APOD: Earth and Moon (2021 Sep 05)

[APOD Robot]

Earth and Moon

Explanation: The Earth and Moon are rarely photographed together. One of most spectacular times this occurred was about 30 years ago when the Jupiter-bound Galileo spacecraft zoomed past our home planetary system. Then, robotic Galileo watched from about 15-times the Earth-Moon separation as our only natural satellite glided past our home world. The featured video combines 52 historic color-enhanced images. Although our Moon may appear small next to the Earth, no other planet in our Solar System has a satellite so comparable in size . The Sun, far off to the right, illuminated about half of each sphere, and shows the spinning Earth's white clouds, blue oceans, and tan continents.

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[stevie]

The Moon looks awfully close to the Earth.

[Ann]

The Moon looks awfully close to the Earth.

I think that is a question of perspective. The Moon is well in front of (or possibly behind) the Earth as seen by Galileo.

Ann

[JohnD]

Serendipitously, this somewhat bland if historic video was automatically followed by one as short, "Descent torwads Bennu", and subsequently by two more from NASA on the later stages of the still incomplete Osiris-Rex mission. Definitely worth following, IMHO! Roll on September 2023!

[neufer]

• What happened to that Blue Moon

[De58te]

Something puzzles me about this robotic Galileo video. Most astronomy books state that the time that the Moon takes to orbit from a full moon to a new moon is about 14 days. Yet if you pay attention to the cloud formations as the Earth turns, it seems the Moon went from full moon to new moon in about 12 or so hours!

[orin stepanek]

Beautiful Earth And Luna

APOD , no other planet in our Solar System has a satellite so comparable in size .

? Maybe Pluto and Charon?

[neufer]

Something puzzles me about this robotic Galileo video. Most astronomy books state that the time that the Moon takes to orbit from a full moon to a new moon is about 14 days. Yet if you pay attention to the cloud formations as the Earth turns, it seems the Moon went from full moon to new moon in about 12 or so hours!

The Earth lies ~30 Earth diameters behind the moon from this distant viewpoint.

So when the moon moves ~4 Earth diameters from left to right the view from Earth doesn't change from full moon to new moon but only slightly.

[Sa Ji Tario]

The Moon looks awfully close to the Earth.

I think that is a question of perspective. The Moon is well in front of (or possibly behind) the Earth as seen by Galileo.

Ann

Ann, due to the direction of the Earth's rotation, the Moon cannot be seen "from behind", since it moves from west to east

[neufer]

The Moon looks awfully close to the Earth.

Earth & Moon, full animation - 17 years ago

54 color frames animated showing the Earth-Moon conjunction as seen from the receding Galileo spacecraft on 16/17 Dec 1992.

At the start, Galileo is 6.15 million km from the Earth. That increased to 6.58 million km at the end. Since the Moon orbits the Earth at less than 400 thousand km, that makes it only 6% closer to Galileo in this sequence. As a result, the sequence is a pretty good comparison of relative Earth-Moon sizes.

[eanagy]

Something puzzles me about this robotic Galileo video. Most astronomy books state that the time that the Moon takes to orbit from a full moon to a new moon is about 14 days. Yet if you pay attention to the cloud formations as the Earth turns, it seems the Moon went from full moon to new moon in about 12 or so hours!

I completely agree. This doesn't make sense.

[neufer]

Something puzzles me about this robotic Galileo video. Most astronomy books state that the time that the Moon takes to orbit from a full moon to a new moon is about 14 days. Yet if you pay attention to the cloud formations as the Earth turns, it seems the Moon went from full moon to new moon in about 12 or so hours!

I completely agree. This doesn't make sense.

From the perspective of the distant background Earth
(~30 Earth diameters behind the moon) the (Galileo foreground) Moon
only moves (west to east against background stars)
about 8º with a corresponding 8º change in phase.

[ta152h0]

Fantastico!!! Is there not a Voyager photo like this of the Solar System? pass the ice cold one

[VictorBorun]

APOD , no other planet in our Solar System has a satellite so comparable in size .

? Maybe Pluto and Charon?

Charon to Pluto is huge!
Charon's radius is 606 km = 51% of Pluto's
Moon's radius is 1737 km = 27% of Earth's

Click to view full size image

See full size infographic here

Charon to Pluto is real close!
Charon's orbital semi-major axis is 19591 km = 16 times Pluto's radius
Moon's orbital semi-major axis is 384399 km = 60 times Earth's radius

As a result Pluto is tidally locked to Charon's orbiting

Click to view full size image

If you are already buying a lot on Pluto mind the longitude or you won't be seeing Charon for very long time!
Or is it in fact an advantage?

[johnnydeep]

APOD , no other planet in our Solar System has a satellite so comparable in size .

? Maybe Pluto and Charon?

Charon to Pluto is huge!
Charon's radius is 606 km = 51% of Pluto's
Moon's radius is 1737 km = 27% of Earth's
...
Charon to Pluto is real close!
Charon's orbital semi-major axis is 19591 km = 16 times Pluto's radius
Moon's orbital semi-major axis is 384399 km = 60 times Earth's radius
...
As a result Pluto is tidally locked to Charon's orbiting
...
If you are already buying a lot on Pluto mind the longitude or you won't be seeing Charon for very long time!
Or is it in fact an advantage?

And because Charon is so large and so close to Pluto, their common center of gravity is outside Pluto. From https://en.wikipedia.org/wiki/Pluto#Satellites:

An oblique view of the Pluto–Charon system showing that Pluto orbits a point outside itself.

---

[orin stepanek]

APOD , no other planet in our Solar System has a satellite so comparable in size .

? Maybe Pluto and Charon?

Charon to Pluto is huge!
Charon's radius is 606 km = 51% of Pluto's
Moon's radius is 1737 km = 27% of Earth's

Click to view full size image

See full size infographic here

Charon to Pluto is real close!
Charon's orbital semi-major axis is 19591 km = 16 times Pluto's radius
Moon's orbital semi-major axis is 384399 km = 60 times Earth's radius

As a result Pluto is tidally locked to Charon's orbiting

Click to view full size image

If you are already buying a lot on Pluto mind the longitude or you won't be seeing Charon for very long time!
Or is it in fact an advantage?

Actually Charon and Pluto are kind of like a double planet dancing around each other! If you lived on either one; you probably wouldn't get too much company;---Brr!

[VictorBorun]

Actually Charon and Pluto are kind of like a double planet dancing around each other! If you lived on either one; you probably wouldn't get too much company;---Brr!

Add to all the woes a sort of white nights.

Just imagine that thing, 7.3 times bigger than the moon in vizual size, 53 times larger in visual area and 100 times greater in albedo*area, sitting still in zenith all the time and changing only its phase from full Charon at midnight to half Charon at sunrise or sunset to a thin sickle at noon.

Does hell to your sleeping pattern.

Moreover, at just 20 thousand km distance it gives you a creepy feeling of being telescoped whenever you sunbathe. The buggers can get away with it in their Charonian night

[orin stepanek]

Actually Charon and Pluto are kind of like a double planet dancing around each other! If you lived on either one; you probably wouldn't get too much company;---Brr!

Add to all the woes a sort of white nights.

Just imagine that thing, 7.3 times bigger than the moon in vizual size, 53 times larger in visual area and 100 times greater in albedo*area, sitting still in zenith all the time and changing only its phase from full Charon at midnight to half Charon at sunrise or sunset to a thin sickle at noon.

Does hell to your sleeping pattern

Ah! You'd get used to it!

[neufer]

Actually Charon and Pluto are kind of like a double planet dancing around each other! If you lived on either one; you probably wouldn't get too much company;---Brr!

Add to all the woes a sort of white nights.

Just imagine that thing, 7.3 times bigger than the moon in vizual size, 53 times larger in visual area and 100 times greater in albedo*area, sitting still in zenith all the time and changing only its phase from full Charon at midnight to half Charon at sunrise or sunset to a thin sickle at noon.

• Near equinox Charon goes through a full monthly phase.

However, around the solstices Charon never gets closer to the Sun than ~60° or further than ~120°.

<<Pluto's rotation period, its day, is equal to 6.387 Earth days. Like Uranus, Pluto rotates on its "side" in its orbital plane, with an axial tilt of 120°, and so its seasonal variation is extreme; at its solstices, one-fourth of its surface is in continuous daylight, whereas another fourth is in continuous darkness. (Note: Charon has an inclination of 0.08° to Pluto's equator)>>

[VictorBorun]

Just imagine that thing, 7.3 times bigger than the moon in vizual size, 53 times larger in visual area and 100 times greater in albedo*area, sitting still in zenith all the time and changing only its phase from full Charon at midnight to half Charon at sunrise or sunset to a thin sickle at noon.

• Near equinox Charon goes through a full monthly phase.

However, around the solstices Charon never gets closer to the Sun than ~60° or further than ~120°.

<<Pluto's rotation period, its day, is equal to 6.387 Earth days. Like Uranus, Pluto rotates on its "side" in its orbital plane, with an axial tilt of 120°, and so its seasonal variation is extreme; at its solstices, one-fourth of its surface is in continuous daylight, whereas another fourth is in continuous darkness. (Note: Charon has an inclination of 0.08° to Pluto's equator)>>

So my picture for a realty disadvertisment under Charon was correct only for equinoxes.
On the winter solstice even at noon Charon's crescent is (1−Sin60°)R thick which is 67‰ of Charon's diameter rather than zero.
On the summer solstice even at midnight Charon's gibbous is (1+Sin60°)R thin which is 933‰ of Charon's diameter rather than 1000.

[JimT]

The Moon looks awfully close to the Earth.

I think that is a question of perspective. The Moon is well in front of (or possibly behind) the Earth as seen by Galileo.

Ann

Ann, due to the direction of the Earth's rotation, the Moon cannot be seen "from behind", since it moves from west to east

...but appears to move from east to west because of the greater relative speed of the Earth's rotation eastward.