Units 5-7: The view from Earth Topics 1.The “Celestial Sphere” (Earth spins) 2.Coordinates (On...

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Units 5-7: The view from Earth Topics 1. The “Celestial Sphere” (Earth spins) 2. Coordinates (On the Earth and in the sky) 3. Seasons (Earth orbits the sun on a tilt) 4. Time (defined by sun or stars?) * Visualize in 3D! * Ask “How do we know?”

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Transcript of Units 5-7: The view from Earth Topics 1.The “Celestial Sphere” (Earth spins) 2.Coordinates (On...

Page 1: Units 5-7: The view from Earth Topics 1.The “Celestial Sphere” (Earth spins) 2.Coordinates (On the Earth and in the sky) 3.Seasons (Earth orbits the sun.

Units 5-7: The view from Earth

Topics 1. The “Celestial Sphere” (Earth spins)

2. Coordinates (On the Earth and in the sky)

3. Seasons (Earth orbits the sun on a tilt)

4. Time (defined by sun or stars?)

* Visualize in 3D!

* Ask “How do we know?”

Page 2: Units 5-7: The view from Earth Topics 1.The “Celestial Sphere” (Earth spins) 2.Coordinates (On the Earth and in the sky) 3.Seasons (Earth orbits the sun.

These 4 topics are all related to the motion of the Earth:

A. The Earth spins on its axis (once per day)

B. The Earth orbits the sun (axis tilted with respect to orbit)

C. The Sun orbits in the Milky Way

D. The Milky Way moves relative to the rest of the universe

These 4 distinct ways that Earth moves are central to all 4 of today’s topics.

Page 3: Units 5-7: The view from Earth Topics 1.The “Celestial Sphere” (Earth spins) 2.Coordinates (On the Earth and in the sky) 3.Seasons (Earth orbits the sun.

1- The Celestial Sphere

A. The Earth spins on its axis (once per day)

Everything in the sky appears to rise and set once per rotation (i.e. once per day).

Star trails show this motion.

Everything (beyond the solar system) appears fixed on the sky.

(why?)

(what are constellations?)

Earth’s spin causes the illusion of a “Celestial Sphere” surrounding the earth.

Page 4: Units 5-7: The view from Earth Topics 1.The “Celestial Sphere” (Earth spins) 2.Coordinates (On the Earth and in the sky) 3.Seasons (Earth orbits the sun.

1- The Celestial Sphere

A. The Earth spins on its axis (once per day)

Everything in the sky appears to rise and set once per rotation (i.e. once per day)

Everything (beyond the solar system) appears fixed on the sky.

(why?)

(what are constellations?)

Constellations = fixed arrangements of stars that are NOT physically related.

Page 5: Units 5-7: The view from Earth Topics 1.The “Celestial Sphere” (Earth spins) 2.Coordinates (On the Earth and in the sky) 3.Seasons (Earth orbits the sun.

A. The Earth spins on its axis (once per day)

We can define a coordinate system as on Earth:

Absolute coordinates (unchanging): North pole South pole Celestial equator

2- Coordinates (on the Celestial Sphere)

Page 6: Units 5-7: The view from Earth Topics 1.The “Celestial Sphere” (Earth spins) 2.Coordinates (On the Earth and in the sky) 3.Seasons (Earth orbits the sun.

An aside:

The Earth’s precesses (like a top) once per 26,000 yrs.The Celestial north pole moves in a circle over time.

Page 7: Units 5-7: The view from Earth Topics 1.The “Celestial Sphere” (Earth spins) 2.Coordinates (On the Earth and in the sky) 3.Seasons (Earth orbits the sun.

A. The Earth spins on its axis (once per day)

We can define a coordinate system as on Earth:

NOT absolute (local to you).– your zenith– your horizon

2- Coordinates (on the Celestial Sphere)

Standing near the Earth’s equator

Standing near the Earth’sNorth pole

Page 8: Units 5-7: The view from Earth Topics 1.The “Celestial Sphere” (Earth spins) 2.Coordinates (On the Earth and in the sky) 3.Seasons (Earth orbits the sun.

A. The Earth spins on its axis (once per day)

We can define a coordinate system as on Earth:

Absolute coordinates: Declination (~ latitude) Right Ascension (~ longitude)

2- Coordinates (on the Celestial Sphere)

Page 9: Units 5-7: The view from Earth Topics 1.The “Celestial Sphere” (Earth spins) 2.Coordinates (On the Earth and in the sky) 3.Seasons (Earth orbits the sun.

A. The Earth spins on its axis (once per day)

We can define a coordinate system as on Earth:

Absolute coordinates: Declination (~ longitude) Right Ascension (~ latitude)

Declination = -90 to 0 to 90[pole – equator – pole]

Right Ascension = 0 - 360[where is RA=0 ?]

2- Coordinates (on the Celestial Sphere)

Page 10: Units 5-7: The view from Earth Topics 1.The “Celestial Sphere” (Earth spins) 2.Coordinates (On the Earth and in the sky) 3.Seasons (Earth orbits the sun.

iClicker question:

If I am standing at the north pole, which of the following is at the zenith?A. The celestial equator

B. The moon

C. The nearby galaxy, M31

D. The north celestial pole

E. The Sun

Page 11: Units 5-7: The view from Earth Topics 1.The “Celestial Sphere” (Earth spins) 2.Coordinates (On the Earth and in the sky) 3.Seasons (Earth orbits the sun.

iClicker question:

Santa Cruz is at about 36o north Latitude and 122o west longitude (~8 hrs west of Greenwich, UK).

From here, can I see an object at The south Celestial Pole?

a - yesb - no

The celestial equator?a - yesb - no

The moon?a - yesb - no

The north Celestial Pole?a - yesb - no

Page 12: Units 5-7: The view from Earth Topics 1.The “Celestial Sphere” (Earth spins) 2.Coordinates (On the Earth and in the sky) 3.Seasons (Earth orbits the sun.

B. The Earth orbits the sun (once per year)

Half the sky is overhead during the day … which half changes throughout the year!

2- Coordinates (on the Celestial Sphere)

Page 13: Units 5-7: The view from Earth Topics 1.The “Celestial Sphere” (Earth spins) 2.Coordinates (On the Earth and in the sky) 3.Seasons (Earth orbits the sun.

B. The Earth orbits the sun (once per year)

This makes a convenient way to define RA=0…

2- Coordinates (on the Celestial Sphere)

Ecliptic path = apparent path of sun through the stars.Ecliptic plane = plane of the earth’s motion (or the sun’s apparent motion)

RA = 0

Page 14: Units 5-7: The view from Earth Topics 1.The “Celestial Sphere” (Earth spins) 2.Coordinates (On the Earth and in the sky) 3.Seasons (Earth orbits the sun.

B. The Earth orbits the sun (once per year)

Let the sun mark the location of RA=0 deg on the Vernal equinox.

2- Coordinates (on the Celestial Sphere)

Stars at RA=0 can be seen in the fall.

RA = 0

Page 15: Units 5-7: The view from Earth Topics 1.The “Celestial Sphere” (Earth spins) 2.Coordinates (On the Earth and in the sky) 3.Seasons (Earth orbits the sun.

Defined in 100AD… constellations/dates are slightly off now. (Why?)

2- Coordinates (on the Celestial Sphere)

B. The Earth orbits the sun (once per year)

Zodiac = constellations on the ecliptic plane

Page 16: Units 5-7: The view from Earth Topics 1.The “Celestial Sphere” (Earth spins) 2.Coordinates (On the Earth and in the sky) 3.Seasons (Earth orbits the sun.

B. The Earth orbits the sun (once per year) …on a tilt!

The Earth’s spin-axis is tilted 23.5o relative to the plane of the orbit.

3- Seasons

Page 17: Units 5-7: The view from Earth Topics 1.The “Celestial Sphere” (Earth spins) 2.Coordinates (On the Earth and in the sky) 3.Seasons (Earth orbits the sun.

B. The Earth orbits the sun (once per year) …on a tilt!

Heating depends on Energy per unit Area!

Experience confirms! (Sun feels hotter at 1pm than 5pm. Shoulders/head gets sunburned first.)

3- Seasons

Page 18: Units 5-7: The view from Earth Topics 1.The “Celestial Sphere” (Earth spins) 2.Coordinates (On the Earth and in the sky) 3.Seasons (Earth orbits the sun.

B. The Earth orbits the sun (once per year) …on a tilt!

Location of the sun at noon changes through the year

3- Seasons

Photo taken every 10 days at noon. Records sun’s highest point in sky through the year.

(Streaks are composite of photos taken every 2 minutes to show the sun ascending on 3 different days)

Which noontime location of the sun corresponds to: Summer Solstice? Winter Solstice? Spring equinox? Fall Equinox?

Page 19: Units 5-7: The view from Earth Topics 1.The “Celestial Sphere” (Earth spins) 2.Coordinates (On the Earth and in the sky) 3.Seasons (Earth orbits the sun.

A+B. The earth orbits and spins….which defines time?

which motion defines time?

Solar time: relative to sun

Solar day = 1 revolution

relative to the sun

Sidereal time: relative to stars

Sidereal day = 1 revolution

relative to the stars

4- TIME

Page 20: Units 5-7: The view from Earth Topics 1.The “Celestial Sphere” (Earth spins) 2.Coordinates (On the Earth and in the sky) 3.Seasons (Earth orbits the sun.

3. The Sun orbits in the Milky Way

The sun (and nearby stars) orbit the center of the Milky Way once per 230,000,000 years.

How do we know? (motion of other stars in the Milky Way wrt the Sun; careful study of stellar positions over time)

Two more ways we move through space…

Page 21: Units 5-7: The view from Earth Topics 1.The “Celestial Sphere” (Earth spins) 2.Coordinates (On the Earth and in the sky) 3.Seasons (Earth orbits the sun.

4. The Milky Way moves relative to the rest of the universe

Space itself is expanding (the space between things is increasing!)

Think of the surface of a No center. No edge. balloon…only in 3D

Two more ways we move through space…

Page 22: Units 5-7: The view from Earth Topics 1.The “Celestial Sphere” (Earth spins) 2.Coordinates (On the Earth and in the sky) 3.Seasons (Earth orbits the sun.

A. The Earth spins on its axis

… rather than the Sky spinning around the Earth?

First real proof that Earth spins:

1851, Foucault’s pendulum

Imagine a pendulum at the North Pole.

The only force on it is gravity,

so it swings 1 plane forever.

The fact that it appears to spin

means the Earth moves under it!

Remember to ask: How do we know?

Page 23: Units 5-7: The view from Earth Topics 1.The “Celestial Sphere” (Earth spins) 2.Coordinates (On the Earth and in the sky) 3.Seasons (Earth orbits the sun.

B. The Earth orbits the sun

… or does the Sun go around the Earth?

Stellar Parallax:

Earth (parallax+orbit) or Sun (no parallax,only orbit)

(demo: wink. background still. thumb “moves.”)

Lefteye

righteyenose

Thumb (extended)

Stuff in background

Remember to ask: How do we know?

Page 24: Units 5-7: The view from Earth Topics 1.The “Celestial Sphere” (Earth spins) 2.Coordinates (On the Earth and in the sky) 3.Seasons (Earth orbits the sun.

iClicker Quiz #1 (09/30/09): Visibility of the Constellations at Different Times of the Year

From the image below, what constellation is overhead at midnight on the vernal equinox (March 21)?

A- Virgo

B- Pisces

C- Sagittarius

D- Gemini

Page 25: Units 5-7: The view from Earth Topics 1.The “Celestial Sphere” (Earth spins) 2.Coordinates (On the Earth and in the sky) 3.Seasons (Earth orbits the sun.

Units 8-10: The Earth/Moon/Sun

Topics 1. Moon phases

2. Eclipses: shadows and visualizing the earth/moon/sun

3. Solar calendars vs Lunar calendars.

4. Distances and angles

* Visualize in 3D!

* Ask “How do we know?”

Page 26: Units 5-7: The view from Earth Topics 1.The “Celestial Sphere” (Earth spins) 2.Coordinates (On the Earth and in the sky) 3.Seasons (Earth orbits the sun.

• What determines the appearance of the moon? – What is moonlight?

– Why does the moon rise in the east, set in the west?

– Why does the moon’s appearance change?

1- Moon phases

Page 27: Units 5-7: The view from Earth Topics 1.The “Celestial Sphere” (Earth spins) 2.Coordinates (On the Earth and in the sky) 3.Seasons (Earth orbits the sun.

• What determines the appearance of the moon? – What is moonlight? Reflected sunlight!

– Why does the moon rise in the east, set in the west?

– Why does the moon’s appearance change?

1- Moon phases

Page 28: Units 5-7: The view from Earth Topics 1.The “Celestial Sphere” (Earth spins) 2.Coordinates (On the Earth and in the sky) 3.Seasons (Earth orbits the sun.

• What determines the appearance of the moon? – What is moonlight? Reflected sunlight!

– Why does the moon rise in the east, set in the west? The earth spins!

– Why does the moon’s appearance change?

1- Moon phases

Page 29: Units 5-7: The view from Earth Topics 1.The “Celestial Sphere” (Earth spins) 2.Coordinates (On the Earth and in the sky) 3.Seasons (Earth orbits the sun.

• What determines the appearance of the moon? – What is moonlight? Reflected sunlight!

– Why does the moon rise in the east, set in the west? The earth spins!

– Why does the moon’s appearance change? Because it ORBITS the EARTH!

1- Moon phases

Page 30: Units 5-7: The view from Earth Topics 1.The “Celestial Sphere” (Earth spins) 2.Coordinates (On the Earth and in the sky) 3.Seasons (Earth orbits the sun.

1- Moon phases

Page 31: Units 5-7: The view from Earth Topics 1.The “Celestial Sphere” (Earth spins) 2.Coordinates (On the Earth and in the sky) 3.Seasons (Earth orbits the sun.

phases:

new

waxing crescent

first quarter

waxing gibbous

full

waning gibbous

third quarter

waning crescent

new

1- Moon phases

Page 32: Units 5-7: The view from Earth Topics 1.The “Celestial Sphere” (Earth spins) 2.Coordinates (On the Earth and in the sky) 3.Seasons (Earth orbits the sun.

When does a FULL MOON rise?

When does a NEW MOON rise?

Does an astronomer on the moon see the Earth “rise” or “set”?

Does he/she see phases of the Earth?

1- Moon phases

Page 33: Units 5-7: The view from Earth Topics 1.The “Celestial Sphere” (Earth spins) 2.Coordinates (On the Earth and in the sky) 3.Seasons (Earth orbits the sun.

1. The earth orbits around the Sun and spins on its own axis in the same sense (i.e. both clockwise or both anticlockwise)

2. A siderial day is defined as the time it takes the Earth to make a complete spin on its axis relative to distant stars

3. A solar day is defined as the time it takes the Earth to do a complete spin on its axis relative to the Sun

1. The length of a siderial day is about 4 minutes shorter than the length of a solar day

Background for iClicker Quizzes: Siderial vs Solar Time

Page 34: Units 5-7: The view from Earth Topics 1.The “Celestial Sphere” (Earth spins) 2.Coordinates (On the Earth and in the sky) 3.Seasons (Earth orbits the sun.

If the earth’s orbit around the Sun and the earth’s spin on its own axis were in opposite senses (i.e. one clockwise and one anticlockwise), which of the following would be true:

A. A siderial and solar day would be of the same length

B. A siderial day would be 4 minutes longer than a solar day

C. A siderial day would be 8 minutes longer than a solar day

D. A solar day would be 4 minutes longer than a siderial day

E. A solar day would be 8 minutes longer than a siderial day

iClicker Quiz #2 (10/02/09): Siderial vs Solar Time

Page 35: Units 5-7: The view from Earth Topics 1.The “Celestial Sphere” (Earth spins) 2.Coordinates (On the Earth and in the sky) 3.Seasons (Earth orbits the sun.

If the earth’s spin rate about its own axis were to slow down to half its present rate (while spinning in the same sense as its orbit around the Sun), so that the length of the day became 48 hours, which of the following would be true:

A. A siderial and solar day would be of the same length

B. A siderial day would be 4 minutes longer than a solar day

C. A siderial day would be 8 minutes longer than a solar day

D. A solar day would be 4 minutes longer than a siderial day

E. A solar day would be 8 minutes longer than a siderial day

iClicker Quiz #3 (10/02/09): Siderial vs Solar Time

Page 36: Units 5-7: The view from Earth Topics 1.The “Celestial Sphere” (Earth spins) 2.Coordinates (On the Earth and in the sky) 3.Seasons (Earth orbits the sun.

2- Eclipses

• Lunar eclipse = Earth blocks sunlight from hitting the Moon• Solar eclipse = Moon blocks sunlight from hitting the Earth

Page 37: Units 5-7: The view from Earth Topics 1.The “Celestial Sphere” (Earth spins) 2.Coordinates (On the Earth and in the sky) 3.Seasons (Earth orbits the sun.

2- Eclipses – Lunar

Partial vs Full shadows … the sun is not a dot!

• Full = Umbra• Partial = Penumbra

Page 38: Units 5-7: The view from Earth Topics 1.The “Celestial Sphere” (Earth spins) 2.Coordinates (On the Earth and in the sky) 3.Seasons (Earth orbits the sun.

Total Lunar Eclipse, Jan 9/10, 2001

2- Eclipses – Lunar

Page 39: Units 5-7: The view from Earth Topics 1.The “Celestial Sphere” (Earth spins) 2.Coordinates (On the Earth and in the sky) 3.Seasons (Earth orbits the sun.

Animations (week 2)Coordinate Systems ComparisonCelestial and Horizon Systems Comparison

Seasons Simulator (NAAP)Sun’s Rays SimulatorUnion Seasons DemonstratorSun’s Position on HorizonDaylight Hours Explorer

Big Dipper 3D

Synodic Lag

Lunar Phases Simulator (NAAP)Lunar Phase VocabularyThree Views SimulatorMoon Inclination

Tidal Bulge Simulation


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