Proc. of the GHOU 2007 in Tokyo Authentic Data in the Classroom with the Sloan Digital Sky Survey M. Jordan Raddick* 1 Student engagement with the process of science is a proven part of high­quality science education, but authentic science activities can be difficult in astronomy because of the difficulty students have in taking data. This paper describes how the Sloan Digital Sky Survey (SDSS) contributes to solving this problem by making its entire dataset available to students and the public, free of charge. The survey's SkyServer website (http://skyserver.sdss.org) includes simple tools to browse and search the data, as well as projects that use the data to teach science. The dataset is also a great source of independent research projects for students. 1. Introduction for each star or galaxy, including magnitudes and object types. Images are available as FITS files. Movements in science education reform in the The survey also measures follow­up spectra for United States and around the world frequently cite stars, galaxies and quasars. These spectra run from engagement with the process of science as a key 3800 to 9200 Ångstroms, and have a resolution of component of effective science learning, and 1.8 Ångstroms per pixel. They are available as GIF scientific inquiry as an important part of images or FITS files, and detailed line widths and understanding science [1,2]. strengths are available for each spectral line. Laboratory activities in other science subjects frequently make use of student inquiry labs, in which 3. SkyServer students make their own observations, interpret the results, and draw conclusions. However, it can Since 2001, we have made the entire dataset of sometimes be difficult to include laboratory activities the SDSS available to the public through the in astronomy courses because of the difficulty and SkyServer web site (http://skyserver.sdss.org). The cost involved with students taking astronomical data. site currently provides access to images of more than One of many possible solutions to this problem is 90 million stars and 130 million galaxies, and more to have students conduct lab activities using existing than 800,000 spectra. data. The activities described here give students The site includes a series of tools to browse access to the entire dataset of the Sloan Digital Sky through and search the data. Two of the most often Survey. This complete access allows students to used are the Navigate tool, a Mapquest­like interface conduct open inquiry activities [3], in which students that allows students to pan and zoom through the sky, ask their own questions and find their own answers. and the Search Form, a tool that lets students request data from a series of drop­down menus. 2. The Sloan Digital Sky Survey Students can retrieve data from the Search Form and analyze it in any spreadsheet program, such as Excel The Sloan Digital Sky Survey (SDSS) is an effort or Graphical Analysis. to make a three­dimensional map of the night sky, for Filter name Symbol Wavelength (Å) the purpose of studying the large­scale structure of Ultraviolet u 3543 the universe. The details of the survey’s operations are discussed in the survey’s data release papers [4, Green g 4770 5]. Red r 6231 The Sloan Digital Sky Survey collects images Infrared (7625) i 7625 from a 2.5­meter telescope at Apache Point Infrared (9134) z 9134 Observatory, New Mexico, USA. The telescope uses five filters; the filters are shown in Table 1. The Table 1. The names, symbols, and wavelengths (in survey's image data includes about 300 types of data Ångstroms) of each of the Sloan Digital Sky Survey’s five imaging filters. 1 © 2007, Japan Association for Hands­On Universe *1 Department of Physics and Astronomy, Johns Hopkins University, USA, [email protected] Proc. of the GHOU 2007 in Tokyo The Explore tool gives students complete access The first step toward creating an H­R diagram is to the SDSS database for a single object, and allows to decide what data to use. In observational students to get FITS files to open in image astronomy, H­R diagrams are traditionally made with processing programs like Hands­On Universe. either spectral type or astronomical color on the x­axis, and apparent magnitude on the y­axis. 4. SkyServer in education Because the SDSS does not record spectral types of stars, this diagram will use color on the x­axis. A number of teachers at all levels have used Traditionally, diagrams are made with visual SkyServer activities in their science classrooms. The colors b and v; b­v goes on the y­axis and v goes on activities are all listed under the Projects link of the the x­axis. The SDSS uses a different filter set (Table main page. Projects come in the following 1), so we will use the nearest filters: g­r on the x­axis educational levels: and r on the y­axis. Creating an H­R diagram requires finding a large • Basic: appropriate for advanced, motivated group of stars at the same distance, to ensure that any middle school students, regular­level high observed magnitude differences between the stars are school students, and introductory college due to genuine luminosity differences rather than students differences in distances. The best way to do find stars • Advanced: appropriate for advanced, at the same distance is to look at a star cluster. Table motivated high school students and 2 shows a few star clusters in the parts of the sky higher­level college students observed by the Sloan Digital Sky Survey [6]. • Challenges: high­level independent research Positions are from the SIMBAD database [7] and projects for highly­motivated students radii are from [8] and [9]. NGC 2420 is an open • For Kids: projects for students with ages of cluster; the rest are globular clusters. This paper will about 8 to 14 use data for NGC 2420 and Palomar 5. • User Projects: projects independently To get the data, use the Search Form tool (Tools designed by teachers who use SkyServer in ­> Search ­> Search Form). Choose the appropriate their classrooms menus so that the tool reads: “Show me stars in the region around RA = Basic projects cover the following topics: a 114.596, dec = 21.573, radius = 5 arcmin). Please “scavenger hunt” through the sky, a search for return 1,000 objects with object IDs, RA and Dec, asteroids, classifying stars into spectral types, the magnitudes.” colors of stars, and classifying galaxies. Advanced When you click Generate Query, the tool will projects include these as well as the H­R diagram, sky surveys, quasars, and image processing. A currently available challenge asks students to find star­forming HII regions in SDSS data. A user project Cluster RA Dec Radius asks students to use ImageJ name (dec deg) (dec deg) (arcmin) (http://rsb.info.nih.gov/ij/), a free image processing NGC 2420 114.596 21.573 5 program, to find asteroids in the SDSS. NGC 2419 114.535 38.882 2 Palomar 3 151.379 0.0709 2 5. Sample Project: H­R Diagram Palomar 4 172.320 28.974 2 Palomar 5 229.013 ­0.123 3 As an example of the types of projects that Palomar 14 24.275 14.962 2 students can do using SkyServer, this paper will discuss how to make a Hertzsprung­Russell (H­R) Table 2. The names, positions, and radii of some Diagram using SDSS data. The project is available as globular clusters in the Sloan Digital Sky Survey. a lesson plan on the site under Projects ­> Advanced ­> H­R Diagram. 2 © 2007, Japan Association for Hands­On Universe Proc. of the GHOU 2007 in Tokyo generate the following SQL query: select top 1000 p.objid, p.ra, p.dec, p.u, p.g, p.r, p.i, p.z from star p, dbo.fgetNearByObjEq(114.596, 21.573, 5) n where p.objid=n.objid Change the “Output Format” to CSV and click “Submit Query to SkyServer.” You will get the results as a CSV file. Save the file to your computer and open it in a spreadsheet program. Then create a graph. (Note that to make a graph in Excel, you must first save the file as an .xls document.) The graph should have color (g­r) on the x­axis and magnitude (r) on the y­axis. It is also possible to transform the colors and magnitudes into the traditional UVBRI system [10]. Repeat the process to create another diagram for Palomar 5. Figure 1 shows the resulting H­R Diagrams. The main sequence is visible as the broad band of points running diagonally below r = 21 in both diagrams. The giant branch can be seen running diagonally Fig.1. A comparison of two Hertzsprung­Russell toward the top right of the diagrams, above r = 20. Diagrams, both from SDSS data obtained through The "turnoff point" where the main sequence SkyServer: one for the open cluster NGC 2420, and intersects with the giant branch can be used to find one for the globular cluster Palomar 5. Note the the relative ages of the two clusters. The cluster with different turnoff points, indicating that the clusters the redder turnoff point is the older cluster; Figure 1 have different ages. shows that Palomar 5 is older than NGC 2420, as expected. In principle, the turnoff points could also be used to estimate the absolute ages of the clusters, but the picture is complicated by the metallicities of • Milky Way Stars: how are stars in the disk the clusters. of the Milky Way similar to and different from stars far from the disk? 6.