1. Homework #1 has been posted
It is due by Friday, Jan. 28, 4 p.m.
Answers can be submitted at any time

2. Look at Applets portion of class website
Look at Applets portion of class website. Applets linked to chapters 1, 2 and S1 are relevant to the current discussion

3. Understanding changes in the sky

4. What about the Sun’s apparent motion in the sky?
We have been examining the daily motion of the stars through the local sky due to the Earth’s rotation.
What about the Sun’s apparent motion in the sky?

5. The Earth makes a complete revolution about the Sun in one year (orbit shown in perspective; it is actually very close to being circular in shape)

6. The Sun moves east to west, full circuit around the sky, each “day” (result of Earth’s rotation)
Relative to the stars, the Sun moves slowly eastward each day (~ 1 degree/day): full circuit around Celestial Sphere in one “year” (result of Earth’s orbit)

7. The Sun moves east to west, full circuit around the sky, each “day” (diurnal motion - result of Earth’s rotation)
Relative to the stars, the Sun moves slowly eastward each day (~ 1 degree/day): full circuit around Celestial Sphere in one “year” (result of Earth’s orbit)
Path of Sun on Celestial Sphere due to Earth’s orbital motion is a great circle called the “Ecliptic” This is the intersection of the Earth’s orbital plane (Ecliptic plane) and the Celestial sphere.

8. Plane of the Celestial Equator
(blue) and the
Ecliptic Plane
(yellow)
are inclined by 23 ½ degrees to each other

9. Today we divide the celestial sphere into 88 regions, referred to as
Today we divide the celestial sphere into 88 regions, referred to as constellations (in a manner similar to dividing the Earth’s surface into countries).

10. The constellations along the ecliptic are called the zodiac (see applet)

11. Two measures of the Earth’s rotational period
Solar day: Rotational period relative to the sun (successive sun crossings of the meridian). This is the common measure of the day.
Sidereal Day: Rotational period relative to the stars (successive star crossings of the meridian, 23h 56m)

12. The Vernal Equinox serves as the origin for measuring Right Ascension (R.A. = celestial longitude)

13. We tell time by the location of the Sun in the sky, relative to our meridian

14. Rotation direction of the Earth
Plane of observer’s meridian
Location of observer
Location of observer
Eastern horizon
Western horizon
Rotation direction of the Earth
The Earth, as seen from above the North Pole
North Pole
The meridian divides the sky into eastern and western halves

15. The meridian is defined by the location of the observer on the Earth
Planes of local meridians at different locations
The meridian is defined by the location of the observer on the Earth
North Pole

16. Planes of local meridians at different locations
The horizon is also defined by the location of the observer on the Earth
North Pole
Planes defining local horizon

17. The meridian is defined by the location of the observer on the Earth
Planes of local meridians at different locations
The meridian is defined by the location of the observer on the Earth
North Pole
The time of day is determined by the position of the sun relative to the observer’s meridian.

18. Time of day determined by the position of sun relative to the observer’s meridian.
Noon: Sun on meridian
Midnight: Sun 180 degrees from meridian
6 pm: Sun 90 degrees west of meridian
6 am: Sun 90 degrees east of meridian

19. (displayed clock times are approximate)
(small arrows “ “ point toward local meridian)
Sunset(6 pm)
3 pm
9 pm
Midnight
Noon
Earth
3 am
9 am
Sunrise (6 am)

20. Where is the local time noon?
blue
red
orange
yellow
Earth
green

21. Where is the local time noon?
blue
red
orange
yellow
Earth
green

22. Where is the sun setting?
blue
red
orange
yellow
Earth
green

23. Where is the sun setting?
blue
red
orange
yellow
Earth
green

24. Where is it midnight?
blue
red
orange
yellow
Earth
green

25. Where is it midnight?
blue
red
orange
yellow
Earth
green

26. Where is the local time 6 am (sunrise)?
blue
red
orange
yellow
Earth
green

27. Where is the local time 6 am (sunrise)?
blue
red
orange
yellow
Earth
green

28. Time is determined by where you are on a sphere, relative to where the sun is located.
What if we view a sphere from different vantage points not on the sphere?

30. Motions and Phases of the Moon The Moon’s orbit around the Earth

31. Two measures of the Moon’s orbital period
Synodic Period: Period relative to the sun (approx. 29 ½ days) – determines phases of the moon
Sidereal Period: orbital period relative to the stars (approx days)

32. Lunar Rotation: Prograde rotation – rotation is in same sense as orbit
Synchronous – rotation period is the same as its orbit period: same side of Moon always faces Earth
No rotation - never seen in astronomical bodies

33. The Lunar Phases is determined by our viewing orientation of the Moon relative to its sunlit half. Thus the relative positions of the Sun, Earth, and Moon determine the phase.

34. An interactive tool and tutorial in Time, the phases of the Moon, and the location in the sky where the Moon is located at different times and phases:
LUNAR PHASES WEB TOOL
Visit this site and become familiar with its contents

37. Viewed from “north” (far above Earth’s north pole)

38. See also http://www. valdosta. edu/~cbarnbau/astro_demos/frameset_moon

40. 1. Suppose you lived on the Moon
1. Suppose you lived on the Moon. If the Moon is in its first quarter phase, what would the phase of the Earth be as seen from the Moon?
2. What time (on Earth) does the first quarter moon rise? Set? In which direction does it rise?
3. At sunrise (in Bloomington) you happen to notice that the Moon is on your meridian. What is its phase?

41. Suppose you lived on the Moon
Suppose you lived on the Moon. If the Moon is in its first quarter phase, what would the phase of the Earth be as seen from the Moon?”

42. Suppose you lived on the Moon.
If the Moon is in its first quarter phase, what would the phase of the Earth be as seen from the Moon?”
First quarter Moon will occur at the position shown. Realizing that the left side of the Earth (as shown in the figure) is in shadow, the Earth as seen from the Moon will appear in its third quarter.

43. What time (on Earth) does the first quarter moon rise. Set
What time (on Earth) does the first quarter moon rise? Set? In which direction does it rise?
setting

44. The first quarter moon is located at position #3 in the figure.
What time (on Earth) does the first quarter moon rise? Set? In which direction does it rise?
The first quarter moon is located at position #3 in the figure.
It will be on the eastern horizon on the earth when it rises and the western horizon when it sets (recall that the Earth is rotating counter-clockwise).These positions are shown on the diagram.
setting

45. At sunrise (in Bloomington) you happen to notice that the Moon is on your meridian. What is its phase?
Sun is rising here

46. At sunrise (in Bloomington) you happen to notice that the Moon is on your meridian. What is its phase?
Sunrise is occurring at position 7.
If the moon is on your meridian, it must be at location 7.
This corresponds to 3rd quarter.
Sun is rising here

47. Understanding the visible sky and motions within the sky is easily accomplished
using the concept of Celestial Sphere
understanding the rotational & orbital motions of the Earth