The Night Sky May 2008
Compiled by Ian Morison
This page, updated monthly, will let you know some of the things that you can look out for in the night sky. It lists the phases of the Moon, where you will see the naked-eye planets and describes some of the prominent constellations in the night sky during the month.
Image of the Month
The Cat's Eye Nebula, NGC 6543,
Image: Vincent Peris, Hubble Space Telescope, NASA
This is a new image of the Cat's Eye Nebula, processed to enhance the visibility of its complex structure. The cat's Eye nebula lies at a distance of three thousand light years and spans over half a light year across. It is a Planetary Nebula - a result of the final outflow of material from a star similar to our Sun. The name "planetary nebula" was given to these beautiful objects as some appear like planetary disks, but they have nothing to do with planets! When nuclear fusion ends in the core of a sun-like star - then composed mainly of carbon and oxygen - there is nothing to prevent gravity compressing it until it reduces in size to about the size of the Earth. At this point what is called electron degeneracy pressure prevents further collapse and the stellar remnant will become a white dwarf. The outer parts of the star are blown off into space producing wonderful images such as this.
Highlights of the Month
April: Saturn in the evening sky
To see more of Damian Peache's Images: Damian Peache's website
Saturn is now high in the southern-western sky during the evening lying, as May begins, in the constellation of Leo just 2 degrees to the left of Leo's brightest star, Regulus. It starts the month at magnitude +0.5 with an angular size of ~18.7 arc seconds and these fall to +0.7 and 17.7 as the month progresses. Saturn is not as bright this year as it sometimes is: the rings are closing (just ~ 9 degrees tilt to us and subtending only 5 arc seconds) and thus there is less apparent reflecting area. The rings will be seen (or rather - not seen) edge on in 2009 and it will not be until 2016 that they will be at their widest again. A small telescope will easily show its largest moon, Titan, and show some bands around the surface.
May 5th: An evening skyscape
Looking west after sunset on the evening of the 5th May, you should see, if clear, Mars, having a salmon pink colour, in line with Castor and Pollux. This is the night that Mars crosses from Gemini into Cancer.
May 6th: Mercury and the thin crescent Moon
Looking west just after the Sun has set on the evening of the 6th May, you may be able to pick out a very thin crescent Moon lying between The Pleiades Cluster, below, and Mercury above. The sky-light has been reduced in the image above, so binoculars will probably help in picking them out. Mercury moves towards greatest elongation on the 13th May but, by then, it will have dropped from -1 to +0.3 magnitudes. These first two weeks of May are the best chance of viewing Mercury this year.
Observe the International Space Station
The International Space Station and Jules Verne passing behinfd the Lovell Telescope on April 1st 2008.
Image by Andrew Greenwood
Use the link below to find when the space station will be visible in the next few days. In general, the space station can be seen either in the hour or so before dawn or the hour or so after sunset - this is because it is dark and yet the Sun is not too far below the horizon so that it can light up the space station. As the orbit only just gets up the the latitude of the UK it will usually be seen to the south, and is only visible for a minute or so at each sighting. Note that as it is in low-earth orbit the sighting details vary quite considerably across the UK. The NASA website linked to below gives details for several cities in the UK. ( Across the world too for foreign visitors to this web page.)
Find details of sighting possibilities from your location from: Location Index
See where the space station is now: Current Position
The Moon at 3rd Quarter. Image, by Ian Morison, taken with a 150mm Maksutov-Newtonian and Canon G7.
Just below the crator Plato seen near the top of the image is the mountain "Mons Piton". It casts a long shadow across the maria from which one can calculate its height - about 6800ft or 2250m.
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|May 4th||May 11th||May 19th||May 27th|
Some Lunar Images by Ian Morison, Jodrell Bank Observatory: Lunar Images
Jupiter is now rising earlier in the night - just before midnight by the end of May. It is lying in the Constellation Sagittarius where it remains during the month. At the beginning of May, Jupiter rises at about 01.30 UT, three hours before the Sun. However, it is now at the lowest point of the ecliptic in the sky and will only rise to about 15 degrees elevation before sunrise when it is just east of south. Thus sadly, this year our views of Jupiter from northern latitudes will be rather poor. Its magnitude is ~-2.5 throughout May and its angular size increases from 41 to 45 arc seconds through the month. Despite the low elevation, even a small telescope will show the Galilean Moons as they weave their way around it. Due to refraction, we see Jupiter at very slightly different elevations in the different colours of the spectrum, thus bluring the image. A cleaner image may seen if one observes through a narrow band filter such as an OIII filter.
Saturn - See highlight above.
Mercury - See highlight above.
Mars can still be seen high in the west after sunset, but it and our Earth are now seperating quite quickly so that both the brightness and angular size of Mars fall quite rapidly this month - the magnitude from +1.2 to +1.5 and the angular size from 5.8 to 5 arc seconds.
On the 5th May it passes from Gemini into Cancer and will make an equally spaced objects with Castor and Pollux see highlight above . The disk is now so small that it will be very hard so see any details on the salmon pink surface.
Venus is so close to the Sun in direction this month that it will be lost in its glare. We will have to wait until the end of July when it will become visible low in the west after sunset.
Find more planetary images and details about the Solar System: The Solar System
The evening May Sky
This map shows the constellations seen in the south after sunset.
The constellation Gemini is now setting towards the south-west and Leo holds pride (sic) of place in the south with its bright star Regulus. Between Gemini and Leo lies Cancer - which is well worth observing with binoculars to see the Beehive Cluster at its heart. Just into Leo, close to the boundary with Cancer, is the planet Saturn. Below Gemini is the tiny constellation Canis Minor whose only bright star is Procyon. Rising in the south-east is the constellation Virgo whose brightest star is Spica. Though Virgo has few bright stars it is in the direction of of a great cluster of galaxies - the Virgo Cluster - which lies at the centre of the supercluster of which our local group of galaxies is an outlying member. High overhead in the north is the constellation Ursa Major which also contains many interesting objects.
The constellation Gemini
Gemini - The Twins - lies up and to the left of Orion and is in the south-west during early evenings this month. It contains two bright stars Castor and Pollux of 1.9 and 1.1 magnitudes respectivly. Castor is a close double having a separation of ~ 3.6 arc seconds making it a fine test of the quality of a small telescope - providing the atmospheric seeing is good! In fact the Castor system has 6 stars - each of the two seen in the telescope is a double star, and there is a third, 9th magnitude, companion star 73 arcseconds away which is alos a double star! Pollux is a red giant star of spectral class K0. The planet Pluto was discovered close to delta Geminorum by Clyde Tombaugh in 1930. The variable star shown to the lower right of delta Geminorum is a Cepheid variable, changing its brightness from 3.6 to 4.2 magnitudes with a period of 10.15 days
M35 and NGC 2158
This wonderful image was taken by Fritz Benedict and David Chappell using a 30" telescope at McDonal Observatory. Randy Whited combined the three colour CCD images to make the picture
M35 is an open star cluster comprising several hundred stars around a hundred of which are brighter than magnitude 13 and so will be seen under dark skies with a relativly small telescope. It is easily spotted with binoculars close to the "foot" of the upper right twin. A small telescope at low power using a wide field eyepiece will show it at its best. Those using larger telescopes - say 8 to 10 inches - will spot a smaller compact cluster NGC 2158 close by. NGC 2158 is four times more distant that M35 and ten times older, so the hotter blue stars will have reached the end of their lives leaving only the longer-lived yellow stars like our Sun to dominate its light.
To the lower right of the constellation lies the Planetary Nebula NGC2392. As the Hubble Space Telescope image shows, it resembles a head surrounded by the fur collar of a parka hood - hence its other name The Eskimo Nebula. The white dwarf remnant is seen at the centre of the "head". The Nebula was discovered by William Herschel in 1787. It lies about 5000 light years away from us.
The constellation Leo
The constellation Leo is now in the south-eastern sky in the evening. One of the few constellations that genuinely resembles its name, it looks likes one of the Lions in Trafalger Square, with its manem and head forming an arc (called the Sickle) to the upper right, with Regulus in the position of its right knee. Regulus is a blue-white star, five times bigger than the sun at a distance of 90 light years. It shines at magnitude 1.4. Algieba, which forms the base of the neck, is the second brightest star in Leo at magnitude 1.9. With a telescope it resolves into one of the most magnificent double stars in the sky - a pair of golden yellow stars! They orbit their common centre of gravity every 600 years. This lovely pair of orange giants are 170 light years away.
Leo also hosts two pairs of Messier galaxies which lie beneath its belly. The first pair lie about 9 degrees to the west of Regulus and comprise M95 (to the east) and M96. They are almost exactly at the same declination as Regulus so, using an equatorial mount, centre on Regulus, lock the declination axis and sweep towards the west 9 degrees. They are both close to 9th magnitude and may bee seen together with a telescope at low power or individually at higher powers. M65 is a type Sa spiral lying at a distance of 35 millin klight years and M66, considerably bigger than M65, is of type Sb. Type Sa spirals have large nuclei and very tightly wound spiral arms whilst as one moves through type Sb to Sc, the nucleus becomes smaller and the arms more open.
The second pair of galaxies, M95 and M96, lie a further 7 degrees to the west between the stars Upsilon and Iota Leonis. M95 is a barred spiral of type SBb. It lies at a distance of 38 million light years and is magnitude 9.7. M96, a type Sa galaxy, is slightly further away at 41 million light years, but a little brighter with a magnitude of 9.2. Both are members of the Leo I group of galaxies and are visible together with a telescope at low power.
There is a further ~9th magnitude galaxy in Leo which, surprisingly, is in neither the Messier or Caldwell catalogues. It lies a little below lambda Leonis and was discovered by William Herschel. No 2903 in the New General Catalogue, it is a beautiful type Sb galaxy which is seen at somewhat of an oblique angle. It lies at a distance of 20.5 million light years.
The constellation Virgo
Virgo, rising in the east in late evening this month, is not one of the most prominent constellations, containing only one bright star, Spica, but is one of the largest and is very rewarding for those with "rich field" telescopes capable of seeing the many galaxies that lie within its boundaries. Spica is, in fact, an exceedingly close double star with the two B type stars orbiting each other every 4 days. Their total luminosity is 2000 times that of our Sun. In the upper right hand quadrant of Virgo lies the centre of the Virgo Cluster of galaxies. There are 13 galaxies in the Messier catalogue in this region, all of which can be seen with a small telescope. The brightest is the giant elliptical galaxy, M87, with a jet extending from its centre where there is almost certainly a massive black hole into which dust and gas are falling. This releases great amounts of energy which powers particles to reach speeds close to the speed of light forming the jet we see. M87 is also called VIRGO A as it is a very strong radio source.
Below Porrima and to the right of Spica lies M104, an 8th magnitude spiral galaxy about 30 million light years away from us. Its spiral arms are edge on to us so in a small telescope it appears as an elliptical galaxy. It is also known as the Sombrero Galaxy as it looks like a wide brimmed hat in long exposure photographs.
The constellation Ursa Major
The stars of the Plough, shown linked by the thicker lines in the chart above, form one of the most recognised star patterns in the sky. Also called the Big Dipper, after the soup ladles used by farmer's wives in America to serve soup to the farm workers at lunchtime, it forms part of the Great Bear constellation - not quite so easy to make out! The stars Merak and Dubhe form the pointers which will lead you to the Pole Star, and hence find North. The stars Alcor and Mizar form a naked eye double which repays observation in a small telescope as Mizar is then shown to be an easily resolved double star. A fainter reddish star forms a triangle with Alcor and Mizar.
Ursa Major contains many interesting "deep sky" objects. The brightest, listed in Messier's Catalogue, are shown on the chart, but there are many fainter galaxies in the region too. In the upper right of the constellation are a pair of interacting galaxies M81 and M82 shown in the image below. M82 is undergoing a major burst of star formation and hence called a "starburst galaxy". They can be seen together using a low power eyepiece on a small telescope.
Another, and very beautiful, galaxy is M101 which looks rather like a pinwheel firework, hence its other name the Pinwheel Galaxy. It was discovered in1781 and was a late entry to Messier's calalogue of nebulous objects. It is a type Sc spiral galaxy seen face on which is at a distance of about 24 million light years. Type Sc galaxies have a relativly small nucleus and open spiral arms. With an overall diameter of 170,000 light it is one of the largest spirals known (the Milky Way has a diameter of ~ 130,000 light years).
Though just outside the constellation boundary, M51 lies close to Alkaid, the leftmost star of the Plough. Also called the Whirlpool Galaxy it is being deformed by the passage of the smaller galaxy on the left. This is now gravitationally captured by M51 and the two will eventually merge. M51 lies at a distance of about 37 million light years and was the first galaxy in which spiral arms were seen. It was discovered by Charles Messier in 1773 and the spiral structure was observed by Lord Rosse in 1845 using the 72" reflector at Birr Castle in Ireland - for many years the largest telescope in the world.
Lying close to Merak is the planetary nebula M97 which is usually called the Owl Nebula due to its resemblance to an owl's face with two large eyes. It was first called this by Lord Rosse who drew it in 1848 - as shown in the image below right. Planetary nebulae ar the remnants of stars similar in size to our Sun. When all possible nuclear fusion processes are complete, the central core collpses down into a "white dwarf" star and the the outer parts of the star are blown off to form the surrounding nebula.