# Calculating distance to object?

• Sock
In summary, astronomers use various methods to calculate the distance to an object. The most common method is to use the sun as the object, and other methods are used for more distant objects.f

#### Sock

First I would like to say sorry for registering just to ask this question. I tried searching but its kind of a long search term. If there is another thread you know of just linking it is fine.

How do astronomers calculate the distance to an object? You can use the sun as the object. It can be a simple explanation, I just want to know the basics.

There are several ways.

Out further, they use Cepheid variable stars. These stars vary in a cycle and the length of the cycle is related to the brightness of the star. This can be used out to the near by galaxies.

Finally, how much the objects are red-shifted (which is dependent on how fast the objects are moving away from us) shows very distant distance. The older the object the greater the red-shift because the universe is expanding.

If general relativity is correct, then this is a difficult and subtle problem in theory.

In practice, distances are often calculated by comparing the amount of detected starlight with the total quantity of light which that type of star is thought to emit (same as guessing the distance of a car by the brightness of its headlights), but you're relying on the models for the different types of star.

Another important method is to look at the object from different positions, just like the parrallax between your two eyes let's you judge distances.

In the case of the moon (or separations on earth), these days we can simply time laser signals to measure its distance.

I think the distance to the sun was found using the length of the year and the weight of the earth.

Alright, thanks.

There are a lot of different methods that astronomers use to measure distances. Ned Wright has a nice summary:

One word: Trignometry
Two words: Trignometry, and Angular Size

These topics are covered in most Trig textbooks. It is explained in the first few chapters of: Barons Guide to Trignometry, which to this date is one of my favorite books.

The first one, Paralax, is used to determine the distance of an object if it is close to Earth, but at large distances, this technique does not work at large distances.