Starship Asterisk*

a question comes to mind after viewing the APOD photo of
> Mercury’s transit of the Sun.
> If a person were standing on the surface of Mercury nearest the Sun –
> how much of the sky is covered by the Sun? Would the sky be
> completely enveloped by the Sun because it is so close, or is it far
> enough away from the Sun that the Sun would only cover a smaller
> portion of Mercury’s sky? Obviously the Sun would appear much larger
> in Mercury’s sky than in ours, but it’s difficult to imagine just how
> much larger it would appear to someone on Mercury.

At the distance from the earth to the moon, the disk of the sun and the disk of the moon appear to be the same relative size. If you were to relocate the moon to Mercury and place it in orbit the same distance away, the disk of the sun would be almost twice the size of the disk of the moon.

To make sure I'm following the logic - I'll try to use some numbers. Using hypothetical figures ... lets say the Sun fills 1% of Earth's sky, you're saying that Sun will only fill 2% of Mercury's sky?

From earth, the sun appears to be approximately half a degree wide.

Mercury averages 58 million kilometers from the sun, and the sun is 1.4 million kilometers in diameter. Doing some trig, it looks like the sun should appear to be 1.4 degrees wide, on average. However, Mercury has a very eccentric orbit, and at it's closest approach the sun would appear 1.75 degrees, while at it's farthest it would only be 1.1 degrees wide in the sky.

So it would range from a little over twice the apparent diameter (and 4 times the brightness...I think), to over 3 times the diameter (and 10 times the brightness). Hmm...I didn't see this brightness change mentioned anywhere in a quick google search, but I'm pretty sure my math is right. Anybody care to comment?

Don't forget that while watching the sun at high noon from the surface of Mercury it would be aroudn 800 degrees F. Wear your sunscreen. I recommend SPF 350 of higher.