Star Color
Description
In this lab, students select red and blue stars from SDSS SkyServer and investigate their magnitudes
Procedure
In this lab, you will learn how to interpret magnitudes, and use them calculate a star's color. Magnitudes are the way astronomers measure a star's brightness. Because the cameras we use only record black and white images, we usually take images through a series of colored filters and compute a magnitude for each filter. In the SDSS the filters, and the magnitudes we measure through them, are called u, g, r, i, and z. To find a star's color we use the difference between two magnitudes--literally one magnitude subtracted from another. For example, if a particular star has a g magnitude of 15 and an r magnitude of 16, it's g-r color is 15 - 16 = -1. With five filters we can compute many colors for each star, which gives us a lot of information right away.
One of the most fundamental pieces of information we can get from this is--because of Wien's law--an indication of the object's temperature: hotter objects glow blue. Yes, usually we think that very hot objects glow red, but that's because very hot objects we have everyday experience with are the same temperature as very cool stars. Hot stars are much hotter than anything we normally experience.
In this lab, instead of answering all the questions in the Voyages page, you will construct a page to show how magnitudes relate to the brightnesses of stars, and how g-r values relate to their temperature. This video demonstrates many of the steps in the lab:
Instead of answering all the questions in the Voyages page, you will construct a page to answer the questions, "how do magnitudes work?" and "how do astronomer's measure color?" Although it's fine to work with someone on this assignment, each person in the class should find their own objects and create their own page.
Navigate to Voyages: Star Color.
As instructed, enter the RA and Dec of your special place in the SDSS, and add about 20 stars of varying colors and brightnesses to the SkyServer Notebook. Stars that aren't round or look "blown out", like in the picture below, don't count--they are too bright to have accurate magnitude measurements.
When you finish collecting your stars (for now--you can always add more later) click on "Show notes" to switch to the SkyServer Notebook. All of the stars' g and r magnitudes are listed, and you should can get thumbnail images by clicking on "Explore".
Create a page (or use the template below) that shows,
thumbnail images of five stars arranged from small magnitudes to large magnitudes, labelled with their r magnitude, and
thumbnail images of five stars (they can be different than the first five!) arranged from small g-r colors to large g-r colors, labelled with their g-r color.
A short explanation of how r magnitudes relate to brightness, and
A short explanation of how g-r colors relate to the star's temperature.
Scientists use posters to show their work at conferences, and in this course we'll use page-sized examples. I find it easiest to make these using presentation software, so I've included a template (see below) for PowerPoint. You're welcome to use any tool that can arrange text on a page, but please submit something Canvas can open (Microsoft Word, Powerpoint, or a pdf).
Suggested Rubric
