The Cosmic Chronicle #2
This week, I explored how to observe Venus, our dazzling "twin," in the morning and evening skies.
Hi ,
A new week is upon us, with it, a new issue of the Cosmic Chronicle. This week, let’s discuss one of the brightest objects in our sky - Venus.
We’re no strangers to Venus, commonly called the twin of Earth. With a diameter of about 12,104 kilometres, Venus is almost as big as the Earth. But unlike Earth, Venus’s atmosphere is a killer, literally. Venus’s atmosphere is mainly comprised of carbon dioxide and sulfuric acid clouds. Venus also has the hottest surface among all the planets.
But this week’s newsletter is focused on observing Venus in the sky, so let’s get to it. Since Venus is situated between the Earth and the Sun, we can only see it in the eastern sky before sunrise or in the western sky after sunset. We can never see Venus overhead at midnight.
Another consequence of its position is that Venus passes through phases like the moon. From Earth, we can see part of its illuminated face and part of its dark face. However, we can never see the complete face of Venus, as it’s only possible when Venus is behind the Sun.
Another interesting consequence is the change in its apparent size and phase. As Venus gets closer to the Sun and farther from the Earth, its phase increases and its apparent size decreases. On the other hand, as it comes closer to us, the phase decreases, but the apparent size increases. The result is that when you can see most of the illuminated face of Venus, it’s at its smallest apparent size. But it's also the thinnest when it’s at its largest apparent size.
No talk about Venus is complete without talking about the greatest elongation. “Greatest Elongation” is a fancy term for Venus being the farthest from the Sun in the sky dome. If you join Venus with Earth by an imaginary line, the greatest elongation happens in the two points where that line is tangent to the orbit of Venus.
As you can see, there are two elongations: the greatest eastern elongation occurs when Venus is in the western sky in the evening, and the greatest western elongation occurs when Venus is in the eastern sky before sunrise.
The greatest elongations are also the best time to observe Venus as it’ll be farthest from the Sun in the sky. However, there’s one more factor at play. Just because Venus is at its greatest elongation doesn’t mean it’ll be at its highest point in the sky. This is because the angle of the ecliptic (the path of the Sun and the planets) varies because of the tilt of Earth’s axis.
The next greatest eastern elongation of Venus will be on January 10, 2025. Don’t miss it in the evening sky! Venus will reach its highest altitude in the evening sky on January 23, 2025, after which it’ll start to dip and eventually wander away to the morning sky.
What to Watch This Week
Monday, January 6
Watch the first quarter moon shine bright next to the square of Pegasus. Can you spot all four stars of the square?
Tuesday, January 7
Around midnight, watch the majestic Orion overhead. With a telescope or a binocular, try if you can observe the great Orion Nebula.
Thursday, January 9
The Moon occults several of the Pleiades. Unfortunately, those in India will miss it, but Americans (evening) and Europeans (late night) will be able to enjoy this spectacle. The stars will disappear behind the dark limb of the 82% waxing gibbous Moon, then reappear from behind the bright limb about an hour later. I suggest grabbing a telescope for this one, although a binocular may also work.
Friday, January 10
The moon shines near Aldebaran and Jupiter.
Depending on where you are, you might even see them line up!
Astrophotography
Can you guess which cluster I’m imaging right now? Reply to this email with your guess!
Fun fact
Did you know that Venus and Mercury are the only two planets in the solar system to have no moons?
That’s all for this week. See you next week!
Wonderful !!!!