At what altitude does the Earth look like a big blue marble?

April 9, 2012 8:20 AM

How far up do you have to go to see the Blue Marble?

Clearly you have to be higher than the International Space Station, but you don't have to go all the way to the moon.

Googling yields lots of info about seeing the curvature of the Earth, but that's not what I'm looking for. I want to know how far you have to go to see the whole Earth as a circle.

posted by alms to Science & Nature (10 answers total)

Best answer: About 12,000 miles according to this
posted by edgeways at 8:33 AM on April 9, 2012 [1 favorite]

Best answer: ooh...i actually did a bit of the calculation for this once...at the height of geosynchronous orbit (which is not that far off from the distance this photo was taken), the earth is approximately the size of a dinner plate held at arms length.
posted by sexyrobot at 8:35 AM on April 9, 2012

Best answer: If you're curious, this also means that the only people who have ever seen the full face of Earth were the two dozen men who flew to the moon.
posted by ROU_Xenophobe at 8:38 AM on April 9, 2012 [1 favorite]

but, as far as seeing the whole thing as a circle? actually? ground level. just turn around. seriously. there really isn't an altitude where it doesn't look like a circle, and thus no really clear transition between 'where it looks like a circle by moving your head around' and 'where it looks like a circle but all fits within your field of view.'
posted by sexyrobot at 8:39 AM on April 9, 2012 [2 favorites]

as far as seeing the 'whole earth'? never. 'the entire hemisphere facing you?' considerably further away from the earth than the moon, i imagine, tho i'd have to sit down and do the math. (the 'blue marble' picture is hardly half the earth...mostly just africa and a bit of the south pole) exactly half the moon isn't visible from the earth, due to curvature cutting off the very edge (it's close though...49.something%) though we can see approx 59% of the moon, due to its 'rocking' back-and-forth during its monthly orbit.
posted by sexyrobot at 8:46 AM on April 9, 2012 [1 favorite]

Yeah this question is a bit subjective. You can never see even the full hemisphere because those tangent lines do not converge. You have to set a threshold, i.e. at what distance can I see 95% of the hemisphere? Otherwise you can see the full "circle" at ground level, it's just a very small percentage of the full hemisphere.

On preview sexyrobot has it.
posted by grog at 8:59 AM on April 9, 2012

Response by poster: The first two answers got it, thanks! I also appreciate ROU_Xenophobe's addendum. I was actually wondering, that, too, but forgot to include it. It's fascinating that with all the decades of space flight since Apollo we still haven't gotten anyone else to that height.

(For the record, I didn't mean this as a trick question. I was looking for the subjective experience of seeing the Earth as a circle within one's field of vision. The first three answers spoke to that.)
posted by alms at 9:14 AM on April 9, 2012 [1 favorite]

Not that you asked, but on the old Concorde flights you could see the curvature--very cool.
posted by Ideefixe at 9:16 AM on April 9, 2012

Yeah this question is a bit subjective

Yeah, but there is a point where you see the entire earth in front of you with space on all sides, that's not subjective.
posted by empath at 10:51 AM on April 9, 2012

After I got glasses in 6th grade I was really bummed about not being an astronaut.
But then my uncle told me that space begins at your feet and I felt better!
posted by Pecantree at 7:59 PM on April 9, 2012