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Thursday, August 21, 2008


When can you first see Venus?

How soon after Sunset can you see Venus? Jupiter? Mercury? Actually, this is a bit of a trick question, as you can see Venus in daylight (although don't try now, Venus is still a bit too close to the Sun for safety), so theoretically you should be able to see Venus immediately after Sunset. But you have to know where to look and be prepared to stare at blankness a lot.

So, if you were to look at the sky and see Venus comfortably, when should you look? Well, I looked 10 minutes after Sunset today, and I saw Venus easily (well, I did know where to look). About 15 minutes after Sunset I could just see Mercury with averted vision. By 20 minutes after Sunset, when I took the leftmost image, Mercury was readily visible (in the image, you can just see Mercury if you click on it and enlarge it). Another 5 minutes later, Venus and mercury were easily visible, and Mars was now visible too (you can see it in the right hand image which was taken 5 minutes after the left hand image, click to enlarge as always).

Civil twilight occurs 25 minutes after Sunset, so if you wait until then, Venus, Mercury and Mars will be easily visible. I didn't check out Jupiter, but Since Venus is magnitude -3.9, Jupiter -2.6, Mercury -0.2 and Mars 1.7, I suspect Jupiter would be visible around 10 minutes after Sunset. I'll check it out tomorrow if cloud lets me.

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