I’m sure you’ve all read in books that Venus is a planet that orbits the Sun and is closer to the Sun than is the Earth. But why learn from books what you can check for yourself?!?
[Note: If you missed Wednesday evening's discussion of particle physics involving me, Sean Carroll and Alan Boyle, you can listen to it here.]
As many feared, Comet ISON didn’t survive its close visit to the Sun, so there’s no reason to get up at 6 in the morning to go looking for it. [You might want to look for dim but pretty Comet Lovejoy, however, barely visible to the naked eye from dark skies.] At 6 in the evening, however, there’s good reason to be looking in the western skies — the Moon (for the next few days) and Venus (for the next few weeks) are shining brightly there. Right now Venus is about as bright as it ever gets during its cycle.
The very best way to look at them is with binoculars, or a small telescope. Easily with the telescope, and less easily with binoculars (you’ll need steady hands and sharp eyes, so be patient) you should be able to see that it’s not just the Moon that forms a crescent right now: Venus does too!
If you watch Venus in your binoculars or telescope over the next few weeks, you’ll see proof, with your own eyes, that Venus, like the Earth, orbits the Sun, at a distance smaller than the distance from the Sun to Earth.
The proof is simple enough, and Galileo himself provided it, by pointing his rudimentary telescope at the Sun 400 years ago, and watching Venus carefully, week by week. What he saw was this: that when Venus was in the evening sky (every few months it moves from the evening sky to the morning sky, and then back again; it’s never in both),
- it was first rather dim, low in the sky at sunset, and nearly a disk, though a rather small one;
- then it would grow bright, larger, high in the sky at sunset, and develop a half-moon and then a crescent shape;
- and finally it would drop lower in the sky again at sunset, still rather bright, but now a thin crescent that was even larger from tip to tip than before.
The reason for this is illustrated in the figure below, taken from this post [which, although specific in some ways to the sky in February 2012, still has a number of general observations about the skies that apply at any time.]
So go dig out those binoculars and telescopes, or use Venus as an excuse to buy new ones! Watch Venus, week by week, as it grows larger in the sky and becomes a thinner crescent, moving ever closer to the sunset horizon. And a month from now the Moon, having made its orbit round the Earth, will return as a new crescent for you to admire.
Of course there’s another proof that Venus is closer to the Sun than Earth is: on very rare occasions Venus passes directly between the Earth and the Sun. No more of those “transits” for a long time I’m afraid, but you can see pictures of last June’s transit here, and read about the great scientific value of such transits here.