How Far Away are the Stars?

Proxima Centauri Sun Earth Light Years Image

While it looks at times like you could reach up into the sky and pluck down the Sun, that giant flaming ball of gas that is our neighbourhood star is actually 150 million kilometers away—and that is by far the closest star to us. The next closest star is around 4 light years away, or 36 trillion kilometres, and that is just barely outside of our front door.

How Far Away are the Stars?

The question can be answered in a very complex or a very simple way, with the simple answer being VERY far. A step outside in the night hours gives a great view of the stars, which all seem to be painting on the roof of sky above. They vary in brightness but all seem to be about the same distance away from the observer. The difference in the brightness of the stars, however, is one of the keys to determining how far away a star actually is.

The Power of Parallax

As early as the sixteenth century, astronomers tossed around the concept of parallax to determine how far away stars are. Parallax is the difference in apparent location of an object when viewed from two different points of view. The greater the difference, the closer the object is to the viewer. A neat example of this can be done by anyone: simply hold out your thumb at arms length and look at it with one eye closed. Then, close the open eye and open the closed eye. Note how your thumb appeared to change position, and then repeat the experiment with your thumb closer to your face. This time the apparent shift in position is much greater.

This is the principle of parallax that was used to determine star distances. There was, however, a problem. There was no distance on Earth great enough for an observed star to seem to shift position—they were simply too far away.

Scientists came up with a solution. Rather than try to observe the same star from different locations, they would observe the same star from the same location, but at different dates. As the Earth travels around the sun it covers roughly 300 million kilometres in a straight line. Now scientists had enough distance to compare observations, which was first done in the nineteenth century.

The Farthest Star

We know the distance to the closest star (150 million kilometres to our Sun) and the next closest star (Proxima Centauri, just over 4 light years), but what about the star that is the farthest away from Earth? That question can be a difficult one to answer, as no one actually knows, but there are some pretty great guesses.

First, we do know the farthest star that is in our Milky Way galaxy has to be around 95,000 light years away, as that is the furthest part of the galaxy from Earth. This means that while the light from Proxima Centauri would take four years to get to Earth, the light from this far-star would take 95,000 years.

As for the farthest star? That would depend on how far away the edge of the Universe is. As some believe the Universe to be infinite, then there would be no way to compute the figure. The farthest recorded star is approximately 25 billion light years away. This means that the light left that star 25 billion years ago, and is a factor that scientists use to predict the age of the Universe itself.

How Far Away are the Stars?

How Far Away are the Stars?

The Power of Parallax

The Farthest Star

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