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Astronomy 210
Spring 2011
Homework Set #1
Due in class: Friday, Jan. 28
Total Points: 50 points + 10 bonus points
Note:
Your homework solutions should be legible and include all calculations, diagrams, and explana
tions. The TA is not responsible for deciphering unreadable or illegible problem sets! Also, homework is
graded on the method of solution, not just the ﬁnal answer; you may not get any credit if you just state
the ﬁnal answer!
1.
SOHO and the Angular Speed of the Sun: a WebBased Exercise
.
(a)
[5 points]
Calculate the average angular speed of the Sun’s motion with respect to the celestial
sphere, as observed from Earth. Express your answer in units of degrees per day. You may
simplify the problem by assuming that the Earth’s orbit is perfectly circular.
(b)
[5 points]
Go to the website for the NASA space mission SOHO, which you can ﬁnd from the
course
links
page or the page for Lecture 3. Look at the realtime movie from the LASCO
C3 camera (the blue LASCO images); note that in each image, a circle indicates the location
and size of the Sun’s disk, which subtends an angle of about 0
.
5
◦
in diameter. Compare two or
more images showing the same star, and ﬁnd the Sun’s present angular speed with respect to
the celestial sphere. Show your work. Compare your answer to your estimate in part (a), and
comment on the agreement or lack thereof.
2. Viewed from the Moon, the Earth shows phases. This is in an image
of the Earth taken by the Apollo 8 astronauts. If the Earth appears
as shown to an observer on the Moon, then:
(a)
[5 points]
What phase does the Earth have? Is the Earth
waxing or waning for an observer on the Moon?
(b)
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 Spring '08
 Fields
 Astronomy

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