Tonight’s a great night to look up. Starting at 2AM EDT and peaking from 3am to 4:30, there will be a lunar eclipse visible from all of North America. To make things better, Mars is currently very close to Earth, making it the brightest object in the night sky.
If you’re lucky enough to be viewing tonight’s events from Central Florida, Space-X will be launching a Dragon 9 capsule to the ISS at 4:58PM EDT – adding a little extra something to the sky.
See you in the stars.
Unfortunately it will be overcast (and eventually rainy) here, but I’m reblogging for people with clearer skies.
Yo, Sally! :-)
10:47pm PDT: Husband reports (from living room) that the edge of the moon has disappeared.
Confirmed from my balcony!
On a side note, I don’t quite like this infographic, because I doubt that the penumbra is the exact width of the moon. This makes it look like the beginning of the partial eclipse (second contact) coincides with the first moment when entire moon is inside the penumbra. Is that actually the case? This image seems to imply not. But if we ignore the penumbra, this is a great diagram.
I suspect this graphic is more or less accurate, while that one you link to is very idealized and not to scale.
That the width of the penumbra matches the width of the moon isn’t a coincidence. It’s just another way of expressing what the penumbra is: The part of the eclipse during which an observer on the moon would see the sun as partly, but not completely, eclipsed by the earth. That is, as the moon enters the earth’s shadow, it must travel exactly one moon-width to go from first entering the shadow to being entirely within it.
An interesting (but unrelated) coincidence is that the moon as viewed from earth is the same size in the sky as the sun (about 1/2 degree). That’s the reason the moon almost exactly covers the sun’s disk during a total solar eclipse. The earth viewed from the moon is substantially larger in the sky (about 2 degrees) which is why the region of totality (the earth’s umbra) in this diagram is substantially larger than the moon’s disk.
Sorry, I’m still confused. I do know more about solar eclipses than lunar, and I believe that you’re probably right about this graphic being more accurate since I’ve now seen multiple versions of it, but your explanation in that middle paragraph there does not make sense to me.
Naturally it will take a full moon-width for the moon to go from first entering anything larger than it to being fully within it. For example, this graphic shows the moon staying within the earth’s umbra (i.e. the shadow where the sun is completely obscured behind the earth) for a long time, longer than it takes to travel one moon-width, because of course the earth appears larger in the sky from the moon than the moon does from the earth (the distance being the same but the earth being larger than the moon). (This is your point in the last paragraph.)
My point of confusion is this: I thought that maybe it could stay in the penumbra a long time before reaching the umbra. So now I’m trying to wrap my brain around this. You’re saying it is not possible for the entire moon to be experiencing a partial solar eclipse; that as soon as the last part of the moon that faces the earth reaches partial solar eclipse, the first part will see a total solar eclipse. (That is the part that starts looking to us like a bite was taken out of the moon.) I’m willing to believe this but for some reason I can’t picture it.
If shown from space, it’s impossible for a picture of the situation to be to scale so that sun, earth, and moon are all visible, because the sun is so much larger. I imagine that’s why I’m so confused.
Him. Yeah, thinking about it more, I now think the width of the penumbra being the same size as the moon actually is related to the coincidence that the sun and the moon both subtend a half a degree when viewed from earth. Because the width of the penumbra is determined by the angular size of the sun as seen from the moon (which is basically the same as the sun’s angular size when seen from the earth). And the width of the moon in that diagram is determined by the width of the moon when seen from the earth. And it just so happens that those are the same.
But if the moon happened to be much smaller, or the sun much larger, and all the other dimensions were the same, then the moon would have to travel several times its own diameter to cross the entire penumbra.
I want to draw a diagram to make sure. But just thinking it through in my head, yeah, I think you were right to question my middle paragraph. Because I now think it was complete bullshit.
My ability to pronounce things in authoritative fashion while having no clue what I’m talking about is kind of breathtaking. Thanks for keeping me (slightly more) honest.
Reposted from http://ift.tt/1t695px.