Equinox, conjunction in busy week for stargazers

This next week is a big one for astronomy fans, with several exciting events to look forward to. The moon reaches its first quarter phase tomorrow at 5.11pm. At sunset, Earth’s only natural satellite will be low in the northern sky; its half-illuminated disk will be some 13 degrees above the horizon. Interestingly, the moon will be moving through the constellation Auriga the Charioteer tomorrow night, which isn’t one of the 12 zodiacal constellations.

At 4.06pm on Wednesday, the sun’s centre crosses the celestial equator heading north. This is the exact instant of the southern hemisphere autumn equinox, which marks the day when the length of day and night is equal, wherever you live on Earth. It is well worth watching for the southern lights after dark over the next few weeks. That’s because auroras are more common at this time of year, due to a lining up of both the sun and Earth’s magnetic fields, which astronomers call the Russell-McPherron effect. Fingers crossed for some auroral action.

For me, though, the real highlight of this week occurs before dawn on Friday. If the skies are clear, stargazers in our region will have a front-row seat to a close conjunction between Venus and Saturn. Both planets are moving through the constellation Aquarius, which, to ancient Egyptian astronomers, represented the god of the Nile. While you can easily see both planets with the naked eye, a telescope will allow you to see the tiny disk of Venus and Saturn’s beautiful rings in the same field of view.

On Friday morning, the planets will be separated by less than the full moon’s diameter, which should be an absolutely splendid sight. Venus will be, by far, the brighter of the two planets. This week, Venus is exactly one hundred times brighter than its planetary sibling. Venus’s blue-white colour will contrast nicely with Saturn’s yellow hue.

The best time to view the close approach is about an hour before sunrise, when both planets will be roughly seven degrees above the eastern horizon.