AST352L--Spring 1998

Positional Corrections

This assignment is DUE on Wednesday, March 4.

The purpose of this assignment is to give you some practice in the kinds of star reductions we've been discussing.

1. Suppose a comet is 0.5 AU from the Earth at its closest approach. Suppose its right ascension is 5 hours and its declination is +50°. Suppose the latitude is +30° and the sidereal time is 10 hours. Calculate the geocentric parallax correction in right ascension and declination for the comet. Hint: Recall that this is very similar to the problem of refraction.
2. Suppose the right ascension of a star is 5 hours and its declination is +40°. Suppose the parallax of the star is 0.1". What is the amount of the parallax motion in right ascension and declination on September 15, 1998 at 0h UT? Hint: The right ascension, declination, and R (true geocentric distance) of the Sun are found in Table C of the ephemeris.
3. Given the same star, calculate the effect of annual aberration + nutation on the position of the star for the same date and time. Hint: The Day Numbers (A, B, C, D, E) that are needed for this calculation will be found in Table B of the ephemeris. Remember that the units of A, B, C and D are seconds of arc, but the units of E are seconds of time!
4. Given the same star, calculate the precession in right ascension and declination from 1995.0 to 2000.0. Hint: You may if you wish get better accuracy by calculating m and n for the time halfway between 1995 and 2000, although the error is not great if you just use the values for 2000.0. What is the error of doing this, approximately?