THE NIGHT SKY - OCTOBER 2007

The chart above shows the night sky as it appears on 1 st October at 21:00 British Summer Time ( 9 o'clock 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 at 8 o'clock at the middle of the month and at 7 o'clock at the end of the month. Due to the Earth rotating once every 24 hours, the stars also appear to move 15º (360º divided by 24) each hour from east to west.

The centre of the chart will be the position in the sky directly overhead. 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 moving towards the North Western 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.

(click on one of the months shown below to view the chart for another month)

The diagram above shows the positions of the planets in their orbits around the Sun. The view is looking down from directly above the Sun. Earth is shown as the green circle below the Sun and all the other planets except Pluto which is no longer classed as a planet have their names against them.

We view the diagram at midnight GMT around the middle of October. Other people who are on the side of Earth facing the Sun are in daytime and people on the opposite side to the Sun are in night time. Anyone on the right side of Earth is at dawn and at dusk on the left. The parts of the diagram that are shaded indicate night sky as seen from Earth. For us in Britain south is at the bottom of the diagram. We are located on the opposite side of Earth to the Sun at midnight . As we look to the south, (down) east is to our left and west to our right.

To use the diagram we must imagine we are standing on the opposite side of Earth to the Sun. At this point we are in the shadow of Earth and therefore it is night. Planets in the shaded part of the diagram are visible during at least some of the night and those in the un-shaded portion are in daylight. Planets just outside the daylight area on the right will be visible just before dawn or on the left for a while after sunset.

Mercury is close to the day / night line but on the night side and to the west (left) of the diagram so it is just visible low in the evening sky. Venus is on the opposite side of the Sun to Earth and therefore cannot be seen.

Mars is to the west and moving into the day side of the diagram so is not visible. Jupiter is to the left so it is moving towards the western horizon as the Sun sets and is not really observable.

THE PLANETS THIS MONTH

VENUS the second planet from the Sun, is observable as the very bright ‘Morning Star'. It rises at 02:16 in the east, 3 hours before sunrise. In a small telescope or a pair of 10 x 50 binoculars, Venus will appear as a bright thin crescent (new moon shape) although no surface features will be visible on this cloud shrouded world. Venus will be at greatest elongation (furthest from the Sun) on 28 th October it will be at magnitude of -4.5 all month. As it moves further away from the Sun it will appear to decrease in diameter but it will gradually become fuller on the 27 th in will be at half phase (left image below).

The appearance of Venus as it moves away from the Sun

MARS is well clear of the Sun and can be seen rising in the south east at about 22:00 GMT in the evening. It is still a long way from us and appears quite small. It is just starting to appear as a reasonable size for observing detail (10 arcseconds).

When viewed through a telescope the shape is distinctly gibbous (like a ¾ moon shape). There is not much visible on the surface at present due to a huge sand storm that is sweeping across the surface of the whole planet. The images below taken by Damian Peach show how the dust storm developed over a 9 day period in July this year.

The dust storm 9 th July and 18 th July Image Damian Peach

As Earth catches up with Mars (around Christmas) the view will be much better and because Mars will be high in the sky a lot of detail should be visible even in a modest telescope (150mm).

JUPITER is just moving out of view into the western twilight. The king of planets has not been in a favorable position for observing this year as it has been low in the southern sky and in the more turbulent air. It will be setting at 20:13.

SATURN rises at 02:47 and may be observed for about an hour before sunrise in the constellation of Leo but needs a clear view to the eastern horizon. The ring system is rapidly closing now and looks a lot narrower than last year. It is moving into a position where we will be viewing the rings side on. The ring system is about 200,000 kilometres in diameter but only a hundred metres or so thick. One advantage is that we will see the moons crossing in front and behind the plant more regularly.

The angle of Saturns rings 2005 and 2006

URANUS rises at 17:09 and is observable for most of the night located in the constellation of Aquarius in the southern sky. It will be visible in binoculars but it is small, faint and quite difficult to find. In a 100mm or larger telescope it appears as a bluish, rather fuzzy star. In a larger telescope a small blue disc can be seen.

Uranus imaged by Kyle Edwards Central Arkansas Astronomical Society

NEPTUNE rises at 16:20 and has recently passed opposition. It is located in the constellation of Capricornus in the south west at midnight . Although Neptune is almost a twin to Uranus it is twice as far away and therefore appears only a quarter as bright. This makes it very difficult to find in a small telescope.

Neptune imaged by Kyle Edwards Central Arkansas Astronomical Society

MOON - The Moon is always worth observing especially if you do not have a telescope but do have a pair of binoculars. It is much better to observe the Moon when it is not full because, at the terminator, there are shadows to give the landscape depth. Even a small telescope will show great detail. Craters, mountains, valleys and vast smooth plains known as seas or mares can all be seen. On 7 th October the Moon will pass in front of the bright star Regulus in Leo at 05:20 and reappears at 05:54.

MOON PHASES THIS MONTH

Last Quarter 3 rd October

New Moon 11 th October

First quarter 19 th October

Full Moon 26 th October

METEOR SHOWER THIS MONTH

Around the 21st to 24th October there will be a meteor shower known as the Orionids. The shower is called the Orionids because the meteors appear to emanate from within the constellation of Orion ‘The Hunter'. If we were to mark the path of each meteor on a sky chart we would see that the meteors all appear to radiate from the same point in the sky.

The meteors in the Orionid shower were created when dust particles that originated in the tail of the famous Comet Halley crash into our atmosphere. As the comet approached the Sun in 1986 and every 76 years before, the dusty ice that the comet is composed of melted and was blown away by the Solar Wind to form the tail. Once a year Earth passes through part of the ring of dust left by the comet.

To observe the shower we do not need any special equipment. The best thing to do is to sit on a garden recliner chair that has been set up so that the observer can see the sky towards the east. Make sure there are no lights shining in your eyes. Cover any light sources or set up a screen to block the light. Look to the east at about 45° above the horizon. The best time to look out for the meteors will be after midnight on the night of 21st / 22nd and the nights before and after. There will be a 76% Moon but it will be setting before 01:00 GMT.

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