# Measuring Distance: How Far Are Stars?

• iGen3
In summary, the conversation discusses the importance of distance measures in astronomy and how they are used at different scales. Parallax is the most fundamental measure, but for larger distances, other methods such as using the brightness patterns of stars and doppler shift are used. There are also specific types of stars that can serve as accurate rulers for distance measurements. These methods are not model-dependent and have been used to confirm the Hubble flow and the LCDM model.
iGen3
Hello,

This may be a dumb question, but I by no means have any background in Astronomy, I'm pretty much regulated to Science Channel, History Channel, etc. I wish I could dive into all the fields on these forums but unfortunately I was not blessed with the gifts of understanding mathematics or physics beyond a basic level.

My question is how do you measure the distance of stars when it's light reaches us? I understand we can see that some planets are closer to us with depth perception, but what happens when we lose track of that depth perception?

I guess I'm just wondering how we know if something is 5 million light years from us vs. 7 million light years?

If I were to flash a light beam at you in pitch black from 10 feet vs. 100 feet, that light I assume would be smaller and dimmer from 100 feet, so you could assume that it was farther. But if I used a brigher flashlight at 100 ft and a much weaker, dimmer flashlight at 10 feet wouldn't it appear to be the same? If all stars vary in brightness (which I assumed is true) how do we standardize distance?

Thanks for the input.

This is a very good question. Distance measures are very important in astronomy and cosmology at a whole range of scales. To get you started have a look at the http://en.wikipedia.org/wiki/Distance_ladder" article.

The most fundamental distance measure is Parallax, which can be used on stars relatively close to us in our own galaxy only. This is the first distance measure to understand and pretty much everything else is calibrated in the end from parallax.

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iGen3 said:
If I were to flash a light beam at you in pitch black from 10 feet vs. 100 feet, that light I assume would be smaller and dimmer from 100 feet, so you could assume that it was farther. But if I used a brigher flashlight at 100 ft and a much weaker, dimmer flashlight at 10 feet wouldn't it appear to be the same? If all stars vary in brightness (which I assumed is true) how do we standardize distance?
Good thought. It turns out that stars all follow brightness patterns based on their size and age, which can be determined by their color. This provides a rough ruler for the measurement you suggest. Some very specific types of stars, such as certain types of variable stars and certain types of supernovas have very specific brightness, which makes them very accurate rulers for that type of measurement.

Over much longer distances, doppler shift is used, under the assumption that the Hubble's theory on expansion is valid (recession speed varies with distance).

Cepheids and SN Ia's are powerful [backed by solid physics] independent confirmations of the Hubble flow. They are not model dependent [cosmologically] as LCDM opponents sometimes suggest. In fact, they are the foundation for the LCDM model.

## What is the unit of measurement used to measure the distance of stars?

The unit of measurement used to measure the distance of stars is light years. A light year is the distance light travels in one year, which is approximately 9.46 trillion kilometers.

## How do scientists measure the distance of stars?

Scientists use various methods to measure the distance of stars, including parallax, spectroscopy, and standard candles. Parallax involves measuring the shift in an object's position when viewed from different angles. Spectroscopy involves analyzing the light emitted by stars to determine their distance. Standard candles are stars with known luminosities, which can be used to calculate distances.

## What is the closest star to Earth?

The closest star to Earth is the sun, which is approximately 93 million miles away. However, the closest star to Earth aside from the sun is Proxima Centauri, which is approximately 4.24 light years away.

## How far can scientists measure the distance of stars?

Currently, scientists can measure the distance of stars up to about 10 billion light years away. This is possible through the use of powerful telescopes and advanced technology.

## Why is measuring the distance of stars important?

Measuring the distance of stars is important for understanding the structure and size of the universe, as well as the evolution of stars and galaxies. It also helps scientists to determine the age of the universe and to make predictions about its future.

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