Eclipses September 12th, 2013

Transcription

1 Eclipses September 12th, 2013

2 Who was the favorite Star Wars character of the class? A) Obi-Wan B) Jar Jar C) Luke Skywalker D) Yoda

3 News! Dark matter New black holes

4 Review - Seasons Question 22: What are the two things most directly responsible for making summer warm and winter cold? Which of these has the strongest impact on the seasons? The least? A) Varying distance between Earth and Sun B) One hemisphere being slightly closer to the Sun than the other C) The Earth s axial tilt What axial tilt would cause the most extreme seasons? The least extreme?

5 Review from last time Every 27.3 days, the Moon completes one orbit around the Earth. Every 29.5 days, the Moon returns to its same position relative to the Sun in the sky. The 29.5 day cycle of illumination patterns are called the phases of the Moon. The rotation period of the Moon (its day ) is also 27.3 days. This is because the Moon is tidally locked, so we always see the same side. During a crescent Moon, we can see the rest of the Moon illuminated faintly due to Earth-shine.

6 Do you know your phases?!? First quarter Waxing crescent New Waxing gibbous Full Waning gibbous Third quarter Waning crescent

7 Question What phase is this? A) Waxing crescent Lets check out an animation. B) Waning Crescent C) New D) Waxing gibbous

8 Description: The figure below shows a top view of the Sun, Earth and six different positions (A - F) of the Moon during one orbit of Earth. Note that the distances shown for the Sun to Earth and for Earth to the Moon are not drawn to scale. Ranking Instructions: Rank (from greatest to least) the amount of the Moon s illuminated surface that is visible from Earth at each of the six positions (A F) shown. Ranking Order: Greatest Least Or, the amount of the Moon s illuminated surface visible from Earth is the same in all positions. (indicate with check mark). Carefully explain your reasoning for ranking this way:

9 Which position of the Moon best corresponds with the moon phase that shown at the upper right?

10 Tutorial: Cause of Moon Phases - p. 81 Work with a group of 2-3 people. Read the instructions and questions carefully Talk to each other and discuss your answers with each another Come to a consensus answer you both agree on If you get stuck or are not sure of your answer ask another group If you get really stuck or don t understand what the Lecture Tutorial is asking as one of us for help. We will discuss as a class when done.

11 What causes eclipses? The Earth and Moon cast shadows. When either passes through the other's shadow, we have an eclipse.

12 Types of eclipses A lunar eclipse occurs when the Earth is directly between the Sun and the Moon. The Earth s shadow falls on the Moon. A solar eclipse occurs when the Moon lies directly between the Sun and the Earth. The Moon s shadow falls on the Earth.

13 Question At which position is a Solar eclipse possible? At which position is a Lunar eclipse possible? B A C D

14 Question Which of these statements is correct: a) Both solar and lunar eclipses occur during new moon. b) Both solar and lunar eclipses occur during full moon. c) Solar eclipses occur during new moon, and lunar eclipses occur during full moon. d) Lunar eclipses occur during new moon, and solar eclipses occur during full moon.

15 Why don t we have an eclipse every month? If the Moon s orbital plane was exactly aligned with the ecliptic, we should have a solar eclipse every new moon, and a lunar eclipse every full moon. However, the Moon s orbital plane is off the ecliptic by 5 degrees. To have an eclipse, the new or full moon has to occur at one of the nodes of the Moon s orbit - the point where the orbit crosses the ecliptic.

16 Lunar eclipse When the Earth blocks the sunlight from hitting the Moon for several hours, occurs when the Moon is in the full phase. The Moon does not go completely dark - rather, it turns a reddish color, due to sunlight hitting the moon after going through the Earth s atmosphere. Its reflecting the light from all of the sunrises and sunsets going on at that time.

17 There are a few types of solar eclipses. The Moon s orbit isn t perfectly circular, so we only see a total eclipse when the new moon occurs at a node at the closest point it its orbit. An annular eclipse occurs when the Moon is at a farther point in its orbit, so its angular size is not large enough to block out the entire Sun. A partial eclipse occurs if you are at a spot on the Earth that does not get completely covered by the Moon s shadow.

18 Solar Eclipse Annular Eclipse Partial Eclipse Total Eclipse

19 Image of eclipse I took from Kyoto, Japan in May What kind of eclipse is this? A) Lunar B) Annular Solar C) Partial Solar D) Total Solar

20 Motions of the Planets Planets known in ancient times: Mercury difficult to see; always close to Sun in sky Venus very bright when visible; morning or evening "star" Mars noticeably red Jupiter very bright Saturn moderately bright

21 What was once so mysterious about planetary motion in our sky? Planets usually move slightly eastward from night to night relative to the stars. But sometimes they go westward relative to the stars for a few weeks: apparent retrograde motion.

22 We see apparent retrograde motion when we pass by a planet in its orbit. Animation

23 Explaining Apparent Retrograde Motion Easy for us to explain: occurs when we "lap" another planet (or when Mercury or Venus laps us). But very difficult to explain if you think that Earth is the center of the universe! In fact, ancients considered but rejected the correct explanation. More about this next time.

24 Homework Don t forget to turn in your sheet of paper! Read text: Section 3.1, 3.2, 3.3 Mastering Astronomy Homework #4 Due by 7:00am Tuesday 9/17/13.