celestial coordinates phys390 (astrophysics) professor lee carkner lecture 1
Post on 20-Dec-2015
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TRANSCRIPT
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
http://helios.augustana.edu/~lc/ph390 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, vr) 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 = 1.5X1011 m
tan p = 1 AU / d Convert from radians to arcsec and use small angle approximation
d = 206265/ 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