Docstoc

Celestial Coordinates

Document Sample
Celestial Coordinates Powered By Docstoc
					     Visualizing Celestial Coordinate Systems with Starry Night Pro
              AST 337 Exercise 1: Due in Class on Moodle!

In this exercise you will explore some relations on the celestial sphere between the four
fundamental coordinate systems: Horizon (Local), Equatorial, Ecliptic and Galactic.

Getting Started. Start Starry Night Pro 6. It will open in the Horizon coordinate system
with a view toward the south, seen from Northampton, MA at the current time. The
zenith is overhead and the horizon rings the bottom of the screen.

Turn on the constellation boundaries and labels to orient yourself in the sky (Options tab
at left, Constellations drop-tab, Boundaries and Labels checkboxes checked). You can
use the viewing direction buttons on the Gaze section of the top toolbar to change your
view toward any of the four cardinal directions or the zenith. You can also reorient your
view with the grasping hand cursor in the main sky view area of the application window.
You can control time (!!!) via the Time and Date and Time Flow Rate sections on the left
side of the top toolbar.


VISUALIZING THE COORDINATE SYSTEMS

Activate the following guides: (Options tab at left, click the Guides drop-tab).
                                Guides: Alt-Az; select Meridian and Poles
                                Guides: Celestial: select Equator and Poles
                                Guides: Ecliptic: select The Ecliptic and Poles
                                Guides: Galactic: select Equator and Poles

1. Set the time to 8 pm this evening and face the south horizon. Find an object that has a
   Declination within a few degrees of 0. Describe what happens to each of the
   equatorial, local horizon, ecliptic and galactic coordinates of this object as you follow
   it from a rising position in the east to a setting position in the west. You will need to
   right click on the star to bring up its information window and look at the position
   menu.




2. Use the Zoom section on the right side of the top toolbar to expand the field of view
   to 120 degrees. Reset the time to 8 pm this evening, and face the south horizon. Turn
   off the daylight (Options tab at left, Local View drop-tab). Flow time forward at
   3000x normal time flow rate. In which of the above coordinate systems are the poles
   and equators invariant relative to the horizon? In which are they shifting?




AST337                                       1                                      12/04/11
3. Reset the time for 8 pm this evening. Find 3 objects at the same RA but with
   Declinations near 0, 45, and 80 degrees. This will be easier if you turn on the Grid
   option under Celestial Guides and display the grid with Fine spacing (left click the
   Celestial Guides name to get an options menu, and set the grid spacing drop-list to
   Fine.).

                        What is the hour angle of each of these objects when they are on
         the meridian?




                        What is the zenith angle of each of these objects when they are on
         the meridian?




                        What is the sidereal time when the objects are on the meridian?




                        What is the sidereal time when they are setting?




4.
     A. Find 2 objects with Declinations near 0 degrees that are separated by
        approximately 1 hr of Right Ascension from each other. Use the sextant cursor
        on the floating toolbar to measure the angular separation between them in decimal
        degrees.




     B. Find 2 objects with Declinations near 80 degrees that are separated by
        approximately 1 hr of Right Ascension from each other. Use the sextant cursor
        on the floating toolbar to measure the angular separation between them in decimal
        degrees. Compare this answer to the angular separation you found for the 2
        objects at DEC = 0 degrees in part A.


AST337                                        2                                     12/04/11
PRECESSION OF THE EQUINOXES

SETUP.
                     Options in TOP menu bar (not left tab bar): Orientation,
     Equatorial
                     Guides: Equatorial; select equator, poles, grid (fine)
                     Guides: Ecliptic: select equator and poles
                     Guides: Local and Galactic; deselect all options
                     Set the Field of View. Scroll down with the scroll wheel on the
     mouse (or just use the Zoom droplist in the upper right) until the full hemisphere
     of sky is visible. The grid of RA and DEC coordinates should be visible in one
     hemisphere of the sky, with the celestial equator and north and south celestial
     poles labeled.
                     Orient the Field of View. Click and drag the celestial equator and
     re-orient it so the equator bisects the view with a straight horizontal line and the
     north celestial pole is at the top.
                     Turn the planets on and off a few times to see that they are on the
     Ecliptic, and then turn them off to concentrate on the stars.


Time Evolution of coordinates. Use the time toolbar to:

1. Set Time Flow Rate for one day. Flow time forward for a few months. Is anything
   changing? Note what you see.



2. Set Time Flow Rate for 100 years and flow time forward for a few thousand years
   into the future --- reverse and go the other way until you're at a few thousand years
   BC. Is anything changing? Note what you see. Pay particular attention to the
   intersection of the celestial equator and the ecliptic.




3. What constellation is at the Vernal Equinox in 2000 AD? In 9000 AD? In 4000 BC?



4. Click and drag the North Ecliptic Pole (NEP) to the center of the view so the ecliptic
   equator rings the edge of the field. Flow time (100 yr interval) and watch the North
   Celestial Pole (NCP).




AST337                                       3                                      12/04/11
                      How does the NCP move relative to the North Ecliptic Pole?


                      Select the Angular Separation cursor (upper left tool bar) and
         measure the angular separation between the NEP and the NCP in 2000 AD and
         9000 AD. How do they compare?




                     What is the closest bright star to the NCP in 2000 AD? In 9000
         AD? In 4000 BC?




5. Select the Arrow cursor and point it to a bright star in the northern hemisphere.
   Double click on it to bring up the Information window and open the position menu
   for that star on the left.
                       Flow time (100 yr timestep) and watch the RA and DEC (J2000).
       Describe how they behave – to an accuracy of the nearest degree.




                       Flow time again, but now watch the Ecliptic coordinates for the
         same star. Describe how ecliptic longitude and latitude behave with time—to an
         accuracy of the nearest degree.




                        Flow time again, but now watch the Galactic coordinates for the
         same star. Describe how galactic longitude and latitude behave—to an accuracy
         of the nearest degree.




                      Compare the behavior of the equatorial, ecliptic, and galactic
         coordinates over time.




AST337                                       4                                      12/04/11
AST337   5   12/04/11
GALACTIC SYSTEM

 SETUP:
                   Guides: Galactic, Equatorial: select equator and poles
                   Guides: Ecliptic, Local: deselect all options
                   Grab the intersection of the galactic and celestial equator in the
     constellation of Sagittarius and center it in the field of view.


6. Select a field of view of 10 degrees from the Zoom droplist in the upper right toolbar
   and estimate the RA, DEC and Galactic Longitude and Latitude of the intersection
   point. Is this consistent with what you learned in class?




7. Return to a large field of view and center your view on the North Galactic Pole
   (NGP). Reset to a field of view of 10 degrees. Estimate the RA and DEC of the NGP.
   What constellation is it in?




8. Keep the 10 degree field of view on the NGP and reset the year to 1950. Record the
   RA and DEC of the NGP at this epoch.




AST337                                      6                                      12/04/11

				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:6
posted:12/4/2011
language:English
pages:6