Converting Arcseconds to Parsecs

Instructor: Yuanxin (Amy) Yang Alcocer

Amy has a master's degree in secondary education and has taught math at a public charter high school.

After reading this lesson, you'll learn how to convert your arcseconds to parsecs using a very simple process. Learn what the steps are and then see it in action.

The Steps

Arcseconds and parsecs are both used to measure distances in the universe. An arcsecond is a way of measuring the distances between objects in space based on observations from Earth while a parsec tells you how far away the object is from the Earth. You can convert between these two measurements because one parsec is equal to the parallax of one arcsecond. Parallax is when objects seem to move when you change locations. For example, say there are two cars parked in the street. From your house, you see that the green car is parked behind the red car. Well, if you went across the street to your friend's house, you will now see that the red car is parked behind the green car. Because your location has changed, it seems like the cars have also changed locations. This change in location is what astronomers see as the earth travels around the sun. The other planets and stars seem to change position as the earth travels around the sun. By noting this change in location in arcseconds, astronomers are able to calculate the distance away in parsecs.

It's not very hard at all to convert your arcseconds to parsecs. Say you have observed a parallax of 2 arcseconds for one star in the universe. To convert this to parsecs, you'll follow these steps.

Step 1: Convert to arcseconds if necessary.

Sometimes, you'll be given a parallax of milliarcseconds instead of arcseconds. If this is the case, you'll need to convert it into arcseconds. Since there are 1,000 milliarcseconds in 1 arcsecond, to convert your milliarcseconds to arcseconds, you'll divide by 1,000. So, 25 milliarcseconds is equal to 25 milliarcseconds / 1,000 = 0.025 arcseconds.

In the above example, we were given 2 arcseconds. Your 2 arcseconds is already in arcseconds, so you don't need to make any conversions here.

Step 2: Divide 1 by your arcseconds.

This is actually the final step that you have to do. You'll take the number 1 and divide it by your arcseconds. This gives you your parsecs.

So, your 2 arcseconds is equal to 1 / 2 arcseconds = 0.5 parsecs.

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