The Universe - Add a Trendline
DR7 Projects
     - Solar System
     - Scavenger Hunt
     - The Universe
     - Asteroids
     - Types of Stars
     - Color
     - Galaxies
 Research Challenges
 For Kids
 User Activities
 Games and Contests
 Links to Others
The Universe
 Your Cosmic Address
 How Big is It?
 Expanding Universe
 How do We Know?
 Making the Diagram
 Diagram and Universe
 The Big Bang
 More Galaxies
 Research Challenges
 Your Results

Add a Trendline to the Diagram

Can you really draw a straight line through your data? When scientists try to figure out what data mean, they often talking about making a "model": in this case, the model you are using to relate magnitude to redshift is a straight line. Scientists often speak of the "fit" - how well the model fits the data. The fit can be described with a percentage that shows how close the points lie to the place where they should lie if the model were true. Because every experiment has some error and every observation has some uncertainty, the fit is never 100% accurate. Generally, astronomers consider a fit above 90% to show that the model probably really does describe the data.

Optional Exercise 1: Find the fit of a straight line model in your Hubble diagram. Excel (or another graphing program) can find the fit automatically using a "trendline." The program tries to find a straight line that passes as close to all the data points as possible, then measures how far each point falls from this straight line.

See SkyServer's Graphing and Analyzing Data tutorial to learn how to make a trendline in Excel.

Multiply the R-squared value by 100 to find the fit as a percentage. What is this number? Is a straight line a good fit to your data?