I get confused by artists impressions of space, especially when it is in the form of movie pictures.
There are many movies, artists impressions of manmade spacecraft travelling through space and approaching a planet.
My question is this. At what distance, would the planet, let us say Mars for example, completely fill the point of view from the spacecraft. So that nothing else of space is visible.
Do artists reproduce this aspect correctly.
The human field of vision is about 120 degrees. Mars has a diameter of about 4,200 miles. Using the tan function, I’d say it takes a distance of about 1,200 miles for an object of 4,200 miles to fill 120 degrees.
Vsauce did a video on (basically) this and related questions: How Much of the Earth Can You See at Once?
One thing which I didn’t appreciate is that at a certain distance you would see something which looks like a complete disc, and yet be seeing far less than 50% of the earth’s surface (e.g. at this point in the video).
Aside: If you’re far enough away, you can actually see 50% or more of a spherical planet’s surface, due to gravitational lensing. For the Earth, the needed distance is about half a lightyear; it’s proportionately further for planets with lower surface gravity.
And be careful with Vsauce. They might get things right occasionally, but there’s a lot of absolute garbage on that channel.
Those are strong words. Example?
When you’re that close, you need to take into account the fact that the object is a sphere. (Also, you calculated the distance from the observer to the center of Mars, not to its surface.)
If the radius of the target sphere is R and the angle it subtends is A, then your distance from the center of the sphere is R/sin(A/2) and hence your distance from the surface of the sphere is R/sin(A/2)-R. For A=120 degrees and R=2100 miles, I get 325 miles as the distance from the surface where Mars will fill 120 degrees.
Paging Chesley Bonestell, Mr. Bonestell to the white courtesy phone!
Wow… we had a copy of The Conquest of Space on the bookshelf when I was going up. Made me want to become an astronomer (at least until I realized I would not get to spend my days staring at beautiful celestial sights through a telescope lens)
That’s a wonderful typo.