1. Astronomy by eye: Motions in the Sky
The Celestial Sphere
Intrinsic and Reflex Motion
Reflex Motion from Earth’s Rotation

2. Recap Astronomy and science Science is data driven
Models, theories and the scientific process
Science in society:
Importance of science in society
judging “quality” of scientic discussion
pseudoscience

3. Astrology What is astrology?
Astrology is something which purports that the position of the planets and the stars at the time of your birth determines the course of your future life
Is wondering about this idea in the first place non-scientific?
Yes No
Given the hypothesis of astrology, what would be the next step in analyzing it scientifically?

4. Observations/data relevant to astrology
There is no evidence that astrology actually works.
Note that the predictions of astrology may work sometimes; almost certainly, some of these predictions will work sometimes by chance! Certainly, astrology is not a fully deterministic theory; if it claimed to be so, even a single example of a failed astrological prediction would invalidate the theory.
Other flaw: not all astrologers even predict the same thing!
Even as a statistical theory, astrology fails to be validated by experiment.
A link to some studies on the predictions of astrology:

5. Theoretical basis for astrology?
Is it surprising that astrology doesn’t work? Are there successful scientific theories that make predictions about astrology?
Current theoretical understanding, which has been well supported by observation, says there are four basic forces in nature:
Gravity
Electromagnetic force
Strong force
Weak force
When quantitatively calculated, the force arising from planets and stars at the moment of your birth from any of these sources is much smaller than the force contribution from many other objects! So in no way would it be expected that the position of astronomical objects would have an impact

6. Part II Astronomy by eye : motions in the sky

7. Observing the night sky
How many objects were you able to identify in the sky: Saturn, Venus, North Star, Vega, Arcturus, others? 1 2 3
4 or more

8. Observing the night sky
Which best describes your observations?
I was unable to detect any motion of any objects across the sky
I was able to detect the motion of objects, but was unable to judge whether they were all moving at the same rate
I was able to detect the motion of objects, and found they all moved at the same rate
I was able to detect the motion of objects, and found that they moved at different rates
I was unable to measure anything or did not complete the assignment

9. Observing the night sky
Which best describes the observations?
The data suggest there is no motion of any objects across the sky
The data suggest that objects move, but we are unable to judge whether they were all moving at the same rate
The data suggest that all obects move at the same rate
The data suggest that objects moved at different rates
We cannot understand these data
Data obtained from measurements taken two hours apart.
Note the “wrap” of the map

10. Testing the model
Observing that stars move across the sky during the course of a night
Proves that the Earth rotates on its axis
Proves that the Earth revolves around the Sun
Proves that the Sun revolves around the Earth
Rejects the model that the Sun is the only object that is moving in space
Rejects the model that the Earth rotates on its axis

11. Class Section II: Motions in the Sky: Astronomy by Eye
What astronomical objects do we see with our naked eyes?
Sun
Moon
Planets
Nearby stars
Many of these are relevant for everyday life: motion of the Sun, phases of the Moon, etc.
Want you to come out of astronomy class understanding “everyday” astronomy!

12. Positions in the Sky
How can we describe where astronomical objects are located in the sky?
Since we can’t immediately infer distances of astronomical objects by just looking at them, all we can describe is what direction they are in
Imagine that stars can be described by their location on an imaginary sphere centered on the earth: the celestial sphere
On this sphere, we can describe locations the way we describe locations on the surface of the Earth, which is also a sphere
Astronomical longitude (right ascension) and latitude (declination)
From a given location on Earth, you can’t see the whole sphere, only the half of it that is above the horizon
Note that local coordinates that we have been using (azimuth / altitude) depend on where you are located on earth, and thus aren’t ideal for a coordinate system that everybody can refer to)

13. Constellations
We notice patterns of stars that are seen in different directions and call these constellations
Different cultures have come up with different constellations
Constellations are nice to know for finding your way around the sky, but are not really associated “astronomically”, because stars in a given constellation may be at very different distances!
Constellations are not usually clusters! (although sometimes they are!)
viewed from some other location in the Galaxy, constellations would be totally different!

14. What’s the declination (astronomical latitude) of …..?
A. around -70o S
B. around -20o S
C. around 0o
D. around 30o N
E. around 70o N

15. Motions of astronomical objects
Looking at astronomical objects, one quickly recognizes that they move across the sky
Apparent motion of objects can come from
intrinsic motion of the object: motion that appears because object itself is moving
Reflex motion: motion that appears because Earth is moving
For distant objects (stars), essentially all observed motion comes from reflex motion
Although stars definitely have intrinsic motion, they are so far away that we don’t see much apparent motion over the course of our lifetimes
As we will discuss later, we can measure radial motion of objects, but this doesn’t give apparent sideways motion

16. Reflex motion from Earth’s rotation
Earth spins around an imaginary axis, once per day
As a result, the celestial sphere appears to spin around the Earth
Stars that happen to be located in the direction of the Earth’s rotation axis appear to stand still
There is such a star above the North pole : Polaris, the North Star
There is NOT such a star above the South pole!
Stars near these directions travel in small circles around the sky
Stars far from these directions travel in large circles around the sky

17. What’s the best description of Earth’s rotation and motion of stars?
A. stars appear to move E to W because the Earth rotates from E to W
B. stars appear to move E to W because the Earth rotates from W to E
C. stars appear to move W to E because the Earth rotates from E to W
D. stars appear move W to E because the Earth rotations from W to E
E. stars don’t appear to move

18. Reflex motion from Earth’s rotation
Depending on where you live on Earth, you might be able to see objects move around their full circles, none of the circles, or part of their circles
You can only see stars when they are above the horizon
Of course, you can’t easily see the stars when the Sun is up, because the light from the Sun overwhelms the light from the stars, but they are still there during the daytime

19. View from the North Pole
Half the stars, all the time!

20. View from the equator
All the stars, half the time!

21. View from Las Cruces
Some stars all the time, some stars some of the time, some stars not at all!

22. An animation

23. Imagine you go out at noon, and you look due south and find the Sun
Imagine you go out at noon, and you look due south and find the Sun. If you were to wait six hours and then look for the Sun
A. you find that it is still due south
B. you would find that it has moved to the east because of the Earth's rotation
C. you would find that it has moved to the west because of the Earth's rotation
D. you would find that it has moved to the west because the Earth has moved partway in its orbit around the Sun

24. Imagine you go out at midnight, and you look due south and find the constellation Scorpio. If you were to wait six hours and then look for Scorpio,
A. you find that it is still due south
B. you would find that it has moved to the east because of the Earth's rotation
C. you would find that it has moved to the west because of the Earth's rotation
D. you would find that the stars in Scorpio are no longer in the same place in the sky because they have moved in their orbits around the center of the Milky Way

25. If you could see stars during the day, this is what the sky would look like at noon on a given day. The Sun is near the stars of the constellation Gemini. Near which constellation would you expect the Sun to be located at sunset?
A. Leo
B. Cancer
C. Gemini
D. Taurus
E. Pisces

26. A different perspective
Imagine you lived in Santiago, Chile, which, at 33 degrees south latitude is about as far below the equator as Las Cruces is above it. From Santiago, the Sun would
A. appear to move left to right across the sky, which is E to W
B. appear to move right to left across the sky, which is E to W
C. appear to move left to right across the sky, which is W to E
D. appear to move right to left across the sky, which is W to E
E. never rise or set

27. Telling time from the stars
Since the stars revolve once around the sky for each rotation of the Earth, their motions can be used to tell time at night: they move one full circle around the sky each day

28. This is a real picture taken by putting a camera on a tripod pointed in the direction of the North celestial pole, and leaving the shutter open. How long did it take to make this picture?
A. about an hour
B. about 2 hours
C. about 5 hours
D. about 11 hours

29. Can you do it? Point to the celestial North Pole
Point to the celestial equator
Can you do this if you were at the Earth’s North pole? The Earth’s equator?

30. To do Canvas homework on science
Look up on web: celestial sphere, daily motion of the stars and Sun, yearly motion of the Sun