Celestial Coordinates PHYS390 (Astrophysics) Professor Lee Carkner Lecture 1

Basic Information  Professor Lee Carkner  Office Hours: MWF 1-2pm  Office: Hanson Science 208  You will need:  “An Introduction to Modern Astrophysics” by Carroll and Ostlie, Second Edition (2007)  Calculator  Pencil and Paper  Bring all to class each day

How the Class Works  Read the material before class  Do the homework and turn in at the start of class  Go to web page and download lecture notes   Web outline also gives readings and homework  Fill in blank areas of notes during class  Do the in-class activities  Give 2 presentations  One on a stellar object and one on an extra-galactic object (TBD)  Take the 3 exams and final

Grading  Two exams -- 30% (10% each)  In Class Activities -- 20%  Can drop (or miss) three  Homework -- 20%  Can drop (or miss) three  Homework due at the start of class  Can be handed in late for reduced credit, but not after the start of the next class  Two class presentations – 10% (5% each)  Final Exam (Partially Comprehensive) – 20%

Celestial Sphere   Zenith – overhead  Meridian – line running from north to south passing through zenith   Horizon system  Altitude (h) --  Azimuth (A) --  Only useful in one place at one time

Equatorial Coordinates  Declination (DEC or  ) –  Measured in (degrees:arcminutes:arcseconds)  Right Ascension (RA or  ) –  measured in (hours:minutes:seconds)  24 hours = 360 degrees  1 hour = 15 degrees

Motions of the Sky  All stars move around the North Celestial Pole   Once per year (~ 1 degree per day) due to annual motion   All 360 degrees of RA pass over your location in one day

The Sun   The larger DEC is for the Sun, the higher it is in the sky   Noon is when Sun’s RA is on meridian

Motion in the Sky   Transverse (in the plane of the sky, v  )   Radial (along the line of sight, v r )  Get from spectroscopy (Doppler shift)  Suppose we observe a star move a transverse distance  in the sky  d =  r  Where d and r are in the same linear units and  is in radians  (whole angle) r d Earth

Distance on the Celestial Sphere  Distance between two points =    How large  is depends on the value of   (  ) 2 = (  cos  ) 2 + (  ) 2  Convert everything to decimal degrees first

Parallax  Earth-Sun distance is 1 Astronomical Unit (AU)  1 AU = 1.5X10 11 m  tan p = 1 AU / d  Convert from radians to arcsec and use small angle approximation d = / p (units of AU)  d = 1/p (d in pc, p in arcsec)  1 pc = 3.26 lightyears

Parallax Issues  Very hard to measure  All stars have parallax angles less than 1 arcsec (1”)   From Earth need several years of measurement and can only go out to ~100 pc  Hipparcos space mission can get to 0.001” or 1000 pc 

Next Time  Read: 1.3, 3.1, 3.2, 3.6  Homework: 1.8, 1.10, 3.3, 3.15a, 3.15b  Download and print out lecture notes