how big is our universehome-download pdf-print-friendly pdf-credits
image five hcg87 image

how far

- the sun
and planets


- across the
milky way



the distant

- how far
can we see
- how big is
the universe

balloon image
try this: far and small

You’ve been asked to award a prize to the balloon that has traveled the furthest from the starting line. But you have only this photo taken from the starting line to go on.

What clues will you use? How do you know that the balloons that look smaller are further away and not just smaller balloons? Which balloon would you choose, and why? Astronomers face the same challenges trying to determine the distance between galaxies.


other galaxies

Even “nearby” galaxies beyond our own Milky Way galaxy are so far that it takes their light millions of years to reach us. The images we take today show how these galaxies looked millions of years ago.

The further a galaxy, the smaller it appears. You can use this method to get a rough idea which galaxies are closer and which are further. Although galaxies come in different shapes and sizes, the spiral galaxies similar to our own Milky Way are thought to be roughly the same size. So if a spiral galaxy looks half as big as another, it is probably twice as far away.

1924. Edwin Hubble presents the first evidence that galaxies
lie far beyond the Milky Way. To date, billions of galaxies have been discovered.

ABOVE: These galaxies - a group called HCG 87 - are a few of the billions of galaxies discovered beyond our Milky Way.