How do astronomers calculate the distance to an object using trigonometry?

  • Context: High School 
  • Thread starter Thread starter Sock
  • Start date Start date
Click For Summary

Discussion Overview

The discussion revolves around the various methods astronomers use to calculate the distance to celestial objects, including the Sun. Participants explore different techniques such as parallax, the use of Cepheid variable stars, and redshift measurements, while also touching on the implications of general relativity.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants describe a basic method for measuring distance using parallax, comparing it to blinking one eye and then the other to observe the apparent movement of a nearby object.
  • Others mention the use of Cepheid variable stars, where the relationship between the star's brightness and its cycle can help determine distances to nearby galaxies.
  • Another method discussed involves measuring redshift to infer distances to very distant objects, suggesting that older objects exhibit greater redshift due to the expansion of the universe.
  • One participant raises the complexity of distance measurement if general relativity is considered, indicating that practical methods often rely on models of stellar brightness.
  • Laser timing is mentioned as a modern technique for measuring the distance to the Moon and other nearby objects.
  • A reference to a "Distance Ladder" is provided, indicating a structured approach to measuring astronomical distances.
  • One participant emphasizes the importance of trigonometry and angular size in these calculations, suggesting that these concepts are foundational in many trigonometry textbooks.

Areas of Agreement / Disagreement

Participants present multiple competing views and methods for calculating distances, with no consensus reached on a single approach. The discussion remains unresolved regarding the best or most accurate methods.

Contextual Notes

Some methods discussed depend on specific conditions, such as the proximity of objects for parallax measurements, and the reliance on models for stellar brightness introduces assumptions that may affect accuracy.

Sock
Messages
2
Reaction score
0
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.
 
Astronomy news on Phys.org
There are several ways.

First, for close objects stick your finger close to your face and blink your eyes, one on and one off and then the other on and the first one off. Note how far your finger moves. Now move your finger out as far as your arm will go and blink your eyes again. Note how far your finger moves. It didn't move as far did it? This same technique can be used in a grand scale with stars. When the Earth is on one side of its orbit, the location of the target star is noted against the background. Then on the other side of the orbit, it is noted again. Some simple trig and wola! The answer pops out. This is good for a few thousand light years.

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:

Distance Ladder
 
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.

http://en.wikipedia.org/wiki/Cosmic_distance_ladder

Has some information on the topic you are seeking.
 
Last edited:

Similar threads

High School How did ancient astronomers track changes in positions of stars?
  • · Replies 13 ·
Replies
13
Views
3K
High School Looking for a list of astronomy collaborations
  • · Replies 2 ·
Replies
2
Views
3K
High School Star like object travels in a zigzagging pattern relative to other stars
  • · Replies 49 ·
2
Replies
49
Views
12K
High School How to calculate Aphelion distance?
  • · Replies 14 ·
Replies
14
Views
2K
High School How well should Astronomers know General Relativity?
  • · Replies 1 ·
Replies
1
Views
2K
High School How do astronomers find the "parallax angle" of a star?
  • · Replies 25 ·
Replies
25
Views
5K
High School What is a parsec and how is it measured?
  • · Replies 7 ·
Replies
7
Views
3K
High School How long it takes the Earth to fall halfway to the Sun--ellipse method
  • · Replies 3 ·
Replies
3
Views
2K
High School Measuring distance between two stars in a binary system
  • · Replies 10 ·
Replies
10
Views
6K
High School Galaxy Database with distances from Earth
  • · Replies 12 ·
Replies
12
Views
3K