[PHY 110] - Midterm Exam Guide - Ultimate 29 pages long Study Guide!

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UM
PHY 110
MIDTERM EXAM
STUDY GUIDE
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Motions of the Stars and Sun
1. Constellations and Asterisms
a. Constellations: one of 88 sections in the sky
i. All countries agree on these regions
ii. Utility of these regions is that if there is a particular object, you can get a
rough idea of where it is in the sky based on what region it is in
b. Asterisms:
2. using asterisms to navigate the sky
a. Polaris is the most important star (North Star)
b. It is very close to the spin axis, so it doesn’t look like it moves, so people use it as
a reference point
c. Some other famous constellations are the Big Dipper, the small dipper (the North
Star is part of this)
i. these are hard to see in cities because of light pollution because Polaris is
close to the horizon
d. people come up with different techniques to navigate through the night sky
e. the zodiacal constellations are famous because the sun passes through these
sectors during particular times of the year
3. all observed celestial motions can be described if our planet spins once each day, and
orbits around our Sun each year
a. from the Northern Hemisphere
i. The Sun, the Moon, and the constellations appear to rise in the East and
set in the West everyday and the constellations shift over the course of the
year
4. Daily motion and the Earth’s Rotation
a. Half of the Earth is always lit by the sun
b. The Earth spins, changing which part is lit by the sun
c. Stars are fixed, but the Earth are rotating underneath them, so you see different
constellations at different parts of the days
5. Yearly motion and the Earth’s Orbit
a. The Earth orbits the Sun in an almost-perfect circle
b. The side turned toward the Sun sees its light
c. The side turned away from the Sun sees a changing pattern of stars
d. If you look outside in the fall, you will see different constellations than if you
were to look outside in the winter.
6. Imagine a giant “celestial sphere” surrounding the Earth.
a. On the celestial pole, there is a north and south celestial pole that are defined by
an extension of the Earth’s spin axis
b. The region around the north celestial pole, the objects in it never set
c. You cant see all the constellations from one point on Earth
7. Motions of the Celestial Sphere
a. Objects near the North celestial pole seems to move in a circle, never setting
i. Circumpolar
b. Your latitude impacts how the stars appear to move
i. Northern latitude: stars appear to rise in the East
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ii. If you are in the North Pole, and you look up, the north celestial pole is
directly overhead, so the objects go in circles. Stars lower down are
running parallel to the horizon. All the objects are just going around in
circles parallel to the horizon over the course of time.
8. The Earth is tilted on its side
a. The Earth’s North Pole is always titled toward the North Star. This will not
change in your lifetime.
b. Earth does not change its tilt toward or away from the sun.
c. Seasons are due to this tilt
d. When the sun is directly over the equator, in the fall and spring, they are called
the Fall and Spring Equinoxes
9. The angle and hours of sunlight change during the year
a. The Northern Hemisphere’s Winter:
i. The North Pole cannot spin into the sunlight
ii. Light at the Tropic of Cancer is weak
b. The Northern Hemisphere’s Summer
i. The North Pole cannot spin out of the sunlight
ii. Light at the Tropic of Cancer is strong
10. The angle and hours of sunlight change during the year
a. The tilt of the Earth causes sunlight to hit the Earth more directly, and for a longer
period of time, during summer
b. When the sunlight hits the ground directly, it heats the ground more efficiently
c. When the sunlight hits the ground for longer periods of time
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