Lights and sights at the crossing of the equator

The southern hemisphere autumnal equinox occurs at 4.33am on Monday morning (March 21). At the equinox, the centre of our nearest star crosses the celestial equator. The autumn equinox is also when the length of the night increases at its fastest rate, which is excellent news for local stargazers. Displays of the southern lights are also common around this time of year, so it is worth keeping an eye open for greenish glows in the southern sky if you are out after dark.

This week, early rising stargazers have a rare chance to spot all five naked-eye planets in the pre-dawn sky. Venus has been putting on an awesome display over the past few weeks and is a magnificent sight before sunrise. The second planet from the Sun is in the constellation Capricornus. It rises well before 4am and its blazing blue-white orb dominates the eastern sky. This week there are three planets in Capricornus. Orange-red Mars is just above Venus, while yellow-white Saturn is just below. All three planets will be more than 25 degrees above the horizon as the sky begins to brighten.

On Monday, Mercury and Jupiter are quite close together in the sky; they will be separated by less than two degrees. Both planets are in the constellation Aquarius. If you want to see them you will almost certainly need a pair of binoculars to assist you in finding them. That’s because they don’t rise until just before sunrise when the sky is getting bright. To stand any chance of locating them you will also need to find an observing location with an unobstructed view of the eastern horizon.

Mercury clears the horizon first, rising just after 6.30 on Monday morning, Jupiter rising about 10 minutes later. The best time to see them will be just before 7am when the pair are about five degrees high just south of east. Jupiter is the brighter. Once you find Jupiter, scan up and to the right; Mercury will appear as a pale orange "star".

 - Ian Griffin