Shepherd Moon Prometheus from Cassini

Shepherd Moon Prometheus from Cassini

Homework #2 will be posted soon. Several “out-of-class” activities will also be posted shortly. Email announcements will be sent

Viewed from “north” (far above Earth’s north pole) 6:00 pm (sunset) Midnight Noon 6:00 am (sunrise)

Viewed from “north” (far above Earth’s north pole) 6:00 pm (sunset) Eastern horizon Zenith Midnight Noon Western horizon 6:00 am (sunrise)

Viewed from “north” (far above Earth’s north pole) 6:00 pm (sunset) Zenith Eastern horizon Western horizon Midnight Noon 6:00 am (sunrise)

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

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

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

GROUP ACTIVITY Assemble into groups of 4 or 5 students Select a moderator for the day Introduce yourselves & “schmooze” for a couple minutes Discuss why you are taking the class Put together a list of names of the group to turn in After a few minutes, we will have an exercise Schmooze: (from a Yiddish word meaning to chat) To converse idly or casually and in a friendly manner, especially in order to make a social connection. (2) The act or an instance of schmoozing.

The moderator is responsible for recording the consensus of the group to the questions posed. Moderator should also print the names of each group participant. At end of activity: 1. each participant should sign their names next to their printed name. 2. the finished group reports should be passed to the aisle to be picked up by Justin.

1. If you see a full moon rising on your eastern horizon, where would you look to see the sun? What is the time of day? 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? 4. 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?

If you see a full moon rising on your eastern horizon, where would you look to see the sun? What is the time of day? The full moon is located at position #5 in the figure (opposite the sun). The location on Earth where the full moon is on the eastern horizon is indicated by the arrow. At this location, it is 6:00 pm and the Sun is on the western horizon.

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? 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 Rising setting

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

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.

Orbital motion, inclination, and seasons

The Ecliptic & Celestial Equator are: are inclined by 23.5 degrees to each other intersect with at two points One of these points of intersection is where the sun is located on the celestial sphere at the moment Spring begins. This point is referred to as the “Vernal Equinox”

Motion of sun along ecliptic causes the sun’s altitude to change with season Farthest north on summer solstice Farthest south on winter solstice On celestial equator at equinoxes

Seasons do NOT occur due to varying distance from the sun We are actually closest to the sun in mid-Winter (northern hemisphere)

(See “Why Does the Flux of Sunlight Vary?” applet) Seasons come from differing “dilutions” of the sunlight as a function of the sun's position in the sky. Summer – sun high in sky Winter – sun low in sky (See “Why Does the Flux of Sunlight Vary?” applet) Compare with daily variations in temperature – hottest when sun at highest elevation (angle above the horizon).

The Cause of the Seasons

We can recognize solstices and equinoxes by Sun’s path across sky: Summer solstice: Highest path, rise and set at most extreme north of due east. Winter solstice: Lowest path, rise and set at most extreme south of due east. Equinoxes: Sun rises precisely due east and sets precisely due west.

Variation in the angle of Sunrise relative to “due east”

Seasonal Change in Sun’s Altitude The “Figure 8” shows Sun at same time each day over a year.

How would seasons change if the Earth's axis were perpendicular to its orbital plane?

There would be no seasons! How would seasons change if the Earth's axis were perpendicular to its orbital plane? There would be no seasons!

If the Earth's axis was tipped by 65o to the ecliptic plane, instead of 23.5o, summers and winters would be: More severe Less severe The same

If the Earth's axis was tipped by 65o to the ecliptic plane, instead of 23.5o, summers and winters would be: More severe Less severe The same

How often will a flag pole situated on the equator cast no shadow because the sun is directly overhead? Everyday at noon Only on the longest day of the year Twice a year Only on the shortest day of the year

How often will a flag pole situated on the equator cast no shadow because the sun is directly overhead? Everyday at noon Only on the longest day of the year Twice a year (on the equinoxes) Only on the shortest day of the year