Chi Cygni is a long period variable star that returns to peak brightness during early to middle August 2015. Already the star has reached naked eye brightness; at the beginning of the month it hit magnitude +5.0 and with a more days to go before maximum it's expected to brighten to at least magnitude +4.0.
What makes Chi Cyg fascinating is that it's a Mira type variable with an extremely large brightness range. Mira type stars are pulsating red giants that vary by at least one magnitude over periods ranging from 80 to over 1,000 day's. These stars are coming to the end of their lives and will eventually form a planetary nebula with a white dwarf at the centre. There are at least 6,000 known Mira type stars.
Chi Cyg is the second brightest Mira star (after Mira - omicron Ceti) and has been known to brighten up to magnitude +3.3 and fade down to magnitude +14.2 over a period of 407 days. However every cycle is different. Often the star is visible to the naked eye at brightest but not always. For example, the 2014 maximum was one of the faintest on record at magnitude +6.5. At the opposite end of the scale Chi Cyg can dip down to about as faint as dwarf planet Pluto, hence requiring at least a 250mm (10-inch) scope to be spotted!
The star is located in the Milky Way rich northern constellation of Cygnus. It's positioned just over half way along an imaginary line connecting phi Cyg (φ Cyg - mag. +4.7) to eta Cyg (η Cyg - mag. +3.9). From northern temperate latitudes, Cygnus is almost overhead during the summer months.
It's fascinating to follow a star through such an extreme brightness range, from naked-eye visibility to the edge of binocular visibility in only a matter of a few months. So don't miss Chi Cygni this year!
You can submit your magnitude estimates to both the British Astronomical Association's Variable Star Section or the American Association of Variable Stars.
The Perseids one of the finest annual meteor showers peaks this year on the night of August 12th/13th. On this date up to 100 meteors per hour can be seen under perfect conditions. This years event promises to be a good one as the New Moon won't interfere at all.
Recent analysis by NASA has rated the Perseids as the best meteor shower when it comes to fireballs. The shower is also extremely reliable, it rarely fails to deliver and has been observed for over 2000 years. Of all other annual showers only the December Geminids is comparable.
Discovery and Parent Body
The Perseids meteor shower is associated with comet 109P/Swift–Tuttle or as it's more often known comet Swift-Tuttle; a Halley-type object with an orbital period of 133 years. The Perseid cloud consists of particles ejected by the comet and stretches along the comet's orbit. It's believed that most of today's dust in the cloud is about 1000 years old, although some parts may be considerably younger. When the Earth passes through a replenished area the meteor rate is increased compared to the older part of the stream.
The Perseids were first recorded by Chinese observers in 36 AD with comet Swift-Tuttle independently discovered by Lewis Swift on July 16, 1862 and by Horace Parnell Tuttle on July 19, 1862. Computations of the orbit of the Perseids between 1864 and 1866 by Italian astronomer G. V. Schiaparelli revealed a very strong resemblance to the recently discovered comet and this was the first time a meteor shower had been positively identified with a comet. The years either side of perihelion, usually exhibit higher rates of Persieds meteors, as was the case during the last perihelion in 1992. Swift-Tuttle on this occasion was visible from Earth with binoculars.
This meteor shower gets the name "Perseids" because it's radiant is located in the constellation Perseus. The radiant, the point in the sky where the meteors appear to originate from is positioned at right ascension (RA) 02hr 27m and declination (DEC) +58 degrees. This is close to the border with Cassiopeia and its well-known "W" shape asterism.
The meteors are visible from about July 17th to August 24th with rates starting low, gradually building up to the peak date, before falling off again afterwards. The shower is best seen from the Northern Hemisphere where the radiant appears high towards the northeastern part of the sky.
For those located in the Southern Hemisphere, the Perseid radiant is either very low down or even never climbs above the horizon. This considerably reduces the number of meteors likely to be seen, although it's possible to see a few meteors per hour coming up from the northern horizon.
Mercury reaches greatest eastern elongation on September 4th and apart from the first few days is visible as an "evening star" throughout August from the tropics and Southern Hemisphere. This also happens to be their most favourable evening apparition of 2015, representing the best chance to catch a glimpse of this small world after sunset. Unfortunately, from northern temperate latitudes the angle of the ecliptic is unfavourable and the planet remains low down and unsuitably placed for observation throughout the month.
On August 7th, Mercury (mag. -0.6) passes 0.6 degrees north of more brilliant Jupiter (mag -1.7). Even brighter Venus is in the same part of the sky but about 6 degrees further south. The waxing crescent Moon passes 2 degrees south of Mercury on August 16th.
The diagram below shows the evening apparition of Mercury from latitude 35S (approx. equal to Sydney, Cape Town and Santiago). Positions are displayed 45 minutes after sunset. It should be noted that Mercury fades from magnitude -1.0 to +0.1 during August.
Venus, mag. -4.2, is now lost to the bright evening twilight from northern temperate latitudes although those living further south the planet may be seen for about the first 10 days of the month. The planet appears low down after sunset above the western horizon. Jupiter (mag -1.7) and Mercury (mag. -0.8) are located nearby with Mercury passing 8 degrees north of Venus on August 5th. When viewed through a telescope or binoculars (keen eyed observers), Venus appears as a very thin crescent only a few percent illuminated.
The planet then speeds through inferior conjunction on August 15th. A few days later it re-emerges in the eastern sky just before sunrise for Southern Hemisphere observers and by the last week of the month should also visible from northern temperate latitudes.
On August 29th, Venus (mag. -4.2) passes 9 degrees south of much fainter Mars (mag +1.7).
Mars reappears this month as a morning object in Cancer. Even though it shines at magnitude +1.8 and is brighter than any of the surrounding stars it's not particularly prominent, tending to struggle against the bright dawn twilight sky. The best time to look for the famous "Red planet" is towards the end of the month when it rises two hours before the Sun from northern temperate latitudes but only about half this time from the Southern Hemisphere. On August 29th, much more brilliant Venus (mag. -4.2) passes 9 degrees south of Mars with the second planet from the Sun outshining the fourth by 100 times.
With the Earth now slowly closing in on Mars the planet's visibility period will gradually start to improve over the coming months culminating on May 22nd, 2016 the date of opposition. Mars will then shine at magnitude -2.1 almost 40 times brighter than it appears now! Observers will also be able to study the planets surface, something that's currently not possible due the planets faintness, position in the sky and small apparent size of just 3.7 arc seconds.
On August 20th, Mars passes 0.5 degrees south of the Beehive Cluster (M44) in Cancer.
Jupiter, mag -1.7, long evening apparition finally ends in August. The giant planet has been illuminating the evening skies for months but is now no longer visible from northern temperate latitudes and likely to be glimpsed only for about the first 10 days of the month from tropical and southern latitudes. During this time it can be seen very low down towards the west-northwest horizon shortly after sunset. As previously mentioned, nearby is more brilliant Venus and elusive Mercury passes close by Jupiter on the evening of August 7th.
Jupiter passes through solar conjunction on August 26th and therefore is positioned too close to the Sun to be safely observed for the remainder of the month.
Saturn is located in Libra reaching its second stationary point on August 2nd; thereafter direct motion is once again resumed. This is often regarded as signaling the end of the opposition period. From mid-northern hemisphere latitudes the beautifully "Ringed planet" is visible as soon as it's dark towards the southwest before setting around or just after midnight. Due to its current southerly declination, Saturn appears low above the horizon. However from more southerly latitudes it's much better placed, higher in the sky with a longer period of visibility.
The Solar System's second largest planet fades slightly from magnitude +0.4 to +0.6 with its apparent diameter shrinking from 17.3 to 16.5 arc seconds as the month progresses.
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 August 6th, 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.
On August 22th, the first quarter Moon passes 2 degrees north of Saturn.
Uranus, mag. +5.8, is an evening object moving retrograde amongst the stars of Pisces. At the start of the month, the distant planet rises in the east before midnight and a little earlier each day as the month progresses. It then remains visible for the remainder of the night.
Uranus is positioned 15 degrees south, 20 degrees east of the centre of the "Great Square of Pegasus" and 3 degrees southwest of star ε Psc (mag. +4.3). The planet is bright enough to be easily spotted with binoculars or a small telescope. It's also just visible to the naked eye although this is a challenging task, requiring dark skies.
A small telescope at high magnification will show the planet as a small green disk, obviously non-stellar (apparent diameter 3.6 arc seconds). However, even when viewed through the largest amateur scopes it's difficult to make out any surface details.
On August 5th, the waning gibbous Moon passes 1 degree south of Uranus with an occultation visible from South America and the Falkland Islands (8:44 UT).
Neptune continues to move retrograde amongst the stars of the sprawling constellation of Aquarius. With now only days to go before opposition (Sep. 1st) the distant planet is superbly placed for observation, rising above the eastern horizon not long after sunset and remains visible for the rest of the evening. With a declination of -9 degrees, Neptune is currently better seen from tropical or southern temperate latitudes, appearing high in the sky.
The planet shines at magnitude +7.8. It's the only planet that's never visible to the naked eye and requires optical aid to be seen, although Uranus requires dark skies to be glimpsed. However, provided you know exactly where to look, Neptune is a relatively easy binocular or small telescope target.
Neptune is located almost exactly in the middle of Aquarius and about halfway along an imaginary line connecting lambda (λ) Aqr (mag. +3.7) with Sigma Aqr (σ Aqr - mag. +4.8). Thirty degrees to the northeast is the "Great Square of Pegasus". The brightest star in the surrounding region of sky Fomalhaut (α Psc - mag. +1.2) is located about 20 degrees to the south of the planet.
On August 2nd, the almost full Moon passes 3 degrees north of Neptune mag +7.8 and again on August 30th.
Observers located at equatorial and southern latitudes have the chance to spot a reasonably bright comet after sunset during the second half of July and into August. The comet named PanSTARRS (C/2014 Q1) is now fading but should remain bright enough to be visible with binoculars and small telescopes for sometime to come. Unfortunately, for Northern based observers it's not observable.
Comet PanSTARRS was discovered on August 16, 2014 using the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) located on the island of Maui in Hawaii. At discovery the comet shone at a feeble magnitude +18.4.
The Pan-STARRS project is in its infancy and eventually it's planned to use an array of four 1.8m astronomical telescopes to survey the sky continuously in the hunt for moving objects. Despite funding problems and only one of the four telescopes currently up and running, the project is producing great results and when more of the telescopes come online, a flurry of asteroid and comet discoveries should occur.
Comet PanSTARRS has a highly eccentric orbit and originates from the Oort Cloud. Its orbital period is approximately 40,000 years.
Location and star chart
Having past perihelion on July 6th, PanSTARRS climbed quickly away from the Sun as it moves from Cancer into Leo. It became visible very low down in the evening twilight sky from about July 15th and passes close to brilliant Venus and bright Jupiter during the following week. At magnitude +6, PanSTARRS is much fainter than the two planets but is visible with binoculars and small scopes. On the evening of July 18th the thin crescent Moon forms a lovely evening grouping with Venus, Jupiter and PanSTARRS.
The comet then climbs higher in the evening sky but at the same time fading as it travels on a southerly path into Sextans. It then briefly cuts a corner of Hydra before entering Crater, back into Hydra and finally to Centaurus where it remains until October.
The finder charts below show the positions of the comet from July 18th to August 8th, 2015.
The Delta Aquarids or Delta Aquariids is an annual meteor shower that takes place every year in July and August. It consists of two branches, the Northern Delta Aquariids and the Southern Delta Aquariids. Of these the Southern Delta Aquariids is the stronger brighter stream with this year's event taking place from July 12th to August 23th. Peak activity occurs on the night of July 28th / 29th where normally up to 16 meteors per hour are expected (Zenithal Hourly Rate). Unfortunately, this year the 91% illuminated waxing Gibbous Moon will significantly interfere. The shower is best seen from the tropics and Southern Hemisphere where the radiant appears higher in the sky compared to northern temperate latitudes.
The Northern stream is feeble in comparison with a maximum ZHR of 4 and peaks around August 7th.
Discovery and Parent Body
Lieutenant Colonel G. L. Tupman, a member of the Italian Meteoric Association made the first detailed recordings of Delta Aquariids meteors between July 27th and August 6th, 1870. The streams were then unidentified, but by plotting data from 65 meteors, he was to a reasonable degree of accuracy able to determine the general area of the radiant.
Between 1926 and 1933, New Zealander Ronald McIntosh improved the position of the radiant based on a greater number of observations. A few years later in 1938, Cuno Hoffmeister founder of Sonneberg Observatory, along with his German colleagues were able to first record the northern part of the stream. It was astronomer Mary Almond, in 1952, who finally confirmed the presence of the two separate radiants.
The parent body of the Southern Delta Aquariids is uncertain. However, comet 96P/Machholz or comet Machholz as it's often referred to is a possible candidate. This Jupiter family comet was discovered in 1986 by amateur astronomer Donald Machholz using just a pair of 130mm binoculars. It has an orbital period of 5.2 years.
The shower radiants are located in the faint zodiac constellation of Aquarius, which is positioned about 30 degrees to the south and southwest of the "Square of Pegasus". The southern radiant is just over 3 degrees west of star Skat (δ Aqr - mag. 3.3), with the northern radiant a further 14 degrees to the north. The brightest star in the surrounding sky is first magnitude Fomalhaut (α PsA - mag. 1.2) in the constellation Piscis Austrinus. Fomalhaut is positioned about 14 degrees south-southeast of the southern radiant.
Mercury remains a morning object for observers in the tropics and Southern Hemisphere for about the first 10 days of July. The nearest planet to the Sun may be spotted about 45 minutes before sunrise in the twilight sky low down above the east-northeastern horizon; brightening from magnitude -0.1 to -0.9 during this time period. Mercury is then unobservable for the remainder of the month as it moves closer ever in the sky to the Sun. The planet reaches superior conjunction on July 23rd.
From northern temperate latitudes Mercury is unobservable during July.
The diagram below shows the June / July morning apparition of Mercury from a latitude of 35S (approx. equal to Sydney, Cape Town and Santiago). Positions of the planet are displayed 45 minutes before sunrise.
Venus continues its run as brilliant evening star this month although from mid-northern temperate locations the observation period shortens noticeably and from about the middle of the month the brightest planet will be lost to the sunset. From more southerly latitudes Venus remains visible throughout July.
On July 10th, Venus attains its greatest brilliance when it peaks at magnitude -4.7. Before this on July 1st it passes only 0.4 degrees south of Jupiter (mag. -1.8) with Venus 15 times the brighter of the pair. Another conjunction occurs on July 19th when the waxing crescent Moon passes 0.4 degrees south of Venus with an occultation visible from northeastern Australia and the French Polynesia (1:07 UT).
On July 23rd, Venus reaches a stationary point in Leo, afterwards retrograde motion commencing. It then draws back towards the Sun with the planet once again passing south of Jupiter on July 31st although this time the separation is more than 6 degrees. Of course the events described during the second half of July are only visible from more southerly climes.
During the month the Venus phase decreases from 33% to a very slim 8% crescent.
Earth is at aphelion - furthest from the Sun - on July 6th at a distance of 1.017 AU (152 million kilometers or 94.5 million miles).
Mars reached solar conjunction on June 14th. The Red planet is currently located on the far side of the Sun and remains unsuitable placed for observation throughout July.
Jupiter, mag. -1.8, continues to be visible as an early evening object during July although observers at northern temperate latitudes are likely to lose the planet to the bright long evening twilight during the third week of the month. The largest planet of the Solar System can be seen low down towards the western horizon as soon as it dark enough.
Now moving direct in Leo, Jupiter's long evening period of visibility is almost over as it heads towards next month's solar conjunction. As previously mentioned, much more brilliant Venus will pass less than half a degree south of Jupiter on July 1st. For those located at tropical and southern latitudes another Venus - Jupiter conjunction occurs on July 31st. On this occasion Venus passes 6 degrees south of Jupiter.
The thin waxing crescent Moon passes 4 degrees south of Jupiter on July 18th.
Only two months passed opposition, Saturn remains an evening object during July. The beautiful planet famous for it's wonderful ring system continues to move slowly retrograde amongst the faint stars of Libra. It appears to the naked eye as off-white or creamy "star" located 10 degrees northwest of orange/red first magnitude red giant Antares (α Sco mag. +1.0).
Saturn is visible as soon as it's dark enough towards the south-southeast from northern temperate latitudes or towards the northeast from south latitudes. It sets just after midnight at months end from northern latitudes although two hours later for those further south.
The planet fades slightly from magnitude +0.2 to +0.4 with its apparent diameter shrinking from 18.1 to 17.3 arc seconds as the month progress.
On July 26th, the waxing crescent Moon passes 2 degrees north of Saturn.
Uranus is now well placed for observation amongst the stars of Pisces. At magnitude +5.8 Uranus is actually visible to the naked eye, albeit faintly. To achieve this goal a dark moonless site is required along with good seeing conditions and a good star chart to pinpoint the exact location.
At the start of July from northern temperate locations, Uranus rises 4 hours before sunrise and by months end is visible from about midnight. The visibility period from locations further south is even better with Uranus visible in the evening sky by months end.
On July 9th the last quarter Moon passes 0.8 degrees south of Uranus with an occultation visible from Western Australia and the Southern Indian Ocean at 2:47 UT. Two weeks later on July 26th, Uranus reaches its first stationary point signaling the beginning of this year's opposition period. The planet then commences retrograde motion.
Neptune (mag. +7.8) is moving retrograde in Aquarius as it heads towards opposition on September 1st. The eighth and most distant planet from the Sun is positioned about 30 degrees southwest of the Great Square of Pegasus and a few degrees southwest of star lambda (λ) Aqr (mag. +3.7). It now rises before midnight from northern temperate latitudes and up to a couple of hours earlier from locations further south.
Although observers may be able to spot Uranus with the naked eye they have no chance do the same with Neptune, it's far too faint. However, the planet is relatively easy to spot binoculars.
On July 6th, the waning gibbous Moon passes 3 degrees north of Neptune.
Capella is the sixth brightest star in the night sky and the third brightest in the northern celestial hemisphere. It's also the northernmost first magnitude star with a declination of nearly +46 degrees and therefore circumpolar (never sets) from many northern temperate locations. However, despite this it's visible at one time or another from almost all inhabited countries including all of Australia, almost all of New Zealand and Argentina. It's not visible from Antarctica and the Falkland Islands.
Capella has an apparent magnitude of +0.08, which mean it's marginal fainter than Vega. To the naked eye the brightness difference is difficult to notice but what's obvious is the colour contrast, deep yellow tinged Capella against stark blue-white Vega. Capella is the standout bright member of the relatively large constellation of Auriga, the Charioteer. The Milky Way passes through the heart of Auriga and therefore it contains numerous bright open clusters, nebulae and interesting stars.
The name Capella is Latin and means "small female goat". The star marks the left shoulder of the Charioteer or according to Ptolemy's 2nd century Almagest, the goat that the charioteer is carrying. The three faint stars that form a triangle close beside it are the Haedi, or the "Kids". In Greek Mythology, Capella represented the goat Amalthea whose horn was accidentally broken off by Zeus. The horn was transformed into the Cornucopia or the "horn of plenty", which would be filled with whatever its owner desired. To the Chinese it was one of the stars making up Woo Chay, the Five Chariots (the others Beta, Theta, Kappa and Gamma Aurigae). To the Arabs it was known as Al Rakib, the Driver as it was often visible in the early evening sky before other stars came into view.
Some ancient astronomers including Ptolemy referred to Capella as reddish but this has to due to atmospheric affects, there isn't the slightest chance the star has changed colour in the past 2000 years. In 1899, William W. Campbell of the Lick Observatory, Mount Hamilton, California and Hugh Newall at Cambridge in England measured the spectrum of Capella and found that the star was not a single star but a binary. The components are so close together they are incredibly difficult to separate visually.
Both components are similar. The brighter Aa yellow star is a type G1 with a diameter of 17 million kilometers (10.6 million miles) or 12 times that of the Sun. The Ab star has a spectral type K0 and therefore orange with a diameter of 12.5 million kilometers (7.8 million miles). This is equivalent to 9 times the size of the Sun. They have masses of 2.7 and 2.6 times and are 90 and 70 more times luminous than our star respectively.
Once it was realized Capella was a binary system immediate efforts were made to visually resolve the components. A partial success was achieved in 1901, when astronomers at Greenwich noted the star as "elongated" when using the 28-inch refractor. Confirmation was achieved in 1919 by John Anderson and Francis Pease using the 100-inch Hooker telescope at Mount Wilson, Los Angeles. However, the star remains as a single point of light in amateur scopes.
Astronomers recently discovered that the Capella system contains a second pair of red dwarfs stars. They are designated Capella H and Capella L and are located around 10,000 astronomical units from the main Aa / Ab pair.
The Capella star system is currently located 42.8 light-years distant from Earth. For 50,000 years from 210,000 BC to 160,000 BC, Capella was the brightest star in the night sky. At best it shone at magnitude -0.82 and was 27.9 light-years distant.
NGC 2360 is an open cluster visible with binoculars in the constellation of Canis Major. It was the first deep sky discovery made by Caroline Herschel - the younger sister of William Herschel - on February 26, 1783. She described it as "a beautiful cluster of pretty compressed stars near 1/2 degree in diameter." It's also known as Caroline's Cluster, Caldwell 58 and Melotte 64.
William included the cluster in his 1786 catalogue of 1000 clusters, crediting his sister as the discoverer. At magnitude +7.2, NGC 2360 is not visible to the naked eye but it's an easy binocular object and a fine sight through small telescopes. The cluster is positioned 8 degrees east-northeast of the brightest star in the night sky Sirius (α CMa - mag. -1.47) and lies 3.5 degrees directly east of gamma CMa (γ CMa - mag. +4.1). At the western edge of NGC 2360 is an unrelated star, HD 56405 (mag. +5.5).
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 it's 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.
Lynx is home to the fascinating globular cluster NGC 2419. Although visually faint and small what makes NGC 2419 special is its distance; at 275,000 light-years it's one of the furthest known Milky Way globulars. In fact, twentieth century American astronomer Harlow Shapley nicknamed it "The Intergalactic Tramp" believing it to have possibly broken away from the Milky Way and headed off into deep inter galactic space. However, recent observations indicate Shapley hypothesis was incorrect and NGC 2419 is still gravitationally bound to the Milky Way just moving in a highly eccentric orbit.
NGC 2419 or Caldwell 25 was discovered by William Herschel on December 31, 1788. It's located 275,000 light-years from the Solar System and about 300,000 light-years from the galactic centre, almost twice as far away as the Large Magellanic Cloud. At such a distance it's estimated NGC 2419 will take about 3 billion years to complete a single orbit around the centre of the galaxy.
NGC 2419 is positioned 7 degrees north and slightly east of Castor (α Gem - mag. +1.58) the second brightest star in Gemini. About 4 arc minutes west of NGC 2419 is a mag. +7.2 star with a double star of mag. +7.9 a few more arc minutes further west. Even Herschel with his super telescopes of the time couldn't resolve NGC 2419 into stars. William Parsons, the 3rd Earl of Rosse, using his 72-inch (1.83 m) reflecting telescope at Birr Castle in Ireland - the largest optical telescope in the world at the time - was first the first to do so in 1850.
NGC 4236 is a tenth magnitude barred spiral galaxy in Draco that's visible through small telescopes, although best seen with larger instruments. The galaxy was discovered by German born British astronomer William Herschel on April 6, 1793 and is a member of the Ursa Major or M81 group of galaxies that contains at least 34 galaxies, including spectacular M81 (Bode's galaxy) and M82 (Cigar galaxy).
NGC 4236 is located in the far northern constellation of Draco about 15 degrees north of the seven stars that form the famous "Plough" or "Big Dipper" asterism of Ursa Major. The galaxy is positioned two-thirds of the way along an imaginary line connecting stars lambda Dra (λ Dra - mag. +3.8) and kappa Dra (κ Dra - mag. +3.9). Star HD 106574 (mag +5.7) is 0.75 degrees directly north of NGC 4236.
Due to its high northerly declination, NGC 4236 is a Northern Hemisphere object. The best months to look for it are March, April or May although from most northern locations it's visible all year round and never sets. It can be seen from the Southern Hemisphere but only from latitudes north of 20 degrees south and even then appears low down above the northern horizon at best.
Mercury passed inferior conjunction on May 30th and was therefore positioned too close to the Sun to be observable. However, it moves rapidly out from the Sun so that two weeks later it becomes visible as a morning object for observers in the tropics and Southern Hemisphere. The planet subsequently climbs higher in the sky and brightens each day until it reaches a peak altitude on June 24th, the date of greatest elongation west (22.5 degrees from the Sun). Also on this day Mercury passes 2 degrees north of orange giant star Aldebaran (α Tau) the brightest star in the constellation of Taurus "the Bull". At magnitude +0.4 Mercury is half a magnitude brighter than the star with the pairing making a lovely early morning binocular / small telescope view.
It should also be noted that once past greatest elongation west, Mercury continues to brighten as it begins to draw into the Sun. For example, the planet shines at mag. +1.7 on June 15 but by month's end it has brightened to magnitude -0.1. From northern temperate latitudes, Mercury is a more difficult catch as it battles against the long morning twilight. The best time to try and catch it is for a few days on and around June 24th when it should be visible low down above the east-northeast horizon just before sunrise. A pair of binoculars will easily show the magnitude +0.4 planet although be careful not to confuse it with nearby Aldebaran.
The diagram below shows the June / July morning apparition of Mercury from a latitude of 35S (approx. equal to Sydney, Cape Town and Santiago).
The brightest object in western sky after sunset is Venus with the planet remaining well placed for observation throughout the month. On June 6th it reaches greatest elongation and on this day is positioned 45 degrees east of the Sun.
Currently moving eastward the declination of Venus decreases by 10 degrees as it moves from Gemini into Cancer and then into Leo. Consequently, the planets period of visibility decreases from 3.5 hours to less than 2 hours for observers located at Northern Hemisphere latitudes. For those living in the Southern Hemisphere the period of visibility remains around the 3-hour mark for the complete month.
There are three superb Venus conjunctions visible during June. On June 12th and 13th the planet slides less than a degree north of splendid open star cluster M44 "The Beehive", making a wonderful binocular sight. Then on June 20th, the waxing crescent Moon passes 6 degrees south of the planet. Finally Venus closes the gap on Jupiter and on the last day of June the two planets will be less than half a degree apart. To the naked eye they will appear stunning. Through binoculars and a telescope at low power both planets will appear in the same field of view, although Venus is about 10x the brighter of the pair.
The magnitude of Venus increases slightly from -4.3 to -4.4 with its phase decreasing from 53% to 34% during June.
Mars reaches solar conjunction on June 14th and therefore is unobservable throughout the month.
Jupiter remains an early evening object throughout June although it's now long past opposition and heading towards solar conjunction. The largest planet of the Solar System is visible towards the west as soon as it gets dark, but sets before midnight by months end. It's brightness decreases slightly from magnitude -1.9 to -1.8 as the month progresses.
The giant planet continues on a direct motion path, starting the month in Cancer before passing into Leo on June 10th. At the start of June, brighter Venus (mag. -4.3) is located about 20 degrees from Jupiter. It then closes the gap each subsequent evening before catching Jupiter at the tail end of the month. On June 30th, the two planets will be less than half a degree apart.
On June 21st, the waxing crescent Moon passes 5 degrees south of Jupiter.
This month Venus and Jupiter dominate the early evening sky with Mercury visible for a time in the morning sky but the night belongs to Saturn. The planet is only just past opposition (May 23rd) and remains superbly placed for observation during June. It's currently moving retrograde in western Libra and visible towards the southeast (NH) / east (SH) as darkness falls. Saturn can be observed practically all night and is better seen from southern latitudes where it's situated much higher in the sky.
Since now past opposition the apparent brightness and apparent size of Saturn will gradually decrease as the Earth moves away. During June, its magnitude decreases from 0.0 to +0.2 with the apparent diameter shrinking slightly from 18.5 to 18.0 arc seconds.
Saturn's wonder of course is its ring system. They are currently tilted at 24 degrees from our perspective and even a small 80mm (3.1-inch) telescope will easily show them. At magnification 100x the rings are nicely visible, tightly circling the central gem of Saturn. Increase the magnification to 200x or greater (seeing permitting) and the ring shadow on the planet, the darker outer A ring, the lighter B ring, subtle shadings and colour changes on Saturn's surface may be detected.
A good quality larger telescope, with its increased light gathering capability and higher magnification capability will of course show greater detail. For example, a 200mm (8-inch) scope can under good seeing be used to up to 400x magnification and will also reveal the 0.7 arc seconds wide Cassini division, the Enke division, the hazy C-ring as well as up to half a dozen of Saturn's satellites.
The almost full Moon passes 2 degrees north of Saturn on June 1st and again on June 29th.
Uranus starts the month as a morning object in Pisces with the planets visibility steadily improving as the month progresses. For Northern Hemisphere based observers at the start of June, it's visible above the eastern horizon for about an hour before twilight interferes. By months end the planet is much higher in the sky, rising more than 4 hours before the Sun.
Observers located further south have it even better with Uranus well placed in the morning sky throughout the month. At the beginning of the June the planet rises some 4 hours before the Sun and by the end of the month it's visible before midnight.
Uranus is a distant ice giant that shines at magnitude +5.9 and therefore bright enough to be seen with the naked eye from a dark site. Unfortunately most people don't have the luxury of such fine seeing conditions and therefore a pair of binoculars or small telescope is usually required to spot the planet.
On June 11th, the waning crescent Moon passes 0.5 degrees south of Uranus and an occultation is visible from South and East Australia, New Zealand, Fiji and Samoa (20:26 UT).
Neptune shines at mag. +7.9 and is now well placed for observation amongst the stars of Aquarius. By months end the most distant planet of all rises around midnight from northern temperate latitudes and much earlier for those located further south. It's currently located about 30 degrees southwest of the Great Square of Pegasus and a few degrees southwest of star lambda (λ) Aqr (mag. +3.7).
On June 9th, the last quarter Moon passes 3 degrees north of Neptune. Three days late Neptune reaches its first stationary point, signaling the beginning of this year's opposition period. The planet then commences retrograde motion.
NGC 2261 is a curious variable reflection nebula in Monoceros that's known as Hubble's Variable Nebula. It was discovered by William Herschel in 1783 and is illuminated by variable star R Monocerotis (R Mon). The nebula is unusual in that it changes shape over just a period of days and can vary by up to 2 magnitudes in brightness. The variations are believed to be due to periodic changes in the amount of dust surrounding R Mon, thus affecting the amount of light that reaches us. With an apparent magnitude of +9.0, it can be spotted with binoculars under dark skies.
The variability of R Mon (between magnitudes +10 and +12) was discovered at the Athens Observatory in 1861 but it wasn't until 1916 that Edwin Hubble realised that the nebula also changes in brightness. The variations are such that even on images taken days apart structural changes can be observed.
NGC 2261 was chosen as the "first light" photograph on January 26, 1949 for the 200-inch (5.1 m) Hale reflecting telescope under the direction of American astronomer Edwin Powell Hubble. At the time, the newly constructed Hale telescope was the largest telescope in the World and remained so until 1976. The nebula is listed as number 46 in the Caldwell catalogue.
NGC 2362 is a small compact young open cluster in Canis Major that surrounds bright star Tau Canis Majoris (τ CMa - mag. +4.37). This attractive grouping of 60 stars is packed into an area spanning just 6 arc minutes of apparent sky. The apparent magnitude of the cluster is given as +4.1, however the value is misleading as its skewed significantly because of the brilliance of τ CMa. The remaining members of NGC 2362 are much fainter, the brightest being of 7th magnitude.
Finding NGC 2362 is not difficult. It's located 2.75 degrees northeast of Wezen (δ CMa - mag. +1.83) the third brightest star in Canis Major. Sirius (α CMa) the brightest star in the night sky (mag. -1.46) is positioned 11 degrees to the northwest. Tau CMa a spectroscopic multiple system that shines with a combined light of tens of thousands times that of the Sun is the stand out cluster member and bright enough to be seen with the naked eye. For comparison, the Sun at the same distance would shine at a feeble magnitude +15.
NGC 2362 was discovered by Giovanni Batista Hodierna sometime before 1654 and then re-discovered by William Herschel on March 4, 1783. It's best seen from southern latitudes during the months of December, January and February.
NGC 457 is the brightest open cluster in Cassiopeia and one of the finest objects of its type in the northern sky. At magnitude +6.4, it's just beyond naked-eye visibility but easily seen with binoculars and a beautiful sight through telescopes. The brightest cluster stars are arranged in prominent lines and curves lines appearing to resemble an Owl shape, hence the popular name "the Owl Cluster". It's located 7,900 light-years distant.
NGC 457 was discovered by William Herschel in 1787. Finding the Owl Cluster is easy; it's positioned two degrees south-southeast of eclipsing binary star system Ruchbah (δ Cas - mag. +2.7). This star is one component of the characteristic "W" asterism of Cassiopeia. The brightest star inside NGC 457 is Phi Cas (φ Cas - mag. +5.0). Despite not being a member of the cluster, this foreground star is visible to the naked eye. Together with another non-cluster star - seventh magnitude HD 7902 (HIP 6229) - they form the bright eyes of the Owl greatly adding to the splendour of the view through backyard scopes.
NGC 457 is best seen from Northern Hemisphere latitudes during August, September and October. It appears high in the sky and even overhead from many locations. From latitudes greater than 32N, the Owl is circumpolar and never sets.
NGC 752 is a large spawling open cluster in the constellation of Andromeda. With an apparent magnitude of +5.7, it's visible to the naked eye from a dark site appearing as a large unresolved fuzzy patch of light. The cluster is one of the finest large open clusters in the sky and contains over 70 stars spread across a huge 1.25 degrees of apparent sky. Due to its size, NGC 752 is best observed with binoculars or through wide field telescopes at low powers.
NGC 752 is located 5 degrees south and slightly west of outstanding double star Almach (γ And - mag. +2.1) the third brightest star in the constellation. It was discovered by Caroline Herschel on September 29, 1783 although it was probably observed sometime before 1654 by Italian astronomer Giovanni Battista Hodierna. Caroline's brother William Herschel subsequently added it to his catalogue a couple of years later. It's best seen from northern latitudes during the months of October, November and December. The cluster is number 28 in the Caldwell catalogue.
NGC 2775 is a magnitude +10.5 spiral galaxy located in the constellation of Cancer, close to its border with Hydra. The galaxy is unusual in that it contains a very smooth nucleus with multiple spiral arms extending outwards from the central region. What makes the spiral arms interesting is their incredible complex detail, tightly wound structures and active star formation. Amateur astronomers should also keep their eye on this galaxy; it's been host to 5 supernovae explosions in the past 30 years and you never know when the next one will go off!
To find NGC 2775 look for the head of Hydra "the Sea Serpent". The asterism of stars that forms the head are ω Hyd (mag. +5.0), ζ Hyd (mag. +3.1), ρ Hyd (mag. +4.4), ε Hyd (mag. +3.4), δ Hyd (mag. +4.1), σ Hyd (mag. +4.5) and η Hyd (mag. +4.3). None of the stars are particularly bright but all can be seen with the naked eye. The galaxy is positioned a few degrees east and slightly north of this grouping.
NGC 2775 was discovered by William Herschel in 1783 and is best seen during the months of February, March and April. The galaxy is located 55.5 million light-years from Earth and has an actual diameter of 70,000 light-years. It's estimated to contain 100 billion stars. NGC 2775 is number 48 in the Caldwell catalogue.
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. It's listed as number 71 in the Caldwell catalogue.
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.
NGC 40 is a planetary nebula located in the northern constellation of Cepheus. It was discovered by William Herschel on November 25, 1788 who described it as "a 9th magnitude star, surrounded with milky nebulosity". Herschel used his 475mm (18.7) inch telescope to make the discovery but for today's amateur astronomers such a large scope isn't required, it can be glimpsed with just a 100mm (4-inch) instrument. NGC 40 is also known as the Bow Tie nebula, a nickname it shares with another planetary nebula, NGC 2440 in Puppis. It's listed as number 2 in the Caldwell catalogue.
NGC 40 is located just over 17 degrees from the North Celestial Pole and therefore circumpolar from most northern latitudes. It's one of the finest examples of its type in the far northern part of the sky. The best time to look for the nebula is during October, November and December when it appears highest in the sky during early evening. The Bow Tie nebula is also visible from most tropical locations although lower down. However, from southern temperate latitudes it's not visible at all.
Locating NGC 40 can be precarious as it's positioned in a star poor region of eastern Cepheus. One method to find it is by imagining a line connecting Errai (γ Cep - mag. +3.21) and γ Cas (mag. +2.15). The planetary lies approximately one-third of the way along this line.
NGC 188 is an open cluster located in the far northern constellation of Cepheus. It was discovered by John Herschel - the son of William Hershel - on November 3, 1831. He originally recorded it as h 34 in his 1833 catalogue and then included it as GC 92 in his subsequent General Catalogue of 1864. The cluster finally became NGC 188 in John L.E. Dreyer's New General Catalogue of 1888.
NGC 188 is the northernmost open cluster in the sky, it's positioned only 4.75 degrees from the North Celestial Pole. Located at such a northerly declination means the cluster is circumpolar from almost the entire northern hemisphere. It can be seen from the Southern Hemisphere but only from latitudes north of 5 degrees south. Even then it never climbs more than a few degrees above the northern horizon.