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How to Measure The Universe

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Here is a fun way to show you and your kids just how big the universe is!

Let's first get a perspective of where you and I are in our immediate solar system. First of all, we need a cosmic tape measure! It's OK if you can only find a regular one though. Try to find one that will measure 25 feet or more at a time to make it easier; the universe is a really big place! A yellow tennis ball makes a nice representation of the sun. Take a plain piece of white paper and a pencil and make a 'dot', about the size of the period in this sentence.

It's time to go outside. The cosmic tape measure also must have a unit of measurement which is:


"How far is that?" your kids will ask. Point in one direction and tell them to start running until they come all the way around the earth and (pointing in the opposite direction) you come back here. But they will have to run around the earth 114 more times to make just one foot on the cosmic tape measure! Stretch out the tape until you measure 31 feet. Hold the tennis ball on one end and the 'dot' on the page at the other. That is the approximate distance apart the earth and the sun would be if we could shrink them down to this size!

On a clear night, go outside with your kids, two tennis balls and the cosmic tape measure. Ask them if they know how far away the nearest star is. The name of that star is Proxima Centauri. Remembering that each foot represents 3 millions miles, give your child one of the tennis balls and tell them we are going to put Proxima Centauri in relative distance from our sun, (if we could make each of them the size of tennis balls). This part will require you to check a road map and find a city that is 1585 miles away, but don't tell the kids yet. Send the one with the other tennis ball out until they can just hear you ask: "Do you know where (the name of the town 1585 miles away) is?" They may or may not know, but when you tell them how far it is, they will be as amazed as we are!

This is only the nearest star. But distances after this are going to get really hard to measure; even relatively speaking! So astronomers measure distance by how long it takes light to travel there. For this demonstration, we need a flashlight. Pretend that it is a really strong flashlight, and it's beam can reach anywhere in the universe. Point it in one direction and turn it on, explaining that if we could make the beam go in a circle around the earth, it would go around 7 times in one second! That is 186,000 miles per second!

Even going that fast, it still takes about 8 seconds for the light from the sun to reach us

Now the fun part! We are going to pretend that someone is living on a planet by our nearest star neighbor Proxima Centauri (you can name the planet and pretend you have a friend that moved there). They have a really strong flash light like ours and we can send messages across space. Give your participants the flash light and point it up toward the stars and tell them to flash a signal 3 times and wait for them to shine a message back. Wait a minute and ask them if they saw anything yet. "Okay," you will say, "how old are you now?" Add 9 years to their age and tell them that is how old you will be when you get a return message! It is 4 1/2 light years to our friend on the planet near Proxima Centauri.

But not all the shiney dots we see are stars. Some are galaxies and clusters of stars that have names like 'Lagoon Nebula', 'Crab Nebula', or 'Whirlpool Galaxy' (I think that is where my socks go when they disappear in the wash!) We live in the 'Milky Way Galaxy'.. It has over 200 billion stars! (Almost as many hamburgers as 'McDonalds' has sold!) To get an idea of it's size using our tennis balls: if we hold one here on earth and dump 200 billion tennis balls into the space between here and the planet 'Mars', which at it's nearest point is about 35 million miles, we will have an idea how big it is! If we take the really strong flash light and send a signal to the other end, it would take 100,000 years to reach the other side and another 100,000 years to get a return reply!

The 'Hubble Space Telescope' has brought us out into space farther that ever. The latest pictures show that the universe has over 50 billion galaxies!

How big is the universe?


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