Shepherd Moon Prometheus from Cassini. Homework #2 will be posted soon. Several “out-of-class” activities will also be posted shortly. Email announcements.

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)

Noon

6:00 pm

(sunset)

Midnight

6:00 am

(sunrise)

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

Noon

6:00 pm

(sunset)

Midnight

6:00 am

(sunrise)

Western horizon

Eastern horizon

Zenith

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

Noon

6:00 pm

(sunset)

Midnight

6:00 am

(sunrise)

Western horizon

Eastern horizon

Zenith

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)

(1)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? In which direction does it rise?

setting

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.

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)

Seasons come from differing “dilutions” of the sunlight as a function of the sun's position in the sky.

Summer – sun high in skyWinter – 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?

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 severeLess severeThe same

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

More severeLess severeThe same

How often will a flag pole situated on the equator cast no shadow because the sun is directly overhead?

Everyday at noonOnly on the longest day of the yearTwice a yearOnly 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 noonOnly on the longest day of the yearTwice a year (on the equinoxes)

Only on the shortest day of the year