how big is our universehome-download pdf-print-friendly pdf-credits
image six deep space image

how far

- the sun
and planets


- across the
milky way



the distant

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

deep field image
try this: can you spot the exploding star?

The picture on the right was taken three weeks after the one on the left. In that time, a star at the edge of one of these distant galaxies has exploded - “gone supernova.” Can you spot the supernova in the picture at right? Even though the explosion is as bright as a billion suns, it is so far away that it is just a speck of light!

+ click here to enlarge image


the distant galaxies

They’re so far that the light arriving on Earth today set out from the galaxies billions of years ago. We see the galaxies not as they are today, but as they looked long before there was life on Earth.

Some galaxies are so far away that they appear as tiny smudges, even through the largest telescopes. It’s tough to determine how large or bright these fuzzy distant galaxies are. But astronomers can figure out the distance to these galaxies, by watching for incredibly bright exploding stars called supernovae.

Some types of supernovae have a known brightness - or “wattage” - so we can figure out how far they are, and therefore the distance to their home galaxy.

1986. Astronomers begin to use supernovae to find the distance to the furthest galaxies we can see.

ABOVE: The deeper we see into space, the more galaxies we discover. Only a few points of light in this image come from stars in our own Milky Way; everything else is a distant galaxy.