how big is our universehome-download pdf-print-friendly pdf-credits
image two sun image

how far

- the sun
and planets


- across the
milky way



the distant

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

point of view image
try this: your "point of view" makes a difference!

Hold up your thumb at arm's length. With one eye closed, line up your thumb with an object in the distance. Now switch eyes so that only the other eye is open. Does your thumb suddenly change position? Move your thumb closer to your nose and try again. Can you see your thumb jump even more?

Astronomers call this effect "parallax." The closer an object, the more it appears to shift against the distant background, when viewed from two different spots.


the sun and planets

The Sun is so far away that it would take the Space Shuttle seven months to fly there. That's why the Sun, which is a hundred times the diameter of the Earth, looks so small!

Three hundred years ago, astronomer Edmund Halley found a way to measure the distance to the Sun and to the planet Venus. Knowing these distances helped find the true scale of the entire Solar System for the first time.

Halley knew that every 121 years the planet Venus passes in front of the Sun. Venus’ position, relative to the Sun behind it, appears very different when viewed from two different places on Earth. How different depends on how far away Venus and the Sun are from the Earth.

1761. Using observations of the "transit of Venus" made by astronomers around the world, the distance to the Sun is determined to be 93 million miles. This photograph is from the 1882 transit of Venus.

ABOVE: Our Sun is the nearest star. At 93 million miles, the Sun provides the warmth that has allowed life to evolve on Earth. Has life evolved elsewhere?