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The Night Sky May 2009

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

Milky Way

Our Milky Way Galaxy
Image: NASA/JPL-Caltech

This is an artist's impression of how our Milky Way galaxy would appear as seen from above.   It is possible to study the structure of the Milky Way both in the radio and far infra-red parts of the electromagnetic spectrum whose wavelengths are not absorbed by the dust that makes it difficult to observe in the visible part of the spectrum.   The infrared observations have been made by the Spitzer Space Telescope   We believe that there are two main spiral arms starting from opposite ends of a central bar.   Our Sun lise in what is called the Orion Spur which lies between the two main arms below the centre of the image as shown in the annotated image below.

Milky Way
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Highlights of the Month

May: Perhaps the last good month to observe Saturn in the evening sky

Saturn
Hubble Image of Saturn
Image NASA

To see some of Damian Peache's Saturn Images: Damian Peache's website

Saturn is now high in the southern sky after nightfall in the constellation of Leo.  It lies well below the body of Leo some 8 degrees below the star Theta Leonis.   It starts the month at magnitude +0.8 with an angular size of ~18.8 arc seconds and these fall to +0.9 and 18.1 as the month progresses.  Saturn is significantly less bright this year than it sometimes is: the rings are very close to edge on (as shown in the Hubble image of Saturn) and thus there is less apparent reflecting area.   During May they are at an angle of ~4 degrees from the line of sight.   The rings will be seen (or rather - not seen) edge-on later this year 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 2nd: Mercury and the Pleiades Cluster after sunset

May2nd
May 2nd: After sunset
Image Stellarium/IM

The image above shows Mercury and the Hyades and Pleiades clusters after sunset on the second of May.   The sky brightness has been reduced to show the possitions more clearly, but you should expect to have a brighter sky background and binoculars may well be needed.   A low western horizon will also be required. However, given this and a clear sky, it will be the last chance to see Mercury for a while as it passes behind the Sun on May 18th. It will make a pretty sight just to the left of the Pleiades Cluster. Its magnitude will be +1.1 on the 1st May falling rapidly to +2.7 in the following week.

May 21st: Venus, Mars and the Crescent Moon in the pre-dawn sky

May21st
May 21st: Pre-dawn Sky
Image Stellarium/IM

The image above shows the positions of Venus, Mars and the thin crescent Moon in the hour before dawn (about 4:15 BST) on the 21st May.   The sky brightness has been reduced to make the positions more obvious.   It will probably be necessary to use binoculars to spot Mars to the left of Venus, and you will need to have a good low horizon towards the East.

Observe the International Space Station

The International Space Station
The International Space Station and Jules Verne passing behind 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.)

Note: I observed the ISS three times in the last week or so of July and was amazed as to how bright it has become.

Find details of sighting possibilities from your location from: Location Index

See where the space station is now: Current Position

The Moon

3rd Quarter Moon
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.
new first quarter full moon last quarter
May 24th May 2nd May 9th May 17th

Some Lunar Images by Ian Morison, Jodrell Bank Observatory: Lunar Images

The Planets

 A montage of the Solar System
A montage of the Solar System. JPL / Nasa

Jupiter

Jupiter
A Cassini image of Jupiter . Nasa
Jupiter becomes more easily visible this month as its elevation in the pre-dawn sky is getting higher - about 23 degrees above the horizon by month's end.   It rises at about 3am BST at the beginning of the month and 1am by month's end.   During May its separation from the Sun increases from 77 degrees to 101 degrees, and its magnitude slowly increases from -2.3 to -2.5.   Sadly at the present time Jupiter is close to the lowest part of the ecliptic and never reaches more than ~25 degrees above the horizon even when it will be seen due south, so highest in the sky, later this year.   It will lie just below the the last quarter Moon on the 17th in the pre-dawn sky.

Saturn

Saturn
The planet Saturn. Cassini - Nasa

Saturn see highlight above.

Mercury

Mercury.
Messinger image of Mercury Nasa

Mercury: see highlight above.

Mars

Mars showing Syrtis major.
A Hubble Space Telescope image of Mars.
Jim Bell et al. AURA / STScI / Nasa

Mars still remains low in the pre-dawn sky this month, but as it rises increasingly earlier than the Sun as the month progresses will become easier to spot.   It has a magnitude of +1.2.   By the end of the month, the angular separation from the Sun has increased to 40 degrees which helps, but as the ecliptic makes such a small angle to the horizon that Mars will then be just 11 degrees above the horizon as the Sun rises.   We will have to wait a month or so until it will be seen easily in the pre-dawn sky.  See highlight above.

Venus

Venus
Venus showing some cloud structure

Venus passed betwen the Earth and Sun in March so is now visible in the pre-dawn sky.   It will only lie 12 degrees above the horizon as the Sun rises on the first of May, so will be easier to spot later in the month.   It is at magnitude -4.4 at mid month, up and to the right of Mars.   In the middle of May, a small telescope will show a crescent phase equivalent to just before a first quarter Moon.   An interesting fact about its brightness is that it stays pretty constant at about -4.4 for most of the time that it is visible even though the apparent phase changes greatly.   When the phase is thin, Venus is nearer to us and the effective reflecting area of Venus as seen from Earth remains pretty constant.   See highlight above.

Radar Image of Venus
Radar image showing surface features

Find more planetary images and details about the Solar System: The Solar System

The Stars

The evening May Sky

May Sky
The May Sky in the south - after sunset.

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
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

Gemini
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.

Gemini
The Eskimo Nebula, NGC2392, Hubble Space Telescope

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

Leo
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.

M65 and M66
The galaxies M65 and M66
M65 M66
M65 - Type Sa spiral, 9.3 magnitude M66 - Type Sb spiral, 8.9 magnitude

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.

M95 and M96
The galaxies M95 and M96
M95 M96
M95 - Type SBb spiral, 9.7 magnitude M96 - Type Sa spiral, 9.2 magnitude

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.

NGC2903
The 8.9th magnitude, type Sb, Galaxy NGC2903

The constellation Virgo

Virgo
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.

M87 MERLIN images
The Giant Elliptical Galaxy M87 HST image showing the jet

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 Sombrero Galaxy
M104 - The Sombrero Galaxy

The constellation Ursa Major

Ursa Major
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.

M81 and M82
M81 and M82

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).

M101
M101 - The Ursa Major Pinwheel Galaxy

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.

M51
M51 - The Whirlpool Galaxy

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.

Owl Nebula Owl Nebula
M97 - The Owl Planetary Nebula Lord Rosse's 1848 drawing of the Owl Nebula