1
Lecture 3: Announcements
Homework:
-HW0 and HW1 are due NEXT thursday.
-If by wednesday you are still trying to get access to M.A. let me know.
-Class code is AY2DURAN2013
My office hours:
Thursdays 2:00-3:30 pm, starting at ISB 201 (my office), check if there is a sign
on the door. We might have gone to ISB 126.
Tutoring services:
You can sign up at https://eop.sa.ucsc.edu/OTSS/tutorsignup/ beginning Jan 16th
at 10:00am.
Enrollment issues:
If you are still trying to enroll in the class, talk to me ASAP!
Class website:
www.ucolick.org/~mfduran/AY2
2
Today’s lecture
•
•
•
•
Stellar Parallax (recap)
The Moon
Eclipses
Motion of planets as a case study for the scientific method.
3
Stellar Parallax (from last class)
•
This is how we know that it is the Earth that orbits the Sun (and not the
other way around)
•
Parallax is the effect that nearby stars appear to move back and forth on 1
year timescales.
If the Earth orbits the sun, you get
background objects
this effect.
If the Sun orbits the Earth, you
don’t get it.
•
We can use the distance-angular
size relation to find the distance
to stars using parallax.
thumb
(extended)
left eye
right eye
4
We are in constant movement...
... we are just used to it and do not notice.
1. The Earth spins on its own axis (and on a tilt!)
2. The Earth orbits the Sun (parallax)
There are 2 more ways we move through space
2 more ways? how?
Ask the person next to you
5
We are in constant movement...
3. The Sun orbits in the Milky Way
(and the Earth follows the Sun)
Remember that this is an artist rendition of the
Milky Way, we cannot take a picture of it
6
We are in constant movement...
4. Our Milky Way is moving relative to the other galaxies
Space itself is expanding
The space between things is increasing!
7
The Moon
What can we say about the Moon, just from looking at it?
•
Is round
•
It shines
•
It rises in the east, sets in the west
•
It changes its appearance
www.hrastro.com
8
The Moon
What can we say about the Moon, just from looking at it?
•
It rises in the east, sets in the west
Due to the Earth’s spin
•
Is round
It is massive enough for gravity to shape it
like a sphere
•
It shines
It only reflects light from the Sun, does not
produce its own
•
It changes its appearance
It goes through phases because it orbits the
Earth!
www.hrastro.com
9
The Moon
What can we say about the Moon, just from looking at it?
•
It rises in the east, sets in the west
Due to the Earth’s spin
•
Is round
It is massive enough for gravity to shape it
like a sphere
•
It shines
It only reflects light from the Sun, does not
produce its own
•
It changes its appearance
It goes through phases because it orbits the
Earth!
www.hrastro.com
10
Phases of the Moon
•
Because the Moon exhibits phases we know:
- That moonlight is just reflected sunlight
- That the moon orbits the Earth
Let’s draw them by hand first
11
Phases of the Moon
•
Because the Moon exhibits phases we know:
- That moonlight is just reflected sunlight
- That the moon orbits the Earth
•
Seen from the North pole,
the Moon rotates
counterclockwise
12
Phases of the Moon
•
Because the Moon exhibits phases we know:
- That moonlight is just reflected sunlight
- That the moon orbits the Earth
•
Seen from the North pole,
the Moon rotates
counterclockwise
N
13
Phases of the Moon
•
Because the Moon exhibits phases we know:
- That moonlight is just reflected sunlight
- That the moon orbits the Earth
14
Phases of the Moon
•
Notice anything ‘special’ about the face of the Moon throughout the month?
We are always seeing the same side!
15
“Dark side” of the Moon
•
Synchronous rotation:
It takes the same time to rotate on its own axis, than it takes to orbit the
Earth once.
•
The side of the Moon that we
cannot see is the so-called
“dark side of the Moon”
•
It is important to realize that
this side is just hidden from out view
but it does receive sunlight
(think about the new moon phase)
16
•
Moon orbits the Earth
Since neither the Earth, nor the Moon
produce their own light, they cast
shadows.
But... why don’t we have
eclipses every month?
This image is only 2D!
17
Moon orbits the Earth
•
•
The Earth orbits the Sun in the ‘Ecliptic’ plane
The Moon orbits the Earth on a plane that is tilted 5° respect to the Ecliptic
This means, we do not have an
eclipse every month.
Eclipses
can happen
here
No eclipse
here!
18
Moon orbits the Earth
•
•
The Earth orbits the Sun in the ‘Ecliptic’ plane
The Moon orbits the Earth on a plane that is tilted 5° respect to the Ecliptic
This means, we do not have an
eclipse every month.
Eclipses
can happen
here
No eclipse
here!
Node Line: where the plane of the ecliptic intersects
the plane of the orbit of the Moon
19
Conditions for eclipses
•
The Moon has to be either
Full or New
(alignment in 2D)
•
AND it has to be in the
nodes line
20
Conditions for eclipses
•
The Moon has to be either
Full or New
(alignment in 2D)
•
AND it has to be in the
nodes line
21
Solar Eclipse
•
The Moon casts a shadow on Earth : New Moon
The alignment has to be: Sun-Moon-Earth
(or Earth-Moon-Sun)
22
Solar Eclipses
•
The Moon casts a shadow on Earth : New Moon
The alignment has to be: Sun-Moon-Earth
(or Earth-Moon-Sun)
•
But the sun is not a point,
it has a size
→Total and partial solar eclipses
•
Also Moon’s orbit is not a
perfect circle. Distance is not
always the same
→Total and Annular eclipses
23
Lunar Eclipses
•
The Earth casts a shadow on the Moon: Full Moon
The alignment has to be: Sun-Earth-Moon
(or Moon-Earth-Sun)
24
Lunar Eclipses
•
The Earth casts a shadow on the Moon: Full Moon
The alignment has to be: Sun-Earth-Moon
(or Moon-Earth-Sun)
•
But neither the Sun nor the Earth
are points, they have sizes
→Total, partial and Penumbral
Lunar eclipses
25
Quizz #2 - 10 minutes
(not graded, look at your notes AND discuss with classmates)
1. When does the New Moon rise?
2. When does the Full Moon rise?
3. When does the First quarter Moon rise?
4. You observe a Solar eclipse, just before sunset. What is the phase of the Moon?
a)Full
b)First quarter
c)New
d)Third quarter
5. You observe a Solar eclipse, just after sunrise. What is the phase of the Moon?
a)Full
b)First quarter
c)New
d)Third quarter
26
Quizz #2 - 10 minutes
(not graded, look at your notes AND discuss with classmates)
1. When does the New Moon rise?
Hint: The time of the day is given by the position of the Sun
2. When does the Full Moon rise?
3. When does the First quarter Moon rise?
Hint: Use your answers for 1 and 2 and interpolate.
4. You observe a Solar eclipse, just before sunset. What is the phase of the Moon?
a)Full
b)First quarter
c)New
d)Third quarter
5. You observe a Solar eclipse, just after sunrise. What is the phase of the Moon?
a)Full
b)First quarter
c)New
d)Third quarter
27
Quizz #2 - Answers
1. When does the New Moon rise?
28
Quizz #2 - Answers
1. When does the New Moon rise? Sunrise.
When the moon is on the new phase, it is very close to the Sun in the sky.
The Moon rises, very close to when the Sun rises.
29
Quizz #2 - 10 minutes
1. When does the New Moon rise? Sunrise.
2. When does the Full Moon rise? Sunset.
For the Moon to be full, the Sun should be at the OPPOSITE side of Earth.
When the full moon is rising, the sun is setting.
30
Quizz #2 - 10 minutes
1. When does the New Moon rise? Sunrise.
2. When does the Full Moon rise? Sunset.
For the Moon to be full, the Sun should be at the OPPOSITE side of Earth.
When the full moon is rising, the sun is setting.
3. When does the First quarter Moon rise?
Hint: Use your answers for 1 and 2 and interpolate.
31
Quizz #2 - 10 minutes
(not graded, look at your notes AND discuss with classmates)
3. When does the First quarter Moon rise?
Hint: Use your answers for 1 and 2 and interpolate.
One thing that might have been missing to answer this question is the direction
of rotation of Earth. But we can figure this one out.
Where does the sun rises first? California or New York?
tilted view
top view
32
Quizz #2 - 10 minutes
(not graded, look at your notes AND discuss with classmates)
3. When does the First quarter Moon rise?
Hint: Use your answers for 1 and 2 and interpolate.
One thing that might have been missing to answer this question is the direction
of rotation of Earth. But we can figure this one out.
Where does the sun rises first? California or New York?
This means the Earth (viewed from the North pole down) rotates counter
clockwise.
tilted view
top view
33
Quizz #2 - 10 minutes
(not graded, look at your notes AND discuss with classmates)
3. When does the First quarter Moon rise?
Earth (viewed from the North pole down) rotates counter clockwise.
first quarter
midnight
34
Quizz #2 - 10 minutes
(not graded, look at your notes AND discuss with classmates)
3. When does the First quarter Moon rise?
Earth (viewed from the North pole down) rotates counter clockwise.
first quarter
sunrise
35
Quizz #2 - 10 minutes
(not graded, look at your notes AND discuss with classmates)
3. When does the First quarter Moon rise?
Earth (viewed from the North pole down) rotates counter clockwise.
first quarter
noon
36
Quizz #2 - 10 minutes
(not graded, look at your notes AND discuss with classmates)
3. When does the First quarter Moon rise?
Earth (viewed from the North pole down) rotates counter clockwise.
The first quarter moon rises at noon!
first quarter
noon
37
Quizz #2 - 10 minutes
(not graded, look at your notes AND discuss with classmates)
1. When does the New Moon rise? Sunrise
2. When does the Full Moon rise? Sunset
3. When does the First quarter Moon rise? Noon
4. You observe a Solar eclipse, just before sunset. What is the phase of the Moon?
a)Full
b)First quarter
c)New
d)Third quarter
5. You observe a Solar eclipse, just after sunrise. What is the phase of the Moon?
a)Full
b)First quarter
c)New
d)Third quarter
For solar eclipses to happen the phase of the moon is
always NEW!