Algol, frequently referred to as the "Demon Star", is a bright eclipsing binary system located in the constellation of Perseus. It was the first of its type to be discovered and one of the best known and most frequently observed variable stars in the night sky. For most of the time Algol shines at magnitude 2.1 and therefore is the second brightest star in Perseus, only marginally fainter than Mirfak (α Per - mag. 1.8). But then every two days, 20 hours and 49 minutes it suddenly dips in brightness to magnitude 3.4 and remains dim for about 10 hours, before returning back to its original state.
The Algol system consists of at least three-stars (β Per A, β Per B and β Per C). The main star (A) is a B8 main sequence star that is nearly 100 times more luminous than our Sun, while the B star is a K2 type subgiant 3 times more luminous than the Sun. These two stars orbit very close together, with a separation of only 0.062 astronomical units (AU). The third star (C) in the system is of type A5, 4 times more luminous than the Sun and is located at an average distance of 2.69 AU from the AB pair. The total mass of the system is about 6 solar masses, with the mass ratios of A, B and C about 3.6 to 0.8 to 1.7. In addition, spectroscopic investigations indicate that the system might also contain a fourth component.
From our perspective, the orbital plane of Algol A and Algol B is in the line of sight of Earth and hence the pair forms an eclipsing binary. The dips in brightness of the Algol system occur when the dimmer B star moves in front of and therefore eclipses the brighter A star. The eclipse lasts for about 10 hours, which corresponds to the time when Algol's dims to magnitude 3.4. They occur every two days, 20 hours and 49 minutes, which is equal to the orbital period of the A and B stars. There is also a secondary eclipse when the brighter star occults the fainter secondary, but this results in a very small dip in brightness that can only be detected photoelectrically.
The variability of Algol was first recorded by Geminiano Montanari in 1667, although it's probable that it had been known for a long time before this. The star was associated with a demon like creature in Greek and Arabic tradition and ancient Egyptians used a calendar of lucky and unlucky days, over 3000 years ago, corresponding to the variability period of Algol. This suggests that the variability had long been known, but no conclusive evidence has yet been found.
Although Montanari was the first to record Algol's variability, its periodic nature was not recognized until more than 100 years later. The British amateur astronomer John Goodricke presented his findings to the Royal Society in May 1783 and even suggested that the dimming was caused by a dark body passing in front of the star. Algol was finally confirmed as an eclipsing binary in 1889 when Potsdam astronomer Hermann Carl Vogel made spectroscopic measurements.
Algol is located in Perseus amongst the stars of the Milky Way. It is positioned west of magnitude 0.1 star Capella (α Aur) and southeast of the "W" of Cassiopeia. At it's brightest the star is the second brightest in Perseus, at it's faintest it drops down the list to only seventh brightest. The finder chart below shows the position of Algol along with magnitudes of some of the surrounding stars for comparison purposes.
M51 (NGC 5194) The Whirlpool Galaxy is a grand design spiral galaxy located in the constellation of Canes Venatici, "the Hunting Dogs". It is one of the most famous galaxies in the sky, appearing face-on when viewed from Earth. At magnitude 8.4, it's relatively bright and easily visible in binoculars especially from a dark site. It has a much smaller dwarf companion NGC 5195 and together they are well-known as the finest and most studied example of an interacting galaxy pair.
M51 was one of Charles Messier original discoveries on October 13, 1773 while his friend Pierre Méchain discovered NGC 5195 on March 20, 1781. Messier described M51 as a faint nebula without stars that was difficult to see. In his catalogue of 1781, Messier describes both M51 and NGC 5195 in the same note and hence there is some confusion over the exact designation of M51. Is he referring to M51 as just the larger galaxy or does he actually mean the pair? If it's the pair then NGC 5194 is sometimes referred to as "M51A", with NGC 5195 separately known as "M51B".
Canes Venatici is a small northern constellation of faint stars that was created by Johannes Hevelius in the 17th century. Apart from its brightest star Cor Caroli (α CVn - mag. 2.9), the constellation contains no stars brighter than 4th magnitude. However, locating M51 isn't difficult as it positioned towards the northeast border of Canes Venatici and only a few degrees from the handle of the seven stars that form the famous "Plough" or "Big Dipper" asterism of Ursa Major.
To locate M51, first identify Alkaid (η UMa - mag 1.9) the end star of the handle of the bowl of the "Plough". Located 3 degrees directly west of Alkaid is magnitude 4.5 star 24 UMa. Positioned a degree to the northeast of 24 UMa is a magnitude 6.5 star. Now imagine a line from this star to 24 UMa and then continue it southwards for a further two degrees. This leads to a triangle of stars of magnitudes 7.1, 7.1 and 7.5. All three stars are easily visible in binoculars with M51 located just west of the southernmost star.
During May, comet PanSTARRS (C/2011 L4) continues its northwards march against the fixed stars, spending most of the month in Cepheus before crossing into Draco at the tail end of the month. Despite fading fast, the comet is now circumpolar for most of the northern hemisphere hence visible towards the north all night. PanSTARRS will fade from about magnitude 7.8 to 9.4 as the month progresses but should remain a small / medium sized telescope target although increasingly more difficult with binoculars. It's currently not visible from southern hemisphere latitudes.
PanSTARRS spent much of April moving through the distinct "W" of the constellation of Cassiopeia before crossing the border in Cepheus on the last day of the month. As it move northwards during May, it passes many dim stars on a journey that takes it towards Polaris (α UMi - mag. 2.0), the Northern Pole Star. At its closest at the end of the month, the comet is only about 5 degrees from the Pole star. In the meantime on the evening of May 13th, PanSTARRS will pass only 0.25 degrees west of magnitude 3.2 star gamma (γ) Cep, the second brightest star in Cepheus.
The charts below show the path of PanSTARRS from April 19th to June 2nd, 2013. As always the comet appearance and particular brightness may change depending on how it performs.
Although past its best, comet Lemmon (C/2012 F6) is now finally visible to those in the northern hemisphere. The comet has already put on a better than predicted show for southern and tropical observers and for a short time was easily visible to the naked eye as it moved through the far southern constellations. When viewed through binoculars and telescopes it was a superb sight, appearing greenish with a bright coma and wispy thin extended tail.
Lemmon then swung around the Sun at the end of March before reappearing in the April morning sky. By the start of May, the comet had moved sufficiently north to also be seen from northern temperate latitudes. Its current northern path is almost parallel to the zero hour line of right ascension and as a result, visibility will improve on a daily basis for northern hemisphere observers. Southern hemisphere watchers can still observer the comet low down about the horizon for some time still, however it won't appear very high above the horizon.
Comet Lemmon's path against the background stars may seem a little familiar; PanSTARRS (C/2011 L4) the other bright comet of 2013, followed an almost identical path earlier this year.
On May 1st, Lemmon was at magnitude 7.2 and within binocular reach. During May it will fade gradually as it recedes from the inner solar system, ending the month at about magnitude 9.4. You should be able to follow the comet with 7x50 or 10x50 binoculars during May, although towards the end of the month it will be increasingly more difficult. A telescope makes the task much easier.
The comet is visible towards the east before sunrise. First locate the four stars that form the "Great Square of Pegasus". The comet is positioned on the eastern side of the square. On May 9th, Lemmon is just over 1 degree east of southeastern square star Algenib (γ Peg - mag. 2.8). It then crawls up the eastern side of the square, reaching the top on May 27th. On this date, it's about 3 degrees east of the northeastern square star Alpheratz (α And - mag. 2.1).
Mercury reaches superior conjunction on May 11th and as result for most of May is unsuitably placed for observation. Only at the end of the month does the chance arise to glimpse the elusive planet; but it won't be easy. For example, from latitude 51.5N (London, England) Mercury is a mere 4 degrees above the northwestern horizon, 45 minutes after sunset on May 23th. The situation is marginally better on May 31st, with Mercury now 7 degrees high.
During this time the planets brightness decreases from magnitude -0.9 to -0.3. With lengthening twilight, northern hemisphere based observers may find spotting the planet difficult with the naked eye. Binoculars will assist greatly but of course only scan the sky when you're sure that the Sun has set and therefore out of harms way.
What always helps in a search like this is a nearby brighter marker. And this time we have one! From May 23rd to May 25th, Mercury will pass just over a degree north of the much brighter Venus (mag. -3.9). Also located a few degrees from the pair is Jupiter (mag. -1.9). However despite being more than twice as bright as Mercury, the giant planet is over six times fainter than Venus.
Observers located at southern temperate latitudes also have the chance to spot Mercury at the end of the month, but the planet is even lower above the horizon than for their northern counterparts.
Having past through superior conjunction at the end of March, Venus is now moving slowly east of the Sun. Now shining at magnitude -3.9, the planet should be visible to those at northern temperate latitudes and in the tropics during the last week of May. It will appear low down towards the northwest after sunset in the twilight sky. On May 4th, Venus moves from Aries into Taurus where it remains for the rest of the month. Its current northern declination makes the planet more difficult to spot for those living in the southern hemisphere.
Venus will pass less than one degree north of Jupiter on May 28th with Mercury passing just over a degree north of Venus between May 23rd and May 25th.
Mars reached solar conjunction last month and remains too close to the Sun to be safely observed this month.
Jupiter's long evening period of visibility is now almost at an end. The planet reaches solar conjunction on June 19th and by the end of May will be lost to the bright glare of the evening twilight. Now down to magnitude -1.9, Jupiter is visible low down towards the west-northwest from about 45 minutes after sunset for those located in the tropics and at northern temperate latitudes. As a consequence of its northerly declination amongst the stars of Taurus, opportunities to glimpse the planet from southern latitudes are even more fleeting.
As previously stated, by the end of May Jupiter will be effectively unsuitably placed for observation, however a possible final chance to spot the planet occurs on May 28th. This is when six times brighter Venus will pass less than one degree north of Jupiter. The pair should by visible very low above the northwestern horizon as soon as it's dark enough.
The famous ringed planet has just passed opposition (April 28th) and remains superbly placed for observation during May. Saturn is visible towards the east-southeast as darkness falls and can be observed practically all night. The planet starts the month in western Libra on a retrograde motion that takes it back into neighbouring Virgo on May 13th.
Now past opposition the apparent brightness and apparent size of Saturn will gradually decrease as the distance between the two planets increases. During May, its magnitude decreases from 0.1 to 0.3 with the apparent diameter shrinking only slightly from 19 to 18.5 arc seconds.
Saturn is positioned 14 degrees to the east of Spica (mag. 1.0), the brightest star in the constellation Virgo. When viewed with the naked eye, Saturn appears cream coloured and about twice as bright as blue-white Spica. Through binoculars the planet appears slightly elongated, hinting at its famous set of rings. Also visible with binoculars when positioned a reasonable angular distance from the planet, is Saturn's brightest moon Titan (mag. 8.4). Much more difficult to detect is fainter Rhea (mag. 9.8), the second largest moon of Saturn.
Comet PanSTARRS is now no longer a naked eye object but remains visible for some time through amateur telescopes. Having recently passed within a few degrees of the spectacular Andromeda Galaxy (M31), the comet has now moved into Cassiopeia and will next pass through the "W" shape before leaving the constellation at the end of April.
The bright constellation Cassiopeia lies in the far northern sky and is easily recognisable due to its distinctive "W" shape. It's bordered by Andromeda (to the south), Perseus (southeast) and Cepheus (north) and is located on the opposite side of the polar region to the "Big Dipper" or "Plough" asterism of Ursa Major. The "W" of Cassiopeia is circumpolar and hence never sets for observers located at latitudes greater than 45N.
PanSTARRS entered into Cassiopeia on April 9th. On this date it was right at the limit of naked eye visibility (mag. 6.2) but an easy binocular and small telescope target. The comet is continuing on an almost direct northern path, roughly parallel to the zero hour of right ascension. On April 16th, PanSTARRS passed less than 2 degrees west of ζ Cas (mag. 3.7) and λ Cas (mag. 4.7). It then reaches the vicinity of the "W" around April 19th, passing 2.5 degrees west of Schedar (α Cas - mag. 2.2). Two day later PanSTARRS crosses the line connecting the western two stars of the "W", Schedar and Caph (β Cas - mag. 2.3) before passing 1.25 degrees west of mag. 6.5 open cluster NGC 129 on April 23rd. It's predicted that it will now be down to magnitude 7.5, hence a more difficult binocular object but still well within the range of small and medium sized telescopes. On April 30th, PanSTARRS finally leaves Cassiopeia and moves into adjacent Cepheus.
This years Lyrids meteor shower lasts from April 16th to April 26th, peaking at about 11 UT on April 22nd. The 2012 event was a favourable one with peak activity occurring under moonless skies. However, this year we're not so fortunate; an 85% illuminated waxing gibbous Moon interferes but still it's well worth looking outside, weather permitting of course!
Unlike sporadic meteors that originate from anywhere in the sky, periodic shower meteors can always be traced back to the same part of the sky - the radiant point of the meteor shower. Therefore, spotting these shooting stars couldn't be easier…just focus on the radiant point…correct? Not quite. The problem is that although the meteors do originate from the radiant point, they streak across almost any part of the sky and are often seen tens of degrees from where the actual radiant is located! Therefore, good advice is to lie down on something like a reclining chair, look skywards and scan a large area of sky surrounding the radiant. Simply relax and enjoy the Lyrids meteor shower along with spring night sky.
Comet Lemmon (C/2012 F6) returns to the morning sky for observers located at southern hemisphere and tropical latitudes
Comet Lemmon is once again observable after a short period of time when it was too close to the Sun to be safely seen. So far, Lemmon has been a comet for southern hemisphere and tropical based observers; those living in the north have not yet had a look in, but that's about to change.
During April, Lemmon is visible low towards the east during morning twilight. Again the comet can only be glimpsed by those located in the southern hemisphere and to a lesser extent the tropics. But it's now heading on a direct northern trajectory and as a result from May, will finally be suitably placed for observation for those located further north.
Between April 15th and 17th, Mercury passes less than 3 degrees north of Lemmon. Having just past greatest elongation on March 31st, Mercury will shine at magnitude -0.1 and act as a perfect guide for locating the much fainter comet.
During May, Lemmon remains low in the eastern sky during morning twilight for observers in the southern hemisphere and tropics. However it never appears very high and it's not long before it's lost to the bright morning twilight. Although past its best, Lemmon's visibility improves on a daily basis for northern hemisphere observers. The comet is visible towards the east at the beginning of May with an improving altitude each subsequent day. However, of course the higher altitude is offset by it's diminishing brightness.
NGC 2392 is a 9th magnitude bipolar double shell planetary nebula located in the constellation of Gemini. Resembling a person's head surrounded by a parka hood, it's commonly known as the "Eskimo Nebula" or "Clown Face Nebula". William Herschel discovered it from his observatory in Slough on January 17, 1787, describing the planetary nebula as a 9th magnitude star with a bright centre, surrounded by equally dispersed nebulosity.
Locating the Eskimo Nebula is relatively easy; it's positioned just east of centre of the bright zodiacal constellation of Gemini, "the Twins", close to mag. 3.5 star Wasat (δ Gem). The easiest way to find Gemini is by identifying its two brightest stars Castor (α Gem - mag. 1.58) and Pollux (β Gem - mag. 1.16). They are positioned east of the familiar "V" shaped asterism of Taurus and to the northeast of the bright prominent constellation of Orion.
Imagine a line extending from Pollux - the brighter of the twins - towards the southwest in the direction of Orions belt. Positioned just over 8 degrees along this line is Wasat and 2 1/3 degrees southeast of Wasat is NGC 2392. The planetary nebula is positioned next to a mag. 8.2 yellow white star. At first glance through a telescope the pair appears like a wide double star, separated by about 100 arc seconds.
During April, Mercury remains well placed for observation before dawn for observers located in the tropics and at southern hemisphere latitudes. For those at northern temperate latitudes, the angle of the ecliptic is unfavourable and the planet is not visible this month.
On March 31st, the closest planet to the Sun reached greatest elongation west (28 degrees from the Sun). On this date, from latitudes of 35S (approx. equal to Sydney, Cape Town and Santiago) it was positioned 20 degrees above the eastern horizon, 30 minutes before sunrise.
The planets altitude will slightly decrease each subsequent morning as the month progresses but at the same time it increases in brightness. Mercury starts April at magnitude 0.3 and finishes the month at magnitude -1.0.
On April 8th, the thin waning crescent Moon will pass 7 degrees north of Mercury and on April 19th, Mercury will be positioned 2 degrees south of Uranus (mag. 5.9).
The diagram below shows the March and April morning apparition of Mercury from latitude of 35S.
Venus passed through superior conjunction on March 28th. The planet is now located on the far side of the Sun and consequently unsuitably placed for observation throughout April.
Mars reaches solar conjunction on April 18th and therefore is positioned too close to the Sun to be observed this month.
Jupiter remains an evening object throughout April. The largest planet of the solar system is visible in the southwest sky as soon as it gets dark, but now sets before midnight by months end from northern temperate latitudes. The period of visibility is even less for those located further south.
The giant planet continues it direct motion in Taurus. At the start of April it's positioned only 5.5 degrees north of magnitude 0.9 orange/red star Aldebaran and the famous "V" shaped Hyades open cluster. By the end of the month Jupiter has moved to 9 degrees northeast of Aldebaran and continues to gradually drift away from this prime section of zodiac "real estate".
The planets magnitude decreases from -2.1 to -2.0 during April with the apparent size diminishing from 36 to 34 arc seconds over the same time period. On April 14th, the waxing crescent Moon passes 2 degrees south of Jupiter between the "horns" of Taurus, the Bull.
Saturn reaches opposition on April 28th (mag. 0.1) and on this date is located 8.816 AU (approx. 1319 million km or 819.5 million miles) from Earth. It rises towards the east-southeast and is visible as soon as it gets darks and remains so all-night. The far away planet with its beautiful set of rings, is currently moving retrograde amongst the faint stars of western Libra.
During April, the brightness of Saturn increases slightly from magnitude 0.3 to 0.1, with an apparent diameter of 19 arc seconds.
From our perspective, Saturn's rings are titled at approx. 19 degrees and are a wonderful sight through telescopes. They are visible in even the smallest of instruments and are a must see on all astronomers observation lists. Larger telescopes reveal subtle details, with many of the planets brightest moons visible.
The full Moon passes 4 degrees south of Saturn on April 26th.
M50 is an appealing and relatively bright open cluster located in the rich star fields of Monoceros, close to the Canis Major border. With an apparent magnitude of 5.9, it's just about visible to the naked eye as a faint patch of nebulosity. Telescopically the cluster is moderately dense, contains a number of bright stars and spans about half the diameter of the full Moon; a nice sized object for owners of small to medium sized scopes.
The constellation of Monoceros straddles the equatorial equator, east of majestic Orion and to the north of bright Canis Major. Despite lying in rich Milky Way star fields, Monoceros is a faint constellation that contains no stars brighter than 4th magnitude. Consequently, tracing the outline of this dim grouping can require some patience. However, although Monoceros is devoid of bright stars it does contain a number of bright and interesting deep sky objects. In addition to M50, the constellation is home to the Rosette Nebula (NGC 2237, 2238, 2239, and 2246), the Christmas Tree Cluster (NGC 2264) and Hubble's Variable Nebula (NGC 2261).
Although Monoceros is faint, finding M50 is relatively easy. Start by aiming your sights on the brightest star in the sky, Sirius (α CMa - mag. -1.46). Sirius can be found by extending an imaginary line from the three bright stars of Orion's belt southwards for about 20 degrees. Located 9.5 degrees NNE of Sirius is M50. Sandwiched halfway between Sirius and M50 is θ CMa (mag. 4.1), a well-placed stepping-stone star.
The cluster was one of Charles Messier's discoveries. He found it on April 5, 1772, although possibly G.D. Cassini had already discovered it before 1711, according to a report by his son, Jacques Cassini, in his book "Elements of Astronomy".
As Comet Lemmon swings around the Sun, it becomes unsuitably placed for observation for about a week from March 24th. Until now, southern hemisphere observers have enjoyed excellent views of Lemmon. Since the start of the year it has been superbly placed for observation; most of the time positioned high in the night sky as it weaved its way through the far southern constellations. Although visible to the naked eye since February, the best views of Lemmon have been obtained using binoculars or telescopes, with the comet displaying a bright coma and wispy tail. When imaged, the coma appeared striking emerald green in colour from gas ionisation.
Lemmon is now no longer visible in the evening sky. After a few days at the end of March when it's unobservable, the comet reappears as a morning object low down towards the east before sunrise on April 1st. As before, this applies to southern hemisphere based astronomers. Those in the northern hemisphere will have to wait one month longer before then can catch their first glimpse of the comet.
After passing perihelion on March 10th and closest approach to Earth on March 5th, comet PanSTARRS has now begun its long return journey towards the Oort cloud and the far reaches of the solar system. With an orbital period estimated at about 110,000 years it will be considerable time before it returns, but until then it remains visible to the naked eye for a few days and with binoculars and telescopes for a few months longer.
On March 12th, mag. 1.6 PanSTARRS crossed the celestial equator in Cetus to begin its long journey through the northern constellations. The comet was now visible for the first time from northern temperate latitudes, and could be seen with the naked eye low down to the west just after sunset. The coma appeared bright with a short fan shaped tail of at least half a degree in length.
Two days later the comet passed into Pisces, continuing on a bearing practically alongside the 0hr 30m line of right ascension. After quickly moving through Pisces, PanSTARRS then crossed the boundary into Andromeda on March 22nd. On this date the comet should be about magnitude 3.1. Although fading it becomes better placed for northern hemisphere observers as it heads north, setting later on subsequent nights. On March 27th, PanSTARRS passes about 1.5 degrees west of mag. 3.3 star δ And. There shouldn't be a great difference in brightness between the two objects, with the comet about a magnitude or so fainter than the star. Both will be visible in binoculars or small telescopes at low magnifications, in the same field of view. From northern temperate latitudes, they appear low down towards the west-northwest about 45 minutes after sunset.
The diagram below shows PanSTARRS as seen from temperate northern latitudes until April 5, 2013.
On April 1st, PanSTARRS will be down to 5th magnitude and close to the limit of naked eye visibility. The comets declination is now 35N and hence already circumpolar for observers living at latitudes north of 55N. Between April 3rd and April 6th, an excellent photo opportunity occurs when mag. 5.6 PanSTARRS will pass only 2 degrees west of M31, the famous Andromeda Galaxy. The comet then continues onwards into Cassiopeia, arriving on April 9th. Ten days later it passes just 2.5 degrees west of mag. 2.2 Schedar (α Cas). With a declination of 56N, PanSTARRS will now be circumpolar from most northern latitudes, although no longer visible to the naked eye. However, at mag. 7.2 it remains an easy binocular and small telescope target.
The charts below show the position of PanSTARRS until April 21, 2013.
On March 31st, the inner planet Mercury reaches greatest western elongation and on this date is positioned 28 degrees from the Sun in the morning sky. This is an excellent opportunity for observers located at southern hemisphere and tropical latitudes; the planet is visible for an extended period of up to 6 weeks from about the middle of March. Unfortunately for those located further north, the angle of the ecliptic is unfavourable and consequently the planet is not suitably placed for observation.
A clear and ideally unobstructed view of the eastern horizon is recommended when searching for Mercury. On March 16th, from latitude 35S (approx. equal to Sydney, Cape Town and Santiago) Mercury will appear 11 degrees above the eastern horizon 30 minutes before sunrise. Although placed in the morning twilight, at magnitude 1.4 the planet should be a relatively easy naked eye target.
For this apparition, a good time period to look for Mercury is between March 21st and April 15th, when the planet will be at least 17 degrees above the eastern horizon, 30 minutes before sunrise. Its magnitude will also increase from 0.7 to -0.1 and therefore spotting Mercury should be very easy now, weather permitting of course! The peak altitude occurs on March 31st, the date of greatest elongation west, when Mercury is just over 20 degrees high with a magnitude of 0.2.
Once past greatest elongation west, Mercury continues to brighten as it begins to draw towards the Sun. For this apparition, the planet does not reach maximum brightness (mag -1.0) until the very end of the visibility period, more than 4 weeks after greatest elongation west!
The diagram below shows the March and April morning apparition of Mercury from latitude of 35S. The view will be similar for observers at latitudes near 35S.
M44 is a sprawling open cluster that is also known as the Praesepe or Beehive cluster. It is the brightest and most prominent deep sky object in the constellation of Cancer. Visible to the naked eye under dark skies, the cluster appears like a large misty cloud covering over 1.5 degrees of sky. The brightness and size of M44 results from its close proximity to Earth; it lies a mere 577 light-years distant. Only the Hyades (at 153 light-years), Coma cluster (280 light-years), M45 Pleiades (425 light-years), Southern Pleiades (480 light-years) and IC 2391 (500 light-years) are nearer. Consequently, M44 is one of the brightest and largest objects of its type in the night sky.
The constellation of Cancer "the Crab" is a faint zodiac constellation that is bordered by much brighter Leo to the east and Gemini to the west. To the north is faint Lynx, with Canis Minor and Hydra located on the southern side. At the heart of Cancer is a grouping of four faint stars. They are Asellus Australis (δ Cnc - mag 3.9), Asellus Borealis (γ Cnc - mag 4.7), η Cnc (mag 5.3) and θ Cnc (mag 5.3). Of these, the brighter two stars are relatively easy naked eye objects, the fainter ones more difficult. Positioned at the centre of this grouping is M44.
An alternative method to locate M44 is to imagine a line extending in a southeastern direction from Pollux (β Gem - mag. 1.1) for 37 degrees to Regulus (α Leo - mag. 1.4). M44 is positioned approximately at the mid-point of this line.
Nearly 2000 years ago, the astronomer Ptolemy described M44 as "the nebulous mass in the breast of Cancer", but it was Galileo who first telescopically observed the Praesepe. He did this in 1609 and was able to resolve 40 stars. Charles Messier added the item to his catalog on March 4, 1769.
So far, Comet PanSTARRS has been visible for many months from the southern hemisphere but now its time for the northern half of the globe to get their first chance to catch a glimpse of this dirty ice ball.
Inevitably, as PanSTARRS heads northwards an abundance of articles have recently appeared in the northern press detailing its up and coming performance. Many articles are excellent but some give a slightly misleading impression. Unfortunately, part of the problem is that PanSTARRS has not lived up to its original star billing. The comet was predicted to be a dazzling sight, reaching magnitude -1 or brighter during the second half of March. At such luminosity, it would have been a spectacular naked eye object, unmistakable in the March evening twilight sky.
From recent observations made from the southern hemisphere, it's now clear that PanSTARRS will fall short of its original stellar predictions. However, certainly all is not lost and the comet should still peak close to 1st magnitude...which is not bad at all. This compares favourably with past comets and comets this bright usually only grace our skies on average about once every 5 years. PanSTARRS has now been visible to the naked since the middle of February and has so far received some glowing reports from those in the southern hemisphere lucky enough to see it.
M38 is the third and faintest of the three Messier objects located in the constellation of Auriga (the other two been M36 and M37). With an apparent magnitude of 7.0 it's almost a magnitude dimmer than both M36 and M37, but still an easy binocular target. The cluster covers over 20 arc minutes of sky and hence due to its large size, is best observed at low magnifications with small to medium size telescopes.
Finding M38 is relatively easy. Start by locating the brightest stars in the constellation of Auriga, "the Charioteer". This relatively large constellation is positioned to the northeast of neighbouring Taurus and to the northwest of Gemini. The main stars of Auriga form an easy to find large polygon shape that is marked at the northern point by brilliant Capella (α Aur - mag 0.08). To trace the polygon start with Capella then move eastwards in a circular like shape to Menkalinan (β Aur - mag 1.90), followed by θ Aur (mag 2.65), El Nath (β Tau - mag 1.68), Hassaleh (ι Aur - mag 2.69), then η Aur (mag 3.18), Almaaz (ε Aur - mag 3.03) and finally back to Capella. Now focus on stars θ Aur and El Nath and imagine a straight line connecting them. Located just east of the mid-point of this line is M37 and to the west M36. Move 2.3 degrees northwest of M36 and you will arrive at M38.
As with M37, M38 was discovered by Giovanni Batista Hodierna sometime before 1654. The cluster was then rediscovered by French astronomer Guillaume Le Gentil in 1749 and subsequently added by Charles Messier to his catalog on September 25, 1764.
Although Mercury reaches inferior conjunction on March 4th, the planet rapidly moves out from the Sun so that only one week later it's 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 March 31st, the date of greatest elongation west (28 degrees from the Sun). From northern temperate latitudes, the angle of the ecliptic is not favourable and consequently Mercury is unsuitably placed for observation this month.
As is often the case with Mercury apparitions, one hemisphere of the Earth is favoured over the other. On this occasion it's the turn of the southern hemisphere with the added bonus that this also happens to be the most favourable morning apparition of the year. With an extended period of visibility, the opportunity to spot the illusive planet is superb; Mercury is visible in the southern hemisphere morning skies for about 6 weeks from about March 11th.
From latitude 35S (approx. equal to Sydney, Cape Town and Santiago), Mercury will appear 4 degrees above the eastern horizon at 30 minutes before sunrise on March 11th. Since Mercury on this day shines at a dim magnitude 2.7, you will probably need binoculars to spot the planet against the bright twilight background. From then on glimpsing Mercury is much easier as it increases in brightness and climbs higher in the sky each subsequent morning. On March 16th, Mercury is now at magnitude 1.4 and 11 degrees above the horizon. The planets altitude continues to improve each day until March 31st when Mercury reaches maximum height, the date of greatest elongation west. On this date the planet is 20 degrees above the eastern horizon with a magnitude of 0.22, 30 minutes before sunrise.
It should be noted that once past greatest elongation west, Mercury continues to brighten as it begins to draw into the Sun. For this apparition, the planet does not reach maximum brightness (mag -1.0) until the very end of the visibility period, more than 4 weeks after greatest elongation west!
The diagram below shows the March and April morning apparition of Mercury from latitude of 35S.
Venus passes through superior conjunction on March 28th. The planet is now located on the far side of the Sun and consequently unsuitably placed for observation throughout March.
Mars is now heading towards solar conjunction in April and is currently positioned close to the Sun. Consequently the "Red planet" is also unobservable this month.
Jupiter is now 3 months past opposition but despite fading in brightness the planet remains a brilliant object in Taurus. The gas giant is moving direct and positioned only 4.5 degrees north of magnitude 0.9 orange/red star Aldebaran and the famous "V" shaped Hyades open cluster. It's also just a few degrees east of M45, the famous Pleiades open cluster. With the planet now heading eastwards, Jupiter is gradually drifting away from this "Golden gate" section of the zodiac.
Jupiter is visible as soon as it's dark. At the end of the month, it sets just after midnight from northern temperate latitudes and a couple of hours before midnight for those living in the tropics and further south. The planets magnitude decreases from -2.3 to -2.1 during March with the apparent size diminishing from 39 to 36 arc seconds over the same time period.
On March 18th, the first quarter Moon passes 1.5 degrees south of Jupiter with the two objects forming a nice pairing.
As Jupiter starts to fade from view, Saturn is becoming increasingly more prominent as it heads towards next months opposition. The "Ringed planet" is located amongst the faint stars of western Libra and is currently moving retrograde.
At the beginning of March, Saturn rises before midnight and a couple of hours earlier by months end. The planet brightens only slightly during March from magnitude 0.4 to 0.3. Likewise there is only a small increase in the apparent diameter of the planet disk (18 to 19 arc seconds).
Saturn's rings are currently wide open and a fantastic telescope sight. The ring tilt from our perspective is 19 degrees and even a small refractor telescope will easily show them. Larger telescopes display them in full glory, along with subtle details on the planet's surface and many of its brightest moons.
On March 2nd, the waning crescent Moon will pass 3 degrees south of Saturn.
After much build up and anticipation Comet PanSTARRS (C/2011 L4) will finally arrive and light up the early evening skies during March. Early predictions forecasted a spectacular display, a dazzling naked-eye comet, rivaling in brilliance the night sky's brightest stars and blazing an unforgettable trail above the western horizon just after sunset for a few days in March.
Sadly, recent observations suggest than PanSTARRS will be much dimmer than originally estimated. Even so, it should still reach naked-eye visibility and it certainly would be bad luck if we were denied a good view of this icy-rock, at least with a pair of binoculars or a telescope.
So far this year PanSTARRS has been a southern hemisphere comet. To a lesser extent it was also visible from the tropics but not from northern temperate latitudes. For the first 6 weeks of 2013, the comet brightened only modestly but just when it seemed we might have a celestial flop on our hands, it suddenly produced a small but noticeable increase in brightness. This small burst of activity coincided with the first batch of naked eye sightings as PanSTARRS hit magnitude 5.4 (February 15th). Only four days later, the comet was now a nice early morning object for southern hemisphere observers. Despite been only a few degrees above the horizon it was visible with the naked eye, even against the bright twilight background. The coma of the comet was concentrated with a short broad tail of at least 30 arc minutes in length. Estimates at this stage put the magnitude at 4.5. The comet then continued to brighten as it switched from the morning to the evening sky. On February 27th, PanSTARRS was now magnitude 3.4 with the coma and tail clearly visible to the naked eye. When viewed through 10x50 binoculars the tail measured more than 1 degree in length and of course extended much further when imaged or photographed.
Location, magnitude and star chart
As PanSTARRS heads northwards against the background stars, visibility switches from observers located in the southern hemisphere to those in the north. The comet on February 27th was located in Sculptor at a declination of 30S and visible as an evening twilight object for southern hemisphere observers, although very low down. For those in the northern hemisphere it was not visible but their waiting time is now almost over.
PanSTARRS continues on an essentially northeastern path. From Sculptor, it then cuts through a corner of Aquarius before heading into Cetus on March 5th. It then makes a short diversion into Pisces (March 9th to March 11th), then back into Cetus for two further days before returning to Pisces on March 13th. This is the period of peak brightness when PanSTARRS reaches perihelion or closest approach to the Sun (March 10th). On this date we estimate a magnitude of 1.6, although given the unpredictability of comets, it could easily be brighter or dimmer than that. What is certain, the comet will be positioned extremely close to the Sun in the sky and as always extreme care must be made when observing in such cases. Never casually sweep for the comet with binoculars or a telescope if the Sun is above the horizon. Make sure that the Sun is below the horizon. Even the shortest glimpse of the unfiltered Sun with binoculars or telescopes can cause permanent eye damage. It's just not worth the risk.
The comet then heads due north for a while, crossing into Andromeda on March 22nd and into Cassiopeia on April 9th before arriving in Cepheus at the end of the month. By now PanSTARRS will be circumpolar for most observers located in the northern hemisphere.
The charts below show the position of PanSTARRS until March 22, 2013.
Comet Lemmon (C/2012 F6) has been delighting observers in recent months while moving through the deep southern constellations. Already, the comet has turned out to be the surprise package of the year so far. When discovered by Alex Gibbs on March 23, 2012 as part of the Mount Lemmon Survey it was extremely faint at magnitude 20.7 and consequently not anticipated to put on much of a show in 2013. However, much to the enjoyment of observers living in the southern hemisphere and the tropics, Lemmon is performing considerably better than expected. It's of the order of a few magnitudes brighter than originally hoped, has recently attained naked eye visibility and continues to improve as it heads towards perihelion (closest approach to the Sun) on March 24, 2013.
As the beginning of February, Comet Lemmon reached naked eye brightness as it moved through Octans and past the South Celestial Pole. By February 11th, it had improved to magnitude 5.4 with a coma of at least 15 arc minutes in diameter along with a small tail. When viewed through 10x50 binoculars, the tail extended in a southeasterly direction for about 0.5 degrees, similar in size to that of the full Moon.
A fantastic visual and photo opportunity occurred between February 14th and 16th when Lemmon slid past the spectacular globular cluster 47 Tucanae and the superb Small Magellanic Cloud (SMC). At time of closest separation, Lemmon was only 4 degrees west of 47 Tucanae with both objects and part of the SMC visible in the same binocular field of view. The comet brightness was magnitude 5.0 and its appearance not too dissimilar to that of 47 Tucanae.
By February 19th, Lemmon had increased in brightness to magnitude 4.7 and although the coma was practically unchanged in size, the tail was now over 1 degree in length. Images revealed the comet in spectacular glory, a bright vivid green in colour with a bright core and a long wispy tail that extended for many degrees.
Location, magnitude and star chart
After passing close by 47 Tucanae and the SMC, Lemmon continued to move through Tucana until February 24th when it enters Phoenix. On this date it is 13 degrees due west of Achernar (mag. 0.45), the brightest star in the long winding constellation of Eridanus.
Continuing on a northern bearing, Lemmon travels through Phoenix until March 10th when it enters Sculptor. The star fields of Phoenix and Sculptor are barren and contain few bright stars. The brightest star of all is Ankaa (α Phe) at magnitude 2.4. On March 8th, Lemmon passes only 5 degrees to the west of Ankaa and at this time it should have brightened to about magnitude 3.5 with a significant tail visible.
The comet then continues on its northern path, running practically parallel to the zero hour line of right ascension. On March 19th / 20th, it will be about 15 degrees to the east of mag. 1.17 Fomalhaut, the brightest star in the constellation of Piscis Austrinus. Lemmon should now also be close to peak brightness. Originally we estimated a high magnitude of 2.4 but based on recent observations it could be more of the order of 3.2.
Lemmon then remains in Sculptor until March 24th, before crossing the border into Cetus. The comet remains in Cetus for the best part of 3 weeks, before arriving in Pisces on April 13th (mag. 4.4). After spending many months in the southern part of the sky, Lemmon finally crosses the celestial equator and moves into northern section on April 20th. Now down to magnitude 5.0, it continues northwards into Andromeda before reaching Cassiopeia on June 21st. At this time, its declination will be almost 50 degrees north and hence circumpolar for many northern hemisphere observers, but now a faint magnitude 10.
The finder charts below show the path of Comet Lemmon against the background stars from February 20 to March 6, 2013 and from March 6 to March 22, 2013.