When NU.nl writes about discoveries in space, you often read how many light-years away something is happening or is located. Readers on NUjij asked how those distances are calculated. That is complicated matter, but we will give you a small introduction.
Speed of light
- There is nothing in the universe that travels faster than light.
- The ‘top speed’ of light is just under 300,000 kilometers per second. Then it should not encounter ‘obstacles’ such as matter.
- The Danish astronomer Ole Rømer was the first to calculate the speed of light with reasonable success in 1676. He did this by comparing eclipses of Jupiter’s moons.
- Rømer arrived at 225,000 kilometers per second. Since then, scientists have been able to calculate the speed of light with increasing accuracy.
- A light year is the distance light can travel in 365.25 days (the duration of one year on Earth). That amounts to approximately 9.46 trillion kilometers (or 9,460,000,000,000 kilometers).
There are several ways to measure distances in space. That depends on how far something is from Earth. Astronomers call that the cosmic distance ladder (literally: the cosmic distance ladder). The further away the object, the more calculations are involved.
The distance of objects that are relatively close to the Earth is measured with laser beams. These are sent from Earth via satellites to an object (such as a planet or a moon) at the speed of light. It then measures how long it takes before it bounces back. So we look at how long it takes light to reach the object.
In this way, for example, the distance between us and the other planets in our solar system has been calculated with millimeter accuracy. But the universe is unimaginably large, and most objects are too far away to reach with a laser. It is easier to see stars because, unlike planets, they have their own light source.
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The further away, the more difficult it becomes
Because objects in space are always moving (just like the Earth itself), they are never in the same place in our starry sky for long. Based on these different positions, astronomers can mathematically calculate how far those stars are from us. This is called the parallax method. This is suitable for stars that are less than 100 light-years away from us.
For stars that are even further away, a fairly accurate estimate can be made based on the brightness. This is done by looking at the difference between the star at its brightest and the moment when the light diminishes. (That’s why stars appear to twinkle or flicker.) We then need to know how big the star is.
For stars that are more than a billion light-years away, we can only make an estimate. That’s because those objects are so far away that we have no way to accurately calculate the distance. Scientists can often make a well-founded estimate based on what we do know, but it really remains a guess.
Such an estimate is made even more difficult because the universe is expanding and the distance between objects is therefore increasing. Think of a balloon on which you draw two dots. The more you inflate the balloon, the greater the distance between the two dots becomes.
Proxima Centauri is the closest star to Earth after the Sun. The distance is 4.3 light years, or almost 40 trillion kilometers. Photo: NASA/ESA/Hubble
Looking back in time
Because we only see something when the light reaches us, we are actually looking back in time when we explore space. The further away something is, the longer it takes light to reach us. When you see a star or planet one light-year away, you are actually seeing what it looked like a year ago.
The furthest galaxies we can see are about 13.5 billion light-years away. This means that they existed 13.5 billion years ago, but the light is only now reaching us. We can only see them with very powerful telescopes, such as the Hubble telescope and the James Webb telescope.
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2024-03-02 15:23:52
#Stars #light #years #measure #Science
