ASTR302 Homework #1
(due in class on Wednesday, January 16, 2008)
1)
Complete and submit LT Seasonal Stars (pp 79 of Lecture Tutorial book)
2)
Mars rotates 668 times per Martian year and it both rotates and revolves in the same
direction.
The length of a mean solar day on Mars is 24:39:35 (HH:MM:SS).
What is
the length of a sidereal day on Mars in HH:MM:SS?
Include both a diagram and a
written explanation in your solution.
We can use the fact that Mars rotates 668 times per year to determine
how many degrees Mars travels around the Sun per rotation:
rotation
rotations
/
539
.
0
668
360
°
=
°
Thus, after one sidereal rotation (360
°
), Mars must rotate an addition
0.539 degrees in order to complete a “solar day” which takes 24h39m35s
(or 88775 seconds).
We use this to determine how quickly Mars rotates.
sec
/
00406
.
0
sec
88775
539
.
360
sec
88775
1
*
/
539
.
0
360
°
=
°
=
°
+
°
rotation
rotation
This can be used to determine how long it will take Mars to rotate through
one sidereal day (or 360
°
.
s
m
h
22
37
24
sec
88642
00406
.
0
sec
1
*
360
=
=
°
°
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What is the approximate sidereal time when it is noon apparent solar time on the
following days: (explain each answer)
i. the first day of spring (March 21)
ii. the first day of summer (June 21)
iii. April 21
For all three problems, we need to know the location of the sun relative to the
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 Winter '08
 Keller
 Orion Nebula, Polaris, Sidereal time

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