Skynotes December 2016

Skynotes

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Month Highlights

Mercury is is low to the south-west horizon after sunset, with Venus and Mars sitting higher above in the western sky. In the early morning, Jupiter can be found in the eastern sky.

Regulus Hides Behind the Moon

Of all the bright stars in the sky, Regulus (in the zodiac constellation of Leo the lion) is the only one that sits very close and almost on the ecliptic or the path that the Sun appears to follow in the sky. Every 9 years, the Moon’s path matches up with the ecliptic and for a stretch of time, the Moon passes directly in front of or occults Regulus as it passes by the bright star each month.

The first of these occultations begins this month and will continue through until April 2018. Only certain locations will see the occultations and this month from Melbourne, we will see the Moon skim past Regulus on the 19th. The star may wink in and out as its light is temporarily blocked by lunar mountains. This is known as a grazing occultation. In February and May next year, Australia will be in the right place to see Regulus disappear and briefly hide behind the Moon.

Sunrise & Sunset Times

Date Rise Set
Thursday 1st 5:52 8:27
Sunday 11th 5:52 8:36
Wednesday 21st 5:55 8:42
Saturday 31st 6:01 8:45

Moon Phases

Phase Date
First Quarter Wednesday 7th
Full Moon Wednesday 14th
Last Quarter Wednesday 21st
New Moon Thursday 29th

The Moon will be at perigee (closest to Earth) on Tuesday 13th  at a distance of 358,462 km.
The Moon will be at apogee (furthest from Earth) on Sunday 25th at a distance of 405,869km.

Let The Moon Be Your Guide

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

  • On the 2nd, the waxing crescent Moon sits above and to the right of Mercury, low in the western sky after sunset.
  • After sunset on the 3rd, the thin crescent Moon sits below bright Venus.
  • Then on the 5th, the crescent Moon is now below Mars, a little higher in the western sky.
  • On the evening of the 13th, the waxing gibbous Moon travels across the sky with the red giant star Aldebaran (Taurus, the bull).
  • Late in the evening on the 16th, the waning gibbous Moon sits to the right of the twin stars of GeminiCastor and Pollux.
  • On the 19th, at approx. 5:20am, the Moon will skim past the bright star Regulus (Leo, the lion), causing a grazing occultation.
  • Before sunrise on the 23rd, the waning crescent Moon will sit below Jupiter.

Planets

Mercury can be found low in the south-west at sunset. On the 2nd, the thin crescent Moon sits just to the right of Mercury and directly below Venus. The best time to see Mercury is until the 12th, after that it starts heading back towards the horizon and will disappear from view around the 22nd.

Venus  is eye-catching in the western sky after sunset. On the 3rd, the crescent Moon sits just below Venus. By the end of the month, the red planet Mars will have drifted towards Venus and will sit just above and to the right. The bright star sitting high above Venus is Fomalhaut (Piscis Austrinus).

Earth experiences the Summer Solstice on Wednesday 21st. At 9:44pm, the Sun has reached its furthest south for the year and begins moving northward (as viewed from Earth). On this day, the Sun is at its highest and it is our longest day totalling 14 hours, 47 minutes of daylight.

Mars is high in the west at sunset and throughout the month the red planet drops lower in the sky to approach bright Venus. On the 5th, the crescent Moon sits just below Mars.

Jupiter can be seen in the eastern sky before sunrise, paired up with the bright star Spica (Virgo, the maiden). On the 23rd, the crescent Moon sits just below the pair. The four bright stars above Jupiter form the kite shape of Corvus, the crow.

Saturn is too close to the Sun to be seen this month. It returns to the morning sky next month.

Meteors

The most consistent meteor shower of the year, the Geminids, occurs between the 6th to 19th. It is quite active throughout this period, with a peak on the morning of the 15th. Unfortunately, this year the peak coincides with the Full Moon, so many of the fainter meteors will be drowned out. The shower is centred near the bright star Castor, which rises in the north-east around 11pm and is visible until dawn. We can usually expect around 20 meteors per hour. This meteor shower is unique because it is associated with an asteroid called Phaethon, unlike other meteor showers that are 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. Sitting high in the south are the Large and Small Magellanic Clouds, two satellite galaxies of our own Milky Way Galaxy. These two galaxies can be seen as fuzzy patches from dark country sites. They lie close to 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 (Canis Major) and Canopus (Carina), 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:

4:50am - 4:56am, Wednesday 7th December.

The Station will appear in the north-west near the twin stars of Gemini, Castor and Pollux, before heading to the south-east where it passes by Jupiter.

Predictions of when to see the ISS can be obtained from the Heavens Above website.

On This Day

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

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

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

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

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 crew of Apollo 17 (USA) were the last astronauts to walk on the Moon.

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

24th 1968Apollo 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.