Skynotes December 2008

Month Highlights

The crescent Moon is well sought after in the western sky this month. On the 1st it lies below the two brightest planets, Jupiter and Venus. Then on the 29th it appears very close to Jupiter (the two are just 0.25° apart), and sitting to their left is Mercury.

Summer School Holidays

Scienceworks is open daily from 10am – 4:30pm during the School Holidays (26th December – 28th January). Planetarium session times are:

12pm: Tycho to the Moon
1pm: Spinning Out
2pm: The Problem with Pluto
3pm: Black Holes: Journey into the Unknown

Sunrise & Sunset Times

Moon Phases 

The Moon will be at apogee (furthest from Earth) on Saturday 27th at a distance of 406 600 km.
The Moon will be at perigee (closest to Earth) on Saturday 13th at a distance of 356 567 km.

Let The Moon Be Your Guide

The Moon can be used as a pointer to find other objects in the sky.

• After sunset on the 1st, the waxing crescent Moon lies just below Venus and Jupiter.
• During the night of the 11th the waxing gibbous Moon lies near the brilliant star cluster Pleiades.
• Late on the 14th the Moon rises just above the twin stars of Gemini, Castor and Pollux.
• On the morning of the 17th, the waning gibbous Moon sits to the left of Regulus (Leo, the lion).
• During the early hours of the 19th, the Last Quarter Moon is above Saturn.
• On the morning of the 22nd the waning crescent Moon sits near Spica (Virgo).
• Before sunrise on Christmas Day, the Moon sits just above Antares (Scorpius).
• After sunset on the 29th, the waxing crescent Moon sits 0.25° from Jupiter with Mercury to the left.
• During the early evening of the 31st, the crescent Moon is below bright Venus. 

Planets

Mercury will rise out of the glow of evening twilight around the middle of the month. It can be faintly seen above the south-west horizon. On the 29th, Mercury sits to the left of Jupiter and the crescent Moon and at the end of the month Mercury lies above Jupiter.

Venus looks stunning this month shining brightly in the western sky at sunset. It begins the month sitting above Jupiter and the crescent Moon. On Christmas Day, Venus has an invisible companion; the planet Neptune sits to its right. And on New Year's Eve the crescent Moon is below Venus once again.

Earth experiences the Summer Solstice at 11:04pm on Sunday 21st. This is when the Sun reaches its most southerly position for the year. It also marks the longest day of the year totalling 14 hours, 48 minutes.

Full Moon occurs this month a few hours before the Moon reaches perigee – that part of the Moon’s orbit which brings it closest to Earth. In principle, it will make for the biggest and brightest Full Moon of the year, but in reality the difference is very subtle. However, it will cause the spring tides to be slightly higher than usual this month.

Mars is in our daytime sky, lying too near the Sun to be seen this month.

Jupiter begins the month lying between Venus and the crescent Moon. As the month goes by, Jupiter sinks towards the western horizon, meeting up with Mercury around the 27th. On the 29th, the crescent Moon returns to this part of the sky and is just 0.25° below Jupiter. By the end of the month Mercury hangs in the sky above Jupiter.

Saturn can be found high in the north-east before sunrise. The bright star Regulus (Leo, the lion) sits to the left of the ringed planet. On the morning of the 19th the Last Quarter Moon sits above Saturn.

Meteors

The most consistent meteor shower of the year occurs this month - the Geminids. The shower is active from the 6th to 19th. It is centred near the bright star Castor, which rises in the north-east around 11pm and is visible until dawn. Unfortunately, the Full Moon will swamp the peak of the shower on the morning of the 14th, but usually Northern Hemisphere observers can see up to 80 meteors per hour. Here in the South where Gemini appears low to the horizon, a more modest 20 meteors per hour is expected. This meteor shower is unique because it is associated with an asteroid called Phaethon, rather than caused by comet debris.

Stars & Constellations

The Southern Cross is now upside-down in the southern sky and the Two Pointers (Alpha and Beta Centauri) sweep just above the southern horizon. A low Southern Cross means the Large and Small Magellanic Clouds, two satellite galaxies of our own Milky Way Galaxy, have now risen high. The two galaxies can be seen as fuzzy patches from dark country sites. They are about 200 000 light years away and are slowly being drawn in towards our Galaxy.

Low in the north-west, the great square of Pegasus (the winged horse) can be seen. In dark skies and with a clear view to the northern horizon, you might just be able to see a faint fuzzy patch below Pegasus. This is the Andromeda Galaxy – M31, the most distant object visible to the unaided eye at 2 million light years away.

Orion, the hunter is back in our skies and can be seen in the north-east from sunset. For us in the south Orion appears to be standing on his head. Many people are familiar with the central stars of Orion that are commonly known as the Saucepan.

North of Orion is Taurus the bull, with the bright star Aldebaran marking the Bull’s fierce red eye. Also part of the constellation of Taurus is the cluster of stars called Pleiades or the Seven Sisters.

The two brightest stars in the night sky, Sirius (in Canis Major, the large dog) and Canopus (in Carina, the keel), are found towards the south-east. Further south shines Achernar within the constellation of Eridanus, the river.

International Space Station

The ISS orbits the Earth every 90 minutes at an average distance of 400 km. From Earth, the ISS appears as a bright star that steadily moves across the sky. It can often be seen from Melbourne, for example at:

9:37pm – 9:45pm, Sunday 14th December.

The Station will first appear above the north-west horizon and travel directly overhead, passing the bright star Canopus before disappearing in the south-east.

Predictions of when to see the ISS can be obtained from the website: www.heavens-above.com

On This Day

2nd 1971, Mars 3 (USSR) made the first softlanding and returned the first signals from Mars.

3rd 1973, Pioneer 10 (USA) made the first flyby of Jupiter and returned the first close-up images of the planet.

4th 1978, Pioneer Venus 1 (USA) became the first spacecraft to orbit Venus.

10th 1901, the first Nobel Prizes are awarded (Sweden).

10th 1993, the faulty optics of the Hubble Space Telescope are repaired.

10th 1993, astronauts entered the International Space Station for the first time.

13th 1920, the size of a distant star, Betelgeuse in Orion, is measured for the first time at Mt Wilson Observatory (USA).

14th 1972, the last walk on the Moon by humans, the crew of Apollo 17 (USA).

15th 1970, Venera 7 (USSR) made the first softlanding and returned the first signals from Venus.

24th 1969, Apollo 8 (USA) became the first manned craft to orbit the Moon.

25th 1758, the return of Halley's Comet, predicted by Edmund Halley in 1705, is observed by Johann Palitzsch (Germany).

31st 1744, James Bradley (UK) announces his discovery of the nutation (wobbling) of the Earth.