Transcript Day_3
Astronomy 1020 Stellar Astronomy Spring_2016 Day-3 Snow-3, Education-0 Just in case … Course Announcements Look over the apsu.edu/astronomy site. The menus on the left hand side have links to: Professors and labs (i.e. the class information) The SmartWorks login page The textbook publisher information (e-material) The ClassAction website (labs, study material, simulations) Observing Nights (dates, report format and information) Other information that could be useful. Lab This Week • SDSS Scavenger Hunt What you need to know (the jargon): Magnitude = brightness • • • • Color = difference between magnitudes • • • • (smaller number is brighter) E.g. (u – g): Defined as: (short – long) wavelength Can be a negative value (bluer). RA, Dec are coordinates (think Long., & Lat.) Type: Star, Galaxy, or … Sky Surveys A sky survey is a large effort which “surveys” a large portion of the sky. These surveys provide a massive volume of data which may be used to study many objects at a time. The earliest “all-sky” survey was the Palomar Observatory Sky Survey (POSS) performed in the 1950s using photographic plates. This was a 2 filter survey – blue and red. But, photographic plates are not convenient for in-depth studies. A second epoch was performed in the 1980s using 3 filters (b,g,r). Combined, the two epochs (dates) yield a lot of motion data. Sloan Digital Sky Survey First modern survey: the Sloan Digital Sky Survey (SDSS). Started in the late 1990s and continues to the present. Northern hemisphere, modern (electronic) detectors. Many discoveries. This survey changed the paradigm in astronomy investigations. Now, you generally need to review what the survey data bases prior to beginning a new effort. Current surveys are the PanSTARRS, SkyMapper, and the Dark Energy Survey (DES). Planned are the Large Synoptic Survey Telescope (LSST). Space-based surveys are also being conducted. Sloan Digital Sky Survey Each of the modern surveys contains an “Education and Public Outreach (EPO)” component – generally required by the funding agencies. For this first lab, we will examine objects in the SDSS – data release 7 (DR-7). The survey is now up to DR-12. Links below so you can explore these survey data – all of the released data is free for the public to use (with proper citations). SDSS DR7 Information Sky Server Link SDSS DR12 release SDSS Site, telescope, camera drawing, and coverage area. SDSS Filters The SDSS filter system: Defined in Fukugita et al. 1996, Astron. J., 111, 1748 Magnitudes: u, g, r, i, z: Defined by Smith et al. 2002, Astron. J., 123, 2121 The SDSS-I spectrograph Some SDSS figures The First Lab In the first lab, you will explore the SDSS-DR7 data base (feel free to use DR-12 if you want – just let us know this) to see what a variety of celestial objects (stars, galaxies) look like; what solar system objects look like (asteroids); and what other things look like (meteors, airplanes, “ghosts” – these are caused by internal reflections from bright objects). There are some comets in the data base, but the major planets were avoided (too bright). You will look for examples using the guide and give us information about them (position, type, brightness). There are about 400,000,000 objects in the data base, so you will probably all have different answers. The purpose of this lab is to have fun and explore. The First Lab An example from the lab sheet: “A star with 15 < g < 18” – this means “look for a star whose g-band magnitude (brightness) is between 15 and 18. “A very red star with r - z > 1.5” – this means “find a red star whose color (r minus z) is greater than 1.5” In the next 3 slides, don’t let the “math” bother you, want won’t have to determine any of this. It is shown if some you have an interest to investigate further. Brightness = Magnitude F2 m2 m1 2.5 log F1 Note that this compares two stars. If a “zero point” is defined, then m 2.5 log F C where C is the zero point offset Color = Magnitude Difference m short m long color • Where the two magnitudes are of the same object at two different wavelengths (). • By definition a color is the (shorter – longer) value. • That is “bluer” – “redder” Celestial Coordinates - Equatorial (Right Ascention) is the angle around from the Vernal Equinox. Think LONGITUDE. d (Declination) is the angle above (+) or below (-) the celestial equator. Think LATITUDE. Types of Objects - Galaxies Types of Objects - Stars Types of Objects - Airplane DES image 505034 on 20151221, Observers: Smith & Balbinot