WHAT'S UP THIS MONTH - SEPTEMBER 2011

THESE PAGES ARE INTENDED TO HELP YOU FIND YOUR WAY AROUND THE SKY THIS MONTH

Whole Sky chart for 15th September 2011 at 21:00 (9 o'clock) BST viewed from Southern England

The chart above shows the night sky as it appears on 15th September at 9 o'clock in the evening British Summer Time (BST). 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 10 o'clock BST at the beginning of the month and at 8 o'clock BST 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 close to the north eastern horizon. 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 in the morning sky are: Mercury and Mars Planets in the night sky are: Jupiter, Uranus and Neptune.

.

CONSTELLATION TO LOOK FOR THIS MONTH - PEGASUS

Chart showing the location of the Constellation of Pegasus

The most striking feature of Pegasus is the ‘Great Square' that can be seen to the lower left in the chart above. Strangely the star Alpheratz at the top left of the square is in fact a member of Andromeda and not Pegasus but it is always joined (dot to dot) to form the Great Square of Pegasus. Pegasus has no interesting objects within the square but the square does have an interesting use for the amateur astronomer. There are up to five stars that can be seen reasonably to the naked (unaided) eye depending on the seeing conditions. If it is a misty evening then no stars will be seen other than the four making up the square and seeing faint objects is likely to be difficult. If two or three stars can be seen then the viewing for the evening should be quite good and some of those eagerly sought after faint objects may be within our light grasp. If four or five stars can be seen then observing is likely to be as good as it gets in this country. So a quick look at the Square of Pegasus before dressing up to keep warm or setting up the telescope could give an indication as to whether it is going to be worthwhile images.

M15 shown at the bottom centre of the chart above is a very nice Globular Cluster. This stunning ball of about 100,000 stars is just visible using 10 x 50 binoculars as a small fuzzy patch of light. A small telescope will show it as a ball of stars but a larger telescope will reveal its true glory and even show individual stars on the edge of the cluster. Globular Clusters are thought to be the remains of smaller galaxies that have ventured too close to our galaxy and had their outer star ripped off by gravity.

.

M15 a beautiful Globular Cluster in Pegasus

THE SOLAR SYSTEM THIS MONTH

The location of the planets this month (Saturn is behind our point of view)

The chart above shows the positions of the planets in the southern night sky this month. .

MERCURY rises at 04:36 on 1st September, 05:23 on 15th and 06:30 on 30th but will be close to the rising Sun. The smallest planet will be at greatest western opposition on 3rd and will be just be observable in the east before sunrise. DO NOT SWEEP ACROSS THE SKY WITH BINOCULARS OR A TELESCOPE LOOKING FOR MERCURY WHEN THE SUN IS IN VIEW OR YOU COULD DAMAGE YOUR EYES. rises at 04:36 on 1st

The locations of Mercury before sunrise in the east during the first half of this month

VENUS rises over the eastern horizon at about 07:00 in daylight and will not be observable this month .

MARS rises at 01:27 on 1st September, 01:21 on 15th and 01:16 on 30th but is still too small and will not really be observable .

JUPITER rises at rises at 21:21 on 1st September, 20:41 on 15th and 19:00 on 30th . It will be low in the east at the time shown in the chart above but will be observable for the rest of the night in the constellation of Aries. Jupiter is now coming into view at a much more convenient hour so this will be a major interest well into next year.

. Jupiter imaged on 2nd September 2010 (south is at the top)

SATURN rises at 09:22 on st September, 08:49 on 15th and 08:16 on 30th but will be in daylight and so will not be observable .

URANUS rises at 19:29 and will be observable all night this month. It will be at opposition (due south at 24:00 GMT) on 26th September and as so will be at its best. A telescope will show Uranus looking like a rather fuzzy blue tinted star in the constellation of Pisces .

NEPTUNE rises at 18:28 and will be observable all night this month. It looks rather like Uranus in a telescope but smaller and fainter. It is located in the constellation of Aquarius.

Dwarf planets CERES and VESTA will be visible in the southern sky this month. These are the two largest objects in the asteroid belt. See the chart above showing the location of the planets this month The images below were taken by the Hubble Space Telescope:

Ceres (diameter 950 km) magnitude +7.6	Vesta (diaameter 530 km) magnitude +5.6

METEORS There are no meteor showers this month but there may still be the odd sporadic meteor to be seen.

THE MOON is always a good target for binoculars or a small telescope. It is also the first object for a beginner to go for because it is large and bright. The best times for observing the features on the Moon will be during the periods 1st – 10th and 15th – 26th March. During these times the terminator (the boundary between light and dark) will cross the surface bringing different areas into better view due to the long shadows being cast by the sunlight. During full Moon there are no shadows so details a difficult to make out. When the Moon is full it can be too bright for using binoculars or a telescope but naked eye views are best when the Moon is full. The dark areas called Maria (seas) can be seen with the unaided eye but these are of course not seas at all. They are in fact large impact sites that filled with molten rock from below as a result of the impact. Some of the largest craters may also be seen using binoculars. A small telescope will show breathtaking detail on the surface. The views of the Moon are always interesting with different features coming into view as the 'Terminator' line between sunlight and night moves across the surface from night to night.

The full Moon looks best to the un-aided eye	Features are best seen on the 'Terminator'

The phases of the Moon during September

THE SUN Observing the Sun is a very interesting thing to do especially in the summer when the sky is light until 10:30 or even 11:00 around mid-summer. Like the Moon the Sun is a large target and is of course very bright. Here we must mention safety. Never use a telescope or binoculars to look directly at the Sun. This must only be done when a special solar filter is fitted or if the image of the Sun is projected on to a screen. The Sun has an eleven year cycle of increasing sunspot activity. The build up to the next maximum activity has been slow to start and sunspots have been few and far between. However a number of large spots appeared during late June and early July. The Solar maximum should reach its expected peak during 2013 when there should be more activity and more Sun Spots .

Sunspots as they appeared on the Sun on 1st July 2011	A closer view of the sunspots on 1st July 2011

A special solar filter must be fitted to a telescope to view the Sun or alternatively the image can be projected on to a screen.

.

RETURN TO HOME PAGE