SKYWATCH - MARCHVERNAL EQUINOX The 20^th is the official date for spring, when the Sun starts positioning itself over the Northern Hemisphere. The nights become noticeably shorter and evenings lighter, especially after the clocks go forward on the 28^th.

PLANETS

We have four planets in our evening sky this month. Venus is back as the ‘Evening Star’, visible in the west at dusk and steadily climbing in the sky as the month goes by. It goes through phases the way our Moon does, and this is best seen at dusk when its glare is much less. By the third week it is joined by Mercury, a smaller dot which never gets very high above the horizon as it orbits the Sun so closely. Mars is also visible at dusk, to the right of Leo, and is due south by the time Saturn rises, to the left of Leo.

CONSTELLATIONS

Gemini is centre stage in the southern sky around 8pm, with its alpha and beta stars (the two brightest) representing the heads of the twins, Castor and Pollux.

Castor is the higher one and an interesting star, mostly because it is not one but six stars. It is a twin star system, a binary, which can be observed. Each of these is also a double, although this is detectable only with a spectroscope, and there is an orbiting binary as well. The bodies of the twins are made up of much fainter stars angled slightly to the right. Over to its left, beyond the inconspicuous constellation of Cancer, is Leo. It is currently favoured with a planet to either side, but in its own right is a good constellation to view. A distinct reverse question-mark or sickle shape of stars on its right side represents the head, mane and forelegs, ending in its alpha star ie brightest, Regulus.

To the left of this a few bright stars give a good enough impression of its back, so that anyone with a bit of imagination ought to be able to make out an animal shape. Leo is of course the Lion, and like Gemini is a Zodiac constellation. There are twelve of these, and so named because they straddle the Ecliptic, which is the orbital plane of the planets. It was this which gave them significance in the early days, when astronomy and astrology were linked; but for modern astronomers this does not make them any more special than other constellations.