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View Full Version : Meausuring distance of Objects in the sky using your fist

aleancook
2006-Oct-21, 05:37 AM
I was told that you can measure the distance of objects in the sky, for example you can measure how far the moon and stars are by using you fists.

(You would have to place one fist directly infront of you, and it has to lined up with the horizon, and then you would place one fist on top of the other until you get to the bottom of the object that you were trying to measure. But this doesn't make any since to me since the objects move every hour or so.) I also remember using AU as a unit of measure.

Does anyone know the correct procedure on how to do this?

If so can you use the moon as an example.

lti
2006-Oct-21, 08:38 AM
The tecnique you mentioned would be an effective method of measuring the angle above the horizon of the object you were looking at.

Serenitude
2006-Oct-21, 08:45 AM
Hrm. In the Army, they taught us how to shoot rough azimuth's (azimi? LOL) with our fist, but haven't heard of gauging distance.

Kiwi
2006-Oct-21, 11:42 AM
Yes, this system is for roughly measuring the distance, in degrees, between two objects, such as two stars, or a planet and the horizon, or for measuring distances around the horizon. Obviously the results may vary depending on one's physical stature and build, but guidelines are as follows:

Holding the hands out at arm's length,
1 finger width = 1 degree
4 fingers width = 5 degrees
fist width = 10 degrees
handspan (fingers spread, thumbtip to little fingertip) = 20 degrees

It is best to check these against known distances (for instance the Big Dipper is about 25 degrees long). Also measure from your true horizon to the zenith, which is 90 degrees, so it should be close to 4 handspans and a fist.

aleancook
2006-Oct-23, 03:39 PM
How does the degrees tranfer to distance?

And the distance of a planet from the horizon? Can we measure the distance of Venus? If so how?

01101001
2006-Oct-23, 03:50 PM
How does the degrees tranfer to distance?

And the distance of a planet from the horizon?
Doesn't transfer at all. You can estimate angular measure by comparing something to your fist, or thumb, whatever, but not know actual distance.

The Sun and the Moon have about the same angular diameter (so a total solar eclipse looks the way it does), but the Sun is much much farther away than the Moon -- and the Moon has a much much small actual diamter than the Sun.

We can measure distances to objects, but not by only measuring angular distances. Your fist alone won't help you know how far away Venus currently is.

Tog
2006-Oct-23, 03:56 PM
How does the degrees tranfer to distance?
They don't. When Venus comes over the mountains in the morning, it is the same agular distance from the horizon as the mountain it just cleared. The two are obvioulsy not the same distance away.

And the distance of a planet from the horizon? Can we measure the distance of Venus? If so how? Again, no. The angle above the horizon won't give you the distance to something in the sky.

The distance to venus can be determined by using Kepler's laws and som trigonometry, but only relative to the Earth. What it will tell us is that Venus is 0.67 times the distance from the Sun as the Earth is. Part of this is the planets distance in degrees frm the Sun as they appear in our skies. That's the trig bit. It wasn't until there was a way to make detailed measurements of Venus as it crossed the Sun's surface that people were able to make a valid estimate of the distnace in Miles/Km/furlongs/whatevers.

Saluki
2006-Oct-23, 05:59 PM
How does the degrees tranfer to distance?

And the distance of a planet from the horizon? Can we measure the distance of Venus? If so how?

This has already been answered, but I wanted to add that Trigonometry tells us that to fully determine a triangle, we need 3 pieces of information out of 6 possible (3 sides, 3 angles). If you are trying to figure the distance between two astronomical objects, you are basically setting up a triangle with you at one point, and the two objects at the other two points. With your fist method, you are (roughly, there are far more precise methods available) gaining one bit of information, namely the angle formed by the lines from each object through you. To determine the distance beteen the objects, you need two other bits of information. If you have a way of determining the distance between you and each object (google "parallax method", for example), this gives you two more bits of information about the triangle, and then you can solve for the distance between the two objects using simple trig formulas.