How Big are the Planets and Stars?

1938 Broadcast of The War of the Worlds
1937 Crash of the Hindenburg Airship
Washington Post - Images From Space
Hubble Ultra Deep Field

How Big is the Solar System?

How Big is our Galaxy?

Find our star (the sun) in this galaxy. How small do you feel now?

Hint: you can't see it, because it's one of the tiniest specks that create the milky white layer that's filled with other tiny stars you can't see. That's why we call that patch of light in our night sky, "The Milky Way." And there are about 100 billion stars in our galaxy.

The disk of the Milky Way galaxy is about 100,000 light years in diameter (one light year is about 6 trillion miles), and about 12,000 light years thick.

Take a tour of the galaxy

What is the closest star?

Proxima Centauri is a red dwarf star approximately 4.22 light-years distant in the constellation of Centaurus, but its brighter neighbor Alpha Centauri, a double star, is so nearly the same distance that data about it are usually given.

If the Milky Way were the size of a penny, how big would the rest of the universe be?

A penny is about 1 inch across. If this equals 100,000 light years as the diameter of the Milky Way, the Andromeda Galaxy is about 23 inches away, the Virgo Cluster of Galaxies is about 60 million light years or 600 inches away, and the nearest quasar, 3C273 is about 1.5 billion light years or 150,000 inches or a bit over 2 miles away.

The visible universe has a horizon at about 14 billion light years and the most distant galaxies seen by the Hubble Space Telescope are nearly at this limit at about 12-13 billion light years. This is about 15 - 20 miles away from the Milky Way 'penny' and is the farthest we can ever see.

Source: Ask the Astronomer

How Old is the Universe?

The universe was born in a "Big Bang" 13.7 billion years ago, and our star is a second or third generation star born 9 billion years later, from what was left over when an earlier, larger star ran out of fuel and exploded. The sun is 4.5 billion years old, and it's a middle-aged star, so it has another 4.5 billion years to go.

How Big is the Universe?

Our galaxy is about 100,000 light years across. Let that equal 1 cm. Andromeda is the nearest spiral galaxy at 2.5 million light years away or 25 cm. Now, the most distant galaxy is 13 billion light years away.

1 cm = 100,000 ly

10 cm = 1 mly
100 cm = 10 mly
1,000 cm = 100 mly
10 km = 1 bly
100 km = 10 bly

So, I would have to drive 130 km (80 miles) to the get to the most distant galaxy if our galaxy was 1 cm wide.


P.S. Here's a neat way to think of 2 raised to the 100th power:

How Many Galaxies are in the Universe?

Want to feel even smaller? The Galaxy you live in, is one out of over 100 billion in the universe. How many galaxies can you count in
this picture ? (click on the picture to magnify it). It's a picture of a group of galaxies that are 10,800 million light-years away (almost six trillion miles), so we are looking back in time at some very young galaxies.

Astronomers are really puzzled to see so many galaxies so soon after the Big Bang.


The International Space Station

August 1, 2008 - "Rishi" (Eaten Sun) at the
Jiayuguan Fort on the Great Wall of China.

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