Astronomy: Facts

The World of Space


For thousands of years, even before we had the word “astronomy,” humans have been looking up at the sky. Astronomy is the study of everything that is or was in space beyond the Earth's atmosphere.

We are still looking up because the sky is such a fascinating place and because we are learning more and more about it every day. Let's stretch our imaginations as we explore the world of space.


Solar System

Long ago people thought that the sun, and all the other planets, revolved around Earth. A scientist named Galileo proved in the 1600's that the Earth and the other planets revolved around the sun. He used a special tool called a telescope to look at the sky.

Here's more about the development of the many different kinds of telescopes. Learn about Arecibo, the largest single-dish radio telescope in the world. And visit this Astronomy Timeline to see where Galileo's discovery fits in with other important events in astronomical history.

The Universe


How big is it?

When you look up at the night sky you are looking at the universe. Everything is inside the universe, even us, and it is impossible to imagine how big the universe is.

Special astronomers called cosmologists are trying to measure it. They analyze the light from a star with an instrument called a spectroscope. By studying the light spectrum, they can tell whether an object is moving away from Earth or toward Earth. Based on the information from this instrument, scientists have learned that the universe is still growing outward in all directions.

The universe is huge, too huge to measure fully. Space.com has details on why the universe is so difficult to measure.



How old is it?

Scientists believe that about 13.8 billion years ago, a powerful explosion called the Big Bang set the universe into a motion which continues today. Scientists are not yet sure if the movement will stop, change direction, or keep going forever.


How do you measure the universe?


Since distances are so huge in the universe astronomers need a way to measure distance on a big scale. They use a unit of length called a light year, which is the distance light can travel in one year. Light travels very fast, so in a year it can go 6,000,000,000,000 (6 trillion) miles, or 9,500,000,000,000 kilometers.

BIG Numbers

As we've already seen, galactic sizes and distances are huge. Really big numbers have names we're not used to hearing, and they have so many places that scientists have adopted a shorthand way to express them. For example, one trillion can be written as 1012 (10 to the 12th power), where the raised 12 represents the number of zeros after the 1. Here are some names of numbers in ascending order (small to large):

  • hundred (100) (102)
  • thousand (1,000) (103)
  • million (1,000,000) (106)
  • billion (1,000,000,000) (109)
  • trillon (1,000,000,000,000) (1012)
  • quadrillion (1015)
  • quintillion (1018)
  • sextillion (1021)
  • septillion (1024)
  • octillion (1027)
  • nonillion (1030)
  • decillion (1033)
  • undecillion (1036)
  • duodecillion (1039)
  • tredecillion (1042)
  • quatuordecillion (1045)
  • quindecillion (1048)
  • sexdecillion (1051)
  • septdecillion (1054)
  • octodecillion (1057)
  • novemdecillion (1060)
  • vigintillion (1063)



Galaxies are collections of billions of stars, gas, and dust held together by gravity. All stars belong to a galaxy and galaxies are huge. Our sun, Earth, and all the stars you see when you look at the night sky belong to the Milky Way Galaxy.

Scientists estimate that there may be 10 billion stars in our own galaxy and 50 billion galaxies in the universe as a whole. Galaxies are classified by their shape: spiral, elliptical or irregular. The Milky Way is a spiral type.

You, too, can classify galaxies if you dare . . .

What does a quasar have to do with a galaxy? Find out at this Windows to the Universe site.


Sun Glasses

Stars are large balls of gas that give off light. Scientists know that you can see about 3,000 stars with your naked eye. With powerful telescopes, scientists can see billions and billions of other stars.

Here's a fun fact: the prefix “astro” means “star” in the Greek language.

Blue Sun

How old is a star?

Did you know that stars vary in their size, color, and brightness? A star can be red, orange, yellow, white, or blue. Its color depends on its surface temperature, which is determined by its age and mass. Stars go through many stages in their lifetimes. Some of the names for these stages are Nebula, Red Giant, Supernova, White Dwarf, Neutron Star and even Black Holes. Stars can shine for up to 10 billion years!

Follow the links below for more informative facts about stars.

The Life Cycle of a star the size of our sun Tan Sun The Life Cycle of a star heavier than the sun Sunny Famous Star Stats Spike Sun

Our Solar System

Girl with Planets

The Roman word for the sun was “sol,” so “solar system” refers to all the natural objects that orbit around our sun. The solar system includes eight planets, a number of planetoids, more than one hundred seventy moons, some comets, lots of asteroids, and other space objects that travel in paths around the sun.

The sun is the biggest object in our solar system, yet it is only a medium-sized star. It will use up its energy and die in about 5 billion years! The sun is the reason why there is life on earth. It provides the light and heat energy that living things need to survive.

Did you know that the solar system is about 4.6 billion years old?

Did you know that if an object orbits the sun it is called a planet but if it orbits something other than the sun it is called a moon?

Do you believe that there are over 30,000 asteroids?

There are so many interesting facts about the solar system that you'll have to explore more at these links:

Fun Facts About the Sun

Age 4.6 billion years
Diameter 870,000 miles (one million earths could fit in the sun)
Mass 2.1645 octillion tons
Distance from Earth 93,000,000 miles, the closest star to Earth
Light Light from the sun takes 8½ minutes to reach earth
Relative Size Sun is the largest object in our solar system, about 10 times in diameter greater than Jupiter, the largest planet
Made of 71% hydrogen, 27% helium, 2% other elements
Surface Temperature 10,800 °F
Core Temperature 29,000,000 °F

Are Constellations real?


Constellations are pictures of objects and characters outlined by stars in the night sky. Ancient peoples imagined these starry figures and created stories about how these images, or constellations, came to be.

Many of the constellations in the northern sky were created and named by the Greeks during the Greek Empire (about 50 BC to 480 AD). Other cultures developed their own stories. Learn more about these stories and the constellations they represent at Windows to the Universe, and Mayan Astronomy.

A Brief Look at Observatories

Observatories are the homes of large telescopes that gather light from distant objects and make the objects appear larger. They let scientists view the sky in more detail than the naked eye allows. There are observatories all over the world. Most optical observatories are located at on top of mountains where the air is calm and dry and the weather is clear. Observatories are located far from city lights which interfere with viewing. Optical telescopes are one kind of telescope used in observatories. Observatories also use other instruments such as cameras, computers, and spectroscopes.

Before cameras, astronomers drew everything they observed! Other non-optical instruments use electromagnetic radiation energy to observe the skies. They observe things like infrared, x-ray, ultraviolet, and radio waves. Infrared telescopes, like one aboard the Hubble Space Telescope, can “see” objects that are smaller and farther away then optical telescopes can see. Hubble is also equipped with an ultraviolet telescope, which is really a mirror coated with special substances that only reflect ultraviolet light. Some of the hottest and brightest stars can be seen with ultraviolet telescopes.

Idaho's Space Expert

Barbara Morgan is Idaho's authority on space travel. Learn more about Barbara, Idaho's first teacher/astronaut at Barbara Morgan: No Limits.

There's a Dog in the Sky!

This poem was written especially for Science Trek, courtesy of Cherry Carl. For additional poems on science, history, language, and holidays visit her website at Carl's Corner.

There's a dog in the sky
And I know why.
He's belongs to the hunter,
And so does the horse, of course!
Maybe they're hunting for the great big bear,
Or perhaps the dragon in its lair.
What do you see when you look in the sky?
There's a lot to see if you really try!

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