WHAT'S UP THIS MONTH - MARCH 2021
(Link to What's Up April 2021)
(Link to What's Up February 2021)
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THESE PAGES ARE INTENDED TO HELP YOU FIND YOUR WAY AROUND THE SKY
The chart above shows the whole night sky as it appears on 15th March at 21:00 (9 o'clock) Greenwich Mean Time (GMT). As the Earth orbits the Sun and we look out into space each night the stars will appear to have moved across the sky by a small amount. Every month Earth moves one twelfth of its circuit around the Sun, this amounts to 30 degrees each month. There are about 30 days in each month so each night the stars appear to move about 1 degree. The sky will therefore appear the same as shown on the chart above at 8 o'clock GMT at the beginning of the month and at 10 o'clock GMT at the end of the month. The stars also appear to move 15º (360º divided by 24) each hour from east to west, due to the Earth rotating once every 24 hours.
The centre of the chart will be the position in the sky directly overhead, called the Zenith. First we need to find some familiar objects so we can get our bearings. The Pole Star Polaris can be easily found by first finding the familiar shape of the Great Bear ‘Ursa Major' that is also sometimes called the Plough or even the Big Dipper by the Americans. Ursa Major is visible throughout the year from Britain and is always quite easy to find. This month it is high in the North East. Look for the distinctive saucepan shape, four stars forming the bowl and three stars forming the handle. Follow an imaginary line, up from the two stars in the bowl furthest from the handle. These will point the way to Polaris which will be to the north of overhead at about 50º above the northern horizon. Polaris is the only moderately bright star in a fairly empty patch of sky. When you have found Polaris turn completely around and you will be facing south. To use this chart, position yourself looking south and hold the chart above your eyes.
Planets observable in the evening sky: Mars and Uranus.
REMINDER: British Summer Time (BST) begins on 28th March
EXPLORING THE NIGHT SKY THIS MONTH
The Southern Night Sky 15th March 2021 at 20:00 GMT
The chart above shows the night sky looking south at about 20:00 GMT on 15th March. West is to the right and east to the left. The point in the sky directly overhead is known as the Zenith and is shown (in red) at the upper centre of the chart. The curved brown line across the sky at the bottom is the Ecliptic or Zodiac. This is the imaginary line along which the Sun, Moon and planets appear to move across the sky. The brightest stars often appear to form a group or recognisable pattern; we call these ‘Constellations'.
Constellations through which the ecliptic passes this month are Aquarius (the Water Carrier), Pisces (the Fishes), Aries (the Ram), Taurus (the Bull), Gemini (the Twins), Cancer (the Crab), Leo (the Lion) and Virgo (the Virgin).
Moving over the south western horizon is the constellation of Aries (the Ram). Aries looks faint and indistinct but it is worth finding this month because the planet Uranus is located within its boundaries. Uranus can be seen using binoculars but looking like a slightly blue ‘fuzzy' star. It does need a telescope to see well as a small blue disc.
High in the south west is the constellation of Taurus (the Bull). The most obvious star in Taurus is the lovely Red Giant Star called Aldebaran. It appears slightly orange to the ‘naked eye' but it is very obviously orange when seen using binoculars or a telescope. Aldebaran is located at the centre of the ‘flattened' X shape formed by the brightest stars in Taurus. It appears to be in a cluster of stars known as the Hyades but it is not a true member and is much closer to us.
The bright orange planet Mars is in Taurus but is now looking smaller as it moves further away from us. At the end of the top right (upper west) arm of the ‘X' of Taurus is the beautiful ‘naked eye' Open Star Cluster Messier 45 (M45) known as the Pleiades (or the Seven Sisters). It really does look magnificent using binoculars. Just above the star at the end of the lower left (east) arm of the ‘X' is the faint Supernova Remnant Messier 1 (M1) the Crab Nebula. This exploding star was seen as a bright new star in 1054 and can still be seen as a faint patch of light using a medium telescope in a dark and clear sky.
Following Taurus is the constellation of Gemini (the Twins). The two brightest stars in Gemini are Castor and Pollux that are named after mythological twins. To the north of Taurus is the odd pentagon shape of Auriga (the Charioteer). Dominating Auriga is the brilliant white star Capella which is almost directly overhead. For those with a telescope there is a line of lovely open clusters to search out in Taurus and Auriga. These are M35 in Taurus and M36, M37 and M38 in Auriga.
To the east (left) of Gemini is the rather indistinct constellation of Cancer (the Crab). The stars of Cancer are quite faint and can be difficult to discern especially in a light polluted sky. It is really worth searching out Cancer using binoculars or a telescope to see the Open Cluster M44 (the Beehive Cluster). M44 is older and further away than M45 (the Seven Sisters) so is fainter than M45 but still looks lovely. It has a group of stars that resemble an old straw Beehive with bees around it.
To the south of Taurus and Gemini is the spectacular constellation of Orion (the Hunter). Orion is one of the best known constellations and hosts some of the most interesting objects for us amateur astronomers to seek out. To the east of Orion are Orion's two hunting dogs represented by the stars Sirius and Procyon. Sirius is his large dog it is our brightest star and the closest that can be seen from the UK. Orion was the constellation of the month last month.
The constellation of Leo (the Lion) follows Cancer along the Ecliptic and will be the constellation of the month next month. It does actually look a little like a lion laying down or the Sphinx in Egypt.
CONSTELLATIONS OF THE MONTH
The constellations of Taurus, Auriga, Gemini, Cancer and Perseus
The chart above shows the constellations of Taurus (the Bull) , Auriga (the Charioteer), Gemini (the Twins) , Cancer (the Crab) and Perseus . The brightest stars in the constellations are joined using ‘dot to dot' stick figures. This is done to make the recognisable patterns of the stars easier to find. These are interesting constellations to search out and have some very interesting objects to see even when using just a pair of binoculars.
Cancer, Gemini and Taurus are located on the Ecliptic (shown as the brown line across the chart above). The Ecliptic is the imaginary line marking the equator of the Solar System. As the equator of Earth is tilted at 23.4º to the Ecliptic we see the Ecliptic tilted at 23.4º. The planets orbit the Sun on the plane of the Ecliptic. Therefore the Moon and Planets occasionally pass through these constellations as they appear to move along this imaginary line.
These spring constellations are especially interesting to the beginners to astronomy because they host some of the best Open Clusters. Open Star Clusters are listed in Charles Messier's Catalogue along with other objects of interest to amateur astronomers. Messier listed these objects along with Globular Clusters, Nebulae and Galaxies so they would not be mistaken for the comets he was searching for. Many of the brighter open clusters do look quite comet-like when viewed through binoculars. They are as the name suggests clusters of related stars and many are very beautiful to look at. M45 in Taurus is the brightest and most beautiful.
It is thought all stars form in vast clouds of gas and dust known as Nebulae (singular Nebula). Gravity pulls the atoms together into denser clumps until the gas and dust is compressed into very dense spheres. The temperature and pressure in the centre of the spheres rises until Nuclear Fusion begins. The Nuclear Fusion in the core produces an enormous amount of energy and the spheres begin to shine as stars and an Open Star Cluster is formed.
The Open Clusters M35, M36, M37 and M38 are further away than M45 so appear smaller and fainter. They can just about be seen using binoculars but a telescope is really required .
Taurus (the Bull)
The bright red star Aldebaran is located at the centre of Taurus. It is easy to find and therefore helps to identify the constellation of Taurus. It is in fact a Red Giant Star and that is why it appears distinctly orange. A Red Giant is a star similar to our Sun (perhaps a little larger) that is approaching the end of life as a normal star. It has used up most of its Hydrogen fuel and has swollen into a giant . Its outer layers are now stretched over a larger area so the available heat is also spread over a bigger area so its surface is cooler and appears orange in colour .
Surrounding the bright red star Aldebaran is an open cluster of Stars known as the Hyades. This is an older cluster and its stars have begun to disperse so Charles Messier did not include it in his Catalogue. It is also quite far away from us so the stars appear fainter. In a dark Moonless sky the cluster can be seen with the naked eye but is best seen using binoculars. The cluster is large, at 3.5° in diameter (about 7 Moon diameters) and is fairly dispersed.
The Open Star Clusters Hyades and Pleiades
The real jewel of Taurus is without doubt the beautiful Open Cluster Messier 45 (M45) that is also called ‘the Pleiades' or ‘the Seven Sisters'. M45 is a relatively young cluster and is close to us so its stars are very bright and appear close together.
Messier 45 (M45) is the brightest and best known of all the Open Clusters. See the following images. This is a cluster of about 300 stars in the constellation of Taurus. The cluster is known as the Pleiades but even more widely known as the Seven Sisters.
Six or possibly seven of the brightest stars in M45 are easily visible to the naked eye in a clear dark sky. They occupy an area of sky about the same size as the full Moon. Using a pair of 9 x 50 binoculars another thirty or so fainter stars can be seen embedded within the Seven Sisters.
M45 is visible to the naked eye initially looking like a patch of light. Closer observation will reveal a cluster of up to seven stars. Using a good pair of binoculars many more stars will be seen. There are in fact about 300 young stars in the cluster that is estimated to be about 100 million years old. M45 is one of the closest open clusters to us at 400 light years away.
The Pleiades look brighter than the stars of the Hyades because they are very bright large young stars and are relatively close to us. The largest star is Alcyone which is about 10 times the mass of our Sun and 1000 times brighter. The larger and brighter stars of the Pleiades are also rotating very fast.
Messier 45 (M45) the Pleiades (Seven Sisters)
The biggest and brightest stars of M45 (the Seven Sisters) have been named after seven sisters from Greek Mythology. They were the seven daughters of the Titan called Atlas and the sea-nymph Pleione and were born on Mount Cyllene.
The names of the Seven Sisters
Impressive as they are, the Seven Sisters are just the brightest (naked eye) stars in a cluster of around 300 young stars. In the images above the Seven Sisters appear to be surrounded by gas remaining from the original nebula. However it is now thought the cluster is just passing through a cloud of Hydrogen gas in space.
As M45 is so close to us the cluster has a relatively high apparent movement across the sky although it is still too slow for us to perceive. It will take 30,000 years to move a distance equal to the diameter of our Moon.
Although the cluster is moving through space the individual stars all have slightly different trajectories and relative speeds. Gradually over millions of years the stars will move further apart and the cluster will disperse, like the Hyades. Binoculars will reveal around 30 to 50 stars in the cluster and a telescope will reveal many more. However the cluster is too large to fit into the field of view of most telescopes so the outline of the cluster will be lost.
Auriga (the Charioteer)
Capella is the brightest star in the constellation of Auriga and the fourth-brightest star in the northern celestial hemisphere after Sirius, Arcturus and Vega. A prominent object in the northern winter sky, it is circumpolar to observers north of 44°N. Its name means "little goat" in Latin. Capella is depicted as the goat Amalthea that suckled Zeus in classical mythology. The Capella system is relatively close, at only 42.9 light-years from the Sun.
Although it appears to be a single star to the naked eye, Capella is actually a quadruple star system with two binary pairs made up of the stars Capella Aa, Capella Ab along with Capella H and Capella L.
Auriga has three Messier Clusters that can be seen using binoculars. These are M36, M37 and M38. See the chart above and the images below. This type of star cluster is called an ‘Open Cluster'. Open Clusters are groups of stars that have formed from the gas and dust in a Nebula (large cloud of gas and dust). These three open clusters appear to form a line across the constellation and there is a fourth cluster M35 in Taurus that also appears to be in this line. See the lower right image below. These clusters look like small smudges of light using binoculars. They are best seen using a telescope which will show many of the individual stars.
Messier 36 (M36)
Messier 37 (M37)
Messier 38 (M38)
Messier 35 (M35) and NGC2158
During the midwinter months Capella is almost directly overhead which makes it very easy to find. During the summer months it can be seen close to the northern horizon. The Milky Way (our galaxy) passes through Auriga and can be seen on the chart above. The three open clusters are seen against the dense star fields of the Milky Way.
The constellation of Auriga is joined to the constellation of Taurus at the most southerly star of Auriga called Elnath. Oddly Elnath is actually included in the lists of the stars belonging to both constellations.
Gemini (the Twins)
There is a fourth Open Cluster that appears to be in the same line as M36, M37 and M38 but is over the border in the constellation of Gemini, this is Messier 35 (M35). M35 is shown in the bottom right picture above. It appears to be in the same line of clusters as M36, M37 and M38 but the reality is none of these clusters are related and are just in the same line of sight. Gemini is named after the twins Pollux and Castor from Greek mythology.
The recognised shape of Gemini is in the form of a rough rectangle with Pollux and Castor at the eastern short side. A line of stars runs south west from Castor to the star Tejat Posterior. The line from Pollux takes a diversion south through kappa (?) then south west through Wasat to Alhena and Alzirr.
The two brightest stars in Gemini are Castor and Pollux which look quite similar and represent the twins. Castor and Pollux were the children of Leda. However Pollux was actually the son of Zeus who seduced Leda but Castor was the son of Tyndareus, King of Sparta and Leda's husband.
Gemini is easy to find because its two brightest stars are quite close together and similar in appearance. The two brightest stars are called Pollux (ß) and Castor (a) and are known as the Gemini Twins. Although Castor has been given the Greek letter designation a (alpha), which is normally given, to the brightest star in a constellation, Castor is not actually the brightest and Pollux is in fact the brighter of the two.
Pollux is brighter at magnitude +1.59 compared to the +1.9 of Castor. However Castor is a double star with a fainter companion that has a magnitude of +2.9 and separated by 6 arc-seconds. The two stars, known as Castor A and Castor B, orbit their common centre of gravity every 467 years. The pair can be separated in a 75mm aperture telescope on a good clear night.
Messier 35 (M35) is located at the end of the upper of the two lines of stars that emanate from Pollux and Castor. It is the most spectacular of the four Open Clusters and is shown above. M35 is particularly lovely as it has a spectacular string of stars that appear to cascade through its centre. NGC2158 is another open cluster located to the lower right of M35 but is further away, much fainter and probably could not be seen by Charles Messier.
Cancer (the Crab)
Cancer is a faint and rather indistinct constellation but it does have a rather nice Open Cluster called Messier 44 (M44) Praesepe or ‘the Beehive Cluster'. The stick figure shape of Cancer is an up-side-down letter ‘Y'. Although M44 is large, the stars are dispersed and fairly faint. It is quite difficult to find in a light polluted area so will require binoculars to see it.
Messier 44 (M44) Praesepe the Beehive Cluster
The constellation of Perseus
The constellations of Perseus and Cassiopeia with NGC884 and NGC 869
The chart above shows the constellation of Perseus that is host to one of the most beautiful and interesting open clusters visible using binoculars. This is the Double Cluster comprised of the two New General Catalogue (NGC) clusters NGC 884 and NGC 869. See the image below.
The Double Cluster in Perseus
The Double Cluster is easy to find and is visible to the ‘naked eye' on a clear and dark night. It is really beautiful to see using a pair of binoculars. It can be found by looking for the very distinctive ‘W' shape of Cassiopeia. Cassiopeia is located on the opposite side of Polaris (the Pole Star) to Ursa Major (the Plough) and is always in the northern sky. From Cassiopeia look for the line of stars leading to Taurus this is Perseus. In the space between the top of the line of stars in Perseus and Cassiopeia is a ‘fuzzy' patch of light, this is the Double Cluster.
THE SOLAR SYSTEM - MARCH 2021
The positions of the planets at midday on 15th March
The planets are not well placed this month. Most of the planets have recently passed through conjunction with the Sun and are moving into the morning sky just before the Sun rises in the east. A very keen astronomer will need to be out observing before sunrise and will need a clear view towards the south eastern horizon. Most planets will be in the sky during the day so will not be observable and will disappear over the western horizon before the Sun sets.
MERCURY will be rising just before the Sun low in the east this month and will be very difficult to see. The smallest planet will be close to Jupiter and Saturn as they rise in the bright dawn sky.
VENUS is now too close to the Sun and will not be visible. It is moving towards the Sun and into Superior Conjunction (behind the Sun) on 25th March 2021. It will emerge into the early evening sky in the west.
MARS is still well positioned in the evening sky for observing and will be in the south as the sky darkens. However it is getting smaller at just 5.8 arc-seconds as Earth pulls further away from it. Mars will be around until May but will be moving closer to the south western horizon and appearing smaller. After it has moved over the horizon we will not see it again for two years.
JUPITER will not be visible this month as it moving out from its conjunction with the Sun on 29th January so is hidden in the glare of the sky just before the Sun rises. From March onwards it will be worth getting up in the early hours to see it rising in the South East from about 05:30. Jupiter and Saturn will move further away from the Sun during the year and will be at their best for observing in August. Jupiter will be at opposition on 20th August.
SATURN will be even more difficult to see than Jupiter in the bright early morning sky. The ringed planet rises just before Jupiter in the South West at about 05:00. It is moving into the early morning sky before sunrise after its conjunction with the Sun on 24th January. Saturn will be at its best this year on 2nd August when it will be at opposition and will be due south at midnight.
URANUS will be more difficult to find and will really need a telescope. This month it will be observable in the south west but sets at about 22:00.
NEPTUNE will not be visible this month as it will be moving into conjunction with the Sun on 11th March. It will reappear in the morning sky after conjunction.
The Sun rises at about 06:35 at the beginning of the month and 05:50 at the end. It sets at 17:45 at the beginning of the month and 18:20 at the end. There have been very few Sunspots recently.
The Sun with some small sunspots imaged by SOHO on 24th February
THE MOON PHASES DURING MARCH
Last Quarter will be on 6th March
New Moon will be on 13th March
First Quarter will be on 21st March
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