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The Cosmological Distance Ladder





Introduction

These pages grew out of a project for an introductory astronomy class. The goal was to provide an overview and brief tutorial on measuring astronomical distances. I found the subject so interesting, I decided to make it a permanent part of my site, and to continue developing the material with the hope that it would become more informative and more useful. To that end, I welcome your suggestions.

How far away is the sun from the earth?  If you ask, you will probably be told that the sun is roughly 93 million miles away.  But how do we know that?  It's not like you can just measure the distance with a tape measure, so how do we know?  And what about the distances to the stars and to other galaxies?  How do we know how far away these objects really are?

The answer is not necessarily a simple one, but it is a fascinating one.  It turns out there is no single method that is used to measure all these distances.  Different methods are used to determine the distances to different types of objects, but the methods don't stand alone; they build one upon the other, like the steps of a ladder.

The goal of this project is to show how each step of the cosmological distance ladder is established, and how one step builds upon the next.  There are two primary areas within this site, the Essential Math area, and the Measuring Distance area.  Measuring Distance is the heart of the site, taking one step by step through the process of determining the distances to the nearby objects in our solar system to the most remote objects in the furthest reaches of the universe.  Essential Math provides a tutorial/review of math concepts used throughout this site.  I will often reference pages in the Essential Math area when I think they will be helpful, but if you are having regular difficulty with calculations in the main thread of the Distance Ladder, you might spend a few minutes reviewing all the topics in the Essential Math area.  My hope is that this organization of the site will make the topic of cosmological distance measurements enjoyable and accessible to a wide audience, and to that end, I welcome any feedback you may have.  It is my desire to continuously make this site more informative, interesting, and accessible.

And with that... let's begin.