Astronomy newsletter for January

by Martin Humphries Carolian Astronomy Society

As this January 2010 newsletter is going out a little earlier than usual, don't forget that there is a partial eclipse of the Moon on 31 December 2009.

It starts at 17:15 UT (Universal time, same as GMT) and ends at 21:30, but the best time to see it is between 18:51 and 19:54.

I hope you had a Merry Christmas and that you are looking forward to a Happy New Year.

On 3 January the Earth is at its nearest to the Sun, known as "perihelion".

Sadly the weather won't be noticeably any warmer though!

The Earth's distance from the Sun varies because its orbit is not quite a circle; it's slightly pear-shaped, known as an "ellipse".

And the Sun is not quite at the centre of the ellipse either, which adds to the orbit's distance variability.

Earthshine

Earthshine is a good indicator of the weather to come

This is a great month for seeing a phenomenon known as Earthshine, caused by sunlight being reflected from the Earth, and dimly illuminating what would otherwise be the dark part of the Moon's surface.

There's a new Moon on 15 January; look in the SW soon after sunset for a few days after this when with a bit of luck you'll see the effects of the earthshine.

Earthshine can also be used as a simple weather forecaster - the brighter the Earthshine, the wetter the weather is likely to be over the next few days.

This is because the brighter the Earthshine, the cloudier is the sky over the Atlantic Ocean, which in turn could mean more rain for us in the next day or two!

The planets

The planet Mercury should, in theory, be low in the E just before sunrise at the end of the month.

However it will be so difficult to spot in the Sun's dawn glare that it's essentially impossible to see.

Venus is at superior conjunction (i.e., the other side of the Sun from Earth), so is also not visible.

Mars gets noticeably brighter as the month progresses

Mars is well positioned throughout January - it's in opposition (i.e., in the opposite part of the sky from the Sun) on the 29th, when it's about as close to the Earth as it ever gets, so is also as bright as it ever gets.

It rises at about 19:00 UT at the beginning of the month and is about 25° high in the E at 22:00 UT.

It rises at about 16:00, and is some 50° high in the SE at 22:00 UT at the end.

It's in the sky during all the hours of darkness throughout the month, bright, and increasing in brightness as it moves towards opposition.

You won't have any difficulty in finding it - its brightness and distinctive orange-red colour and will ensure that!

Look at Mars particularly on 3rd/4th and 29th of the month, when it is, on both occasions, very near to the Moon in the sky.

This spectacular shot of the Moon is from Paul Wilde

The Moon' phase is, on both occasions, close to being full.

There's no astronomical significance in this, but both will be spectacular sights worth seeing - and photographing!

The planet Jupiter is even brighter, but is not nearly as well placed.

It's in the sky throughout the month as the Sun sets, itself setting soon afterwards.

It's about 25° high in the S just after sunset on New Year's Day.

It will become lower in the sky at sunset each day as the month progresses until it's only 15° high in the SW at Sunset on 31st.

Saturn was in conjunction (i.e., on the far side of the Sun with respect to Earth) in September last, so was in the sky during daylight hours and hence was not visible.

It's now visible again, rising in the E at about 23:45 at the beginning of the month, and at about 22:00 at the end.

Once risen, it will be in the sky, quite bright, for the rest of the hours of darkness throughout the month.

Pictures from the specially designed Cassini spacecraft

You might remember that, also last September, the Earth passed through the plane of Saturn's rings. (There is a rigorous mathematical definition of the word "plane" in this context, but is itself fairly complicated, so I'm using a simplified version here: "a flat, two-dimensional, imaginary surface". Hope that helps!)

The result was that Saturn's beautiful rings were "edge-on" to us, so couldn't be seen from Earth.

They are now beginning to open up and become visible again, although you do need a telescope (130 mm - 5 inches - or larger) to see them.

Meteors

Thanks to the weather, I didn't manage to see the Geminids meteor shower ("shooting stars") in December.

I don't suppose you did either.

However, we can take some consolation from the fact that the Quadrantids, another very good meteor shower, is visible in January.

The meteors will be around from 1st to the 6th of the month, but the best time to see them is during the night of 3rd/4th.

This is only three or four days after the 31 December full moon, so once the Moon is up at about 20:00 UT, the bright moonlight will "wash out" many of the meteors.

Fortunately they are at their very best at 18:00 UT on 3rd, so early evening is the best time to look for them.

The meteors are blue and yellow in colour with long silvery "trains".

They can be seen in any part of the sky, so look at the darkest part of the sky in your area.

Watch the skies!

Martin Humphries.