Monday 10th to Sunday 16th April 2023
On the evening of Tuesday 11th, planet Mercury reaches its greatest eastern elongation from the Sun. In other words it will appear to be as far away from the Sun as it ever gets and so this is the best time to try and observe it.
If you venture outside just as it's getting dark, say around 8.30pm, then Mercury will be setting below the horizon to the west. A little above and to the left of Mercury will be Venus shining brightly.
Wait until it is properly dark and you should see that Venus is very close to the Pleiades open cluster of stars. By then, Mercury will have disappeared below the horizon. To the left of Venus and the Pleiades will be the red giant star Aldebaran that I mentioned last week and further left again you will see the constellation of Orion with its red giant Betelgeuse and much younger, hotter star Rigel.
Orion is considered to be a "winter constellation". During the winter months it appears high in the sky and you can easily observe it through most of the night. During summer months it is close to the horizon and soon after dark, the constellation disappears below the horizon.
I was asked the other day why sometimes you can see Venus, but not at other times. The reason is that Venus is orbiting the Sun closer than us - when the planet is the same side of the Sun to us, then we can see it close to sunrise or sunset. When it is the opposite side of the Sun to us in its orbit, then we can't see it simply because the Sun is in the way! I have created a diagram that plots the orbit of Venus as seen from the Earth and at the moment, the planet is placed very favourably.
Screenshots courtesy of Stellarium
Copyright Adrian Dening and Radio Ninesprings 2023
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