1. Chapter 1: The Cycles of the Sky
When you look up at the night sky you notice that after a few hours many of the stars and the moon has changed position. In fact all celestial objects move in the sky, nothing is stationary. Things only look stationary because sometimes it takes a long time for us to detect a change in motion and other times, we are moving with the object. for example, the Sun is moving in an orbit in the Milky Way galaxy, but since we are moving with it, we can’t really detect it. Also our view is not changed because it takes a long time for the Sun to move; maybe in the order of millions of years so it’s hard to detect these motions. In Astronomical times scales, it is not so slow, in fact the stars are traveling at high speeds several hundreds of kilometers per second. It’s just that the distances are so vast that it takes them a long time. and in terms of the human lifespan, it is a very long time indeed.
In this section, we will learn what these motions imply and the astronomical concepts that occur as a result of these motions in the sky.
This picture shows a time exposure of the stars, evidence that they move in the sky, but what is this motion due to? Do they really traverse in circles? This picture gives evidence that it is the Earth that is rotating.

2. Constellations
help astronomers
know the positions
of celestial
objects

3. Zodiac signs

4. These coordinates can be used to describe the position of stars locally
zenith
write on black board the definitions: zenith: the point directly above you in the sky. altitude, the angular position from the horizon. azimuth: This is the direction of a celestial object, measured clockwise around the observer's horizon from north. Use an object in the classroom as an example.

5. Altitude
The altitude of the object is its angular height from the horizon. The horizon by definition is where the ground meets the sky. By definition the horizon represents 0 degrees altitude and straight up above represents 90 degrees altitude.

6. Azimuth
The azimuth of the object is its angular distance with respect to North. If you are facing an object that is located due North, the azimuth is O degrees. If the object is located due West, the azimuth is 90 degrees. If the object is due South, it is 180 degrees azimuth, and if it is due East, it is 270 degrees azimuth.
In this slide, the object is located at approximately 60 degrees azimuth.

7. Angular distances of stars are measured in degrees
Can approximate the separation using your hands.

8. An imaginary Celestial Sphere surrounding Earth aids in navigating the sky
Bring globe to show RA and Dec, celestial equator, celestial north pole, celestial south pole, and RA and declination.

9. What is wrong with this cartoon?
What is wrong with this cartoon? There is no east or west stars, only the north star remains fixed at night because it points in the same line as the axis of rotation so you can only use this star to find the direction. All other stars move in the sky.
What is wrong with the second cartoon?
From the northern hemisphere, you can never see the south star. You would have to go to the Southern hemisphere. the sky looks completely different in the southern hemisphere. Orion would seem to be standing on his head. and you see a different part of the sky. that is why we need telescopes in both the northern and southern hemisphere.
Have students work in groups to answer this question.

10. Rotation vs. Revolution
Rotation represents the Earth’s spin on its axis.
This defines the length of 1 day.
1 day= 24hours
Revolution represents the Earth’s orbit around the Sun.
This defines the length of 1 year
1 year= days
In the previous section, we learned about the rotation of the Earth, which is the Earth’s spin on its axis. This is our definition of a day which is 24 hours because that is how long it takes for the Earth to spin. As the Earth is spinning, it is also orbitting around the Sun. The orbit of the Earth around the Sun is called revolution. It takes the Earth about days to orbit around the Sun. This is our concept of a year.
Do not get confused by rotation and revolution. It is incorrect to say that the Earth rotates around the Sun because rotation does not refer to its orbit but to its spin on its axis. You would have to say the Earth revolves around the Sun.
Interestingly since our calendar only has 365 days in the year, but the real time it takes the Earth to revolve around the Sun is days, every four years we need to add an extra day to be accurate because 4 times 0.25 = 1 extra day needed. This is why we have a leap year every 4 years and this day is usually added to the month of February.

11. Earth’s counter- clockwise rotation causes the Sun and stars to appear to move from East to West
If you stay up for several hours during the night and find a good, dark location, you would notice that the stars change their positions at night. But is this caused by the motion of the stars? No, this is caused by the rotation of the Earth. Stars to have their own motion, but they are so distant, that they don’t appear to move at all in the sky. The motion that you see, which you will notice will that the stars move from east to west. That is because the Earth rotates counterclockwise. The earth is turning on its axis and the stars are holding steady. Earth’s axis of rotation extends from the North pole through the South pole. If you extend the Earth’s axis beyond the north and south poles, they point to the celestial poles.
Since the Earth’s axis doesn’t change very much relative to the distance of the stars, the celestial poles doesn’t appear to move in the course of the night. From our latitude, we can see the north celestial pole, but not the southern celestial pole because that is way below our horizon. If you were on the southern hemisphere, you would see the southern celestial pole, not the northern celestial pole. We named the star Polaris, the “north star” or the “pole” star because it just happens to be along the same line as the north pole.
All other stars will appear to move at night. The direction of their motion depends upon the latitude that you are observing the night sky at. Talk about circumpolar stars: stars that don’t rise or set and altitude of North star is the same as the latitude you are looking at the sky from. At our latitude, what is the altitude and azimuth of the North star? USE globe for this also. As you move North star to higher latitudes, more circumpolar stars.

12. Motion of Stars at the North Pole
At the north or south poles, the poles will always be directly overhead; the stars would never rise or set. We’ll see what happens to the star trails in the planetarium.

13. Motion of Stars at the Equator
But at the equator, the celestial north and south poles would be located due north and south along the horizon, and the stars would rise in the eastern half of the sky, go straight up and set in the western half of the sky. If you expose the camera, you would see star trails almost perpendicular to the horizon.

14. Precession causes the position of the North Celestial Pole to change over a period of 26,000 years.
However, with time, Polaris will no longer be the north star because of a phenomenon called precession. As the Earth spins, its axis of rotation wobbles slightly like a giant top because of the gravitational pull of the Sun and the Moon. As a result of this precession, the axis traces out a large circle in the sky with a period of 26,000 years. So Polaris will eventually not be orientated in the direction of our axis. We will also see this demonstration in the planetarium. Talk about the ice age...etc.
As the Earth precesses, the north celestial pole slowly traces out a circle among the northern constellations. The total precession time is 26,000 years. At the present time, the north celestial pole is near the moderately bright star Polaris.
Precession is a slow circular motion of the Earth’s axis of rotation due to gravitational tug of moon and Sun
Use styrofoam ball to indicate precession. Talk about ice age and global changes.

15. UNLEARN

16. Common Misconception
The seasons occur due to the changing distance of the Earth from the Sun. When we are in our part of the orbit that is closer to the Sun, it is Summer, and when we are farther away from the Sun, it is winter This statement is NOT correct!

17. LEARN

18. Some Facts
When the Earth is physically closer to the Sun, it is winter time in the Northern Hemisphere, NOT summer
When the Earth is physically farther from the Sun, it is summer time in the Northern hemisphere, NOT winter
The Northern hemisphere and Southern hemisphere have opposite seasons from each other.
Thus, Earth’s seasons are NOT caused by its changing distance from the Sun!!!

19. Birds in the Northern Hemisphere fly south for the Winter...
That is when it is winter in the Northern Hemisphere, it is summer in the Southern Hemisphere!
...which means that the Earth’s revolution around the Sun can not be the only explanation for seasons!

20. The correct reason for the seasons:
the tilt of the Earth’s axis of rotation and
2) Earth’s revolution around the Sun
Contrary to popular belief, the seasons are not caused by the distance of the Earth to the Sun. Seems to be logical conclusion because if we are closer to the fire, we are hotter. Some people believe that during Summer time the Earth is closer to the Sun so it is hotter than winter. Actually, in the northern hemisphere, the Earth is farther from the sun in summer time than it is in the winter time. It makes northern hemisphere winters more mild. distance affects it, but not as much as tilt because difference between far position and near position is not too diffferent. Also if there was no tilt, both the northern hemisphere and the southern hemisphere would experience the same seasons and seasons would just depend upon the distance to the Sun.
This is not the main reason why we have seasons. The reason is because of the tilt of the Earth’s axis. The Earth gets more direct illumination for a longer period of time during the day during summertime.
Do seasons demo. One with just two styrofoam balls, the other with one large styrofoam ball and bright lightbulb.
Also you can see that when it is winter in the northern hemisphere, it is summer in the southern hemisphere and vice versa. In the North and South Poles; the Sun is continuously visible for 6 months of the year followed by 6 months of darkness. Tell Alaska story. That is why birds fly south for the winter.
Earth’s revolution around the Sun determines the length of a year (365 days)

21. Earth is tilted!

22. Summer solstice Equinox position Winter solstice
The tilt of the Earth’s axis causes the Sun to be higher in the sky at noon during the summer time than during winter. It also causes the Sun to rise and set in different directions and be up in the sky for different amounts of time.
The Sun is highest in the sky on the summer solstice; marks the beginning of summer in the Northern hemisphere. As the Sun moves southward, the amount of daylight decreases. The autumnal equinox marks the midpoint in the amount of heat deposited by the Sun onto the northern hemisphere and is the beginning of autumn. When the Sun reaches the the winter solstice, it is lowest on the northern sky and is above the horizon for the shortest amount of time. This is the beginning of winter.

23. The “altitude” of the Sun impacts how much energy is received on Earth.
Feel hotter if Sun is shining straight above you than at an angle. During summer time, Sun is at higher altitude than during winter time. Sun is highest in the sky at noon= warmest. Sun reaches highest position in the sky during summer time. Noon altitude for summer is higher than noon altitude for winter. Determines how directly the rays fall upon you. Longer days (more hours of sunlight during summer)
What causes this effect?

24. Concept Question What would be different if the Earth had no tilt?
Do phases of the moon activity.

26. UNLEARN

27. The phases of the Moon occurs because
Common Misconception
The phases of the Moon occurs because
as the Moon orbits the Earth, the Earth
casts a shadow on the Moon and blocks
some or all of the sunlight from reaching the
the Moon causing the amount of sunlight
reflecting off the Moon to change.
This statement is NOT correct!
Do phases of the moon activity.

28. LEARN

29. The correct reason for the phases of the Moon:
Although half of the Moon is always lit by the Sun, we can only see the side of the
Moon that is facing the Earth and only on that side does
the amount of illumination change
as the Moon orbits the Earth.
Probably all of you in the room know that the moon exhibits phases; But why does it exhibit the phases? does anyone know? this is the topic of one of your observing projects. It is because it revolves around the Earth. as it revolves around the Earth, the Sun illuminates different amounts of the moon. Here is a diagram of the Sun , the Earth, and the positions of the moon and the phases that it exhibits in one complete cycle. It takes about one month for the moon to complete its cycle of phases; that is where the definition of the month came from. The name month comes from the name “moon”.
So here, the moon is a new moon when it is in between the Earth and the Sun. Here the new moon is up in the sky during the day, but it’s hard to see it because the Sun is illuminating the back of the moon. During this time, you would not see the moon at night. As it rotates to this position, the moon gets more illuminated. You see a crescent shape. The waxing phases of the moon, is when the moon goes from less illumination to more illumination. Whereas the waning phases of the moon; the moon goes from being more illuminated to less illuminated.
When it is opposite from the Earth and the Sun, it is the full moon, the entire face gets illuminated because it is facing the Sun.
Do phases of the moon demo. Big styrofoam ball and lit light bulb.

30. Concept Question If the moon was between the Earth and the
Sun, what phase do you think it will be?
A) full
B) new
C) first quarter
D) third quarter
Do phases of the moon activity.

31. In other words ...
The Earth’s rotation on its axis determines the length of the day.
The moon’s orbit around the Earth determines the length of a month.
The Earth’s orbit around the Sun (revolution) determines the length of the year.

32. Lunar eclipses occur only when the Moon crosses the ecliptic during the full phase
What should the phase of the moon be when there is a lunar eclipse? The Earth blocks the light from the sun so that the moon should appear darker. So where should the Earth be in relation to the moon? What phase is this?
Line of nodes: when the Sun, moon, and Earth are located along the same line and plane as the ecliptic. So sometimes the moon is in the new or full phase, but because of the inclination of its orbit, it is below the plane of the ecliptic and an eclipse cannot occur.
During lunar eclipse, moon is in the full phase, Earth blocks the light from the Sun from reaching the moon.
During solar eclipses, moon is in the new phase, moon blocks the light from the sun from hitting the Earth.
Demo with small and large styrofoam spheres and a light bulb.

33. Lunar Eclipses Lunar eclipse only happens
when the moon travels through
the Earth’s shadow
eclipses only happen during full phase or new moon. Lunar eclipses happen during full moon.
Lunar eclipses happen when the Earth gets in between the Sun and the moon so that it block’s the Sun’s light and thus the light from the moon.
Why doesn’t a lunar eclipse happen every month?
Because of 5 deg tilt of the Earth with respect to the plane of the Earth’s orbit so the moon usually passes above or below the Earth’s shadow. This happens a few times a year. But even so, most of the time it is only a partial eclipse. It is not exactly along the same line of orbit. The moon must travel though the Earth’s shadow in order to be eclipsed. Also you have to be in a good angle on Earth, a lunar eclipse may happen, but you won’t be able to see it because you are on the other side of Earth when it is daytime. So even though it happens you have to be at the right part of the world.
But, total lunar eclipse only occurs when it travels through the darkest part of the Earth’s shadow. This part is called the Umbra. The other part which is not so dark, there is only a partial eclipse. This part is called the Penumbra.
All people can see a lunar eclipse.
Darkest part of the shadow =
Partial
Full
Intermediate part of the shadow =

34. Lunar Eclipses
Even during totality, the moon is not completely dark. This is because of the Earth’s atmosphere; as the Sun’s rays graze off the atmosphere; light gets diffracted, so we see this extra scattering of light during the eclipse on the moon; so instead of completely dark; it has a reddish tint to it.
Also lunar eclipses are useful because as it gets eclipsed; from finish to end; you can see the curvature of the Earth. This proved that the Earth is round, not flat. So you can calculate the diameter of the Earth during a lunar eclipse.
There will be a lunar eclipse in the US in 2004 on October 28th, but we can’t see it because it won’t be visible in the West coast.
Show Lunar eclipse in planetarium (October 28th 2004 US)
From start to finish the lunar eclipse can last for a few hours. If take exposure of moon, can get a picture of the curvature of the Earth and can calculate the diameter of the Earth by determining how long it takes the moon to go from here to here and how fast the moon orbits the Earth.
The moon is not completely dark during a total lunar eclipse

35. Lunar Eclipses
Even during totality, the moon is not completely dark. This is because of the Earth’s atmosphere; as the Sun’s rays graze off the atmosphere; light gets diffracted, so we see this extra scattering of light during the eclipse on the moon; so instead of completely dark; it has a reddish tint to it.
Also lunar eclipses are useful because as it gets eclipsed; from finish to end; you can see the curvature of the Earth. This proved that the Earth is round, not flat. So you can calculate the diameter of the Earth during a lunar eclipse.
There will be a lunar eclipse in the US in 2004 on October 28th, but we can’t see it because it won’t be visible in the West coast.
Show Lunar eclipse in planetarium (October 28th 2004 US)
From start to finish the lunar eclipse can last for a few hours. If take exposure of moon, can get a picture of the curvature of the Earth and can calculate the diameter of the Earth by determining how long it takes the moon to go from here to here and how fast the moon orbits the Earth.
The moon is not completely dark during a total lunar eclipse since
small amount of light is bent around the edge of the Earth’s atmosphere!!!

36. Solar eclipses occur only when the Moon crosses the ecliptic during the new phase
What should the phase of the moon be when there is a solar eclipse? The moon blocks the light from the sun so that the sun should appear darker. So where should the moon be in relation to the Earth? What phase is this?

37. Solar Eclipses The moon has the same angular size as the Sun!
Moon = 400 X smaller than
the Sun, but 400X closer
The moon has the same
angular size as the Sun!
A solar eclipse happens when the moon gets in between the Earth and the Sun and covers the Sun’s light. First of all why should this happen? If the moon is so much smaller than the Sun, why would it be able to cover the Sun’s light. Although the true size is smaller, it might be possible that if you place it at a closer distance, the apparent size will be bigger than something that is farther away right? So you might be holding an apple, but if the apple is close to you, it will appear bigger than a tree off in the distance.
Well, here is a happy coincidence; our moon is 400 times smaller than the Sun, but at the same time, it is 400 times closer than the Sun so in the sky, the moon is about the same size as the Sun. That means it subtends the same angle as the sun at that distance.
Again, there is only an eclipse if the Earth passes through the moon’s shadow.
This means that the moon must be on the part of its orbit that is exactly on the plane of the Earth’s orbit. Solar eclipses are much more rare to see than lunar eclipses because only a small part of the moon’s shadow falls on the Earth,
and unless you are in that small region, you will not see a total eclipse. Whereas for a lunar eclipse, the moon lies entirely within the Earth’s shadow so people can see the eclipse from on an entire hemisphere of the Earth. Also a total solar eclipse only occurs somewhere in the world about every 18 months.
This shadow only sweeps across the Earth in a band that is 300km wide; so you have to be in this narrow band to see it. Anywhere close to the band, you can only see a partial eclipse. Also a lot of times the Moon, Sun, and Earth are not exactly aligned so the umbra (which is the darkest part of the Earth’s shadow), never hits the Earth; only the intermediate part of the shadow; the penumbra.
Also totality only lasts for a few minutes because as the Earth rotates, the moon’s shadow falls in a different area of the Earth. Not all people can see a solar eclipse even when it happens.
Do demo of angular size. Bring styrofoam balls, one small, one large. Calculate radius of each and bring meter stick.

38. Solar Eclipse from Space

39. Solar Eclipse Annular Eclipse Partial Eclipse Total Eclipse
When the apparent size of the moon is too small to cover
the photosphere, yet the entire moon is silhouetted against the photosphere
The moon covers a smaller angle in the sky than the Sun
because it is on its part of its orbit that is relatively far
from the Earth.
An annulus (ring of photospheric light) remains visible

40. Solar Eclipses
Last annular eclipse visible in the U.S. was May 20, 2012!
Next total solar eclipse visible in the U.S. is August 21, 2017!
Show redshift 2 Movie on celestial sphere movie, time and seasons.