Craters On the “Dark Side”
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Craters on the "dark side". Don't see "craters"? Read on. Credit:NASA/Goddard Space Flight Center/Arizona State University.
Here is an image from the Lunar Reconnaissance Orbiter. The image shows secondary craters. Secondary craters are those craters formed not by an foreign body hitting the moon, rather they are formed by the stuff blown out from a crater forming impact.
The NASA caption for the image is below, but before you get there, I know there are some of you taking issue with the title…Dark Side indeed. The dark side of the moon exists maybe in some of the areas around the poles and in Pink Floyd songs…the reality is there is no dark side. Yes I know that, interestingly enough the LRO site titled the page “Craters on the dark side of the moon” (linked below).
Now how many of you don’t see craters and instead you see “lumps”? It’s a trick your eyes are playing on you, click here and you will see the very same image just rotated 180o. The image opens in a new window so you can move it around and get the two side by side (you may need to resize the new window). Did you do it? Pretty cool eh?
Ok here’s the caption from the LRO site:
When people envision a “moonscape” it probably looks something like this — craters, craters everywhere.
There are two types of impact craters on the Moon: primary and secondary. Primary craters form as the result of an asteroid or comet (or spacecraft) impacting the Moon. Secondary impact craters formed from the impact of ejecta expelled during primary crater formation. Secondary impact craters dominate this scene, possibly from the relatively recent impact that created nearby Jackson crater (43.5 miles across), located 42 miles to the west.
Geologists use small secondary craters to help unravel the stratigraphy of the lunar surface. These secondary craters reside on the floor of a 8.7 mile wilde crater. What is the age of this host crater? If these secondary craters originated from the Jackson event, then it is a fair bet the Jackson impact was more recent. If you look at the bottom of this NAC frame in the LROC Image Gallery at ASU, you can see that this crater also has a very subdued rim, in contrast to Jackson’s well-defined rim, providing more evidence of it’s age.
I think most people understand the phrase “dark side of the moon” to mean the side which is never seen from a vantage point on Earth, not that it is literally in eternal darkness.
The term “dark” was used as a synonym for unknown or unexplored in centuries past. Think “dark continent” or “darkest Africa” for example.
It was an entirely appropriate adjective for the far side of the moon not long ago, but of course is getting to be less so as we “explore” with space probes.
Hmmm, I don’t think most people even know that one side of the moon faces the earth at all times, the reason for the orbital phases, that the moon rotates, or that the sun illuminates the “far side” of the moon. So I would tend to disagree. On the basis of that lack of knowledge, most people can understand that you cannot see something when it is in darkness, but not that it is just never viewable from our vantage point. Once the “light goes on” then I would agree that the use of “dark side” might just be out of habit.
On Earth, the dark side is called “night” and the light side is called “day.”
On the Moon, the dark side is called “night” and the light side is called “day.”
Any questions?
If you are interested, look at the Moon tonight.
What you are seeing is the dark side of the Moon which is not illuminated by the Sun. However, you can still see the dark surface of the Moon, because it is illuminated by reflected light from the Earth.
Far side = the side of the Moon that is never seen from the Earth.
Dark Side = the side not illuminated by the Sun during it’s 28 day period of rotation.
I’ve noticed the effect of moon craters looking like lumps before. It seems like we expect the light to be coming from the top of our screens, or something.
DO you know why this is?
Well Mr. Schmoe
I think you have answered your own question, that is exactly what I was always told, and in fact looking at a laptop screen from the top makes all the difference. I’d also like to know WHY this is for sure, so if anyone knows let us know.
Bingo!