Chang'e_4 (Turn and Face the Strange)
January 3, 2019 3:38 AM   Subscribe

 
I can't seem to find out why the rover has solar panels if it's on the dark side of the moon. Anyone?
posted by DenOfSizer at 4:01 AM on January 3 [2 favorites]


The dark side of the moon is called dark because it's never visible from earth, it still experiences a day/night cycle from the sun. The moon is tidally locked to earth, from our perspective it does not rotate. The BBC article has some info on this.
posted by diziet at 4:03 AM on January 3 [10 favorites]


It’s on the far side of the moon, not the dark side of the moon. There is no permanently dark side of the moon. The Sun rises and sets on both sides of the moon. The moon always has the same side facing the Earth, so there is a permanent far side of the moon, that we never see from Earth.
posted by Anne Neville at 4:09 AM on January 3 [5 favorites]


Derp, i am an idiot who needs more coffee.
posted by DenOfSizer at 4:10 AM on January 3 [5 favorites]


DenOfSizer, deploy your solar panels before coffee! :)
posted by Brandon Blatcher at 4:12 AM on January 3 [5 favorites]


月球上沒有黑暗的一面。事實上,這一切都是黑暗的。
posted by fearfulsymmetry at 4:23 AM on January 3 [5 favorites]


"There is no dark side in the moon, really. Matter of fact, it's all dark. The only thing that makes it look light is the sun."
posted by mmoncur at 4:59 AM on January 3 [10 favorites]


The neat thing is that the moon does rotate—it completes one rotation around its axis in the same time it takes to complete one rotation around the Earth, such that it appears from the Earth not to rotate at all. This also means that a day on the moon lasts roughly a month (the length of one lunar cycle, which is obvious once you think about it).
posted by dephlogisticated at 5:27 AM on January 3 [1 favorite]


Right now we have a waning crescent and are a few nights away from new moon, so from Earth we see a mostly dark circle but the other side where Chang'e 4 has landed is fully illuminated.
posted by sukeban at 5:30 AM on January 3 [5 favorites]


I can't seem to find out why the rover has solar panels if it's on the dark side of the moon. Anyone?

We have sun on this side, but on the dark side of the moon is the Dark Sun; it can still power robots with solar panels, but also drives anything mad if its light touches them. That's why the robot is mondo insane
posted by Greg Nog at 5:31 AM on January 3 [21 favorites]




I can remember reading a second hand science book - from like the 60s - as a kid with maps of the moon that still had parts of the dark side 'unknown'... that seems amazing now.
posted by fearfulsymmetry at 5:55 AM on January 3 [2 favorites]


The obvious question about landing on the dark side of the moon that should come to mind is how they communicate with earth from there. It's answered in the planetary.org link, with a diagram helpfully showing the communications relay satellite orbiting around an empty point in space way out behind the moon. It's a neat trick.
posted by sfenders at 6:15 AM on January 3 [1 favorite]


But did it land in time to stop Bowser and Peach's wedding????
posted by The Pluto Gangsta at 6:43 AM on January 3 [6 favorites]




One of the missions of the lander is to do some radio astronomy. Being on the far side of the moon means that the moon blocks all the radio noise coming from the earth. From the CBC coverage:
"The far side of the moon is a rare quiet place that is free from interference of radio signals from Earth," mission spokesperson Yu Guobin said, according to Xinhua. "This probe can fill the gap of low-frequency observation in radio astronomy and will provide important information for studying the origin of stars and nebula evolution."
posted by heatherlogan at 7:21 AM on January 3 [3 favorites]


Also, Chang'e is a moon goddess.
posted by heatherlogan at 7:25 AM on January 3 [2 favorites]


It was a sharp and clear winter dawn this morning and up a hand from the horizon there was the crescent moon, a steel eyelash, Jupiter and Venus glittering near, watching over the darkside guest.
posted by notyou at 7:51 AM on January 3 [3 favorites]


I'm just interested in the fact that the lander does use solar panels. Either the mission duration is going to be under two weeks, or the lander is going to heave to go into hibernation for two weeks when the sun sets.
posted by happyroach at 9:17 AM on January 3


Happyroach, the Yutu rover on the first Chinese lunar lander used solar panels, and it made it through 31 months.
posted by Quindar Beep at 10:33 AM on January 3


The neat thing is that the moon does rotate—it completes one rotation around its axis in the same time it takes to complete one rotation around the Earth, such that it appears from the Earth not to rotate at all. This also means that a day on the moon lasts roughly a month (the length of one lunar cycle, which is obvious once you think about it).

There is a very good science fiction short story, "A Walk In The Sun" by Geoffrey A. Landis (which you can read for free here - it's short!) about an astronaut stranded on the Moon and relying on solar panels to stay alive.
posted by straight at 10:55 AM on January 3 [2 favorites]


So—does the non-rotation of the moon extend to it not rotating on an axis perpendicular to the Earth's surface? If, for example, you're at sea, do you always see the same lunar features touching the horizon at moonset and moonrise at the same points in the lunar cycle, or does that change? Living somewhere without a flat horizon this is somewhat difficult to determine observationally. Though maybe I just need to build my own Stonehenge, that would be a fun project...
posted by XMLicious at 11:31 AM on January 3


On the far side of the moon, your solar panels and batteries have to save enough energy in the two weeks of light to last through the two weeks of dark. But on our side of the moon, your solar panels and batteries have to save enough energy in the two weeks of light to last through the two weeks of dark.
posted by M-x shell at 1:34 PM on January 3 [2 favorites]


One of the missions of the lander is to do some radio astronomy....

Was just looking at that. The project is called Dutch NCLE . (Somebody has a sense of humor.) Their antenna is attached to the relay orbiter (Queqiao).
NCLE is considered a pathfinder mission for a future low-frequency space-based or moon-based radio interferometer which has the detection and tomography of the 21-cm Hydrogen line emission from the Dark Ages period as the principle science objective.... Low-frequency radio astronomy, i.e. below ~30 MHz, can only be done well from space due to ... noise [from Earth] that make sensitive measurement from ground-based facilities impossible....
posted by Twang at 2:10 PM on January 3 [1 favorite]


So like I said, "The Chines land on them moon, then I'll vacuum!" Hey, the place looks great, and it looks as if they took along a great camera! I am excited to see more images.
posted by Oyéah at 3:14 PM on January 3


So—does the non-rotation of the moon extend to it not rotating on an axis perpendicular to the Earth's surface?


The moon's axis of rotation is perpendicular to its orbit around the Earth, with a tiny bit of wobble that gives a bit of a peek to the "other" side. I guess you could say that the moon has a north and a south pole. As explained above, its "day" and "night" cycle takes about 28 of our earthly days to complete.

But the position of the moon in the sky depends on your latitude.

Fun fact 1): the axial tilt of the Earth to its orbit around the sun is about 23 degrees.
Fun fact 2): The axial tilt of the moon to its orbit around the Earth is about 6 degrees. But the angle of inclination of the moon's orbit around the Earth is about 5 degrees.
Fun fact 3): The moon's apparent path across the sky is an illusion. It's actually going the other way; the rotation of the Earth makes it seem as though it's circling the Earth in the opposite direction.

Sending a vehicle to the moon seems like using a BB gun to hit a basketball on a rollercoaster in Boston from another moving rollercoaster in San Francisco.

Now. I must get back to envisioning what it must have been like to hit that other damned rock from 4.1 billion miles.
posted by mule98J at 3:26 PM on January 3 [1 favorite]


sfenders: "the communications relay satellite orbiting around an empty point in space way out behind the moon. "

TIL: one can orbit a Lagrange point.
posted by Mitheral at 6:45 PM on January 3 [1 favorite]


straight: "There is a very good science fiction short story, "A Walk In The Sun" by Geoffrey A. Landis (which you can read for free here - it's short!)"

I've read several stories where one of setups is that a person/colony/settlement/etc. has to keep moving on the surface of Mercury to either stay in the sun shadow or remain in sunlight. I think Ir features in Saturn's Children and at least one story in Niven's expanded Known Space.
posted by Mitheral at 6:51 PM on January 3


GIF of moon phases showing a little more than half its surface due to libration.
posted by ShooBoo at 9:00 PM on January 3 [3 favorites]


Kim Stanley Robinson's Mars trilogy includes a city on Mercury that sits on a giant set of rails and stays in the twilight zone perpetually
posted by vibratory manner of working at 9:46 PM on January 3


> There is a very good science fiction short story, "A Walk In The Sun" by Geoffrey A. Landis

Holy crow, thanks for that.
posted by lucidium at 5:34 AM on January 4


There is a very good science fiction short story, "A Walk In The Sun" by Geoffrey A. Landis (which you can read for free here - it's short!) about an astronaut stranded on the Moon and relying on solar panels to stay alive.

Oh, that is nice! Thank you for that!
posted by notsnot at 8:25 AM on January 4


Happyroach, the Yutu rover on the first Chinese lunar lander used solar panels, and it made it through 31 months.

I just wish my phone batteries could do that well.

Kim Stanley Robinson's Mars trilogy includes a city on Mercury that sits on a giant set of rails and stays in the twilight zone perpetually

Likewise Saturn's Children, where the city is pushed forward by the expansion of the rails.

Or they could have just put the damn city in one of the polar craters. You know, the craters that are sheltered enough from the sun to have ice in them.

But then SC wouldn't have had the "tied to the tracks" scene. So.
posted by happyroach at 11:35 AM on January 6 [1 favorite]


CGTN has released footage of the Chang'e-4 landing, compiled from 4000+ photographs it took during its approach and touchdown. (about 3 mins, the final if which is pretty much the same patch of moonground.)
posted by not_on_display at 11:09 PM on January 11 [2 favorites]


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