Color-Color Diagrams

Color-color diagram

Astronomers study the temperatures of other stars using a graph called a color-color diagram. To make a color-color diagram, find two colors of a single star; for example, g-r and u-g. Then, make a graph with u-g on the x-axis and g-r on the y-axis. The star you found will plot into a point on the diagram. Find colors of several other stars and plot them on the same graph. The image at the right shows what a hypothetical color-color diagram might look like.

Explore 5. Use SkyServer’s Object Explorer to find the stars with the following object IDs in the SDSS database. Click on one of the Object IDs to open the Object Explorer. Write down each object’s ID and its magnitudes through SDSS’s five filters – they are the quantities u, g, r, i, and z in the second row on the right of the object’s image.

Record your data in this workbook.

Object ID

ra

dec


1237655130384631215

261.53089

27.8252


1237659326573642860

259.45503

26.13354


1237663783128006843

10.01782

-0.75441


1237663784211054802

31.16766

0.16188


1237648720144367845

151.18504

-0.92994


1237648702968430736

187.87919

-1.08739


1237648704042893633

189.45609

-0.29485


1237659896710562048

262.90111

57.66249


1237663783142359239

42.6732

-0.75043


1237648720689496156

169.97091

-0.53913


1237655503501722501

261.36639

27.56075


1237648720715186525

228.71353

-0.4823


1237648704582058231

194.75972

0.1813


1237648704049184997

203.88511

-0.32011


1237657191447527658

12.51927

0.39023


1237648721785717058

221.42084

0.32477

Launch Explore

Download workbook
Open a spreadsheet program such as Excel. Enter all the data you just collected. Find the g-r, r-i, u-g, and i-z colors of each of the 16 stars in the above list. Make a graph for the 16 stars with g-r on the x-axis and r-i on the y-axis.

If you need help with using Excel, see SkyServer’s Graphing and Analyzing Data tutorial.

Question 3. Where on your diagram are the hotter stars? Where are the cooler stars? How do you know?