The Inferior Planets			       Name & ID;____________________________________

Date; ________________

Today we will use SkyMap Pro to ?observe? the positions of the planets Mercury and Venus relative to the position of the Sun. The necessary observations (in the ?real world?) would have to be made over an extended period of time. SkyMap Pro will let us ?speed up? time so that we can acquire all of the necessary observations. From these observations we will make scale drawings of the inner part of the solar system. 
terminology:(other important terms appear throughout the exercise in bold print) 
Elongation ? the angle between the earth-sun direction and the sun-planet direction.
 (i.e. the angle in the sky between the sun and a planet) 
Synodic Period ? a period relative to the sun; a period of time for a cyclic event 
Conjunction ? when two objects are seen to be in the same direction from earth.
 (i.e. they appear close together in the sky) 

I. Observations of elongations and brightness. 
Start at May 1, 2001 (18:00, 6pm DST). 
Find, center, and lock on the sun. 
Click on ?Scroll in RA/Dec? (button is near top left of screen). 
Make sure that the horizontal ?width? of your view is at least 100 degrees. 
Turn off everything but the Sun, the planets and the ecliptic.
  (even though we will only take data for Mercury and Venus),
Place the compass on the sky. 
Use a time step of 7 days to acquire data for Mercury, 28 days for Venus.
  (Take data for Venus each fourth interval for Mercury.) 
For each planet, generate a table with columns giving date, elongation, direction (E or W), and brightness
 (read magnitude from information window).  Leave room for a comment column. 
Continue to take data for a given planet until at least one complete cycle in the data has become apparent.
Use template #2 to keep track if needed. (This period is the synodic period of the planet.) 

II. Calculations & Questions 
Determine the dates of maximum western elongation and maximum eastern elongation for each of the planets. 
Determine the following time intervals: maximum eastern elongation to next maximum western elongation; maximum western elongation to next maximum eastern elongation. 
For each planet, are the two maximum elongations the same?
 If so what is the value?  If not, what is the average value? 

III. Incorporation of Your Data Into the Copernican Model 
Using Template #1, draw orbits for each planet consistent with the maximum elongations observed. 
Using this drawing, determine the radius of each orbit in units of the radius of the earth?s orbit (AU) shown
  (i.e., in Astronomical Units) 
Qualitatively, how do your answers to # II - 2 above relate to the orbits you have drawn? 
Can you express this relationship quantitatively? 
For each planet, determine the maximum and minimum distance from the earth (in AU?s).
 Using this information, find the ratio of maximum and minimum apparent angular diameters
 that you would expect to observe for each of these planets. 
Indicate the following planetary configurations on the diagram: inferior conjunction, greatest western elongation, superior conjunction, greatest eastern elongation. 

IV. Comparison with Telescopic Data 
In Sky Map Pro, reset the time to May 1, 2001. 
Using the search and zoom menu items, examine the disk of Mercury and lock onto it. Just as before, step forward in time by 7 day intervals, observing and recording any information you find important. In particular, pay attention to the maximum and minimum angular diameters of the planet throughout a cycle, as well as the relation between phase of the planet and the size of the disk. (The angular diameter can be read from the information box.) 
Repeat the same procedure for Venus (using a 28 day interval). 
Calculate the ratio of the maximum and minimum angular sizes for Mercury and Venus. Compare these values to those obtained from your scale drawings based on the Copernican model. 
Compare the phase of each planet to your expectations, given your experience with observing the Moon?s phases. What are the similarities, what are the differences ?
In Excel plot your data sets through at least one complete cycle, be sure to note above terms & features in your diagram..  (Data in Y-axis, Date & Time in X-axis)

Attachments: 
Template #1 
Template #2 
Table for recording Data 
Inferior_Planets_Copernican.doc    v 3/21/02  MjPepe	Printed on  03/24/02