Astronomy

March is the month in which we change British civil time from Greenwich Mean Time (GMT) to British Summer Time (BST).

This happens during the night of 28/29 March, so put your clocks forward one hour.

We shall continue to use Universal Time (UT) on this web site as that is used by astronomers the world over, so don't forget to add one hour to convert to BST from 29th onwards.

The Spring Equinox occurs on 20 March this year - the equinox is not a particular day; it is the precise time that the Sun crosses the celestial equator (an imaginary line directly above the Earth's equator), this year at 11:44 UT – Universal Time, the same as GMT.

Before this, the Sun is in the sky for less than 12 hours each day, and after it, for more than 12 hours.

For a couple of weeks either side of the equinox the days are lengthening faster than at any other time of the year.

Planets

The planets put on a fairly miserable show again this month, with a couple of exceptions: Venus is spectacularly bright, high in the West in the early evening sky, and setting at about 21:00 UT at the beginning of the month.

However, it will set progressively earlier as the month passes, and will actually set before Sunset by the end of the month, so obscured by the bright daylight sky.

The rings of Saturn

Saturn is the only planet that will be in the sky this month for more-or-less all of the hours of darkness.

It will be exactly opposite the Sun (known as "in opposition") on 8 March, so throughout the month will be high in the S at about midnight UT and at its brightest for the entire year.

Mercury rises just after Sunrise and sets just before Sunset throughout the month, so can't be seen at all during March.

Mars and Jupiter both rise before Sunrise so, theoretically at least, should be visible low in the E at about 06:00 UT.

In reality, Mars will be lost in the dawn glare but Jupiter, because of its brightness, should be visible in the E from about 05:00 UT at the end of the month.

Spring MoonWatch

As we know, UNESCO declared 2009 as the International Year of Astronomy, and amateur astronomers throughout the world are taking part in various astronomical activities during the year.

One such event is a Spring MoonWatch, which runs from 28 March to 5 April.

The Moon

We don't talk about the Moon much in this Newsletter, perhaps because it's so obvious in the night sky that familiarity breeds contempt.

But perhaps we should talk about it a bit more, and certainly we must cover this International Year of Astronomy spring MoonWatch, so here goes.

The Moon is our nearest astronomical neighbour, and it's unique as far as the Earth is concerned, as it's the only body in the night sky on which we can see surface features with the naked eye.

We'll talk about some of them as we see what's going to happen during the MoonWatch.

The Moon is in orbit around the Earth, and it takes just over 29 days to make one complete orbit.

It is this ever-changing position relative to a given point on the Earth's surface and its position relative to the Sun that causes the 29-day "New Moon – Full Moon – New Moon" cycle.

There is a New Moon at 16:07 UT on 26 March - you won't be able to see anything as the Moon is placed approximately between the Earth and the Sun and the illuminated face is pointing away from us.

The MoonWatch officially starts on 28 March, when you should be able to see the thin sliver of the two day old Moon, about 20° high in the W at 19:00 UT.

You won't be able to see much detail with the naked eye at this stage, but with a modest pair of binoculars part of the dark area Mare Crisium should be visible.

"Mare", pronounced “maray”, is Latin for sea, and early astronomers thought that these distinctive dark patches were indeed seas.

Maria (plural of mare) are not, and never have been, seas - they were created millions of years ago when the Moon was still geologically active and part of the landscape was flooded by lava from erupting volcanoes.

You should also be able to see several craters along the terminator, the rather sinister name given to the boundary between the illuminated and shaded areas of the Moon's surface.

Based on the Lunar calendar

By the evening of 29 March, all of Mare Crisium will be visible, along with the crater Cleomedes, just to its north.

There are a number of maria on the Moon's surface, and most of them are joined together, but Mare Crisium is the exception, being clearly isolated from the others.

On the 30 the Moon will be close to the Pleiades star cluster, and the terminator will run through Mare Tranquillitatis (site of the first manned Moon landing) and Mare Nectaris.

Finally, on 31 March, Mare Serenitatis, joined to Mare Tranquillitatis, will come into view as will the chain of large craters (from N to S) Theophilus, Cirillus and Catharina, very close to the terminator.

More about the spring MoonWatch in April, but meanwhile, watch the skies!

Martin Humphries.