THE WINTER SKY

Sky chart for 1st July 2009 at 23:00 (11 o'clock) BST viewed from Southern England

The chart above shows the night sky as it appears on 1 st July at 11 o'clock British Summer Time (10 o'clock 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 10 o'clock p.m. BST at the beginning middle the month and at 9 o'clock am BST at the end. 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 summer night sky is dominated by the Summer Triangle made up of three bright stars: Deneb in Cygnus, Vega in Lyra and Altair in Aquila .

CYGNUS is a beautiful constellation and has a number of interesting things to see. During late Summer and Autumn, it is almost directly overhead. It forms a distinctive cross shape that does actually look a bit like the Swan it is named after. When viewed through binoculars or a telescope, the observer will be amazed by the number of stars in the field of view. This is because Cygnus sits right on the Milky Way and has a background of rich star fields. Look for Cygnus on the chart above.

The bright star Deneb is one of the brightest stars that we can see in our skies. Unfortunately Deneb is in the swan's tail, if it had been in the head it would have made a great eye. It is a bright hot white star, much brighter and hotter than our own sun at 10,000 ° C (the Sun is 6,400 ° C).

The star at the swan's head, furthest from Deneb on the centre line forming Cygnus, is called Albireo and it is beautiful to look at in a small telescope. It is actually a double star comprised of non identical twins. One star is a bright golden colour while the other is a beautiful sky blue.

Because they are so close together the colour difference is very noticeable. Also in Cygnus just north of Deneb, M39 is a small open cluster of about 20 stars all about 900 light years away.

LYRA can be found on the chart above, between the constellations of Hercules and Cygnus. The brightest star is Vega, the most westerly of the stars that form the summer triangle. Vega is one of the brightest stars in our night sky, the name Vega means 'Eagle' or 'Vulture'. Like Deneb, Vega is a bigger and brighter star than our Sun and much hotter at 10,000°C. It also appears bright because it is very close at only 27 light years away. Vega forms a triangle with two fainter stars Sulaphat and Sheliak.

Sheliak is a variable star of a type known as an eclipsing binary. This is a pair of stars that are orbiting each other in a very close orbit. When one passes in front of the other only one is seen so there is less light, when they are apart we see the light of the pair so it is brighter. The brightening period is about 12 days.

Between Sulaphat and Sheliak is a beautiful Planetary Nebula called the Ring Nebula. The Ring Nebula is number M57 in Charles Messier's catalogue. A small telescope should show the Ring Nebula as a tiny 'smoke ring' like object, a larger telescope will show the ring clearly. It is the remnant of an old star that has used up all its hydrogen fuel. It has blown off its outer layers (the ring) and collapsed to form a small white dwarf star.

The chart above is from Richard Fleet's GRAPHDARK application that can be downloaded free from his website at: www.rfleet.clara.net .

The dates for the from July 2009 through to December 2009 are shown along the bottom of the chart and the time up the sides. The areas shown light blue at the top and bottom indicate daylight. The lower thick curved line shows the start of dusk and the upper shows the end of dawn (full daylight). The conical curved black line shows full darkness. The thinner curved black lines show the legal ‘lighting up' times. The curved vertical bands show the Moon phases (white the moon is in the sky, black it is not). The coloured lines show the times when the planets are visible.

MERCURY is not observable at beginning of this month but will be in its best viewing position of the year by the end of the month in the western evening twilight.

VENUS will be visible in the dawn twilight for the whole of the summer but will not be in a dark sky until the beginning of August. The disc of Venus is large as it emerges from inferior conjunction (between Earth and the Sun) its crescent is thin but will become wider as it starts to move further from the Sun . The disc of Venus has become larger as it moves closer to Earth but its crescent will become narrower.

MARS is starting to become observable this month in the brightening eastern sky before sunrise. However it will not be in a good position until August .

JUPITER rises over the eastern horizon before midnight. However it will be very low in the sky for the whole of summer in the constellation of Capricornus. The four brightest moons will be visible even in a small telescope but detail on the surface will be difficult to make out due to the poor atmospheric conditions close to the horizon.

Jupiter is the largest of all the planets and is over ten times the diameter of Earth. Unlike the inner planets Jupiter has no solid surface because it is comprised almost entirely of gas, although it may have a small rocky and metallic core.

Jupiter has an orbit approximately 778 million km from the Sun and its diameter at the equator is 142,984 km (Earth 12,756 km). Its volume is large enough to swallow all the other planets. Despite being so large Jupiter rotates very fast, in fact, a day on Jupiter is equivalent to only 9.9 Earth hours. This is so fast that the centrifugal force of the spin causes the planet to bulge noticeably at its equator.

The surface of the planet has many coloured bands or ‘belts' of different colours some of which can be seen even in a small telescope. These belts are mainly different shades of browns with variations from white through orange to chocolate brown. There are even reds especially in the famous giant Red Spot although it is in fact more pink than red. The Red Spot is a massive storm larger than the size of the Earth that has been raging since before the invention of telescopes and observed by Galileo 400 years ago.

.SATURN rises will be well placed and observable by mid evening. The ring system is currently closed up and the ring appears as a thin line crossing the disc of the planet. The rings will become even thinner around September 2009 before they gradually begin to open again but it will take a couple of years for them to return to their full glory.


Saturn imaged by Damian Peach on 4th January 2009	A computer simulation of Saturn on 30th September 2009

By the middle of the summer Saturn will be moving closer to the western horizon. Using a small telescope (80mm to 100mm aperture) it will be possible to see the line formed by the edge on view of the ring system. Titan the largest moon will be visible with possibly a couple of the smaller moons on a good night. They will be located in a direct line with the ring. A larger telescope (150mm to 200mm) will reveal a further two moons and a hint of the cloud bands on the planet. The ring will not be visible through binoculars.

Saturn located to the south of Leo

For anyone who has access to a larger telescope there is a chance to see transits of the moons across the face of the Saturn. This will be difficult because only the smaller moons transit the disc as seen from the UK but from the other side of Earth the largest moon Titan will give a better show.

The Sun was expected to be beginning is climb into increased activity by now but it is still very quiet. There have been no significant Sun Spots but there have been some minor flares seen around the edge of the Sun.