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

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

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