Discussion in 'Amateur Radio News' started by AG4YX, Jul 6, 2019.
Can you see stars in the daytime?
I've been... and thinking about it some more.
It's like how they paint the word STOP on the road in really tall letters viewed from directly above, but when viewing from a distance it LOOKS 'normal'.
The shadow IS oblong, but LOOKS like it's not.
Or maybe Universal too cheap to paint stars? Or someone misunderstood the work-order for "stars," thought those were the people that portray main characters, so scheduling so many SAG-certified actors, transportation, food and lodging will break the budget? yeow, I couldn't resist. I love the comment by K4DL that daytime sky is also fake because don't see any stars.
Getting back on topic, I'd like to see some rovers examine the Apollo sites as I wonder how solar winds/radiation affected materials (obviously this will turn into a major dispute of disturbing "US sovereign sites"). Or a rover to look at S-IVB stage impact sites.
I am all for 'disturbing sovereign sites' if that establishes that the USA owns the Moon!
You're thinking way too hard.
Seriously, it's much simpler than that. The moon is round, and so is its shadow. As seen from the moon, its shadow on a target will therefore also appear round no matter what shape that target may be or what orientation it may have. It could be a flat plate at some random angle. It could even have a totally irregular shape. As long as it's big enough to intercept the entire shadow, that shadow as seen from the moon would still look round. (I am assuming that the target is small compared to its distance from the moon. The earth's diameter is only about 3% of the earth-moon distance, so that's true.)
Sure, if you were in low earth orbit looking directly down at the center of the moon's shadow, then it would not appear round. But then you're looking at it from a totally different angle.
Nahhh.... that's not possible for me!
Seriously though, I do got it now. It wasn't until I remembered that old optical illusion of writing really tall letters on a piece of paper (or the road) and viewing from an oblique angle that I understood that the shadow on the Earth COULD be oblong, yet viewed from the angle of the Moon WOULD look circular.
I'm sure there are sines, cosines, tangents, etc that could explain it but that would put my synapses to sleep!
is it just me, or does the vehicle in image 3 look a lot like the U.S. luner lander circa 1969?
It's not just you, but it's more like 1972 than 1969.
I know sines, cosines and tangents quite well but you don't need them here. The answer is much simpler.
Consider that you see the very same effect during a lunar eclipse as seen from the earth. The only difference is that the earth is 4x the size of the moon so the moon intercepts only part of the earth's shadow. During the partial phase you see the edge of the earth's shadow on the moon as a circular arc even though it would appear oblong if you looked at it from a different direction in space.
In both cases the shadow's edges are a little fuzzy because the sun is not a point source. Additionally, during a lunar eclipse we see diffraction of sunlight through the earth's atmosphere, which is not an effect we see in the Chinese picture of the solar eclipse as seen from the moon because the moon has no atmosphere.