APOD: A Harvest Moon (2019 Sep 13)

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APOD: A Harvest Moon (2019 Sep 13)

Post by APOD Robot » Fri Sep 13, 2019 4:09 am

Image A Harvest Moon

Explanation: Famed in festival, story, and song the best known full moon is the Harvest Moon. For northern hemisphere dwellers that's a traditional name of the closest full moon to the September equinox. In most North America time zones this year's Harvest Moon will officially rise on Friday, September 13. In fact the same Harvest Moon will rise on September 14 for much of the planet though. Of course the Moon will look almost full in the surrounding days. Regardless of your time zone the Harvest Moon, like any other full moon, will rise just opposite the setting Sun. Near the horizon, the Moon Illusion might make it appear bigger and brighter to you but this Harvest Moon will be near lunar apogee. That's the closest point in its orbit, making it the most distant, and so the smallest, full moon of the year. On August 15 a wheat field harvested in south central France made this a harvest moon scene too, the full moon shining on with beautiful iridescent clouds at sunset.

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Re: APOD: A Harvest Moon (2019 Sep 13)

Post by Ann » Fri Sep 13, 2019 4:27 am

Which ones are the obvious five bright stars that can be seen to the right of the tree in the picture?

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Re: APOD: A Harvest Moon (2019 Sep 13)

Post by jks » Fri Sep 13, 2019 4:33 am

Please clarify: Apogee is the farthest point in the orbit, not the closest, right?

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Re: APOD: A Harvest Moon (2019 Sep 13)

Post by Chris Peterson » Fri Sep 13, 2019 4:42 am

jks wrote:
Fri Sep 13, 2019 4:33 am
Please clarify: Apogee is the farthest point in the orbit, not the closest, right?
Yes. The caption needs a bit of tweaking...
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Re: APOD: A Harvest Moon (2019 Sep 13)

Post by Ann » Fri Sep 13, 2019 4:43 am

jks wrote:
Fri Sep 13, 2019 4:33 am
Please clarify: Apogee is the farthest point in the orbit, not the closest, right?
Yes, that sounds strange. A Moon that looks particularly big and bright should be comparatively close to us, right?

On the other hand, as someone pointed out to me: In the summer, the Sun is high in the sky and the Moon is low. In the winter, the Sun is low in the sky and the Moon is high. The small-looking brilliantly bright Moon high in a black winter's sky makes those winter nights seem particularly cold and forbidding to me.

But maybe the opposite is also true. In the summer the Moon is low in the sky, and therefore it looks big, even if it is near the apogee in its orbit around the center of gravity in the Earth-Moon system?

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Re: APOD: A Harvest Moon (2019 Sep 13)

Post by Chris Peterson » Fri Sep 13, 2019 4:51 am

Ann wrote:
Fri Sep 13, 2019 4:43 am
jks wrote:
Fri Sep 13, 2019 4:33 am
Please clarify: Apogee is the farthest point in the orbit, not the closest, right?
Yes, that sounds strange. A Moon that looks particularly big and bright should be comparatively close to us, right?

On the other hand, as someone pointed out to me: In the summer, the Sun is high in the sky and the Moon is low. In the winter, the Sun is low in the sky and the Moon is high. The small-looking brilliantly bright Moon high in a black winter's sky makes those winter nights seem particularly cold and forbidding to me.

But maybe the opposite is also true. In the summer the Moon is low in the sky, and therefore it looks big, even if it is near the apogee in its orbit around the center of gravity in the Earth-Moon system?
There's not that much difference in size between an apogee and a perigee moon. Few observers could tell the difference visually. The horizon effect is much stronger. That is, an apogee moon near the horizon will almost certainly appear larger than a perigee moon higher in the sky.

Yes, in the summer the path of the Moon is lower in the sky. But it is still far enough above the horizon at most latitudes that the horizon effect won't come into play except near its rising and setting (although that will obviously be a longer period at high latitudes).
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Re: APOD: A Harvest Moon (2019 Sep 13)

Post by FLPhotoCatcher » Fri Sep 13, 2019 5:24 am

Chris Peterson wrote:
Fri Sep 13, 2019 4:51 am
Ann wrote:
Fri Sep 13, 2019 4:43 am
"...as someone pointed out to me: In the summer, the Sun is high in the sky and the Moon is low. In the winter, the Sun is low in the sky and the Moon is high. The small-looking brilliantly bright Moon high in a black winter's sky makes those winter nights seem particularly cold and forbidding to me.

But maybe the opposite is also true. In the summer the Moon is low in the sky, and therefore it looks big, even if it is near the apogee in its orbit around the center of gravity in the Earth-Moon system?
Yes, in the summer the path of the Moon is lower in the sky. But it is still far enough above the horizon at most latitudes that the horizon effect won't come into play except near its rising and setting (although that will obviously be a longer period at high latitudes).
To clarify further, the Moon is only higher in the winter, and lower in the summer - during the part of its orbit that is away from the sun. It does seem strange to me that the moon's max height above the horizon doesn't depend mostly on the season. Or am I wrong about that?

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Re: APOD: A Harvest Moon (2019 Sep 13)

Post by Boomer12k » Fri Sep 13, 2019 6:45 am

Nice image... we had a very pretty sunset the other evening...

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Re: APOD: A Harvest Moon (2019 Sep 13)

Post by ThargTheObserver » Fri Sep 13, 2019 10:07 am

The two brightest are Delta and Gamma Capricorni, the three above are, from top to bottom, 42,44 & 45 Capricornus. I doubt that you'd be able to see any of these stars in this scene with the naked eye (with the Moon being so bright) 42 Capricornus is just above magnitude 6 so the sky would have to be properly dark to have a chance of seeing them at all.

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Re: APOD: A Harvest Moon (2019 Sep 13)

Post by Ann » Fri Sep 13, 2019 10:23 am

ThargTheObserver wrote:
Fri Sep 13, 2019 10:07 am
The two brightest are Delta and Gamma Capricorni, the three above are, from top to bottom, 42,44 & 45 Capricornus. I doubt that you'd be able to see any of these stars in this scene with the naked eye (with the Moon being so bright) 42 Capricornus is just above magnitude 6 so the sky would have to be properly dark to have a chance of seeing them at all.
Thanks! I would never have guessed!

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Re: APOD: A Harvest Moon (2019 Sep 13)

Post by orin stepanek » Fri Sep 13, 2019 11:39 am

Beautiful Photo! Shine on Harvest Moon! :D 8-)
HarvestmoonGraffand.jpg
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Re: APOD: A Harvest Moon (2019 Sep 13)

Post by neufer » Fri Sep 13, 2019 11:48 am

Click to play embedded YouTube video.
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Re: APOD: A Harvest Moon (2019 Sep 13)

Post by Chris Peterson » Fri Sep 13, 2019 1:26 pm

FLPhotoCatcher wrote:
Fri Sep 13, 2019 5:24 am
Chris Peterson wrote:
Fri Sep 13, 2019 4:51 am
Ann wrote:
Fri Sep 13, 2019 4:43 am
"...as someone pointed out to me: In the summer, the Sun is high in the sky and the Moon is low. In the winter, the Sun is low in the sky and the Moon is high. The small-looking brilliantly bright Moon high in a black winter's sky makes those winter nights seem particularly cold and forbidding to me.

But maybe the opposite is also true. In the summer the Moon is low in the sky, and therefore it looks big, even if it is near the apogee in its orbit around the center of gravity in the Earth-Moon system?
Yes, in the summer the path of the Moon is lower in the sky. But it is still far enough above the horizon at most latitudes that the horizon effect won't come into play except near its rising and setting (although that will obviously be a longer period at high latitudes).
To clarify further, the Moon is only higher in the winter, and lower in the summer - during the part of its orbit that is away from the sun. It does seem strange to me that the moon's max height above the horizon doesn't depend mostly on the season. Or am I wrong about that?
The path of the full Moon is high in the winter and low in the summer, because the Moon approximately follows the ecliptic, and the ecliptic is high in the sky on winter nights and low in the sky on summer nights. The height of the path of the full Moon very much depends mostly on the season.

(Because the Moon's orbit is inclined about 5° from the ecliptic, it does wiggle around on either side of it over time. But that variation is small compared with the seasonal shift of the ecliptic.)
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Re: APOD: A Harvest Moon (2019 Sep 13)

Post by TheZuke! » Fri Sep 13, 2019 1:58 pm

As long as we're discussing on the winter Moon being "high in the sky", is that subject to 19 year lunar cycle? Or Earth's precession? When will it be be low in the winter sky?

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Re: APOD: A Harvest Moon (2019 Sep 13)

Post by Chris Peterson » Fri Sep 13, 2019 2:10 pm

TheZuke! wrote:
Fri Sep 13, 2019 1:58 pm
As long as we're discussing on the winter Moon being "high in the sky", is that subject to 19 year lunar cycle? Or Earth's precession? When will it be be low in the winter sky?
The full Moon can never be low in the winter sky compared to the summer sky. Between winter and summer the ecliptic varies in height by 47°. The farthest the Moon gets from the ecliptic is 5°. So the lowest possible full Moon in winter is still much higher than the highest possible full Moon in summer. (The deviation of the Moon from the ecliptic is related to the 18.6 year cycle, but that pattern isn't readily apparent in observing the height of the Moon in the sky, which varies in declination over a two-week period.)
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Re: APOD: A Harvest Moon (2019 Sep 13)

Post by neufer » Fri Sep 13, 2019 3:29 pm

Chris Peterson wrote:
Fri Sep 13, 2019 2:10 pm

The full Moon can never be low in the winter sky compared to the summer sky.
At midnight the full Moon can never be low in the winter solstice sky compared to the summer solstice sky.
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Re: APOD: A Harvest Moon (2019 Sep 13)

Post by Chris Peterson » Fri Sep 13, 2019 3:44 pm

neufer wrote:
Fri Sep 13, 2019 3:29 pm
Chris Peterson wrote:
Fri Sep 13, 2019 2:10 pm

The full Moon can never be low in the winter sky compared to the summer sky.
At midnight the full Moon can never be low in the winter solstice sky compared to the summer solstice sky.
Indeed. The assumption here is that we're talking about the intersection of the ecliptic with the meridian. Obviously, the Moon is always low in the sky near its rise or set, regardless of season.
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Re: APOD: A Harvest Moon (2019 Sep 13)

Post by keythewish » Sat Sep 14, 2019 2:40 pm

The description of the Harvest Moon currently has an error. It states: "For northern hemisphere dwellers that's a traditional name of the farthest full moon to the September equinox." It should be the "nearest".

This is apparently a botched attempt to fix the description of apogee, which is now correct. Please fix the Harvest Moon definition.

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Re: APOD: A Harvest Moon (2019 Sep 13)

Post by BillLee » Sat Sep 14, 2019 9:42 pm

Something strange with this picture. Somebody please explain.

The picture looks like, and the caption says "...the full moon shining on with beautiful iridescent clouds at sunset." but the full moon can NOT be in a picture of a "sunset"!

The moon is full when it is opposite the sun. At sunset, the moon is just rising in the east, at least in the universe I inhabit.

Can someone please explain to me what I am REALLY seeing?

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Re: APOD: A Harvest Moon (2019 Sep 13)

Post by MarkBour » Sat Sep 14, 2019 9:55 pm

This isn't really an astronomy question. The current definition of the Harvest moon is the full moon whose date is closest to the September equinox. With our changing climate, it might be more appropriate to pick the first full moon that occurs after the September equinox, even if there is a full moon just before it. Like I say, this is not really an astronomy question ... but aren't harvest dates slipping ever later in the calendar lately? (Of course, this is a northern-hemisphere-centric term, at any rate.)

The change in the total length of the growing season for each state in the US is shown at:
https://www.climatecentral.org/gallery/ ... ing-season .

I'd love to see similar data for a country in the southern hemisphere. I'm guessing it is the same general pattern, though with lots of noise in the data, and of course shifted by 6 months. But that's a simple first guess. There may be lots of factors that would surprise me and it might be that the southern hemisphere is not a good mirror of the northern on this measure.
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Re: APOD: A Harvest Moon (2019 Sep 13)

Post by Chris Peterson » Sun Sep 15, 2019 4:41 am

BillLee wrote:
Sat Sep 14, 2019 9:42 pm
Something strange with this picture. Somebody please explain.

The picture looks like, and the caption says "...the full moon shining on with beautiful iridescent clouds at sunset." but the full moon can NOT be in a picture of a "sunset"!

The moon is full when it is opposite the sun. At sunset, the moon is just rising in the east, at least in the universe I inhabit.

Can someone please explain to me what I am REALLY seeing?
You're seeing the Moon rising in the east at sunset. Not sure what the problem is, either with the picture or the caption.
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Re: APOD: A Harvest Moon (2019 Sep 13)

Post by BillLee » Mon Sep 16, 2019 1:55 am

Chris Peterson wrote:
Sun Sep 15, 2019 4:41 am
BillLee wrote:
Sat Sep 14, 2019 9:42 pm
Something strange with this picture. Somebody please explain.

The picture looks like, and the caption says "...the full moon shining on with beautiful iridescent clouds at sunset." but the full moon can NOT be in a picture of a "sunset"!

The moon is full when it is opposite the sun. At sunset, the moon is just rising in the east, at least in the universe I inhabit.

Can someone please explain to me what I am REALLY seeing?
You're seeing the Moon rising in the east at sunset. Not sure what the problem is, either with the picture or the caption.
Sorry, but that picture looks NOTHING like a mooonrise in the east with a sunset in the west!

I was driving east bound on I-20 last Friday evening when the full moon in question was rising. The sunset a few minutes earlier was a LOOOONG ways away from where the moon rose, way back the other way! There is no way a full moon will appear against a sunset sky like the picture portrays.

I say it is photoshopped.

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Re: APOD: A Harvest Moon (2019 Sep 13)

Post by Chris Peterson » Mon Sep 16, 2019 2:34 am

BillLee wrote:
Mon Sep 16, 2019 1:55 am
Chris Peterson wrote:
Sun Sep 15, 2019 4:41 am
BillLee wrote:
Sat Sep 14, 2019 9:42 pm
Something strange with this picture. Somebody please explain.

The picture looks like, and the caption says "...the full moon shining on with beautiful iridescent clouds at sunset." but the full moon can NOT be in a picture of a "sunset"!

The moon is full when it is opposite the sun. At sunset, the moon is just rising in the east, at least in the universe I inhabit.

Can someone please explain to me what I am REALLY seeing?
You're seeing the Moon rising in the east at sunset. Not sure what the problem is, either with the picture or the caption.
Sorry, but that picture looks NOTHING like a mooonrise in the east with a sunset in the west!

I was driving east bound on I-20 last Friday evening when the full moon in question was rising. The sunset a few minutes earlier was a LOOOONG ways away from where the moon rose, way back the other way! There is no way a full moon will appear against a sunset sky like the picture portrays.

I say it is photoshopped.
You're not seeing a full Moon against a sunset. The sunset is behind the camera. A long way from the Moon, which is the bright blob you see rising above the horizon in this image.
Chris

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