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INST 2403
STUDY GUIDE for Midterm 1
SPRING 2014
List of Warm-Up Questions
Warm-up #1:
1) What is a "constellation"?
2) Explain the concept of the celestial sphere? (What is it? Why is it useful?)
3) Why is the Celestial North Pole directly "above" the earth's (geographic) north
pole?
Warm-up #2:
1) How is the view of the sky different for observers further north?
2) How do astronomers define "noon"?
3) Why is it impossible to tell the size of an object without knowing its distance
from the observer?
Warm-up #3:
Read Section 0.2 "Earth's Orbital Motion" and review previous Powerpoint slides to answer
these questions.
1. How do we know that there is a difference between a solar and a sidereal day, i.e. what do we
observe in the sky that lets us conclude that there is a difference?
2. Why do we prefer to measure time according to the solar (not the sidereal) day?
Warm-up #4:
1) Starting from the definition of "noon" in the lecture, define "midnight".
2) What do we observe (in the sky) that makes us conclude that there is not just diurnal motion,
but also (much slower) seasonal changes. List at least two observations.
Warm-up #5: Star Maps
1. Go to http://www.fourmilab.ch/yoursky/ and make a sky map for Westerville (40° N latitude,
83° W longitude) for 8pm of the day of the class, i.e. Wed Feb 12. Remember that 8pm means
20:00 EST, and that universal time (UT) is 5 hours ahead ( Next day, change date!). To
remove clutter from the sky map, uncheck the following boxes: Deep sky objects, Constellation
culminates at midnight?
Names, Constellation Boundaries, Star Names, Star Bayer/Flamsteed Codes. Set the Color
Scheme to “Black on white background”, print out the map and bring it to class.
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2. Why is the Celestial North Pole not at the center of this map?
3. Why are East and West permuted?
Warm-up #6: Seasonal Motion:
1. Daily motion of the sky is described well with the help of the Celestial Sphere model, with the
stars fixed to an invisible sphere that is turning around the Earth in a “day”. Is this “day” the
solar or the sidereal day?
2. The sun is not a fixed star, so why is it a good approximation to model the Sun to be fixed to
the Celestial Sphere to understand daily motion?
3. Due to the difference between the sidereal and the solar day, does the sun rise later or do the
stars rise earlier each day? Explain.
Warm-up #7: The Seasons
1. A common misconception about the reason for the seasons is the opinion that it’s hotter in the
summer because we are closer to the sun. Why can’t this be true?
2. It is true that when the earth axis happens to be pointing toward the sun (which means that the
geographic north pole is closer to the sun than the geographic south pole) in the northern
hemisphere’s summer, the northern hemisphere is closer to the sun by about one earth radius.
Argue that this position change does not make a noticeable difference by comparing the change
in distance due to the tilt with the distance of the earth(’s center) to the sun.
This is warm-up #8 on the motion and the phases of the moon.
Noticing the relative position of Sun, Earth and Moon during New Moon, when does the New
Moon rise (relative to sunrise)?
How do we know that the Moon orbits Earth and reflects the Sun's light?
Warm-up #9: based on Section 1.1. “Motion of the Planets” and on activity “Seasons” (starting
on p.93 in Lecture-Tutorial book, 3rd ed.).
1. Describe the motion of the planets with respect to the stars without using words like
“retrograde”, “prograde” etc. What pattern do you *see* in the sky, and why is this motion
strange, in particular, when compared to sun and moon?
2. Provide one piece of evidence to support the fact that the varying distance between the Sun
and Earth *cannot* account for the seasons.
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3.Which two things are most directly responsible for the cause of the seasons on Earth?
Warm-up #10: based on Section 0.4. “The Measurement of Distance”
1. Operationally describe the method of triangulation, i.e. explain what you would have to *do*
to measure a distance by this method.
2. Give an operational definition of “parallax”, i.e. describe what it is and how you measure it.
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