Spammer
11-12-2015, 02:38 PM
It's this again.
Ask me a question that you want to know the answer to; a question which you're unlikely to find the answer to using Google of similar. I'll get in touch with the appropriate expert and find your ass an answer.
Here's an example of one I've had:
Dear Chris,
Sorry for bothering you, but I've tried Google to answer this and haven't found a satisfying answer. I wasn't sure who to ask so thought I''d find an Astrophysics department for someone to contact.
My question is this: If I were to stand on the moon, say with the Earth directly above me, what would the light/dark cycle from the sun be like? I know that a day is around 4 weeks, but my understanding is that the sun won't be in the sky for simply half of that time in a whole block, as the moon's movements around the Earth make it a bit more complex than that. Is that right?
I'm wondering then if there is a pattern for when the sun is visible and when it isn't, and what that might be.
Hope you can help.
Kind regards,
David Hammer
Dear Mr Hammer,
That's an interesting question. The Moon rotates on its axis every 27.3 days. The "day" on the Moon (i.e. the period of time between successive "noons") is a bit longer: 29.5 days. This is because the Moon (together with the Earth) is in orbit around the Sun, which means that the Moon has to go a bit more than one rotation to bring the Sun back to the same place in the sky. (The difference between the rotation period and the "day" for the Earth is about 4 minutes, rather than about 2 days for the Moon. Look up "sidereal day" and "solar day" if you don't know about these.)
There would be small effects due to the orbit of the Moon about the Earth, like you mention. Superimposed on the Sun's (very slow) motion across the sky would be a (very slow) wobble in its position because of the changing perspective as the Moon moves around. I estimate that this wobble would be a little less than the Sun's diameter.
The other effect is the slight eccentricity of the Earth's (and Moon's) orbit around the Sun, which means that the Earth+Moon vary their distance from the Sun and their orbital speed around it. This has an effect referred to as "analemma" - which is an interesting change in position of the Sun as measured at successive noons (as measured on a clock). A similar thing would happen on the Moon too.
Finally, the Earth would stay fixed in the sky from the Moon's perspective. So on the Moon's near side (as we see it) the Earth would always be in the sky, while if you were on the far side you'd never see it. Solar eclipses would be more common, because the Earth is about 4 times bigger than the Moon. You'd also get Terran eclipses, but the Moon's shadow on the Earth would just be a big dark spot. The Earth would be very bright in the sky (it's a lot bigger and a lot more reflective than the Moon which is very un-reflective) but it wouldn't create a bright "nighttime" sky because there's no atmosphere on the Moon to scatter the light about.
Hope this helps,
Chris
Obviously it doesn't have to be science. It could be anything, and I'll find the appropriate person and assuming they're not a miserable cunt like Lewis they'll be happy to answer. Most people have been.
Fire away.
Ask me a question that you want to know the answer to; a question which you're unlikely to find the answer to using Google of similar. I'll get in touch with the appropriate expert and find your ass an answer.
Here's an example of one I've had:
Dear Chris,
Sorry for bothering you, but I've tried Google to answer this and haven't found a satisfying answer. I wasn't sure who to ask so thought I''d find an Astrophysics department for someone to contact.
My question is this: If I were to stand on the moon, say with the Earth directly above me, what would the light/dark cycle from the sun be like? I know that a day is around 4 weeks, but my understanding is that the sun won't be in the sky for simply half of that time in a whole block, as the moon's movements around the Earth make it a bit more complex than that. Is that right?
I'm wondering then if there is a pattern for when the sun is visible and when it isn't, and what that might be.
Hope you can help.
Kind regards,
David Hammer
Dear Mr Hammer,
That's an interesting question. The Moon rotates on its axis every 27.3 days. The "day" on the Moon (i.e. the period of time between successive "noons") is a bit longer: 29.5 days. This is because the Moon (together with the Earth) is in orbit around the Sun, which means that the Moon has to go a bit more than one rotation to bring the Sun back to the same place in the sky. (The difference between the rotation period and the "day" for the Earth is about 4 minutes, rather than about 2 days for the Moon. Look up "sidereal day" and "solar day" if you don't know about these.)
There would be small effects due to the orbit of the Moon about the Earth, like you mention. Superimposed on the Sun's (very slow) motion across the sky would be a (very slow) wobble in its position because of the changing perspective as the Moon moves around. I estimate that this wobble would be a little less than the Sun's diameter.
The other effect is the slight eccentricity of the Earth's (and Moon's) orbit around the Sun, which means that the Earth+Moon vary their distance from the Sun and their orbital speed around it. This has an effect referred to as "analemma" - which is an interesting change in position of the Sun as measured at successive noons (as measured on a clock). A similar thing would happen on the Moon too.
Finally, the Earth would stay fixed in the sky from the Moon's perspective. So on the Moon's near side (as we see it) the Earth would always be in the sky, while if you were on the far side you'd never see it. Solar eclipses would be more common, because the Earth is about 4 times bigger than the Moon. You'd also get Terran eclipses, but the Moon's shadow on the Earth would just be a big dark spot. The Earth would be very bright in the sky (it's a lot bigger and a lot more reflective than the Moon which is very un-reflective) but it wouldn't create a bright "nighttime" sky because there's no atmosphere on the Moon to scatter the light about.
Hope this helps,
Chris
Obviously it doesn't have to be science. It could be anything, and I'll find the appropriate person and assuming they're not a miserable cunt like Lewis they'll be happy to answer. Most people have been.
Fire away.