Download 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