[John Salerno]

First off, hi everyone! This is my first post because I just found these forums (by Googling "science forums" in hopes of finding a good forum to ask science questions!). Anyway, lately I've been really interested in the moon and I've been reading about the lunar phases. (I assume this is the appropriate sub-forum? Or perhaps it should be moved to "Other Sciences"?)

My question involves something I've noticed on a couple of different websites that list the optimal time to view particular phases of the moon. In at least two different sources I've seen that the full moon is best viewed around noon local time. But I don't understand how this is possible if, in order for a moon to be full, it must be on the other side of the Earth from the sun, and in order for someone to see the moon in this specific location, they would have to be on the far side of the Earth (i.e. the dark side) as well? So wouldn't it only be visible at night?

I've certainly noticed the moon up in the sky during the day, so maybe this is the same type of case. I just didn't understand how it would be possible to see a full moon during the day since it seems like you'd have to be on the side of the Earth not facing the sun.

Thanks!
John

[D H]

Please show a link. A full is not visible at noon. To see a full moon at noon you would need to look down at your feet and be able to see through the Earth. The best time to view a full moon is at midnight.

[John Salerno]

D H, on 8 August 2010 - 10:41 AM, said:

Please show a link. A full is not visible at noon. To see a full moon at noon you would need to look down at your feet and be able to see through the Earth. The best time to view a full moon is at midnight.

Well, that's good to hear since that's exactly what I'd expect. As it turns out, I was wrong about one of those sources: one image (the image on the Wikipedia page for lunar phases) shows that the *new* moon is best viewed at noon -- although this still leads me to wonder how people on the other side of the Earth would be able to see a moon then. If the moon is in between the Earth and the sun, does that mean people on the far side of the Earth don't have a moon at all?

As for the full moon at noon, I can't find the site I was looking at last night which allowed me to enter my specific time zone (US CST), but this site is basically the same: http://www.lunarrepu...fo/phases.shtml

It lists 17:05 on August 24 as the time of the full moon, which for my time zone would be 12:05pm. Does this mean something other than what I think, or does it mean that by the evening of the 24th the moon will already be waning?

Thanks.

Edit: Actually that link above is the same site as the one I saw last night. This link is the one I used for my time zone: http://www.timeandda...year=2010&n=104

This post has been edited by John Salerno: 8 August 2010 - 03:53 PM

[insane_alien]

it lists the time(down to the minute) in UTC when it is at peak fullness. this happens to coincide with your noon. thus, you will not be able to see it at its peak(as its on the other side of the world).

it will still look like a full moon when it does become visible to you.

[^_^]

http://www.stellarium.org/ is your friend. Play around with the time, remove the ground and see where the moon is

[Sisyphus]

John Salerno, on 8 August 2010 - 03:51 PM, said:

Well, that's good to hear since that's exactly what I'd expect. As it turns out, I was wrong about one of those sources: one image (the image on the Wikipedia page for lunar phases) shows that the *new* moon is best viewed at noon -- although this still leads me to wonder how people on the other side of the Earth would be able to see a moon then. If the moon is in between the Earth and the sun, does that mean people on the far side of the Earth don't have a moon at all?

When the moon is new, it is only visible during the day, yeah. It's in between the Earth and the sun, which means from our perspective it is in the same part of the sky as the sun, and is visible at the same times. People on the other side of the Earth don't have a sun at all, either. It's called night time.

[D H]

insane_alien, on 8 August 2010 - 04:03 PM, said:

it lists the time(down to the minute) in UTC when it is at peak fullness. this happens to coincide with your noon. thus, you will not be able to see it at its peak(as its on the other side of the world).

Minor correction: Those times are in US Central Time. Other than that, what you said is correct.

This is not necessarily the best time to see the moon. For example, the moon will reach fullness on Aug 24, 2010 at 12:05 PM Central Daylight Time. You could see the full moon at that moment quite nicely from Tibet, but not from Houston.

[John Salerno]

Sisyphus, on 8 August 2010 - 11:54 PM, said:

People on the other side of the Earth don't have a sun at all, either. It's called night time.

Well yeah, but since it is nighttime, I figured they would have some sort of moon. But you're saying when the moon is new, then anyone on the "dark" side of the Earth can't see the moon at all?

insane_alien, on 8 August 2010 - 04:03 PM, said:

it lists the time(down to the minute) in UTC when it is at peak fullness. this happens to coincide with your noon. thus, you will not be able to see it at its peak(as its on the other side of the world).

it will still look like a full moon when it does become visible to you.

Ah, that makes sense! So I suppose I misunderstood what those times represented. Thanks!

[Sisyphus]

John Salerno, on 9 August 2010 - 03:34 AM, said:

Well yeah, but since it is nighttime, I figured they would have some sort of moon. But you're saying when the moon is new, then anyone on the "dark" side of the Earth can't see the moon at all?

Yup. The moon travels across the sky just like the sun does. And just like the sun, when it's on the other side of the Earth, you can't see it. It takes 24 hours 50 minutes to "circle" the sky (compared to 24 hours for the sun), so the moon falls behind, and the sun laps it once a month. The closer it is to the sun, the more overlap there will be between visible sun time (daytime) and visible moon time, and therefore the less overlap between visible moon time and night time.

[John Salerno]

Sisyphus, on 9 August 2010 - 10:57 AM, said:

Yup. The moon travels across the sky just like the sun does. And just like the sun, when it's on the other side of the Earth, you can't see it. It takes 24 hours 50 minutes to "circle" the sky (compared to 24 hours for the sun), so the moon falls behind, and the sun laps it once a month. The closer it is to the sun, the more overlap there will be between visible sun time (daytime) and visible moon time, and therefore the less overlap between visible moon time and night time.

Fascinating stuff! Thanks! That explains why the moon was nowhere to be seen last night (on a clear night). According to the calendar, it's a new moon right now. I need to head outside in about 30 minutes and go look for it! (It's 11:30am right now.)

[insane_alien]

D H, on 9 August 2010 - 01:48 AM, said:

Minor correction: Those times are in US Central Time. Other than that, what you said is correct.

This is not necessarily the best time to see the moon. For example, the moon will reach fullness on Aug 24, 2010 at 12:05 PM Central Daylight Time. You could see the full moon at that moment quite nicely from Tibet, but not from Houston.

http://www.lunarrepu...fo/phases.shtml

says universal time. thats the site i was talking about. i'd assume universal time = UTC

[John Salerno]

Sisyphus, on 9 August 2010 - 10:57 AM, said:

Yup. The moon travels across the sky just like the sun does. And just like the sun, when it's on the other side of the Earth, you can't see it. It takes 24 hours 50 minutes to "circle" the sky (compared to 24 hours for the sun), so the moon falls behind, and the sun laps it once a month. The closer it is to the sun, the more overlap there will be between visible sun time (daytime) and visible moon time, and therefore the less overlap between visible moon time and night time.

I just want to be clear on something: during a new moon, is it the case that you can't see the moon at night simply because the Earth-facing side is not being illuminated (but the moon is still physically there in front of you), or is it the case (which I think you are saying) that the moon is on the other side of the Earth and is physically absent from the viewable portion of the sky?

[Sisyphus]

John Salerno, on 24 August 2010 - 04:54 PM, said:

I just want to be clear on something: during a new moon, is it the case that you can't see the moon at night simply because the Earth-facing side is not being illuminated (but the moon is still physically there in front of you), or is it the case (which I think you are saying) that the moon is on the other side of the Earth and is physically absent from the viewable portion of the sky?

The latter. If the moon is new, that means it's near the sun in the sky, and therefore is only in the sky when the sun is, i.e. during the day.

[John Salerno]

Sisyphus, on 24 August 2010 - 09:24 PM, said:

The latter. If the moon is new, that means it's near the sun in the sky, and therefore is only in the sky when the sun is, i.e. during the day.

Thanks again!

[needimprovement]

John Salerno, on 8 August 2010 - 03:51 PM, said:

As for the full moon at noon, I can't find the site I was looking at last night which allowed me to enter my specific time zone (US CST), but this site is basically the same: http://www.lunarrepu...fo/phases.shtml

The times listed are UT(universal time), which is the modern equivalent of Greenwich Mean Time. Universal time is the same worldwide, If it is 1200 UT in England, it is 1200 UT in Japan. Depending on where you are in the world, the difference between UT and local clocks will differ. In one part of the world, at 1200 UT, it will be the middle of the night.

Thus the times listed are when a full Moon occurs by UT, not when it is visible by local time. The full Moon is never visible at noon local time, even though it is occurring at that moment. It would only be visible in those parts of the world where the Moon has risen.

So basically only some people are able to see the true full moon or the exact time it gets there. but the rest are close when it comes around to them.

This post has been edited by needimprovement: 3 September 2010 - 11:54 PM