MEASURE THE UNIVERSE!

Our motto: Don't look it up... look UP!

Using the MicroObservatory telescopes -- and a little cleverness -- you can measure the size of the Earth, the size and distance to the Moon, the height of a mountain on the Moon, the distance to nearby stars... even the speed of light!

Try some of the challenges below and send us your results, including images you used and estimated uncertainties in your measurements. We'll publish your results in the User's Lounge.

CHALLENGE #6:
SIZE OF THE EARTH

How's your geometry? Using two telescopes and a little geometry, you can determine the size of the Earth. Here's the challenge:

First, take two simultaneous images of the same distant object -- e.g. the North Star -- using two widely separated telescopes, such as the MicroObservatory telescopes in Arizona and Massachusetts. When you control the telescopes, don't forget that the telescopes are in different time zones!

After you've taken the images, look at the Info page for each image. (The Info link is next to your image's filename on the Get Images page.) Under the heading Altitude, you'll find the angle that the line-of-sight of the telescope made with the ground (horizon). If the Earth were flat, this angle would be the same for both telescopes -- but as you can see, the two angles are different. That is, when pointing toward the same object at the same time, two widely separated telescopes will make different angles with the ground.

Your challenge is to use these two angles to estimate the size of the Earth. You'll need to draw a picture first to figure out what's going on. Don't forget to send us your results.

CHALLENGE #7:
DISTANCE TO THE MOON... part 1.

This one's on the Starfleet Entrance Exam: If a cow jumped over the Moon, how far would she have to jump?

Using the telescope and your knowledge of the SIZE of the moon from the MOON CRAZY Challenge, can you figure out: How far away is the Moon?

Here are three different ways to try it. The first uses visual observations, the second uses the telescope, and the third uses the laws of motion and some common facts:

HEADS UP! Here's a quick and easy way. You'll need to know how wide the moon is in miles. (Use your result from the first MOON CRAZY challenge.)

You'll also need to know how wide the Moon appears in the sky, in degrees. Here's a great rule of thumb... or knuckle: Hold your fist extended at arm's length. Your first two knuckles are about 3 degrees apart. Sighting the Moon between your knuckles, try to estimate the width of the Moon, in degrees.

Then use these numbers, a simple diagram, and your knowledge of geometry to determine the Moon's distance!

'SCOPE IT OUT! For a more precise result, use the telescope to first get a good image of the Moon. (Use "Zoomed Out" mode in the Main Tube.) The telescope's field of view is 5 arc-seconds per pixel at this magnification. To determine the angular width of the Moon, just multiply this scale (5 arc-seconds/pixel) times the number of pixels in the width of your moon. To convert to degrees, remember that there are 60 arc-seconds in an arc-minute, and 60 arc-minutes in a degree. (To measure the Moon's width in pixels, use a software program like NIH Image, SkyProbe, Graphic Converter, or PhotoShop.)

Now you can use the Moon's width in miles, along with the Moon's angular width on the sky, to calculate the distance to the Moon. How does it compare with your bare-knuckle estimate at left?

GO FIGURE! Do you trust the laws of physics? Kepler showed that the time it takes a satellite to orbit a planet (its "period", T) depends on how far from the planet it is. The square of the period is proportional to the cube of the distance. (Newton showed how to derive this from his laws of motion. and the law of gravitational attraction.)

Use Kepler's Law and the following facts to calculate the Moon's distance: The space shuttle Challenger flies 250 miles high and takes 90 minutes to orbit the Earth. (How do we know?) (Don't forget, its orbital distance from Earth is 250 miles PLUS the radius of the Earth!) The Moon takes 28.5 days to orbit the Earth. (How do we know?)

How do your results compare to the telescope measurements? Does Kepler's Law fit your observations?

"Use what talents you possess: the woods would be very silent if no birds sang there except those that sang best."
-Henry Van Dyke