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From a million miles away, NASA camera shows moon crossing face of Earth

nasa.gov

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Re: From a million miles away, NASA camera shows moon crossing face of Earth

#21

Post by mnw21cam »

bumbledraven wrote: post #16
gerhardi wrote: post #12

Earlier quoted context omitted.

Earth is a sunlit object in this picture, the luminosity is the same level as during the day on earth - would you see stars in your photos if you took a correctly exposed photo of something during daylight on earth? I don't think this would happen :) The dynamic range difference between day light objects on earth and the stars on the sky is huge.

The satellite is 1 million miles away from Earth at the L1 Lagrange point. What is it about optics that allows us to compare a photo of the stars taken at such a distance with one taken from the surface of the earth? [Edit: "compare", in the sense of understanding whether or not the stars will or won't show up in each case. I get that the laws of optics are the same throughout the universe.] > The dynamic range diffe…

Yes, our eyes just do have a fantastic dynamic range.

Having said that, if you were sitting on the satellite, you would see even more stars if you blinkered out the brightness of the sun, moon, and earth.

Re: From a million miles away, NASA camera shows moon crossing face of Earth

#22

Post by xedarius »

mnw21cam wrote: post #20
xedarius wrote: post #17

Should I be able to see Earth orbiting satellites in this picture?

You mean like the moon? Yes. You mean like meteosat? No. A 4 metre wide object is going to be such a small proportion of the size of a single pixel that it will be completely invisible.

Ok thanks.

Re: From a million miles away, NASA camera shows moon crossing face of Earth

#23

Post by bumbledraven »

InclinedPlane wrote: post #18
xedarius wrote: post #17

Should I be able to see Earth orbiting satellites in this picture?

How close are satellites to the spacecraft that took these photos? Well, it's about a million miles from Earth, generally the farthest satellites away from Earth are at about 40,000km altitude in geostationary orbit, which would put them maybe 4% closer to the spacecraft than Earth, so it wouldn't affect perspective hardly at all. So that leaves resolution and physical size. How big are satellites? About the size of…

> it's about a million miles from Earth, generally the farthest satellites away from Earth are at about 40,000km altitude in geostationary orbit, which would put them maybe 4% closer to the spacecraft than Earth

No, that puts satellites in geostationary orbit 2.5% as close to Earth as the satellite that took this picture (in other words, it is 40 times as far away from Earth).

Re: From a million miles away, NASA camera shows moon crossing face of Earth

#24

Post by gonvaled »

geofffox wrote: post #9

Maybe as interesting is where this satellite is: The Lagrange L1 point. The 5 Lagrange points in essence allow orbiting bodies to break Kepler's laws. A satellite a million miles closer to the Sun shouldn't have the same orbital period as the Earth... but it does.

So the satellite is not orbiting Earth? What is the advantage of putting the satellite there, as opposed to a regular orbit?

Re: From a million miles away, NASA camera shows moon crossing face of Earth

#25

Post by lqdc13 »

mnw21cam wrote: post #20
xedarius wrote: post #17

Should I be able to see Earth orbiting satellites in this picture?

You mean like the moon? Yes. You mean like meteosat? No. A 4 metre wide object is going to be such a small proportion of the size of a single pixel that it will be completely invisible.

Does anyone know why they decided to go with just a 4 megapixel camera?

I guess they could settle for taking more narrow images and recombining later but it seems better to take one image and crop if they are just interested in small parts.

Plus you have the option for digital zoom.

Re: From a million miles away, NASA camera shows moon crossing face of Earth

#26

Post by gonvaled »

Moon is tidally locked to Earth, which is interesting. How long will this last? How long has this been going on? Does this happen to all satellites in all planets?

Another question: is the Moon orbiting plane aligned with the Earth rotation axis? Why or why not?

Re: From a million miles away, NASA camera shows moon crossing face of Earth

#27

Post by gonvaled »

rogeryu wrote: post #13
aspirin wrote: post #2

Is this the real reflectance of the moon? Seems so dark. Usually we see the moon at night surrounded by night sky, which probably skews our perception of the real color of the surface material.

Probably because that's the Dark Side of the Moon? https://en.wikipedia.org/wiki/The_Dark_Side_of_the_Moon

Is that a joke? The dark side of the moon is not more often dark than the visible side. It is just never visible from Earth.

Re: From a million miles away, NASA camera shows moon crossing face of Earth

#28

Post by Cogito »

gonvaled wrote: post #24
geofffox wrote: post #9

Maybe as interesting is where this satellite is: The Lagrange L1 point. The 5 Lagrange points in essence allow orbiting bodies to break Kepler's laws. A satellite a million miles closer to the Sun shouldn't have the same orbital period as the Earth... but it does.

So the satellite is not orbiting Earth? What is the advantage of putting the satellite there, as opposed to a regular orbit?

The satellite, like everything in our solar system, is orbiting the sun.

The sun-earth L1 lagrange point is between the sun and the earth (in every two-body gravitational system there are 5 lagrange points, so there are earth-moon lagrange points etc)

These points are interesting because the orbit behaviour of items in them is weird! Specifically, the gravitational effects of the two bodies involved work in tandem to produce interesting effects.

Any bodies positioned at the L1 lagrange point of a two-body system will stay in the same position relative to both the larger bodies. Normally, the closer you get to the thing you are orbiting the faster you orbit. If you are appropriately near another large body (like the earth) that second body "pulls" back on you [edit: as long as you are on the inside of it - if you're on the outside it pulls you forward, and you get the L2 point], causing your orbit to slow down. At L1, those forces are balanced, and the third, smaller body has the exact same orbital period as the second body.

That is, the satellite is always on a straight line drawn between the earth and the sun.

The main reason for it to be there is to measure the solar wind, an early detection system.

It also happens to be in a great position to take pictures of the sunlit side of the earth.

Re: From a million miles away, NASA camera shows moon crossing face of Earth

#29

Post by avar »

gonvaled wrote: post #26

Moon is tidally locked to Earth, which is interesting. How long will this last? How long has this been going on? Does this happen to all satellites in all planets? Another question: is the Moon orbiting plane aligned with the Earth rotation axis? Why or why not?

You can get the answer to all these questions by reading:

https://en.wikipedia.org/wiki/Tidal_locking

and:

https://en.wikipedia.org/wiki/Orbit_of_the_Moon

Re: From a million miles away, NASA camera shows moon crossing face of Earth

#30

Post by gojomo »

These pictures, at this angle, imply that the Earth regions under the moon were experiencing a solar eclipse, right? (Odd that the NASA article doesn't mention this.)

EDIT: There was no solar eclipse at the "last month" time-frame these pictures were taken. So that isn't a real earth-shadow under the leading edge of the moon, and as close as the moon seems to pass over the perspective-center of Earth, it must have actually been off somewhat, casting its shadow into space.

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