The Evening Sky in January 2018

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The Evening Sky in January 2018

Bright stars appear in the eastern half of the evening sky in January. Sirius is the brightest. Left of Sirius are bluish Rigel and orange Betelgeuse, the brightest stars in Orion the hunter. Between them, but fainter, is a line of three stars making Orion's belt. To southern hemisphere star watchers, Orion's belt makes the bottom of 'The Pot' or 'The Saucepan'. A faint line of stars above and right of the belt is the pot's handle or Orion's sword. The sword has a glowing cloud at its centre: the Orion Nebula. There are no bright planets in the evening sky except at the end of the month when Venus might be seen setting 20 minutes after the sun.

Left of Orion is the V-shaped pattern of stars making the face of Taurus the Bull. The V-shaped group is called the Hyades cluster. It is 150 light years away. Orange Aldebaran, making one eye of the bull, is not a member of the cluster but on the line of sight, half the cluster's distance.

Left again, toward the north and lower, is the Pleiades/Matariki/Seven Sisters/ Subaru star cluster. Pretty to the eye and impressive in binoculars, it is 440 light years* from us. From northern NZ the bright star Capella is on the north skyline. It is 90,000 times brighter than the sun and 3300 light years away.

Low in the south are Crux, the Southern Cross, and Beta and Alpha Centauri, often called 'The Pointers'. Alpha Centauri is the closest naked-eye star, 4.3 light years away. Beta Centauri, like most of the stars in Crux, is a blue-giant star hundreds of light years away. Canopus is also very luminous and distant: 13 000 times brighter than the sun and 300 light years away.

The Milky Way is in the eastern sky, brightest in the southeast toward Crux. It can be traced towards the north but becomes faint below Orion. The Milky Way is our edgewise view of the Galaxy, the pancake of billions of stars of which the sun is just one. Binoculars show many star clusters and a few glowing gas clouds in the Milky Way, particularly in the Carina region. The Milky Way is faint left, or north, of Orion because we are looking toward its thin outer edge. The centre region of the Galaxy, in Sagittarius, is hidden by the sun at this time of year.

The Clouds of Magellan, LMC and SMC, are high in the southern sky and easily seen by eye on a dark moonless night. They are two small galaxies about 160 000 and 200 000 light years away.

A total eclipse of the Moon begins on the 31st just before midnight NZDT but isn't immediately obvious. The Moon will be moving through the outer part of Earth's shadow till 12:48 a.m. on February 1, when it begins to move into the darker part. By 1:51 it will be totally in the dark central part of the shadow, the umbra. It should be darkest around 2:30. It begins to exit the umbra at 3:08 and is fully out of it by 4:11. It leaves the outer part of the shadow, the penumbra, at 5:08.

All the bright planets are in the morning sky except Venus which is behind the Sun most of the month. At the beginning of the month golden Jupiter rises after 2:30 and is the brightest 'star' in the morning sky. Above and left of it, and much fainter, is reddish Mars. Jupiter and the background stars rise earlier each morning but Mars moves more slowly. This causes Jupiter to overtake Mars, the two will be close around the 7th. Their apparent closeness is a line-of-sight effect: Mars is 285 million km from us and Jupiter is 880 million km away.

Mercury is bright in the morning sky for most of the month. In early January it is rising 90 minutes before the Sun, toward the southeast. Saturn rises slowly out of the dawn twilight in the first fortnight. On the 14th it is beside Mercury and the fainter of the two. At that date Mercury is 182 million km away and Saturn 1640 million from us. Mars, Jupiter and Saturn continue to rise earlier each day as we catch up on them. Mercury, much faster than us, slips lower in the dawn as it moves to the far side of the Sun.

*A light year is the distance that light travels in one year: nearly 10 million million km or 1013 km. Sunlight takes eight minutes to get here; moonlight about one second. Sunlight reaches Neptune, the outermost major planet, in four hours. It takes sunlight four years to reach the nearest star, Alpha Centauri.

Newsletter editor:

Alan Gilmore Phone: 03 680 6817
P.O. Box 57 Email: This email address is being protected from spambots. You need JavaScript enabled to view it.
Lake Tekapo 7945
New Zealand