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Night Sky Diary: Moon With a View of Total Eclipse

Posted on: Saturday, 1 May 2004, 06:00 CDT

May opens with a total lunar eclipse on the 4th. The full moon will rise at about 7.25pm already partly hidden by the Earth's shadow.

Some 25 minutes later the moon will be totally eclipsed and will remain so until just after 9 pm when it will then gradually emerge to become whole once more at around 10.10 pm.

The moon shines only by reflected light from the sun. As there haven't been any major volcanic eruptions on Earth recently there will be little volcanic dust in our atmosphere to distort the sunlight and so colour our view of the moon.

As long as it's clear, it should be relatively easy to see the eclipsed moon. Careful observation will show it passing in front of stars. By timing the precise moment at which stars, whose properties are known, disappear behind the moon and then reappear, its orbit can be determined. A useful by-product of lunar eclipses.

Mercury is very low on the horizon and so is lost in the early morning sunrise.

Venus, however, is at its most brilliant in the evening sky on the 2nd.

In fact, it will be quite a busy time for our nearest planetary neighbour over the next few weeks. May sees it dropping lower down in the sky as it appears to race towards the sun.

Next month the planet will be seen to cross in front of the sun's disc. When a smaller body passes in front of a larger body it is called a transit.

This has not happened to Venus since 1882 and so is a very important event to astronomers. As with eclipses, all sorts of measurements can be made and predictions verified when an event like this occurs. Before that, on the 21st of this month, the reverse will take place -a crescent moon will pass in front of a crescent Venus -a larger body crossing in front of a smaller one -this is called an occultation.

Mars enters the constellation of Gemini and sets before midnight. It appears to be really small now but may be seen about three degrees south of the moon on the evening of the 22nd.

Jupiter may still be seen shining brightlyin Leo but is starting to drop lower in the western sky as the month progresses. On the 27th it will be four degrees south of a quarter moon.

Saturn is still in Gemini, too, but has set by midnight so if you want to catch a glimpse of those rings, take a look early on in the evening.

Uranus and Neptune are both early morning risers so difficult to view. Only real enthusiasts with big telescopes will manage to observe Pluto later this month, and then, only from a very dark site in the early hours. As for the stars, Leo is still prominent in the south-west while Ursa Major is high overhead with The Plough's two end stars pointing faithfully towards the north Pole Star.

Below may be seen a circlet of stars called Corona Borealis (Northern Crown) and nearby lies the orange star Arcturus in the constellation of Bootes.

Bootes (the Herdsman) is constellation of the month. So named because its shape is supposed to represent a man herding a bear -- the adjacent constellation of Ursa Major (Great Bear).

If you look out at around 10pm in the evening you will see it riding high in the south. It is dominated by Arcturus, a brilliant orange star and the fourth brightest star in the entire sky.

It is easy to find Arcturus by following the sweep of the Plough's handle downwards. The name literally means 'Guardian of the Bear'.

It is a giant star about 20-25 times the size of our sun and 37 light years away. In fact, in another five billion years or so the sun will probably evolve into a red giant itself and expand to a similar size!

Bootes contains a fine selection of binary (double) stars. The best known is Izar, a glorious but difficult double star to observe.

Glorious to see because of its contrasting colours of orange- yellow and blue. Difficult to resolve into its two component stars due to their apparent closeness so a good telescope with a high magnification is a must.

Following behind Bootes is the constellation of Hercules which contains the beautiful Messier object M13.

This may be seen through a telescope for the globular cluster that it is -a dense ball of hundreds of thousands of very old stars more than 25,000 light years away.

Low in the south-east rises Antares (meaning 'like Mars'), a red star in the constellation of Scorpius and so named because of its colour. It is a red supergiant and around 500 times larger in diameter than our own Sun!

Unable to sleep in the early hours of the morning? Look out of your window on a clear night and watch the Summer Triangle slowly emerging out of the east.

Its three corners are marked by Vega, Deneb and Altair, lead stars in the constellations of Lyra, Cygnus and Aquila. It is a familiar herald of the summer nights to come.

Lastly, from about the 7th a visitor will grace our evening skies in the form of Comet 2001 Q4 (NEAT). It should be a good binocular object by mid-month with its head in the constellation of Cancer and its long tail running towards Regulus in Leo.

Comets are small bodies composed mainly of ice and dust which revolve around the sun in an elliptical orbit of many years.

For most of their lives they travel around the solar system as a solid 'dirty snowball' in the cold and dark.

But as they approach closer to the sun, the heat evaporates gas and dust from the surface to form a tail.

This tail always points away from the sun. You can tell from the direction of the tail as to whether it is coming towards the sun or whether it has passed by.

To find out more about comets, constellations and how to make your own telescope -check out our website at:www.birmingham- astronomy.co.uk Report from the Birmingham Astronomical Society

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