From a million miles away, NASA camera shows moon crossing face of Earth • Hacker News Board

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

#41

Post by simias » Thu, Aug 06, 2015, 9:34 AM UTC

lqdc13 wrote: post #25

mnw21cam wrote: post #20

Earlier quoted context omitted.

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.

Those are not iphone cameras, they need to work under extreme conditions and for a very long time. The camera must also have been chosen years ago.

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

#42

Post by [deleted] » Thu, Aug 06, 2015, 9:34 AM UTC

gurtwo wrote: post #32

Why don't we see the Moon's shadow projected over the Earth in the pic? I guess it has to do with the relative distances of the 2 bodies to the Sun and the Moon's penumbra or something. Can someone make a digital image simulation of this to verify?

[deleted]

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

#43

Post by Tobold » Thu, Aug 06, 2015, 9:38 AM UTC

Someone tweeted this yesterday and some of the replies were really disheartening.

Several people were calling it fake, with varying explanations of either "The earth is flat" or "Everybody knows the whole space program is fake".

I knew people out there actually believe this, but damn...

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

#44

Post by Cyykratahk » Thu, Aug 06, 2015, 9:40 AM UTC

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?

Interestingly, the moon's tidal lock is not perfect, resulting in a wobble that can be seen in time lapses: http://svs.gsfc.nasa.gov/cgi-bin/details.cgi?aid=4236

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

#45

Post by Cogito » Thu, Aug 06, 2015, 9:40 AM UTC

gonvaled wrote: post #33

Cogito wrote: post #28

Earlier quoted context omitted.

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…

Interesting, thanks. I understand that the satellite needs to have some form of propulsion to keep it at L1 (it is unstable), so it must have a limited life. How long?

From a Q&A session https://www.nasa.gov/content/goddard/qa-on-noaas-dscovr-miss...

The mission is slated for 2 years, and they have fuel for 5. I also happen to know that they reached L1 faster than anticipated thanks to a really nice insertion from the SpaceX Falcon 9 launch vehicle.

This means that the operational life might be even longer, but I haven't found any sources for what that might be.

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

#46

Post by Cogito » Thu, Aug 06, 2015, 9:47 AM UTC

lqdc13 wrote: post #25

mnw21cam wrote: post #20

Earlier quoted context omitted.

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.

It's also worth noting that the camera is quite old. The satellite was built in the late 90s, and was flown more-or-less unchanged when it eventually took to the sky.

So not only do you need to account for the space hardening that has gone into the technology (it was designed to keep working through the middle of a solar storm), you also have to take into account the state of the art over 15 years ago.

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

#47

Post by TeMPOraL » Thu, Aug 06, 2015, 9:55 AM UTC

coldtea wrote: post #34

avar wrote: post #29

Earlier quoted context omitted.

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

The magic of reading!

Reading is the old-school local processing. Asking people is cloud computing, which is hot so it must obviously be better!

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

#48

Post by 13hours » Thu, Aug 06, 2015, 10:02 AM UTC

Tobold wrote: post #43

Someone tweeted this yesterday and some of the replies were really disheartening. Several people were calling it fake, with varying explanations of either "The earth is flat" or "Everybody knows the whole space program is fake". I knew people out there actually believe this, but damn...

I find Twitter to be second only to YouTube in comment trolls.

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

#49

Post by TeMPOraL » Thu, Aug 06, 2015, 10:02 AM UTC

gonvaled wrote: post #33

Cogito wrote: post #28

Earlier quoted context omitted.

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…

Interesting, thanks. I understand that the satellite needs to have some form of propulsion to keep it at L1 (it is unstable), so it must have a limited life. How long?

It's nost just with Lagrange points. Actually, most of the satellites need to carry some fuel for station-keeping - the combined effects of non-uniform mass distribution in the orbited body, solar radiation, gravitational pull of other bodies and even air drag will slowly alter, or even completely degrade your orbit.

See [0] for more: https://en.wikipedia.org/wiki/Orbital_station-keeping

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

#50

Post by TeMPOraL » Thu, Aug 06, 2015, 10:07 AM UTC

acqq wrote: post #15

bumbledraven wrote: post #11

Why aren't the stars more visible in the background? Does it have to do with the camera's exposure?

Note that the Moon is fully lit by the Sun (it's a "full Moon" from the perspective of the satellite). And it's gray on the picture, as the Earth is significantly brighter. Now, you can check it yourself, take the best camera you can have, go one night when the Moon is full somewhere outside of the city where you see the stars and then try to make a photo where on the photo both the stars and the Moon surface are vis…

Isn't this just because of the processing? I imagine if you took additional logarithm of the values returned by the sensor, you could have both starts and the bright moon visible at the same time.