in the large constellation of Boötes, the Herdsman or Plowman. A vague legend has it that the herdsman was placed in the heavens for successfully inventing the plough. The constellations next brightest star Izar (ε Boo) shines much fainter than Arcturus at magnitude +2.35. As one of the nighttime's brightest stars Arcturus has been significant to observers since antiquity. The star is mentioned in the Bible and was featured on old Chinese star maps, named Dajido. In India it was sometimes referred to as Nishtya or the Outcast, presumably because of its position in the sky far away from the zodiac and Milky Way band.
The name Arcturus derives from Arktouros, which means in ancient Greek the "Bear's Tail" or equally could refer to "the Keeper of the Bear". The name in Greek literature goes back to at least the time of Hesiod, who wrote about the star in his book "Works and Days." Despite Arcturus being a beautiful star it has not always been held in high regard. For example, seamen of ancient times regarded it as an unlucky omen.
More recently, Ptolemy called it "golden red" and curiously in 1852 some well-respected astronomers observed a change in the star's colour before it reverted back to normal a few years later. It's difficult to believe any intrinsic changes to Arcturus had occurred - it's not that type of star - and it's likely that the colour changes were due to atmospheric effects.
Finding the star is easy, just follow the tail of the Plough or Big Dipper asterism of Ursa Major southwards to arrive at the distinct orange hue of Arcturus. Located at a declination of 19N it's visible from every inhabited location on Earth except from Antarctica science stations. It appears highest in the sky from tropical and Northern Hemisphere latitudes during the months of April, May and June.
Arcturus is a giant type K0 III star with a diameter 25 times larger than the Sun. If placed at the centre of the Solar System it would extend more than half the way to the orbit of Mercury. Although large, it's nowhere near as vast as supergiant stars such as Betelgeuse (α Ori) and Antares (α Sco).
Arcturus is relatively close at 37 light-years distant and 170 times more luminous than the Sun. It's 7.1 billion years old and therefore 2.5 billion years older than our star. The star is single and noted for its high proper motion, two arc seconds a year, greater than any first magnitude star other than alpha (α) Centauri. It's currently at about its closest point to the Sun and to date no planets have been identified surrounding it.
In 1933, the light from Arcturus was used to open the "Century of Progress" exposition in Chicago. The star was selected at that time as it was though to be 40 light-years distant and therefore the light arriving had left the star at the time of the previous exposition.
47 Tucanae or 47 Tuc is a spectacular globular cluster located in the southern constellation of Tucana. At magnitude +4.5, it appears to the naked eye as a slightly fuzzy star similar to the head of a tail-less comet. Always hidden from view for European and North American observers, 47 Tuc was discovered by French astronomer Nicolas Louis de Lacaille on September 14, 1751. Initially Lacaille though he had found a comet until further inspection revealed its true nature.
47 Tuc is the second brightest globular in the sky, only Omega Centauri is more brilliant. It has an extremely dense core and is one of the most massive globular clusters surrounding the Milky Way. The cluster is located 2.5 degrees west of the Small Magellanic Cloud (SMC) and from most of the Southern Hemisphere it's circumpolar and never sets. In contrast from latitudes of 18N or greater, the globular can never be seen as it fails to rise above the horizon.
Through 7x50 or 10x50 binoculars, 47 Tuc appears as a bright starlight nucleus surrounding by a halo of soft pearly light. It's clearly non-stellar in nature. Telescopically the cluster is stunning and a showpiece object of the night sky. It total it spans 31 arc minutes of apparent sky, almost exactly the same diameter as the full Moon. For comparison, 47 Tuc is 50% larger and 3x brighter than M13 "the Great Hercules Globular Cluster" widely regarded as the finest globular in the northern section of the sky.
A small 100mm (4-inch) scope reveals a bright compact core surrounded by a large 15 arc minute sphere with the brightest members resolvable. Even through small telescopes it's a superb sight. A 200mm (8-inch) instrument shows a swarm of stars in a glittering 3D view. The dense centre remains unresolvable in stark contrast to the less dense outer regions. Overall it's a breathtaking object for all sizes and types of telescopes.
47 Tuc is located 16,700 light-years from Earth and contains at least 500,000 stars. These include exotic stars with at least 23 blue stragglers and 23 millisecond pulsars known. The globular is estimated to be 13.1 billion years old.
The 2015 annual Lyrids meteor shower peaks on April 22nd and this year's event promises to be a good one as the four-day-old waxing crescent Moon (21% illuminated) will not interfere. The Lyrids are not one of the strongest annual displays and the peak period is short but up to 20 meteors per hours can be seen. This include occasional fireballs that streak through the sky, casting shadows for a short time and leaving a trail of dust and debris as they disintegrate in the Earth's atmosphere.
The Lyrids radiant is located inside Hercules very near to the border with Lyra and only 6 degrees from the fifth brightest star in the sky, Vega (magnitude 0.0). Unlike sporadic meteors that originate from anywhere in the sky, periodic shower meteors can always be traced back to the same region the radiant point of the meteor shower. Therefore, spotting these shooting stars could not be easier…..just focus on the radiant point? The answer is not so simple. The problem is that although the meteors do originate from the radiant point they can streak across almost any part of the sky! Therefore its best to scan a large area surrounding the radiant without directly looking at it.
The shower activity lasts from April 16th to April 26th with the best time to observe around midnight on the evening of April 22nd / 23rd.
Comet Lovejoy continues on its northern path during April as heads towards Polaris and the North Celestial Pole. This superb comet has put on an excellent performance so far. At peak it was far brighter that originally expected and bright enough to be seen with the naked eye. Through binoculars and telescopes it was a stunning sight. The good news is that although Lovejoy has now faded and not as impressive as previous, it remains within the range of binoculars and small scopes.
Location and star chart
Lovejoy spends all of April in Cassiopeia. At the start of the month it's positioned just north of the famous "W" asterism of the constellations brightest stars. It then continues to move northwards through the barren patch of sky towards Cepheus. During this time, there are many nearby fainter stars that can be easily seen in binoculars for star hopping purposes.
Lovejoy is expected to fade from +6.5 to +8.2 during April. It's circumpolar from almost all the Northern Hemisphere but can't be seen from southern temperate latitudes. Comets are unpredictable so keep watching as you never know what might happen!
The finder charts below show the positions of the comet from February 12th to May 3rd, 2015.
Mercury reaches superior conjunction on April 10th and is therefore too close to the Sun to be seen at this time. However it doesn't take long before the fast moving planet reappears in the early evening sky. From northern and equatorial latitudes, it's visible from about April 21st or so, low down above the west-northwestern horizon just after sunset. For northern observers this also happens to be the most favourable evening apparition of the year.
The following day Mercury (mag. -1.4) passes just over a degree north of Mars (mag. +1.4). Binoculars will show both objects in the same field of view with Mercury 15 times the brighter. A 200mm (8-inch) telescope at medium to high magnification should reveal the disks of both planets although they are both small (Mercury 5.7 arc seconds, Mars 3.8 arc seconds). In the same region of sky and positioned a few degrees to the northeast of the pair is much more brilliant Venus (mag. -4.1).
Mercury then continues to climb higher each subsequent evening, although at the same time fading in brightness, until it reaches greatest eastern elongation on May 7th. From the Southern Hemisphere the planet is nowhere near as well placed for observation but may still be glimpsed extremely low down above the west-northwestern horizon just after sunset towards the end of the month.
The chart below shows positions of Mercury and Venus from latitude 52N (e.g. London, England). The view will be similar from other northern temperate locations.
Brilliant Venus, mag. -4.1, continues to dominate the western sky after sunset. The unmistakable planet is visible as soon as dark enough although the period of visibility varies considerably depending on location. From northern temperate latitudes Venus sets almost 3.5 hours after the Sun at the start of the month, increasing to 4 hours by months end. However, much further south the planet can be seen for as little as 2 hours.
On April 11th, Venus passes 2.5 degrees south of beautiful open cluster the Pleiades (M45). This grouping makes a wonderful pairing for binoculars or wide-field telescopes. Later in the month (April 21st) it's located 7.5 degrees north of Aldebaran and another open cluster, the large sprawling Hyades. On the same evening the waxing crescent Moon passes 7 degrees south of Venus.
The long Mars period of visibility finally comes to an end in April. For sometime now the famous Red planet has kept ahead of the Sun in the early evening sky but this month it's eventually lost to the bright twilight. From Northern Hemisphere latitudes the planet can be glimpsed just after sunset towards the west during the first half of April. With an apparent magnitude of +1.4 it's looks like an unremarkable first magnitude "star". On April 22nd, Mercury (mag. -1.4) passes just over a degree north of Mars (mag. +1.4).
From southern latitudes, Mars is to all intent and purpose only visible during the first few evenings of the month.
Jupiter is now two months past opposition and despite fading in brightness it remains a brilliant evening object. As soon as darkness falls, the Solar System's largest and dominant planet is easily recognisable as a bright beacon of light amongst the faint stars of Cancer. From latitudes of Northern Europe and America, the giant planet sets after midnight by months end although the period of visibility is much reduced for those located further south.
Jupiter begins the month moving retrograde until April 8th when it reaches its second and final stationary point for 2015. After this direct motion (eastward) is again resumed with the event widely regarded as signalling the end of the opposition period. To the unaided eye, Jupiter will essentially appear stationary during April. However during the upcoming months direct motion will be obvious as it finally leaves Cancer and marches on towards Leo and Regulus.
On April 1st, Jupiter shines at magnitude -2.3 with an apparent diameter of 41 arc minutes. At the end of April the brightness has decreased to magnitude -2.1 and the apparent diameter to 38 arc minutes.
The waxing gibbous Moon (57% illuminated) passes 6 degrees south of Jupiter on April 26th.
Saturn continues to move slowly retrograde in northern Scorpius. The stunning "Ringed Planet" is located near the stars of the Scorpion "Sting" as it heads towards next month opposition. Saturn rises during the evening and remains visible for the rest of the night although it can be seen for considerably longer from equatorial and Southern Hemisphere latitudes. The planet also appears higher in the sky from such locations.
To the naked eye Saturn appears creamy in colour. It makes a nice contrast compared to the orange/red hue of first magnitude red giant Antares (α Sco mag. +1.0) located 8 degrees to the southeast. Through a telescope the planets rings are a beautiful sight. They are visible with just a small instrument and currently tilted so that they are wide open (tilted at 24 degrees). A medium size telescope of 150mm (6-inch) or 200mm (8-inch) aperture will show a wealth of details including subtle planet formations, divisions in the rings as well as up to half a dozen of Saturn's satellites.
During the month, Saturn brightens slightly from magnitude +0.3 to +0.1 with it apparent size increasing marginally from 17.8 to 18.4 arc seconds. On April 8th, the waning gibbous Moon passes 2 degrees north of Saturn.
Uranus reaches solar conjunction on April 6th and is therefore unsuitably placed for observation throughout April.
Neptune, mag. +8.0, reached solar conjunction at the end of February but remains unsuitably placed for observation from northern temperate latitudes during April. However, it can be seen in the early morning sky towards the east from equatorial and southern regions. By months end it rises up to four hours before the Sun from such locations.
The outermost planet of all is currently located in the faint constellation of Aquarius. Neptune never comes close to naked eye brightness though it can be seen with binoculars or small telescopes. On April 14th, large asteroid Vesta passes 2.7 degrees south of Neptune. Both objects are of the same magnitude and wide field scopes should easily show them in the same field of view.
The following day, the waning crescent Moon passes 3.6 degrees north of Neptune.
Vega is a brilliant magnitude +0.03 blue-tinged white main sequence star located in the constellation Lyra. Its marginally brighter than Capella (α Aur - mag. +0.08) and slightly fainter than Arcturus (α Boo - mag. -0.04) making it the second brightest star in the northern section of the sky. With a declination of 38 degrees north, Vega appears high in the sky and even overhead from northern temperate latitudes. The star is visible at sometime or another from anywhere north of 51 degrees south and therefore can been from the majority of Southern Hemisphere including all of Australia, New Zealand, South Africa and most of Argentina and Chile.
Vega is a dazzling beacon of light amongst the relatively faint but prominent constellation of Lyra. It was originally named Wega from a derivative of the Arabic phrase "Al Nasr al Waqi" or Swooping Eagle. Around 12,000 BC, Vega was the North Pole star and will return there again around 13,700 AD. It's probably unsurprising given its brilliance and prominent northern position that Vega is one of the most investigated of all stars. It was one of the first stars to have its distance determined by parallax and was the first star other than the Sun to be photographed and have its spectrum determined. Vega also makes up the brightest corner of the well-known Summer Triangle, along with Altair (α Aqr - mag. +0.77) and Deneb (α Cyg - mag +1.25). This bright asterism was popularised by American author H.A. Rey and British astronomer Sir Patrick Moore in the 1950s.
Vega is a spectral class A0Va star that's positioned within the main sequence of the Hertzsprung-Russel diagram. It's a nearby star that's only 25 light-years distant and relatively young at 455 million years, equal to about 1/10 the age of the Sun. However, Vega is burning through its hydrogen fuel at a much faster rate than our star and is expected to start becoming an M class red giant in another 500 million years. For comparison, the same scenario will not happen to the Sun for over 5 billion years! Even though it's more than twice as massive as the Sun and over 40 times more luminous, Vega is not massive enough to explode as a supernova and will end its life, just like the Sun, as a white dwarf. Visible in amateur scopes are two faint companions at magnitude +9.5 and +11.0, although both are unrelated and much further away than Vega.
Recent observations suggest that the star is slightly variable and of the Delta Scuti type and if confirmed it would be the brightest example of this type. Surrounding Vega are disks of dust and debris extending for hundreds of astronomical units (AU).
The charts below show the position of Vega. It's best seen during the months of June, July and August.
A total lunar eclipse takes place on April 4, 2015 and is visible from western North America, the Pacific, East Asia, Australia and New Zealand. A lunar eclipse occurs when the Moon passes within Earth's shadow (umbra) resulting in a darkening or reddening of its appearance. The Moon doesn't usually disappear completely due to scattering of sunlight by the Earth's atmosphere.
Eclipses of the Sun and Moon occur in pairs. When a solar eclipse occurs, a lunar eclipse takes place either before or after with this lunar eclipse following last month's solar eclipse. The partial phase begins at 10:15:45 UT with totality reached at 11:57:54. The duration of totality is short on this occasion; it lasts just 4 minutes and 43 seconds. Once totality ends the partial stage again resumes, ending at 13:44:46 UT.
Unlike a total eclipse, which can only be seen from a very narrow band across the Earth, a total lunar eclipse can be seen from any place where the Moon is above the horizon. The charts below show the visibility of the upcoming lunar eclipse.
Betelgeuse is a red supergiant in Orion that's one of the most famous stars in the sky. It's an irregular variable that usually fluctuates between magnitudes +0.3 and +0.8, though on rare occasions its been known to peak at magnitude 0.0 and dim down to magnitude +1.2. The star currently hovers around magnitude +0.42 and marks the upper left-hand corner of the ancient hunter figure.
Although lettered alpha (α) Orionis, Betelgeuse is usually fainter than Rigel (β Orionis - mag. +0.13) and therefore the constellations second brightest star. The first person to record brightness fluctuations was Sir John Herschel in 1836 and on two occasions, in October 1837 and November 1839, he observed it to be brighter than Rigel. At best, Betelgeuse is comparable in brightness to Rigel and Capella (α Aur - mag. +0.08) but at the opposite end of the scale it appears more like Aldebaran (α Tau - mag(v). +0.75->+0.85).
The stars name is Arabic and is derived from "Ibt-al-Jauza", which means "the shoulder of the central one". It's often alternatively written as Betelgeuze or Betelgeux and pronounced in a number of ways; many people refer to it as "Beetlejuice", though "Beteljerze" is closer to the original Arabic. Eminent English 19th century astronomer William Lassell - who discovered Neptune's largest moon Triton, Saturn's moon Hyperion (co-discovered) and Uranus moons Ariel and Umbriel - described Betelgeuse majestically as "A most beautiful and brilliant gem; a rich topaz in hue and brilliancy different from any other star I have ever seen!".
As with all M type stars the surface temperature of Betelgeuse is much cooler than the Sun; about 3,400 K compared to 5,800 K. The star is truly enormous in size with a diameter that could be as large as 1.67 billion kilometers (1.04 billion miles) or about 1200x that of the Sun. If placed at the centre of the Solar System it would easily contain the orbits of Mercury, Venus, Earth and Mars. However, Betelgeuse is much less denser that the Sun and therefore only between 8 to 20 times more massive. It's also likely that the star has used up its supply of hydrogen and is now fusing helium at its core. Eventually, it will explode as a supernova and that will be a spectacular event. The explosion will temporarily shine as bright as a crescent Moon, cast strong shadows on the ground and easily be visible in daylight. It could go bang tomorrow but we may have to wait another million years or so...only time will tell.
Betelgeuse is located 640 light-years distant and is the nearest of the vast red supergiants. As a result, it was the first star to be directly imaged by the Hubble Space Telescope in 1995; angular size is 0.05 arc seconds. The star is about 10,000x more luminous than the Sun. The chart below shows its position in Orion. Since located just north of the celestial equator it can be seen from every permanently inhabited location in the World. The best months are December, January and February. It appears overhead or near overhead from tropical regions.
A new 6th magnitude nova that was discovered in Sagittarius on March 15th by John Seach of New South Wales, Australia brightened quickly to magnitude +4.3 on March 22nd. On this day it could be easily seen with the naked eye and was bright in binoculars. Although now fading, the nova should remain within amateur range for days if not weeks to come. On March 24th, it stood at magnitude +5.5.
Novae are out-bursting stars. They occur when a compact white dwarf star accretes so much material from a close companion that it undergoes a thermonuclear explosion on its surface. This leads to a brief dramatic sudden increase in brightness. They are different to supernovae, where a catastrophic destructive event is caused by the collapse of the core of the star.
The finder chart below shows the position of the nova. It's located in the northern part of the middle section of the famous Sagittarius "teapot" asterism. It has been designated as Nova Sagittarii 2015 No. 2.
The Seated Queen
Cassiopeia is a prominent northern constellation named after Queen Cassiopeia, the wife of King Cepheus of Ethiopia. In Greek mythology the Queen was arrogant and extremely boastful about her beauty. Legend has it she claimed her and daughter Andromeda were more beautiful than all the Nereids, the nymph-daughters of the sea god Nereus. This brought the wrath of the ruling god of the sea Poseidon who decided to destroy the kingdom.
After consulting a wise oracle, the only way the King and Queen could stop Poseidon from carrying out his threat was to scarify Andromeda. The princess was left helplessly chained to a rock at the sea edge awaiting her fate at the hands of Cetus, the sea monster. However, just in time the hero Perseus arrived saved Andromeda and in the process killed the sea monster. Although Andromeda lived to marry Perseus, Poseidon deemed that Cassiopeia should not escape punishment and banished her forever to the sky, tied to the chair of torture!
The constellation is one of the original 48 plotted by second century astronomer Ptolemy and remains as one of the 88 modern constellations. It's one of the most recognisable constellations due to the distinctive "W" shape of its five brightest stars. This asterism forms part of the chair and consists of γ Cas (mag.(v) +1.6 -> +3.0), Schedar (α Cas - mag. +2.24), Caph (β Cas - mag. +2.28), Ruchbah (δ Cas - mag. +2.66) and ε Cas (mag. +3.35). Variable star γ Cas can peak at magnitude +1.6 hence making it easily the brightest member of the group, but currently it hovers around magnitude +2.15.
Since located right bang at the centre of the rich northern Milky Way, Cassiopeia is full of wonderful deep-sky objects. It contains of over a dozen bright open clusters visible in small scopes. In addition, there are also some beautiful double stars and interesting variable stars. At Cassiopeia's southern end are three faint galaxies, two of which are dwarf ellipticals and members of the M31 Group. For larger scopes there are four faint nebulae.
From most northern temperate latitudes Cassiopeia is circumpolar and therefore visible all year round. It appears highest in the sky during October, November and December. From Southern Hemisphere latitudes the constellation appears low above the northern horizon or never even rises at all. Positioned on the opposite side of the North Celestial Pole is another famous constellation, Ursa Major "The Great Bear".
Cassiopeia is bordered by Andromeda to the south, Perseus to the southeast and Cepheus to the north. The famous supernova outburst of 1572, observed by Tycho Brahe, occurred near the star kappa (κ) Cas. The remains of another supernova, which erupted around 1660 but went unseen at the time, forms the brightest extrasolar radio source Cassiopeia A. It lies near open cluster M52.
Bright Star, Variable Star, Double Star
Gamma Cas (γ Cas) - a remarkable blue giant variable star known as a "shell star". Rotating at high speed the star is partly unstable, ejecting rings of material at irregular intervals. This behaviour causes it to vary unpredictably between magnitudes +1.6 and +3.0. It currently shines at magnitude +2.15 and therefore marginally the constellation's brightest star.
Gamma Cas is the middle star of the "W" and is located 613 light years from Earth. Unusual for a bright star it has no traditional Arabic or Latin name. However, in Chinese it has the name Tsih meaning "the whip". It was also given the nickname Navi by American astronaut Gus Grissom who used it for navigational purposes.
The star is a spectroscopic double with an orbital period of about 204 days. It's also a very challenging optical double with a faint 11th magnitude yellow-white (F6) dwarf companion; separation 2.1 arc seconds. Splitting the pair requires decent aperture, steady seeing conditions and quite high magnifications. A minimum 250mm (10-inch) scope is recommended.
Gamma Cas is 70,000 times more luminous than the Sun and is surrounded by two faint reflection nebulae, IC 59 and IC 63.
Bright Star, Double Star
Schedar (alpha Cas - α Cas) - is a magnitude +2.24 orange giant star located 228 light years distant. It has a wide (mag. +8.9) unrelated companion that's visible at low magnifications in small telescopes. The separation is 65 arc seconds. A couple of centuries ago observations thought that Schedar was variable in nature but recent measurements have determined no such variations.
Caph (beta Cas - β Cas) - is the far western star of the "W" asterism. It's a white (F2) Delta Scuti type variable that shines at magnitude +2.28 and almost identical in brightness to Schedar. Although variable the range is very small and changes in brightness can't readily be noticed with the naked eye. At peak brightness Caph reaches magnitude +2.25, at minimum slightly dimmer at magnitude +2.31.The period is only 2.5 hours.
Delta Scuti type variable stars are subgiant or main sequence stars between 1.5 and 2.5 times more massive that the Sun within the spectral class range A0 to F5. They are nearing the end of their hydrogen fusion lifetime and as a result exhibit a slight pulsating effect resulting in a small brightness variation. Of the known Delta Scuti variables, only Altair (α Aqr - mag. +0.77) is brighter than Caph.
Caph is also a spectroscopic binary star with a faint companion. The orbital period is 27 days but little else is known about its companion. The system is located 54 light-years from Earth.
Ruchbah (Delta Cas - δ Cas) - is another slightly variable star in the "W". It's an Algol-type eclipsing binary star that fluctuates between magnitudes +2.68 and +2.74 over a period of 759 days. Ruchbah is located 99 light years distant and telescopically it appears as single blue-white star. It's the second most eastern star of the "W".
Epsilon Cas (Ε Cas) - mag. +3.35, is a blue-white B type giant star located 440 light years from Earth. It forms the eastern star of the "W" and is also the faintest of the five.
Epsilon Cas has the traditional name Segin and is more than 2,500 times more luminous than the Sun.
Multiple Stars, Double Stars
Achird (Eta Cas - η Cas) - is a beautiful double star for small telescopes. It consists of a magnitude +3.4 yellow G2 star similar to the Sun and a fainter orange-red K class dwarf secondary star of magnitude +7.5. They are separated by 13 arc seconds. A small 80mm (3.1-inch) scope at 80x magnification will easily split them. Both stars are classified as an RS Canum Venaticorum variables. They fluctuate very slightly (0.05 magnitudes) due to active chromospheres.
At a distance of 19.4 light years from Earth, Achird is the nearest Cassiopeia star to us.
Iota Cas (ι Cas) - is an impressive triple star located 142 light years from Earth. A 100mm (4-inch) scope at about 120x magnification easily reveals a white primary star of magnitude +4.6 along with a wide fainter red star of magnitude +8.5, separated by 7.3 arc seconds. More difficult but also visible is the closer yellow star of magnitude +6.9 (separation 2.8 arc seconds from the primary).
The triple system may just be a chance alignment. However, the main star is itself a spectroscopic binary.
Psi Cas (ψ Cas) - another multiple star in Cassiopeia. Although not as impressive as iota Cas it's a nice target for medium size scopes. It consists of a magnitude +4.7 orange primary star with a magnitude +9.0 wide companion, which itself is a double. The separation between the primary and faint pair is 20 arc seconds. The faint pair consists of white stars of magnitudes +9.4 and +10.0, separated by 2.9 arc seconds. The primary itself has a very faint close companion (14th mag.) making this a quadruple system. It's 193 light years distant.
Although not visually spectacular, the three brightest members are visible in medium size scopes. A 200mm (8-inch) scope at about 200x should show them all.
Sigma Cas (σ Cas) - is located 1 degree southwest of open cluster NGC 7789. Sigma Cas consists of magnitude +5.0 and +7.1 components separated by 3 arc seconds. It's a challenging double for owners of 80mm (3.1-inch) scopes but relatively easy with a small increase in aperture. With a magnification of about 150x, a 150mm (6-inch) scope will easily split them and on nights of good seeing smaller scopes should also do the job.
Sigma Cas is located 1,500 light years distant.
Rho Cas (ρ Cas) - is a rare yellow hypergiant star and one of the most luminous stars in the galaxy. Rho Cas is half a million times more luminous than the Sun and has a diameter of 630 million kilometers. To give an idea of it's enormous size; if the star were at the centre of our Solar System, it would be larger enough to completely swallow Mercury, Venus, Earth and Mars, and almost reach the orbit of Jupiter!
Rho Cas is classified a semi-regular pulsating variable star with a minimum magnitude of +6.2 and a maximum magnitude of +4.1. The period is approximately 320 days and it can be seen with the naked eye when towards the brighter end of the range. It's located 8,200 light years from Earth.
Open cluster NGC 7789 is positioned 1.5 degrees southeast of rho Cas.
V509 Cas - although only around a dozen yellow hypergiant stars are known in the Milky Way there is another example in Cassiopeia, V509. This star is slightly smaller and less luminous than Rho Cas, but still incredibly powerful and large in its own right. It varies between magnitudes 4.6 and 5.2 over a period of about a year.
R Cas - is a long period variable star of the Mira type that changes between magnitudes +4.7 and +13.5 over a period of 430.5 days. At its brightest it's visible to the naked eye and easily seen with binoculars. The star is positioned at the southwestern part of the constellation and is located 410 light years from Earth.
RZ Cas - is an Algol type variable for binocular and small telescope observers. It varies between magnitude +6.2 and +7.7 over a period of 28.7 hours.
YZ Cas - another Algol type variable for binocular and small telescope observers. The brightness variation (mag. +5.7 -> +6.1) is not as large as RZ Cas and therefore more challenging. It has a period of 4.47 days.
YZ also has a faint magnitude +10.5 wide companion separated by 36 arc seconds.
NGC 457 - at magnitude +6.4, NGC 457 is the brightest open cluster in Cassiopeia and one of the finest examples in the northern sky. Since not a Messier item it's often overlooked and therefore not as well known as other bright clusters. However, it's a stunning object with the main stars arranged in curves resembling an Owl shape, hence the popular name "the Owl Cluster".
NGC 457 is just beyond naked-eye visibility. The brightest star inside is Phi Cas (φ Cas - mag. +5.0), which can be seen with the naked eye but it's not a true member. Together with another 7th magnitude foreground star they form the Owl's bright eyes.
Binoculars easily show the two brightest stars immersed in a cloud of just about resolvable nebulosity. A small 80mm (3.1-inch) scope reveals tens of mainly white stars. The notable exceptions are the brightest two stars, which appear yellow and blue in colour. With medium and larger scopes many dozens of stars spread over 20 arc minutes of apparent sky are visible.
NGC 457 is located 7,900 light-years distant and is estimated to be 21 million years. It's also known as Caldwell 13.
NGC 129 - is a beautiful mag. +6.5 cluster located midway between Caph and gamma (γ) Cas. This sparkling group contains at least 35 stars with the brightest members being of 8th magnitude and visible in binoculars. The cluster is a fine telescope object with many dozens of stars visible arranged in chains across a diameter of 21 arc minutes.
NGC 129 is 9,900 light years distant and estimated to be 76 million years old. It was discovered by William Herschel on December 16, 1788.
NGC 7789 - is a superb open cluster for medium or large size telescopes. It's located 3 degrees southwest of Caph and about halfway between stars rho Cas and sigma Cas.
The cluster is one of the richest clusters in the sky, consisting of at least 300 faint stars spread across 15 arc minutes of sky. At mag. +6.7 it appears as a faint hazy patch of light in binoculars. Telescopically, NGC 7789 is a treat. A 200mm (8-inch) scope shows dozens of faint stars extending into the hundreds with larger instruments. It gives the appearance of a loosely populated globular cluster.
It's located 7,600 light-years distant.
NGC 663 - mag. +7.1, is a prominent open cluster well suited for telescopes. It contains at least 80 stars visible in amateur scopes spread over a diameter of 16 arc minutes with the brightest cluster members visible with binoculars. A 100mm (4-inch) scope reveals a bright rich open cluster with many stars visible, immersed in a hazy glow. The cluster is striking in large scopes where dozens of stars can be seen across the cluster face. It's more concentrated towards the centre.
The cluster is located 3 degrees northeast of Ruchbah and 3 degrees southwest of epsilon (ε) Cas. Next to it are clusters NGC 654 and NGC 659 and M103.
NGC 663 is located 7,000 light years distant. It's also known as Caldwell 10.
IC 1805 - is a large scatted bright mag. +6.5 open cluster located in eastern Cassiopeia. Its positioned 8 degrees east of Ruchbah and about 4 degrees north-northeast of the "Double Cluster" (NGC 869/884) in Perseus. IC 1805 is located just over 1 degree directly west of NGC 1027 with small cluster IC 1848, 2.5 degrees southeast of IC 1805. This part of the sky is an excellent region for scanning with binoculars. Also surrounding the three clusters is a network of faint nebulosity that's difficult to detect visually, even with large amateur scopes.
The cluster contains about 40 stars spread over 22 arc minutes. The brightest members are 8th magnitude. IC 1805 is visible in binoculars. It appears like a detached part of the Milky Way with the brightest stars resolvable. In small and medium scopes it's a nice object that's fully resolvable.
NGC 1027 - another fine binocular and small telescope open cluster is NGC 1027. Located in the same region of sky as IC 1805 and IC 1848, this cluster is similar in size and appearance to IC 1805 only slight fainter at mag. +6.7. It also contains 40 members.
IC 1848 - mag. +6.5 is the last of our eastern Cassiopeia open clusters. Although not as impressive as its two neighbours, it contains only 10 stars and about half the size, the cluster is easily visible with binoculars and small scopes.
M 52 - is located towards the constellations western boundary. This is the brightest of Cassiopeia's two Messier clusters and a fine northern Milky Way cluster. Shining at magnitude +7.2, it's easily visible in binoculars appearing as a somewhat fan or "V" shaped haze with a prominent 8th magnitude yellow star positioned at the southwest corner. Small scopes reveal some fainter stars sprinkled across the diameter of the cluster. In larger scopes, M52 is a wonderful sight with dozens of stars visible.
In total, M52 contains 200 stars spread across 13 arc minutes of sky. It's located between 3,000 and 7,000 light-years distant and estimated to be 35 million years old. The emission nebula NGC 7635 (the Bubble Nebula) is one degree southwest of M52.
NGC 225 - mag. +7.0, is a loose open cluster consisting of 20 stars spread across 12 arc minutes of sky that's visible in binoculars. Telescopes reveal stars of similar brightness without any particularly great concentration.
NGC 225 was nicknamed the "Sailboat Cluster" by Rod Pommier.
M 103 - is a small open cluster positioned 1 degree east of Ruchbah (δ Cas). It contains at least 40 members with a combined magnitude of +7.4. The stars are packed into a small area just 6 arc minutes across, which is equivalent to 1/5th the diameter of the full Moon. M103 is too faint to be seen with the naked eye but easily visible in binoculars, appearing like a faint wedge of light. Through a 100mm (4-inch) scope it's brightest four stars are resolvable and shaped like the Greek letter lambda (λ). With averted vision a nebulous triangular patch of light is revealed that extends beyond the brightest stars.
A 7th magnitude star (Struve 131) is the stand out star in the group but it's not a true member. This is an interloper, a star that's closer to us and just happens to be in the line of sight. Struve 131 is also a multiple star that's easily split in small scopes.
M103 is located 10,000 light years distant. A few degrees east of it are open clusters NGC 654, NGC 659, Trumpler 1 and NGC 663. The latter is occasionally confused with M103.
NGC 659 - half a degree southwest of NGC 663 is magnitude +7.9 cluster NGC 659. This is small and compact with about 40 stars crammed into 5 arc minutes of apparent sky. It appears in binoculars as very small faint patch of light that best seen with averted vision. Also visible in the same binocular field of view are NGC 663, NGC 654, Trumpler 1 and M103.
Through a 200mm (8-inch) scope, NGC 659 appears almost circular with at least 15 stars visible with direct vision and many more with averted vision. It's a wonderful sight.
NGC 654 - is located 0.75 degrees north of open cluster NGC 663. Like NGC 659 this is a small compact cluster with 60 stars across 5 arc minutes. It shines at magnitude +6.5 although often described as looking fainter than NGC 663. The dominant star is a magnitude +7.3 star towards the cluster southeast, which is easily visible with binoculars. At 100x magnification a 150mm (6-inch) scope reveals at least 40 stars configured in streams that look like a "V" shape.
Trumper 1 (Tr 1) - is the first entry in a catalogue of star clusters compiled by America astronomer Robert Trumpler during the 20th century. It's a small cluster of 20 stars spanning 4.5 arc minutes of sky. Trumpler 1 has a combined magnitude of +8.1 with the member stars being of 10th magnitude or fainter. Although faintly visible in binoculars it appears nothing more than a slightly denser clump of the surrounding Milky Way. Telescopes reveal a sprinkling of faint stars.
One of the great natural events takes place on March 20, 2015 when a total solar eclipse is visible from the North Atlantic. This time, the narrow band of totality streaks across a path that starts in the ocean just south of Greenland, touches land in the Faroe Islands and Svalbard before finally ending at the North Pole. A partial eclipse is visible in Europe, North Africa and North and East Asia.
A solar eclipse occurs when the Moon passes between the Earth and the Sun, thereby totally or partially obscuring the Sun's image for an observer on Earth. Total eclipses are only possible due to a piece of nature's luck. By sheer coincidence the Sun is about 400 times larger in size than the Moon but also about 400 times more distance and therefore to the observer on the ground, both the Sun and the Moon present about the same (apparent) size in the sky. The apparent size or diameter of the Sun and the Moon do exhibit small variations; at times the Moon appears slightly larger in the sky than the Sun and vice-versa.
A total solar eclipse occurs when the Moon's apparent diameter is larger than the Sun and blocks all direct sunlight, turning day into darkness. This path of totality occurs inside a narrow band that touches the surface of the Earth. It has a maximum width of only 267 kilometres (167 miles). On the other hand, for a partial solar eclipse the shadow is many thousands of kilometres wide and the partial eclipse is visible over a much larger region.
Eclipse Path on March 20, 2015
The diagrams below shows the visibility of this eclipse and the path of totality (Moons umbral shadow). The only populated places where the totality can be seen and can be reached by public travel are the Faroe Islands and Svalbard. The longest duration of totality is 2 minutes 46 seconds off the coast of the Faroe Islands at 9:46 UT. From the Faroe Islands capital city Torshavn, 2 minutes 2 seconds of totality occurs at 9:42 UT. Totality occurs 30 minutes later at 10:12 UT from Svalbard and lasts for 2 minutes and 25 seconds.
The penumbral shadow of the Moon (partial part of the eclipse) is visible over a much greater region. For example, Scotland and northern parts of England will experience at least a 90% partial eclipse, London an 84% partial eclipse and places in Netherlands, Belgium and northern Germany 80% obscured. From these locations, maximum partial eclipse occurs at about 9:30 UT.
A total lunar eclipse follows on April 4, 2015 and is visible over Australia, and the Pacific coast of Asia and North America.
NGC 2477 is a stunning open cluster located in the Milky Way rich constellation of Puppis. It's arguably the constellations finest cluster which also contains other superb examples such as M46, M47 and M93. At magnitude +5.8, NGC 2477 is faintly visible to the naked eye but easily seen with binoculars and a fantastic telescope object, especially in medium to large scopes.
The cluster was discovered by French astronomer Nicolas Louis de Lacaille during his tour of South Africa in 1751-52. In total it contains about 300 stars packed into an area 27 arc minutes in diameter with the brightest member star shining at magnitude +9.8. The four-magnitude difference between the combined cluster magnitude and the brightest component is an indication of how rich the cluster is.
NGC 2477 is too far south to have been included in Charles Messier's catalogue, but if he had observed from a more southerly latitude than Paris he almost certainly would have noticed this striking object. Twentieth century America astronomer Robert Burnham described NGC 2477 as "probably the finest of the galactic clusters in Puppis".
The cluster is easily found 2 degrees northwest of zeta Pup (ζ Pup - mag. +2.2) and just northwest of magnitude +4.5 star, b Pup. Located 1.5 degrees west of NGC 2477 and in the same binocular field of view lies large loose open cluster NGC 2451. Another binocular open cluster, NGC 2546, is positioned 4 degrees east of NGC 2477. They are best seen from southern latitudes during the months of December, January and February.
Mercury starts March about halfway through an extended morning visibility period for observers at equatorial and southern latitudes. On February 24th, the fast moving planet reached greatest elongation west and was at highest altitude for this apparition. For example, from latitude 35S (approx. equal to Sydney, Cape Town and Santiago) Mercury was easily visible at magnitude 0.0, hovering 16 degrees above the eastern horizon, 45 minutes before sunrise.
During March, its altitude decreases each subsequent morning but the planet remains visible until lost to the bright twilight glare a few days before months end. However, it should be noted that Mercury doesn't reach maximum brightness (mag -0.7) until the very end of the visibility period, more than 4 weeks after greatest elongation west!
On March 6th, Mercury reaches aphelion - the point in its orbit where it's farthest from the Sun - and is located 0.467 AU (approx. 69.9 million kilometres or 43.4 million miles) from our star. Later in the month on March 17th, the planet passes 1.6 degrees south of much fainter Neptune (mag. +8.0). The difference in brightness between the two planets is about 1,500 times. Two days later, the thin waning crescent Moon passes 5 degrees north of Mercury.
Unfortunately, from northern temperate latitudes the angle of the ecliptic is not favourable and the planet always remains very low down and unsuitably placed for observation throughout the month.
Venus, mag. -4.0, is now a brilliant evening object visible towards the west after sunset. From Northern Hemisphere latitudes the planet sets almost 3 hours after the Sun at the start of the month, increasing to nearly 3.5 hours by months end. The visibility period from southern latitudes is not so favourable but Venus can still be seen for about 1.5 hours. Despite this the planet is unmistakable, a dazzling beacon of light illuminated the early evening skies.
The closest planet-planet conjunction of 2015 occurs on March 4th when Venus at 20 UT passes just 0.1 degrees north of much fainter Uranus (mag. +5.9). Use binoculars or a small scope to spot Uranus, which is 10 magnitudes or 10,000 times fainter than Venus. Also visible five degrees southwest of the pair is Mars (mag. +1.3).
Later in the month on March 22nd, the waxing crescent Moon passes 3 degrees south of Venus making a lovely evening pairing.
Mars continues its direct motion spending most of the month in Pisces although it does make a small cut through one corner of Cetus on March 2nd. The "Red planet" exits Pisces on March 30th, moving into neighbouring Aries.
Throughout March, Mars appears as an inconspicuous early evening object visible above the western horizon as soon as it's dark enough. At the start of the month the planet's located 4 degrees southwest of brilliant Venus. By months end Venus has distanced itself to 17 degrees. To the naked eye, Mars (mag. +1.3) resembles a first magnitude star that sets about 2 hours after the Sun from northern temperate latitudes but only 1 hour for those located further south.
On March 11th, Mars passes just 0.3 degrees north of Uranus with at least binoculars required to spot Uranus. Telescopes at medium to high magnifications reveal the disks of the two planets, Mars at 4.1" across appears slightly larger then Uranus (3.4").
On March 21st, the waxing crescent Moon passes 1 degree south of Mars.
While Venus is the brilliant "star" above the western horizon for a short time after sunset the planet that reigns for the rest of the night is Jupiter. The giant planet is now just one month past opposition and a stunning object moving slowly retrograde amongst the faint stars of Cancer. The current declination of Jupiter slightly favours Northern Hemisphere observers, but even from Southern Hemisphere latitudes where the planet appears lower down, it's unmistakable due to its brightness.
Jupiter is visible towards the east as soon as it's dark enough and remains so until the early hours of the morning. It starts March at magnitude -2.5 with an apparent diameter 45 arc seconds. By months end its slightly fainter and smaller at magnitude -2.3 and 42 arc seconds respectively. Even when viewed through a small telescope a wealth of surface details are visible including cloud bands, twists, knots and storms; including the most famous of all "The Great Red Spot". Also easily visible, but not always at the same time are the four bright Galilean moons: Io, Europa, Ganymede and Callisto.
On March 3rd and 30th, the waxing gibbous Moon passes just over 5 degrees south of Jupiter.
Saturn is located in Scorpius and on March 14th reaches the first of its two stationary points for 2015. This date signals the change in the planets motion from direct to retrograde and is also widely regarded as the beginning of this year's opposition period. By the end of March, Saturn rises before midnight for observers at northern temperate latitudes but nearly 3 hours earlier for those located further south.
As the month progresses the planet brightens slowly from magnitude +0.5 to +0.3 with its apparent size marginally increasing from 17 to 18 arc seconds. Saturn is easy to find in the northern section of Milky Way rich Scorpius. The only nearby star of similar brightness is supergiant star Antares (α Sco mag. +1.0). Visually the two cannot be mistaken, slightly brighter Saturn appears white in colour compared to the stark deep red hue of Antares (a few degrees to the southeast).
Of course the rings of Saturn are its most famous feature and even a small telescope will show them. Through medium and large aperture scopes they are a fantastic breathtaking sight. In addition to the rings a handful of Saturn's moons are also visible. The largest and brightest Titan shines at eight magnitude and can be seen with binoculars. In addition, small size scopes will also show other moons including Rhea, Tethys and Dione.
At the beginning of the month a good opportunity exists to spot bizarre moon Iapetus. This world is famous for its "two-tone" colouration with one side being much darker in colour than the other. As a result, Iapetus when positioned on the western side of Saturn (when viewed from Earth) appears brighter than from the opposite side. On March 3rd, Iapetus reaches greatest western elongation and therefore at it's brightest. At magnitude +10.1, it can be seen with a small scope of 80mm (3.1-inch) aperture.
The 65% illuminated waning gibbous Moon passes 2 degrees north of Saturn on March 12th.
The first half of March offers the last opportunity to view Uranus before it's lost to the bright evening twilight sky. The first planet to be discovered in the telescope age is located in Pisces and starts the month setting about 3 hours after the Sun from northern latitudes but much less from further south. Although technically visible to the naked eye at magnitude +5.9, optical aid will be required to spot Uranus as it battles low down against the twilight sky.
An interesting conjunction occurs on March 4th when brilliant Venus (mag. -3.9) passes just 0.1 degrees north of Uranus. Although 10,000x brighter than Uranus it should be possible to spot the distant planet with a binoculars or a small scope. A second close planetary conjunction occurs a week later on March 11th when Mars passes 0.3 degrees north of Uranus.
Neptune reached solar conjunction on February 26th. The planet is currently located in Aquarius and remains unsuitably placed for observation throughout March from northern temperate latitudes. However, during the second part of the month observers located at tropical and southern latitudes should be able to locate the planet low down above the eastern horizon just before sunrise. At magnitude +8.0, optical aid is recommended to glimpse the planet.
On March 17th, Mercury passes 1.6 degrees south of Neptune. At magnitude -0.3, Mercury is easily visible to the naked eye and over 1,500x brighter than much more distant Neptune. The thin waning crescent Moon passes 4 degrees north of Neptune on March 19th.
As it heads towards the outer depths of the Solar System, comet Lovejoy remains visible with small telescopes and even good binoculars during March. Although now fading and past its best the comet has been a delight over recent months and should remain well within amateur astronomer range for some time to come. For a number of days in late December / early January it even was visible to the naked eye (peak mag. +3.9).
Lovejoy was the fifth comet to be discovered by prolific Australian comet hunter and amateur astronomer Terry Lovejoy. He captured it on August 17, 2014 using nothing more than a 200mm (8-inch) scope with a digital camera attached. The subsequent set of time-lapsed images revealed nothing just a faint point of light (mag. +15) that moved slightly from image to image.
Location and star chart
Comet Lovejoy is now very much a Northern Hemisphere object as it continues to move in the direction of the North Celestial Pole. It spends the end of February in Perseus before crossing into Cassiopeia on the last day of the month. Magnitudes of comets are notoriously difficult to predict but we estimate on March 1st it will shine at +6.0 and therefore at the limit of naked eye visibility but easily seen with binoculars and small telescopes. For those located at southern temperate latitudes the comet is too far north to be seen at all.
From latitudes of at least 35 degrees north Lovejoy never sets during March and is visible all night. It's best seen during the middle two "Moonless" weeks of the month. Highlights include on March 10th when the comet passes 1 degree east of the brightest open cluster in Cassiopeia, NGC 457 the Owl Cluster (mag. +6.4). At magnitude +6.5, Lovejoy is fractionally fainter than the splendid open cluster. A few days later on March 16th it passes 0.1 degrees west of Ruchbah (δ Cas - mag +2.7). As the comet is expected to be more than 4 magnitudes fainter than the star it will probably be difficult to spot against the bright stellar glare. However, it should be easier to see over the next few evenings when it passes just west of two more bright open clusters, M103 (mag. +7.4) and NGC 663 (mag. +7.1). At closest separation Lovejoy is 1 degree from M103 and 3 degrees from NGC 663. It should be noted that Messier Catalogue hunters often mistakenly identify NGC 663 as M103!
The finder charts below show the positions of the comet from January 28th to April 1st, 2015.
NGC 2506 is a magnitude +7.6 rich open cluster located in the constellation of Monoceros. Although its member stars are faint the cluster itself appears quite bright and can be seen with a pair of binoculars. Through telescopes it's an impressive object and of all the Monoceros open clusters is probably the finest. With an age of 1.1 billion years old this is an old cluster. For comparison, M45 (The Pleiades) in Taurus is a youthful 115 million years old with the Hyades cluster 625 million years old. However, NGC 2506 is not nearly as old as the 4 billion years of M67 in Cancer.
William Herschel discovered NGC 2506 on February 23, 1791. Locating the cluster can sometimes be a bit tricky as it's positioned in an area of sky devoid of bright stars. It can be found 5 degrees east-southeast of alpha Mon (α Mon - mag. +3.94) the brightest star in Monoceros. Located 19 degrees southwest of NGC 2506 is the brightest star in the sky, Sirius (α CMa - mag. -1.46). Although α Mon and Sirius are the brightest stars in their respective constellations the difference in apparent brightness between them is enormous; more than 100x.
Large open cluster M48 lies 6 degrees northeast of NGC 2506 with open cluster pair M46 and M47 positioned 6 degrees southwest of NGC 2506. They are best seen during the months of December, January and February.