APOD: Full Moon Silhouettes (2013 Jan 30)

[tbrander]

Brought tears to my eyes! Love the music! The moon truly is a "...faithful witness in the skies..." (Ps 89:37) The people enjoying this moon rise are what truly makes this special.
The optical phenomon of green on the top and red on the bottom is quite noticeable in this magnified image, truly beautiful!

[MargaritaMc]

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From two kilometers distant, the people would have tiny angular dimensions, accounting for how much smaller they look than the half-degree wide Moon.

Can you explain, please, Anthony?
Many thanks
Margarita

[Anthony Barreiro]

<<

From two kilometers distant, the people would have tiny angular dimensions, accounting for how much smaller they look than the half-degree wide Moon.

Can you explain, please, Anthony?
Many thanks
Margarita

I'll try.

The Moon is about 3500 kilometers in diameter and about 385,000 kilometers distant from the Earth. From the surface of the Earth, the Moon appears about half a degree wide, or thirty arcminutes wide. Your pinkie finger is about a centimeter wide. If you hold your pinkie finger out at arms length it's about a degree wide, twice as wide as the Moon, and will easily cover the Moon.

From two kilometers away, a 1.75 meter tall human body looks tiny, about 3 arcminutes tall, or about one tenth as tall as the width of the Moon. In this video Mark Gee used a telescope to magnify both the Moon and the people, so the Moon looks huge and we see a lot of detail on the surface of the Moon, and the people are magnified enough to show detail in their silhouettes. No matter how much you magnify the Moon and the people, with the people two kilometers away and the Moon 385,000 kilometers away, the Moon appears 10 times as big as the people. If you were looking through a telescope one kilometer away from the people, the Moon would look 5 times as big as the people. From four kilometers away, the Moon would look 20 times as big as the people. The important principle is that the angular size of an object shrinks by half when the distance to the object is doubled.

By the way, the relationship between diameter, distance, and angular size is why we experience total solar eclipses here on Earth. The diameter of the Sun is 400 times greater than the diameter of the Moon. The Sun is also 400 times farther away from the Earth than the Moon is. Voila, both the Sun and the Moon appear about one-half degree wide, and when the Moon passes exactly in front of the Sun (and when she is close to the Earth in her elliptical orbit), she completely covers the Sun, causing an eclipse. The Earth is the only planet in our solar system where this happy coincidence occurs.

[luigi]

Stand up applause.

Love the choice of music and I'm marveled by the research and hard work done for such a beautiful final result.

This made my day much much much better.

[geckzilla]

I was resisting the impulse to write one of those tedious "this is not up to apod's usual standards" comments.

Hah, perspective meant as much for you in this case as it did for the composition of the video itself.

[BDanielMayfield]

The moon truly is a "...faithful witness in the skies..." (Ps 89:37)

I agree. Nice reference.

Anthony, I enjoyed your answer to Margarita's question.

[MargaritaMc]

Thank you very much, Anthony, that was a beautifully clear explanation and, as with all good teaching, is so obvious once set out clearly.

Margarita

[DavidLeodis]

Excellent video.

It was a bit surprising to me seeing just how much the Moon moves (relative to our view) in such a short period. Also, though I know from seeing it that the moon rises later each day, if I was asked for a quick guess (with no time to do any mental arithmatic) I would have guessed much less than 50 minutes. Seeing the Moon go through its phases is for me always an awesome sight, particularly so its thin crescents and Full Moon ones.

[Anthony Barreiro]

Excellent video.

It was a bit surprising to me seeing just how much the Moon moves (relative to our view) in such a short period. Also, though I know from seeing it that the moon rises later each day, if I was asked for a quick guess (with no time to do any mental arithmatic) I would have guessed much less than 50 minutes. Seeing the Moon go through its phases is for me always an awesome sight, particularly so its thin crescents and Full Moon ones.

I love watching the Moon every evening, night, or morning, depending on her phase (taking two or three nights off for the mysterious new Moon). I'm fascinated by her movements from west to east against the stars of the zodiac, and how she transits through more northerly and southerly paths during her different phases over the different seasons of the year. And of course how her illuminated appearance changes from one night to the next. I'm starting to keep track of her north and south movements relative to the ecliptic, and to notice how closely she passes by planets and stars that are near to the ecliptic. Guy Ottewell's Astronomical Calendar is very helpful in this regard.

Our sister planet is endlessly fascinating!

By the way, the Moon rises 50 minutes later each day on average (everything about the Moon is mutable). When the ecliptic rises steeply from the eastern horizon, e.g. during full Moons near the fall equinox, she rises only about 30 minutes later each day. Thus we have bright moonlight before the end of twilight for more evenings than usual after the full Moons during autumn, very helpful to farmers harvesting their fields, at least before the invention of combines equipped with racks of stadium lights. Conversely, when the ecliptic follows a more shallow path relative to the eastern horizon, e.g. during full Moons near the spring equinox, the situation is reversed and the Moon rises about 70 minutes later each day.

[bystander]

Silhouettes and Moonrise in Real Time
Slate Blogs | Bad Astronomy | Phil Plait | 2013 Jan 31

Watch a Magical Moonrise
Universe Today | Nancy Atkinson | 2013 Jan 31

[DavidLeodis]

I guess a video of moonrise from the equator would blow northern and southern hemispheric minds.

I wonder how a Moon rise does look at the Equator? Does it just rise and subsequently fall vertically? I'm having trouble trying to picture what it does at the Equator in view that it appears to move right to left when viewed in Earth's southern hemisphere but left to right in the northern hemisphere.

[neufer]

Click to play embedded YouTube video.

I guess a video of moonrise from the equator would blow northern and southern hemispheric minds.

I wonder how a Moon rise does look at the Equator? Does it just rise and subsequently fall vertically?

More or less. (Which is basically the way
I picture a Moon rise/set to first order anyhow.)

[Beyond]

Well... that would seem to be a wonderfully crazy Zany movie

[yellowbag]

this video is the best and most beautiful video i've seen here. great job!

[Ann]

It's a lovely video. When I see it, though, I'm reminded of the enormous differences between the Earth and the Moon. The Earth is relatively large, wonderfully colorful, and brimming with life. The Moon is much smaller, gray in color, dry, airless and dead. It is as if it had been "sucked dry" by the interaction with the Earth (although there are of course so many other explanations for the differences between the Earth and the Moon).

Click to view full size image

Copyright: Donald Waid

The Earth-Moon pair makes me think of galaxies NGC 4631 and NGC 4627. NGC 4631 is large, brilliant, marvellously colorful and brimming with star formation. NGC 4627 is smallish, monocolored and "dead" when it comes to forming new stars.

Ann