We will discuss this in class, these are the volunteers so far

• Richard Avis

• Jillian Capano

• Brendan Forte

• Samantha Hunt

• Christian Madonna

• Shaina Singer

Preceptors and Times

End of Ch. 1

Looking back in time• Light, although fast, travels at a finite speed.• It takes:

– 8 minutes to reach us from the Sun– 8 years to reach us from Sirius (8 light-years away)– 1,500 years to reach us from the Orion Nebula

• The farther out we look into the Universe, the farther back in time we see!

1.1 Our Modern View of the Universe

• What is our place in the universe?We are on a planet, orbiting a star, in a galaxy (which is a member of the Local Group of galaxies in the Local Supercluster).

• How did we come to be?— The matter in our bodies came from the Big Bang, which produced hydrogen and helium.— All other elements were constructed from H and He in stars and then recycled into new star systems,

including our solar system.

• How can we know what the universe was like in the past?—When we look to great distances we are seeing events that

happened long ago because light travels at a finite speed.

• Can we see the entire universe?– Nope!

Our goals for learning:

1.1 Our Modern View of the Universe

• What is our place in the universe?We are on a planet, orbiting a star, in a galaxy (which is a member of the Local Group of galaxies in the Local Supercluster).

• How did we come to be?— The matter in our bodies came from the Big Bang, which produced hydrogen and helium.— All other elements were constructed from H and He in stars and then recycled into new star systems,

including our solar system.

• How can we know what the universe was like in the past?— When we look to great distances we are seeing events that happened long ago because light

travels at a finite speed.

• Can we see the entire universe?—No, the observable portion of the universe is about 14 billion

light-years in radius because the universe is about 14 billion years old. ALSO (not in Ch. 1 of the book), we can “see” only about 4% of the universe, 96% is made of “dark matter” and “dark energy”.

Our goals for learning:

What have we learned?

• How is Earth moving in our solar system?—It rotates on its axis once a day and orbits the

Sun at a distance of 1 AU = 150 million km• How is our solar system moving in the Milky

Way Galaxy?—Stars in the Local Neighborhood move

randomly relative to one another and orbit the center of the Milky Way in about 230 million years

What have we learned?

• How do galaxies move within the universe?—All galaxies beyond the Local Group are

moving away from us with expansion of the universe: the more distant they are, the faster they’re moving

• Are we ever sitting still?—No!

1.2 The Scale of the Universe

• How big is Earth compared with our solar system?• How far away are the stars?• How big is the Milky Way Galaxy?• How big is the universe?• How do our lifetimes compare to the age of the

universe?

Our goals for learning:

The scale of the solar system• On a 1-to-10 billion

scale:— Sun is the size

of a large grapefruit (14 cm)

— Earth is the size of a tip of a ball point pen, 15 meters away.

How far away are the stars?

On our 1-to-10 billion scale, it’s just a few minutes walk to Pluto.

How far would you have to walk to reach the nearest star, Alpha Centauri?

A. 1 mileB. 10 milesC. 100 milesD. the distance across the United States

(2500 miles)

How far away are the stars?

On our 1-to-10 billion scale, it’s just a few minutes walk to Pluto.

How far would you have to walk to reach the nearest star, Alpha Centauri?

A. 1 mileB. 10 milesC. 100 milesD. the distance across the United States

(2500 miles)

Answer: D, the distance across the United States

How do our lifetimes compare to the age of the Universe?

• The Cosmic Calendar (p.14 and 15): A scale on which we compress the history of the universe into 1 year.

What have we learned?• How big is the Earth compared to our solar system?

—On a scale of 1-to-10 billion, the Sun is about the size of a grapefruit. The Earth is the size of a tip of a ball point pen about 15 m away. The distances between planets are very large compared with their sizes.

• How far away are the stars?—On the same scale, the stars are thousands of kilometers

away.

• How big is the Milky Way Galaxy?—100 billion stars; it would take more than 3,000 years to

count the stars in the Milky Way Galaxy at a rate of one per second. The Milky Way Galaxy is about 100,000 light-years across.

What have we learned?

• How big is the universe?—100 billion galaxies in the observable universe—14 billion light-years—As many stars as grains of sand on Earth’s beaches

• How do our lifetimes compare to the age of the universe?—On a cosmic calendar that compresses the history of

the universe into one year, human civilization is just a few seconds old, and a human lifetime is a fraction of a second.

1.3 Spaceship Earth

• How is Earth moving in our solar system?

• How is our solar system moving in the Milky Way Galaxy?

• How do galaxies move within the universe?

• Are we ever sitting still?

Our goals for learning:

Are we ever sitting still? Earth rotates on axis: > 1,000 km/hr

Earth orbits Sun: > 100,000 km/hr

Solar system moves among stars: ~ 70,000 km/hr

Milky Way rotates: ~ 800,000 km/hr

Milky Way moves in Local Group

Universeexpands

How do galaxies move within the universe?

Galaxies are carried along with the expansion of the universe. But how did Hubble figure out that the universe is expanding?

Hubble discovered that…

• all galaxies outside our Local Group are moving away from us.

• the more distant the galaxy, the faster it is racing away.

Conclusion: We live in an expanding universe.

1. Patterns in The Sky: Stars and constellations

Celestial coordinates: Celestial sphere, poles, equator, ecliptic, right ascension*, declination* (*not in book)

Seasons: Tilt in Earth’s axis (23.5 degrees), Equinoxes and soltices, precession

2. The Moon and Eclipses Lunar and Solar Eclipses

3. Ancient Mystery of the Planets: Apparent Retrograde motion of planets

Outline of lecture 2 (Ch 2)

2.1 Patterns in the Night Sky

• What does the universe look like from Earth?

• Why do stars rise and set?

• Why do the constellations we see depend on latitude and time of year?

Our goals for learning:

• What is a constellation?• A constellation is a region of the sky. The sky is

divided into 88 official constellations.

Constellations• Most official constellation names come from

antiquity. • The patterns of stars have no physical significance!

Stars that appear close together may lie at very different distances.

• Modern astronomers use them as landmarks.

Constellations: Orion

• What is the celestial sphere?• An

imaginary sphere surrounding the Earth upon which the stars, Sun, Moon, and planets appear to reside.

The Celestial SphereNorth & South celestial poles

the points in the sky directly above the Earth’s North and South poles

celestial equatorthe extension of the Earth’s equator onto the celestial sphere

eclipticthe annual path of the Sun through the celestial sphere, which is a projection of ecliptic plane

The Celestial Sphere

The Milky Way

You’ve probably seen this band of light across the sky.What are we actually seeing?

The Milky Way•Our Galaxy is shaped like a disk.•Our solar system is in that disk.•When we look at the Milky Way in the sky, we are looking along that disk.

Measuring the Sky

We measure the sky in angles, not distances.

• Full circle = 360º

• 1º = 60 arcmin

• 1 arcmin = 60 arcsec

Measuring Angles in the Sky

The Local Sky

zeniththe point directly above you

horizonall points 90° from the zenith

altitudethe angle above the horizon

meridiandue north horizon zenith due south horizon

Review: Coordinates on the Earth• Latitude: position north or south of equator

• Longitude: position east or west of prime meridian (runs through Greenwich, England)

The Daily Motion

• As the Earth rotates, the sky appears to us to rotate in the opposite direction.

• The sky appears to rotate around the N (or S) celestial poles.

• If you are standing at the poles, nothing rises or sets.

• If you are standing at the equator, everything rises & sets 90 to the horizon.

Time Exposure Photograph:

Star Trails

The Daily Motion

daily circles --- CCW looking north, CW looking south

Annual Motion

• As the Earth orbits the Sun, the Sun appears to move eastward with respect to the stars.

• The Sun circles the celestial sphere once every year.

2.3 Seasons

• What is the cause of the seasons on Earth?

Annual Motion• The Earth’s axis is tilted 23.5° from being

perpendicular to the ecliptic plane.

• Therefore, the celestial equator is tilted 23.5° to the ecliptic.

• As seen from Earth, the Sun spends 6 months north of the celestial equator and 6 months south of the celestial equator.

• Seasons are caused by the Earth’s axis tilt, not the distance from the Earth to the Sun!

Annual Motion

eclipticthe apparent path of the Sun through the sky

equinoxwhere the ecliptic (the Sun) intersects the celestial equator

solsticewhere the ecliptic (the Sun) is farthest from the celestial equator

zodiac

the constellations which lie along the ecliptic

The Cause of the Seasons

Coordinates on the Celestial Sphere (not in book)

• Latitude: position north or south of equator

• Longitude: position east or west of prime meridian (runs through Greenwich, England)

• Declination: position north or south of celestial equator (in degrees)

• Right Ascension: distance (in hours, 0 to 23h 59 min.) East of vernal equinox (where the sun crosses the celestial equator going North)

What point on the celestial sphere is defined by a Right Ascension of zero hours and a Declination of zero degrees?

Question 1

What point on the celestial sphere is defined by a Right Ascension of zero hours and a Declination of zero degrees?

The vernal (spring) equinox

Question 1

What point on the celestial sphere is defined by a Right Ascension of 12 hours and a Declination of zero degrees?

Question 2

What point on the celestial sphere is defined by a Right Ascension of 12 hours and a Declination of zero degrees?

The autumnal (fall) equinox

Question 2

What is an equinox?

Question 3

What point on the celestial sphere is defined by being on the ecliptic at a Declination of +23.5 degrees?

Question 4

What point on the celestial sphere is defined by being on the ecliptic at a Declination of +23.5 degrees?

The Summer Solstice

Question 4

What point on the celestial sphere is defined by being on the ecliptic at a Declination of minus 23.5 degrees (i.e. 23.5 degrees South)?

Question 5

What point on the celestial sphere is defined by being on the ecliptic at a Declination of minus 23.5 degrees (i.e. 23.5 degrees South)?

The Winter Solstice

Question 5

Axis tilt causes uneven heating by sunlight throughout the year.

When is summer?(in the Northern Hemisphere)

• The solstice which occurs around June 21 is considered the first day of summer.

• However, it takes time for the more direct sunlight to heat up the land and water.

• Therefore, July & August are typically hotter than June.

2.4 Precession

• What is the Earth’s cycle of precession?