1. ## Earth/Sun relative height?

Being a skydiver, I was wondering, what height would I have to be above the sun for the horizon to look like the earths when I am at 12500 feet on earth? Or, if the earth were as big as the sun, what height would I have to be above sun sized earth so it looked as big as earth when I am 12500 feet above it?

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I can't picture the sun looking much like Earth at any heigth: But mathematically the sun has about 110 times the diameter of Earth, so the answer is 1,375,000 feet above the photosphere. The temperature of the corrona is about one million degrees.
Very advance beings could possibly build a hollow sphere (the size of the Sun) that is a 110 times larger replica of Earth with high vacuum inside. If the radius is 700,000 kilometers: A = 12.56 times radius squared = 615,440,000,000 square kilometers. For an average thicknss of one kilometer, that's 615 billion cubic kilometers or 615 billion times a billion tons if the average density is one. 615 billion tons of raw material is enough if the average thickness is one micrometer, but that requires a material about a quadrillion times stronger than diamond. Neil
Last edited by neilzero; 2008-Feb-24 at 03:48 AM.

3. Thanks Neil. Was trying to get a feel for the difference in size in other than the pictures showing earth relative to the sun. A 260 mile freefall huh? I've jumped from 20,000 feet for a minute and half fall. I know other factors such as air density and all come in but, let's see ignoring difference in height/velocity changing with altitude, 260 miles would be .5 minutes times 260 = 2hr 10 min. Cool visualization. Be a bit less as I have assumed an acceleration time in the 30 second/1 mile fall. Usually jumpers figure between 4 and 5 seconds/1000ft at terminal velocity. So that would mean at 5 seconds.... 1 hr 55 min or so. Still cool.

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If this Earth replica has an atmosphere, with 14.7 pounds per square inch at the surface, the analysis gets compliated. Some sphere thickness would produce one g at the surface, but the gravity and air pressure at other altitudes would be much different due to the much larger radius and empty interior, I think. Neil

5. 1960. 19.5 miles in 4.5 minutes. Joe Kittinger.

"An hour and thirty-one minutes after launch, my pressure altimeter halts at 103,300 feet. At ground control the radar altimeters also have stopped-on readings of 102,800 feet, the figure that we later agree upon as the more reliable. It is 7 o'clock in the morning, and I have reached float altitude …. Though my stabilization chute opens at 96,000 feet, I accelerate for 6,000 feet more before hitting a peak of 614 miles an hour, nine-tenths the speed of sound at my altitude."
Most of my jumps were 30 second falls from 7500 feet. The air was fairly warm during the summer. This exercise was to get some idea of the enormity of the sun. I was figuring for a 260 mile freefall at the 30 second rate. Kittinger was haulin' butt. There is talk of private attempts to break Kittinger's record, perhaps from one of Rutan's rocket birds.

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I suspect that if he wasn't using a stabilization chute, he'd have exceeded the speed of sound.

The longest fall I've experienced was jumping off cliffs into a lake. I calculated I hit speeds of around 47 mph when I hit the water. Quite a jolt! I couldn't begin to image hitting water freefal speeds at twice the velocity (and four times the kinetic energy...).

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