APOD: A Year of Full Moons (2017 Nov 05)

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APOD: A Year of Full Moons (2017 Nov 05)

Postby APOD Robot » Sun Nov 05, 2017 4:08 am

Image A Year of Full Moons

Explanation: Do all full moons look the same? No. To see the slight differences, consider this grid of twelve full moons. From upper left to lower right, the images represent every lunation from 2016 November through 2017 October, as imaged from Pakistan. The consecutive full moons are all shown at the same scale, so unlike the famous Moon Illusion, the change in apparent size seen here is real. The change is caused by the variation in lunar distance due to the Moon's significantly non-circular orbit. The dark notch at the bottom of the full moon of 2017 August is the shadow of the Earth -- making this a partial lunar eclipse. Besides the sometimes exaggerated coloring, a subtler change in appearance can also be noticed on close examination, as the Moon seems to wobble slightly from one full moon to the next. This effect, known as libration, is more dramatic and easier to see in this lunation video highlighting all of the ways that the Moon appears to change over a month (moon-th).

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Re: APOD: A Year of Full Moons (2017 Nov 05)

Postby daddyo » Sun Nov 05, 2017 7:22 am

I had no idea that the apparent view of the moon rotated around 90 degrees over the seasons. This is way more than subtle and maybe why people sometimes have a hard time to recognize Mikey Mouse on the Moon.

heehaw

Re: APOD: A Year of Full Moons (2017 Nov 05)

Postby heehaw » Sun Nov 05, 2017 11:41 am

Useful to have this image when some naive friend asks you about a story in the newspaper about an upcoming SUPERMOON !!!

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Re: APOD: A Year of Full Moons (2017 Nov 05)

Postby Chris Peterson » Sun Nov 05, 2017 1:58 pm

daddyo wrote:I had no idea that the apparent view of the moon rotated around 90 degrees over the seasons. This is way more than subtle and maybe why people sometimes have a hard time to recognize Mikey Mouse on the Moon.

It depends on your point of reference. With respect to the horizons (probably the most reliable reference for most people) the Moon rotates about 180° just between moonrise and moonset.
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Re: APOD: A Year of Full Moons (2017 Nov 05)

Postby BDanielMayfield » Sun Nov 05, 2017 3:27 pm

The explanation mentions "the sometimes exaggerated coloring" but offers nothing further about it. It is most apparent in the two adjacent maria in the upper (northern?) side. One's brown, the other is blue. Why is this?

They remind me of a dog I once had with a brown and a blue eye.

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Re: APOD: A Year of Full Moons (2017 Nov 05)

Postby Chris Peterson » Sun Nov 05, 2017 3:36 pm

BDanielMayfield wrote:The explanation mentions "the sometimes exaggerated coloring" but offers nothing further about it. It is most apparent in the two adjacent maria in the upper (northern?) side. One's brown, the other is blue. Why is this?

It reflects mineralogical differences in the regions. Pun intended.

https://apod.nasa.gov/apod/ap131219.html
https://apod.nasa.gov/apod/ap150731.html
https://apod.nasa.gov/apod/ap120901.html
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Re: APOD: A Year of Full Moons (2017 Nov 05)

Postby De58te » Sun Nov 05, 2017 4:27 pm

One of the moon myths that completely puzzled me was the man on the Moon. I could just not see him. Now with these pictures and the colors I see it. You tilt you head to the left a bit and you see a rough image of Bart Simpson kicking a gray soccer ball. Bart has a yellow head, he is wearing a blue soccer jersey and he has gray socks and soccer shoes, and is running to kick the ball.The July and August full Moons are the most obvious.

Ironwood

Re: APOD: A Year of Full Moons (2017 Nov 05)

Postby Ironwood » Sun Nov 05, 2017 5:21 pm

It looks to me that the moon's north pole is rotated away from the top in some of these. The difference between the fourth and the tenth picture is almost 90 degrees of rotation. The moon librates a bit, but not that much. The moon's poles should be kept the same to be able to compare the pictures properly. Tycho should always be in the south.

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Re: APOD: A Year of Full Moons (2017 Nov 05)

Postby Chris Peterson » Sun Nov 05, 2017 5:39 pm

Ironwood wrote:It looks to me that the moon's north pole is rotated away from the top in some of these. The difference between the fourth and the tenth picture is almost 90 degrees of rotation. The moon librates a bit, but not that much. The moon's poles should be kept the same to be able to compare the pictures properly. Tycho should always be in the south.

The images are presented with the zenith always at the top, which reflects the way the Moon would appear to the observer visually while facing it. (The changing angle of the polar axis has nothing to do with libration.)
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Re: APOD: A Year of Full Moons (2017 Nov 05)

Postby alter-ego » Mon Nov 06, 2017 3:49 am

Chris Peterson wrote:
daddyo wrote:I had no idea that the apparent view of the moon rotated around 90 degrees over the seasons. This is way more than subtle and maybe why people sometimes have a hard time to recognize Mikey Mouse on the Moon.

It depends on your point of reference. With respect to the horizons (probably the most reliable reference for most people) the Moon rotates about 180° just between moonrise and moonset.

Chris Peterson wrote:
Ironwood wrote:It looks to me that the moon's north pole is rotated away from the top in some of these. The difference between the fourth and the tenth picture is almost 90 degrees of rotation. The moon librates a bit, but not that much. The moon's poles should be kept the same to be able to compare the pictures properly. Tycho should always be in the south.

The images are presented with the zenith always at the top, which reflects the way the Moon would appear to the observer visually while facing it. (The changing angle of the polar axis has nothing to do with libration.)

Not knowing the details of camera orientation, interpreting libration from apparent tip/tilt in each image is murky. In fact a changing polar axis angle is a component of libration as viewed from earth. Ideally, libration is best seen if North is up for each image (geocentric reference effectively) This north-up alignment eliminates the apparent east/west rocking arising from earth's rotation (as you noted wrt horizons). However, Moon rocking towards / away from earth is not affected by earth's rotation (at least to first order). In today's sequence of images, a zenith-up image alignment (in Pakistan) results is a false libration (in lunar position angle) average PA error = 38°, and a total PA error range: -19° to 80°.

Libration PA ErrorJPG.JPG
Although the precise error will vary with location, the general plotted behavior can be expected for any location in the Pakistan region. Oh, the normal full amplitude range for Libration PA ~49°
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