Astronomy confusion

[veremchuka]

OK, I'm not the sharpest knife in the drawer when it comes to this stuff but I have some experience. Can anyone explain how the 1st appearance of the crescent moon can appear in the morning?

Here's the story called "The Thinnest Crescent".

Spaceweather.com Time Machine

Here's the statement that got my attention and caused my confusion

This image shows the tiny lunar crescent at the precise moment of the New Moon, in full daylight at 7h14min UTC on July 8 2013," says Legault. "It is the youngest possible crescent, the age of the Moon at this instant being exactly zero.

So here's some points to consider -

1. UTC is a 24 hour clock at Greenwich England right?
2. So this means it was 7:14 AM at the UTC longitude because 7:14 pm would be 19:14 right?
3. So I looked at the weather for Elancourt, France on Weather Underground. It says the time is +2:00 UTC. That means when it is 07:14 ( 7:14 am) at UTC it is 09:14 (9:14 am) at Elancourt, France right?
4. The new moon is when the moon appears for the 1st time and then day by day gets larger until it is a full moon right?

Now assuming the answer has been yes to all of the above then I'm confused because I have always read the 1st appearance of the new moon happens on the western horizon directly above the setting sun! How can he photograph this at 9:14 am local time?

Maybe the answer is that it is not possible to see this thin a crescent (see text from the article below) and the 1st time you can see the crescent moon is at sunset?

the blue sky being about 400 times brighter than the crescent itself in infrared and probably more than 1000 times brighter in visible light.

 

[LOL!]

A new moon occurs when the moon is between the Sun and the Earth.
A full moon occurs when the Earth is between the Sun and the Moon.

So at the time of a new moon, the moon is always in the direction of the Sun, right? It seems to me that the newest crescent moon occurs as the moon moves slightly off the line drawn between the Sun and the Earth. Probably in the morning around sunrise. Right?

 

[ER Eddie]

When I was younger, I was an astronomy buff and might've been able to answer this question. Now, it's all over my head. All I know now is that a crescent moon is my favorite type of moon. I find it very serene.

Did that help? lol.

 

[ERD50]

I don't see where morning/evening has much to do with it. I drew a diagram to refresh myself, and as LOL! says,

A new moon occurs when the moon is between the Sun and the Earth.
A full moon occurs when the Earth is between the Sun and the Moon.

Morning/evening is probably just a matter of how the synchronization happens, but I can't follow down to that detail. But I don't see any reason to be surprised if it is one over the other.

-ERD50

 

[veremchuka]

Thanks but the point of the thread is this question - doesn't the 1st visible appearance of the crescent moon occur directly above the setting sun which would be on the western horizon. If that is correct, and I remember reading this years ago, then how can this thin crescent appear at 9:14 am local time?

So I thought about this and all can think, but I am asking for opinions, is that the answer is in the final 2 paragraphs ie - it may well appear in the morning but it is so incredibly thin that the brightness of the sun totally obscures it.

Where's Issac Asimov when you need him?

 

[LOL!]

It all depends on the relative rotation of the earth and the revolution of the moon around the earth, right?

I can see where perhaps the last appearance of the crescent moon appears at sunset in some months, where the first appearance might be at sunset 6 months later.

And I can see where it can occur at slightly different times depending on where on earth one is standing since the earth has a certain size.

 

[Nodak]

OK, I'm not the sharpest knife in the drawer when it comes to this stuff but I have some experience. Can anyone explain how the 1st appearance of the crescent moon can appear in the morning?

Here's the story called "The Thinnest Crescent".

Spaceweather.com Time Machine

Here's the statement that got my attention and caused my confusion

So here's some points to consider -

1. UTC is a 24 hour clock at Greenwich England right?
2. So this means it was 7:14 AM at the UTC longitude because 7:14 pm would be 19:14 right?
3. So I looked at the weather for Elancourt, France on Weather Underground. It says the time is +2:00 UTC. That means when it is 07:14 ( 7:14 am) at UTC it is 09:14 (9:14 am) at Elancourt, France right?
4. The new moon is when the moon appears for the 1st time and then day by day gets larger until it is a full moon right?

Now assuming the answer has been yes to all of the above then I'm confused because I have always read the 1st appearance of the new moon happens on the western horizon directly above the setting sun! How can he photograph this at 9:14 am local time?

Maybe the answer is that it is not possible to see this thin a crescent (see text from the article below) and the 1st time you can see the crescent moon is at sunset?

I believe you are right. My experience has always been the earliest crescent after new moon appears just above the setting sun. I suspect there is an error in the time specified in the article.

 

[mugwump]

I think there are two kinds of crescent moons; the first of the waxing new moon appears at sunset, and the last of the waning old moon appears at dawn. I can't vouch for the visibility of the morning one, because I am rarely up that early. A long time ago, I learned the mnemonic, "D" is for daring, "C" is for coy. If the moon has the curve in the same place as a D, it is getting bigger, or waxing; same place as a C, it is coy, or waning. The moon rises 50 minutes later every day; if you keep track, you will see that the illuminated side always faces the sun.

 

[ERD50]

Thanks but the point of the thread is this question - doesn't the 1st visible appearance of the crescent moon occur directly above the setting sun which would be on the western horizon. If that is correct, and I remember reading this years ago, then how can this thin crescent appear at 9:14 am local time?

So I thought about this and all can think, but I am asking for opinions, is that the answer is in the final 2 paragraphs ie - it may well appear in the morning but it is so incredibly thin that the brightness of the sun totally obscures it.

Where's Issac Asimov when you need him?

I'm no astronomer, but when I look at a diagram, I don't see why it would need to occur specifically at sunrise or sunset. I would think it would all depend on the synchronization at that point of time.

But you seem to be basing all this on what you recall you read previously. Who is to say that is right, or that your memory is accurate? I think you need a current, reliable, published source to reference to set this straight for yourself. I am not a reliable source!


-ERD50

 

[mugwump]

I'm no astronomer, but when I look at a diagram, I don't see why it would need to occur specifically at sunrise or sunset. I would think it would all depend on the synchronization at that point of time.

But you seem to be basing all this on what you recall you read previously. Who is to say that is right, or that your memory is accurate? I think you need a current, reliable, published source to reference to set this straight for yourself. I am not a reliable source!
-ERD50

Sorry, I need to clarify; The waning crescent moon always appears just above the setting sun at sunset; the waxing crescent moon (oxymoron there) should appear just above the rising sun at sunrise. This is necessary because of the geometry of the phases of the moon. At those times, the moon is close to being in between the earth and the sun. The full moon always shows up on the opposite horizon as the sun (eg in the east at sunset) because at that time the earth is between the moon and the sun. Does that make sense?

Edit to add: so, for a better answer to your question; either the caption was wrong or your memory of it was wrong. The crescent moon at sunset is the new moon.

 

[veremchuka]

Sorry, I need to clarify; The waning crescent moon always appears just above the setting sun at sunset; the waxing crescent moon (oxymoron there) should appear just above the rising sun at sunrise. This is necessary because of the geometry of the phases of the moon. At those times, the moon is close to being in between the earth and the sun. The full moon always shows up on the opposite horizon as the sun (eg in the east at sunset) because at that time the earth is between the moon and the sun. Does that make sense?

Edit to add: so, for a better answer to your question; either the caption was wrong or your memory of it was wrong. The crescent moon at sunset is the new moon.

I believe you have it backwards. The waxing moon is when the moon is growing and the waning moon is when it is shrinking... both relative to the lit surface.

So a waxing moon 1st appears at sunset directly above the setting sun, the moon is close to or on the horizon. The moon sets very quickly.

Conversely the waning moon last appears on the eastern horizon at sunrise close to or on the horizon. The moon disappears quickly as the rising sun obliterates it with light.

Yes the 1st appearance of the waxing moon is the new moon.

The movements of the moon are very complex. I used to study this and I am certain I am correct re where the new moon crescent appears and the same for the waning moon on the last day you see it.

The full moon rises on the eastern horizon exactly as the sun is setting on the western horizon.

The moon is "full" at exactly 1 moment in time per month. Seconds prior to that it is not full and seconds later it is not full. we think of the moon as being full for a day or two but it is for a moment in time.

 

[mugwump]

I believe you have it backwards.

Doh! Yes, I misswrote. The waxing moon is at sunset and the waning moon at sunrise. Thanks for catching that. Every time I get dogmatic, I make a stupid mistake like that unless I double-check.

 

[Animorph]

The new moon happens when the Moon aligns between the Earth and the Sun, as noted before. This happens at a precise UTC time, whatever it is. If you can see the Sun at that time, you could see the new Moon if you had whatever special equipment made it possible. It might be close to your sunrise or sunset or noon. Each point on Earth will see it at a different local time. The Earth's rotation has nothing to do with the moon phases, so it might be in any rotational position at the precise time of a new Moon.

The moon will be a little ahead or behind the sun and will appear as the other posters said just before sunrise or sunset. However that might be +/- 12 hours away from the true new Moon time. It'll still look like a pretty small crescent.

 

[mugwump]

The new moon happens when the Moon aligns between the Earth and the Sun, as noted before. This happens at a precise UTC time, whatever it is. If you can see the Sun at that time, you could see the new Moon if you had whatever special equipment made it possible. It might be close to your sunrise or sunset or noon. Each point on Earth will see it at a different local time. The Earth's rotation has nothing to do with the moon phases, so it might be in any rotational position at the precise time of a new Moon.

The moon will be a little ahead or behind the sun and will appear as the other posters said just before sunrise or sunset. However that might be +/- 12 hours away from the true new Moon time. It'll still look like a pretty small crescent.

Oh, that makes sense.

 

[ERD50]

... The full moon always shows up on the opposite horizon as the sun (eg in the east at sunset) because at that time the earth is between the moon and the sun. Does that make sense? ...

Yes, but I don't see what it has to do with a crescent moon first appearing only at sunrise or sunset.

Common Ground (I think): A full moon appears when the Earth is nearly between the Sun and the Moon. And that full Moon will be in the West at sunrise, and in the East at sunset. I can see that with my napkin sketch with the Earth turning CCW when viewed looking down at the North Pole, and the Moon on the far side of the Sun/Earth.

Question: But the Moon takes ~ 28 days to circle the Earth, so its motion is relatively slow. So that Full Moon appears both at sunrise and at sunset (and we observe this of course). So I guess I don't see any reason why the exact point of the fullest of the full moon (or the narrowest of the crescent) would need to occur at only one or the other. Wouldn't it just all depend on how things are synchronized. They aren't integer relationships, so it will vary over time. Plus, everything is slowly slowing down due to friction.

Unless there is some other force at play that I'm not considering, like the way the gravitational offset of the moon keeps the same side facing the Earth, I just don't see any reason for it to only occur at either a sunrise or a sunset. Maybe things are aligned such that that is how it is now, but I don't see why it has to be?

Or did I just confuse things further?

PS - for other things in the sky, a very cool site is heavens-above.com

you can track ISS, satellites, and Iridium flares (my favorite!)

-ERD50

 

[mugwump]

Yes, but I don't see what it has to do with a crescent moon first appearing only at sunrise or sunset.
-ERD50

Boy, you folks make a person think! The crescent moon must be in the same place relative to the sun all day, so it must only be visible at sunrise and sunset because the sun doesn't shed so much light.

I grew up in the Midwest, where I rarely even saw sunrise and sunset. It in only since I moved West that I have started noticing these things.

 

[ERD50]

...
The moon is "full" at exactly 1 moment in time per month. Seconds prior to that it is not full and seconds later it is not full. we think of the moon as being full for a day or two but it is for a moment in time.

I cross posted with this, but I think it gets to my point/question. Since the moon appears mostly full for a day, but is only technically a 'full-full' moon for some precise instant - what would dictate that it would need to be an instant near either sunrise or sunset? Couldn't that moment occur at any point in the day, depending on all these relationships (or maybe not at all - if it happened between moon-set and moon-rise at our vantage point?)? This would apply to the narrowest crescent moon as well, right?

-ERD50

 

[ERD50]

OK, I think I get it. It does have to do with being able to see it, away from the sun's glare. Now here's one source (of several I found) that agrees with the OP's memory:

Understanding waxing crescent moon | Moon Phases | EarthSky

A waxing crescent moon – sometimes called a young moon – is always seen in the west after sunset.

At this moon phase, the Earth, moon and sun are located nearly on a line in space. If they were more precisely on a line, as they are at new moon, we wouldn’t see the moon. The moon would travel across the sky during the day, lost in the sun’s glare.

And now I see this - it has to do with this crescent being the first crescent after a new moon, so this diagram shows the Earth and the Moon orbit around Earth moving CCW. So the first crescent after a new moon will appear between 12:00 and 11:00 (thinking of this diagram as a clock face, not the actual times). Now picture sunrise from the Earth - the Sun will appear first, blocking the human eye view of that crescent. But at sunset, the sun has dropped below the horizon, and the new crescent moon is just above it.

Maybe the OP article was referring to the technical point in time of the new crescent, rather than the human visible time? Ahhhh, here's a quote from the article:

In order to reduce the glare, the images have been taken at near-infrared wavelengths using a pierced screen placed just in front of the telescope to block direct sunlight."

That must be it. No human could see it directly.

Mystery solved? Do I win a prize?

-ERD50

 

[veremchuka]

Well yes and no! I was saying the same thing I think.

As I stated earlier the moon is full at a precise moment in time - 1 second before it is not full and 1 second after it is not full. Now this is an extremely minute difference but to be accurate it does happen for only a second plus or minus yet we see the moon full for a day or two.

Likewise, the new moon happens at a precise moment in the day BUT and here's the key point - we can't see it at that precise moment due to the sun's brightness... this was pointed out in the original link I posted (last quote) and this (that I just said in this paragraph) is what I posed as the answer to my question. So with the help of all here I feel this is confirmed.

So the evening that the new moon appears is when we first see it (minutes or hours later depending upon when that precise moment was that it was the new moon) on the western horizon, just above the setting sun, for just a few minutes and then it sets. I was absolutely positive of that and likewise the last day we see it as it wanes is just at sunrise, on the eastern horizon, for a few minutes but then it sets as the sun rises above the horizon and again I was absolutely sure of that. Remember each evening the moon rises or appears earlier by about 50 minutes and a little farther away from the western horizon as it works it's way back to rising on the eastern horizon exactly when the sun sets on the western horizon and that is the full moon.

As I said, the movements of the moon are quite complex - it goes through an 18.6 year cycle iirc. How the ancients were able to know it's movements, predict eclipses, it's amazing to me because it wasn't just by observation. Cloudy skies would occur for days, the monthly cycle is 28 point sometime or 29 point something days in addition to that 18.6 cycle.

Whew this is confusing for a mere mortal!

 

[ERD50]

Well yes and no! I was saying the same thing I think.
....

Whew this is confusing for a mere mortal!

Yes, I think so. I think I got focused on exactly when it occurred (astronomically), and you were focused on when you could first see it. I think we've got both points now.

I almost gave up, my head was spinning. I'm also amazed that people figured these things out centuries ago. I have trouble understanding it when it's explained, and they figured it out with limited tools and limited previous information. Impressive. And humbling.

-ERD50

 

[GalaxyBoy]

It seems to me there's possibly a bit of confusion between the astronomer's definition of new moon and a lay person's. The astronomer defines it as the instant when the sun and moon are aligned (more precisely, it is the instant when the moon and sun have the same ecliptical longitude), as noted several times above, whereas a lay person may define it as the first time it is visible to the naked eye, which must occur just after a sunset. In fact, this is very important to Muslims who define their months and certain holy days by a lunar calendar. Ramadan might start on different days in different parts of the world depending if the crescent moon was visible or not.

Edit: I forgot to add that the youngest new moon is actually visible only during a solar eclipse.