At what time does the full Moon rise?

[ceptimus]

I would say at sunset.

My reasoning is that in order for the moon to be full, it has to be on the opposite side of the Earth to the Sun, so the one will rise as the other sets.

Perhaps my reasoning is faulty here? Has Randi posted this as a trick question?

Or was the guy who asked the question correct in his assertion that people "just don't think"

[Brown]

When I first heard the question, I thought that the question called for a specific hour, like, oh, 6:00 p.m. But if memory serves, the correct answer is "It depends."

[Abdul Alhazred]

Originally posted by Brown
When I first heard the question, I thought that the question called for a specific hour, like, oh, 6:00 p.m. But if memory serves, the correct answer is "It depends."

The latest World Almanac and Book of Facts might help you. Don't let the fact that it also lists the original names of movie stars throw you off.

It's still a real almanac, and a good one.

[ceptimus]

That, "It depends" answer is always a safe bet. It's one of my favourites. :)

[The Bad Astronomer]

Since the commentary just appeared, I will hold off on posting the correct answer, but I will note that the answer may surprise you. I hope Randi gets it right; I'd hate to have to put him on my website...:re:

[Skeptical Greg]

I'm sure there is a scientifically correct answer, but my first thoughts would be, that the Moon cannot become completely full until after it has risen..

Determining that time on a clock is the part I haven't worked out..

I'm sure someone will correct me if I'm wrong..

[Brown]

Originally posted by Abdul Alhazred
The latest World Almanac and Book of Facts might help you. Don't let the fact that it also lists the original names of movie stars throw you off.

It's still a real almanac, and a good one. This is an valuable reference for any crossword puzzle constructor!

[Blondin]

The full moon rises shortly after sunset. How shortly depends on how many degrees of latitude you are North or South of the equator.

[Thumbo]

From geometry, when the moon is full the sun, earth and moon are in a roughly straight line, with the earth in the middle.

If the line was perfect (and the sun and moon sufficiently far away) then the sun would be visible from exactly one half of the earth and the moon visible from exactly the other half. Ignoring refraction, from any point you would be able to see one or the other (or half of both, each bisected by the horizon). Therefore the moon rises when the sun sets, and vice-versa.

If you include refraction, which lets you see round the curve of the planet a tad, then typically the moon will rise a little before sunset: I guess about half an hour, without doing any maths.

I wait with trepidation for the bad astronomer to shoot me down in flames. :)

[edited for typo]

[subgenius]

Originally posted by Abdul Alhazred


The latest World Almanac and Book of Facts might help you. Don't let the fact that it also lists the original names of movie stars throw you off.

It's still a real almanac, and a good one.
You have an al-manac? Homeland security wants to talk to you.
( http://www.centredaily.com/mld/centredaily/news/7594643.htm)

[ceptimus]

I was thinking about this last night. I suppose we have to define how near to 'full' the full moon has to be. If it is only full when the Sun, Earth and Moon are perfectly in line, then it is never absolutely full, and whenever it gets pretty close, there will be a lunar eclipse anyway.

As it is generally accepted that there is a full moon once per lunar month, I suppose the nearest it gets to the straightline position is defined as full moon, but this only occurs at an instant in time. So for virtually the whole Earth, the Moon will have already either risen, or set, at the instant of full moon.

If you're well inside the artic or antarctic circles at certain times of the year, the moon will be in the sky, or below the horizon, continuously for a week or more. I suppose the full moon doesn't rise or set at these locations - it would become full while already in the sky.

Also, 'rise' is a bit of a misleading term. The Sun and moon appear to rise, mainly because of the Earth's spin. But I suppose everyone knows what is meant anyway.

So I think the question could be more definitely put as, "At that moonrise which is closest to full moon at your location, what is the local time when the moon rises?"

[El Greco]

As we approach the longest day of the year, the full moon rises later and later after sunset, while as we go towards winter solstice the full moon rises earlier and earlier in respect to the sunset. December's full moon may rise before sunset in the northern hemisphere. Interesting...

[Prester John]

I saw the moon yesterday and it was daylight :)

[Prester John]

Gonna put my answer in for all to see:

Midday

(thought about it coming home from work, that was my answer)

[Peter Morris]

Knowing Randi it might be a trick question:

The Moon does not rise, the rotation of the Earth brings it into view.

I'm not an astronomer, does the phase of the moon affect the time of moonrise at all? My first thought on seeing the puzzle was "the same time it rises in any other phase for your geographical location and time of the year"

[The Bad Astronomer]

Thumbo, congrats! You are correct.

Due to the Earth's atmosphere bending light, the full Moon rises before sunset. If we didn't have air, the full Moon would rise just at sunset. But the air bends the light, so the Moon can actually be visible to us when it is physically below the horizon. I am not sure how much time elapses between it being seen and being above the physical horizon, but it's probably only a couple of minutes. This also means the Sun will be visible even when it is physically below the horizon, so the effect of the full Moon rising before sunset is doubled.

And this assumes the Earth is a perfect sphere, the Moon is in the ecliptic plane, etc. etc. If you want to go into those effects, I'd have to really think about it -- and probably get it wrong myself! ;-)

[Blondin]

Because I'm Bad, I'm Bad-Come On
(Bad Bad-Really, Really Bad)
You Know I'm Bad, I'm Bad-You Know It
(Bad Bad-Really, Really Bad)
You Know I'm Bad, I'm Bad-Come On, You Know
(Bad Bad-Really, Really Bad)
And The Whole World Has To Answer Right Now
Just To Tell You Once Again,
Who's Bad . . .

Thanks, Phil.

[Trebuchet]

Originally posted by The Bad Astronomer
Thumbo, congrats! You are correct.

Due to the Earth's atmosphere bending light, the full Moon rises before sunset. If we didn't have air, the full Moon would rise just at sunset. <snip>

And this assumes the Earth is a perfect sphere, the Moon is in the ecliptic plane, etc. etc. If you want to go into those effects, I'd have to really think about it -- and probably get it wrong myself! ;-)

I must confess that like Randi my knowledge of basic astronomy is weaker than I thought. My original thought was that the full moon would rise at 6:00 P.M. based on an assumption that it was in an equitorial, rather than ecliptic, orbit.

So, Phil, is the moon's orbit actually in the ecliptic? Slightly off? Or what?

[The Bad Astronomer]

The Moon's orbit is tilted by about 5 degrees to the ecliptic. But the time it rises full depends on many things, including the time of year.

Think of it this way: the full Moon must be opposite the Sun in the sky (that is, 180 degrees away), by definition. So in the summer, the full Moon rises later than in the winter, because sunset is later in the summer.

[Prester John]

but doesn't the sun technically start going down at midday, thus the full moon would start to rise even, tho' you may not be able to see it?




(Or should i just admit that im a Bad astronomer!

boom boom.)

[Skeptical Greg]

"At what time does the full Moon rise?"


' time ' Infers a sytem of measurement by a specific intrument. The correct answer, would include a reading from said instrument at a precise moment, which of course would vary from day to day ( days on which a full moon is visible ) during the solar year..


If the question had been " When does the full Moon rise ", then I feel the generalized answer of " When the Sun sets .. " would have been more appropriate...


The mechanics of when and why a full moon is visible; orbits, inclination & etc. is related, but was not part of the question..


I feel the correct answer would have been:

" It ' depends ' ( as noted by ceptimus and Brown ) on what time it is, when it happens.. "



I think Randi was suggesting that the question, and what it revealed of the person being asked, was not as profound as the poser seemed to be implying it was.. I agree..

[Blondin]

I think that may be exactly the red herring that the questioner was talking about. People get hung up about the exact wording of the question. If you stop and think about it you have to realize that the answer is not going to be a specific time in hours & minutes. If you consider basic principles you realize that the answer must be in terms of relationship to something else.

I think what Randi was getting at is that not everybody remembers their high-school astronomy well enough to apply the basic principles and come up with the "about sunset" answer.

It suprizes me that many people seem to find it a surprize when you explain that the phases of the moon and its rising and setting times are directly related.

If I may be allowed to hijack the thread here...

This often comes up when I am confronted by people who insist that emergency workers, police dispatchers, etc will all tell you that there is more mayhem and abberent behaviour around the time of the full moon (you know that schtick). I usually just ask if they know when the last full moon was. I find that most people not only don't know when the last full moon occured but they have no idea what the current phase of the moon is or when the next full moon is or (in some cases) what even causes the phases of the moon.

A lady I know swears that when she was a day-care worker the children were all little beasts around the time of the full moon yet she admits that she never actually went outside and checked the phase of the moon. I have my own little theory about a monthly cycle that causes everybody around you to suddenly become an insufferable pain but lets not go into that right now...

I think it would be interesting to conduct a little survey to find out what percentage of nurses, psychiatric care workers, emergency workers, etc are actually aware of the phase of the moon at any point in time.

[WanderingKnight]

My wife is a nurse and informs me that her floor has a calender posted to keep track of the phases of the moon. The reason, of course, is that everyone "knows" that things get crazy aeound that time so they want to be prepared for it.

Of course, if someone acts crazy any other time of the month, they are just nuts. but if they act crazy around the full moon, then it gets attributed to this. What logical fallacy are the nurses falling for here?

[Skeptical Greg]

Originally posted by Blondin
I think that may be exactly the red herring that the questioner was talking about. People get hung up about the exact wording of the question. If you stop and think about it you have to realize that the answer is not going to be a specific time in hours & minutes. If you consider basic principles you realize that the answer must be in terms of relationship to something else.

I was just waxing a bit pedantic by pointing out that time is measured in hours and minutes , and that a question about time should have an answer that includes those units..



I think what Randi was getting at is that not everybody remembers their high-school astronomy well enough to apply the basic principles and come up with the "about sunset" answer.

It suprizes me that many people seem to find it a surprize when you explain that the phases of the moon and its rising and setting times are directly related.

If I may be allowed to hijack the thread here...

This often comes up when I am confronted by people who insist that emergency workers, police dispatchers, etc will all tell you that there is more mayhem and abberent behaviour around the time of the full moon (you know that schtick). I usually just ask if they know when the last full moon was. I find that most people not only don't know when the last full moon occured but they have no idea what the current phase of the moon is or when the next full moon is or (in some cases) what even causes the phases of the moon.

A lady I know swears that when she was a day-care worker the children were all little beasts around the time of the full moon yet she admits that she never actually went outside and checked the phase of the moon. I have my own little theory about a monthly cycle that causes everybody around you to suddenly become an insufferable pain but lets not go into that right now...

I think it would be interesting to conduct a little survey to find out what percentage of nurses, psychiatric care workers, emergency workers, etc are actually aware of the phase of the moon at any point in time.

Regarding the highjack..

Actually you have given the thread new life....

When someone brings up the subject of people acting luny during a full moon, I point out that people behave the same way at other times, and ask " What causes it then? ( When the moon is not full )...

[whitefork]

I'd like to ask another question. Where does the full moon rise? Full moon for this month occurred on the 7th at 10:40AM EST, according to the almanac. Does anyone have a formula to determine the longitude (at the equator, say) where the moon is rising at 10:40 AM EST?

My spherical geometry skills are sadly atrophied.

[BillyJoe]

If you were to ask the man on the street "At what time does the full moon rise" and he was able to think about it sufficiently to answer "At sunset", you would not tell him he was wrong.

On the other hand, if he started discussing refraction, solstices and ecliptics you would simply KISS him and walk on.

[Thumbo]

Originally posted by Kullervo
I'd like to ask another question. Where does the full moon rise? Full moon for this month occurred on the 7th at 10:40AM EST, according to the almanac. Does anyone have a formula to determine the longitude (at the equator, say) where the moon is rising at 10:40 AM EST?

My spherical geometry skills are sadly atrophied.
You don't need spherical geometry, at least for a first approximation.

Make two simplfying assumptions:

1) There is no refraction.

2) The earth's orbit is perfectly spherical.

If both of the above were true, then at the equator the sun would always rise at 6 A.M. solar time and set at 6 P.M. This is because the equator is a great circle, and the line dividing night and day is also a great circle (near enough), and any two great circles on a sphere always bisect one another.

So if it is 10.40 A.M. EST, then where is it 6 A.M? One hour of day is equivalent to 15 degrees of longitude, so it would be 6 A.M. about 70 degrees west of the eastern time zone - somewhere in the Pacific, I think.

That's an approximation. To get a better answer you need to know a few more things:

1) How 10.40 A.M. clock time relates to solar time (the time measured by the sun), and at what actual location.

2) The equation of time - that is, the difference between clock time and solar time, which due to the eccentricity of the Earth's orbit can be up to 20 minutes, if I recall correctly. (Hmm - now I think about it, this correction probably cancels out most of the previous one).

3) The effect of refraction, which would move the point you are interested in a bit further west.

[teddosan]

Okay, I have a basic question for Thumbo and Bad Astronomer: If the earth, the sun, and the moon are in a straight line i.e. half of the earth sees the sun and half sees the moon, how does the light from the sun hit the dang moon? Is that not the condition for a new moon? Is the earth not blocking the sunlight from the moon?
Or is the sun big enough and the moon far enough away that the light from the sun still illuminates the moon even with the earth "in the way?" In that case, what is a new moon?

[whitefork]

I think I can answer that one. The new moon occurs when the moon is between the earth and sun - the condition for a solar eclipse if the alignment is right. The full moon happens when the earth is between the sun an moon, the condition for a lunar eclipse. The moon is not orbiting in the exact plane of the earth, so the eclipses don't occur every time there's a new or full moon, but only when the moon is crossing that plane at the right time.

Correct me if I have that wrong please.

[Skeptical Greg]

Some good diagrams here to show how Lunar eclipses occur..

You can also see how full moon occurs when Moon, Earth and Sun are aligned properly..

Solar and Lunar Eclipses (http://www.essex1.com/people/stauffer/MLS/eclipse.html)

The right diagram shows how the shadow of the moon is above the earth at this point. This is how the ecliptic got its name. You can only have eclipses when the moon is near the ecliptic.

http://www.essex1.com/people/stauffer/MLS/eclipseshad.gif

[BillyJoe]

In other words, when the moon is full but not eclipsed, it is not really "full", but so nearly full you can't tell the difference.

[The Fool]

Originally posted by WanderingKnight
My wife is a nurse and informs me that her floor has a calender posted to keep track of the phases of the moon. The reason, of course, is that everyone "knows" that things get crazy aeound that time so they want to be prepared for it.

Of course, if someone acts crazy any other time of the month, they are just nuts. but if they act crazy around the full moon, then it gets attributed to this. What logical fallacy are the nurses falling for here?
This is a common belief among hospital workers and police.... People act more crazy and end up in hospital more during a full moon. My personal theory is it is simply the light levels. Under a full moon night becomes virually day...more ligt, more activity, more crazy things happening, more people injured etc....

[gnome]

Originally posted by The Fool

This is a common belief among hospital workers and police.... People act more crazy and end up in hospital more during a full moon. My personal theory is it is simply the light levels. Under a full moon night becomes virually day...more ligt, more activity, more crazy things happening, more people injured etc....

Would anyone say there is possibly a suggestive effect... reversing cause and effect, so to speak... in much the same way that a redhead might develop a temper from everyone around them expecting it so much... or someone, aware of their sun sign, acting in accord with what they've been told is their "nature"?

I would imagine there could also be a collective effect...

[BillyJoe]

.....except that there is no full moon effect (http://www.skepdic.com/fullmoon.html)

[sophia8]

Originally posted by The Bad Astronomer
Thumbo, congrats! You are correct.

Due to the Earth's atmosphere bending light, the full Moon rises before sunset. If we didn't have air, the full Moon would rise just at sunset. But the air bends the light, so the Moon can actually be visible to us when it is physically below the horizon. I am not sure how much time elapses between it being seen and being above the physical horizon, but it's probably only a couple of minutes. This also means the Sun will be visible even when it is physically below the horizon, so the effect of the full Moon rising before sunset is doubled.

And this assumes the Earth is a perfect sphere, the Moon is in the ecliptic plane, etc. etc. If you want to go into those effects, I'd have to really think about it -- and probably get it wrong myself! ;-)
And it's that refraction effect that's also responsible for the fact that the longest/shortest days of the year actually come a few days before the Solstices?

[Gestahl]

Originally posted by ceptimus
I was thinking about this last night. I suppose we have to define how near to 'full' the full moon has to be. If it is only full when the Sun, Earth and Moon are perfectly in line, then it is never absolutely full, and whenever it gets pretty close, there will be a lunar eclipse anyway.


Not correct, or there would be 12 lunar eclipses a year. This is not so. You are assuming that the plane of the moon's orbit is co-planar with the earth's orbit around the sun, and additionally that the elliptical orbit changes orientation along with earth's position in the orbit of the moon. Here is a picture, greatly exaggerated for clarity:
<pre>
(M)
\
(S)-----------------(E) (Slant is exaggerated plane of moon's orbit).
\
</pre>
In this case, the only time you get an eclipse is when the Moon is in the point of orbit between S and E (90 degrees "out of the page"). In fact, Earth will have to revolve 90 degrees around the Sun, and the Moon 90 degrees clockwise from the viewpoint of the Sun.

Question from teddosan:

Quote:

Okay, I have a basic question for Thumbo and Bad Astronomer: If the earth, the sun, and the moon are in a straight line i.e. half of the earth sees the sun and half sees the moon, how does the light from the sun hit the dang moon? Is that not the condition for a new moon? Is the earth not blocking the sunlight from the moon?

The moon's orbital plane is not coincident with the earth's orbital plane: see illustration above.

The criterion for a new moon is Sun---Moon---Earth in line, and the critreion for a full moon is Sun---Earth---Moon.

Of course, if my illustration were accurate, most of the time we would have a half-ish moon, and almost never a full or new moon.

My answer would be "whenever the Weather Channel says it does."

[BillyJoe]

Gesthahl

Originally posted by Gestahl

------------------------------------------------------------------------------------
Originally posted by ceptimus
I was thinking about this last night. I suppose we have to define how near to 'full' the full moon has to be. If it is only full when the Sun, Earth and Moon are perfectly in line, then it is never absolutely full, and whenever it gets pretty close, there will be a lunar eclipse anyway.
------------------------------------------------------------------------------------

Not correct, or there would be 12 lunar eclipses a year. This is not so. You are assuming that the plane of the moon's orbit is co-planar with the earth's orbit around the sun, and additionally that the elliptical orbit changes orientation along with earth's position in the orbit of the moon. No, you have misunderstood him.
He is saying that IF the "Full Moon" were TRUELY to be a "FULL Moon", then we would only get a "Full Moon" when there was a lunar eclipse (and even then maybe it isn't full either :D ). All the other times it would not be TOTALLY ONE HUNDRED PERCENT FULL but merely ALMOST ONE HUNDRED PERCENT FULL.

Originally posted by Gestahl
If the earth, the sun, and the moon are in a straight line i.e. half of the earth sees the sun and half sees the moon, how does the light from the sun hit the dang moon? Is that not the condition for a new moon? Is the earth not blocking the sunlight from the moon? Yes, this was ceptimus' point.....the Earth would block the Sun's rays from hitting the Moon....in other words.....we would have a lunar eclipse. This is why he says that the Moon must be at least slightly off line from the Sun and the Earth and that, therefore, the Moon would not be truely full but ALMOST full.

BillyJoe

[Walter Wayne]

I over analyzed this question when I saw it. I assumed that there is an instant the moon becomes full, the very moment it is neither waxing nor waning. If that is the case, then for many people the full moon doesn't rise, it occurs when the moon is already in the sky.

Another way of thinking of this, at the exact moment of sun-earth-moon alignment, for some folks its around dusk, some folks its middle of the night, and for some dawn.

Walt