ASTRONOMY

Dr. White

Mrs. Griffin

Learning from Light: The Big Bang

Objective: Explain the origin of the universe according to the Big Bang theory

http://www.rug.nl/museum/tentoonstellingen/archief/ruimte

Review purposes onlyA. Electromagnetic radiation is energy released by

stars in the form of waves.1. Many types, together known as electromagnetic

spectrum (visible light is only 1 kind)

2. Types have different wavelengths

http://www.yourdictionary.com/images/ahd/jpg/A4wavele.jpg

Review purposes only3. Wavelength varies indirectly with energy content

4. ROYGBIV, which is more energetic red or violet?

Observe an exploded star at different wavelengths. Vis.

http://www.spacetoday.org/images/DeepSpace/Telescopes/GreatObservatories/Chandra/ChandraSpectrum.jpg

Review purposes onlyB. Astronomers use a spectroscope to study types of star

spectra (sing. spectrum)1. Continuous spectrum- source emits light of all wavelengths

2. Emission spectrum- source emits some wavelengths

3. Absorption spectrum- cool gases absorb some wavelengths depending on their composition

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http://www.myastrologybook.com/MilkyWayCOBE8x2@72.jpg

http://antwrp.gsfc.nasa.gov/apod/image/0402/skymt_payne_big.jpg

Review purposes only

Define galaxy and describe the various types

A. Galaxies are clusters of millions to billions of stars

B. Ours is the Milky Way

C. Likely 50-100 billion galaxies

D. Many shapes exist

The Universe

A. Includes all visible galaxies

B. Age thought to be 10-20 billion years old

C. ‘Big Bang’ is best theory of formation1. Initial hot explosion

2. Gases & dust cooled & condensed locally into planets, stars, & galaxies

3. Material still spreading out from explosion

4. Best evidence includes red shift of light from other galaxies

The Universe

• Light from distant galaxies all appear to have a longer wavelength than expected.

• The most obvious reason is that they are moving away from us as they emit light so the light looks ‘stretched’ to us.

Longer wavelengths Shorter wavelengths

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A look at our nearest neighbor in Space

The Moon

Free powerpoints at http://www.worldofteaching.com

It’s Just A Phase

• Moonlight is reflected sunlight

• Half the moon’s surface is always reflecting light

• From Earth we see different amounts of the Moon’s lit surface

• The amount seen is called a “phase”

Waxing and Waning

• New moon

• Waxing Crescent moon

• First Quarter moon

• Waxing Gibbous moon

• Full moon

• Waning Gibbous moon

• Third Quarter moon

• Waning Crescent moon

• New moon

earth

moon orbit`searth

last (third)quarter

gibbous moon

full moon

gibbous moon

first quarter

crescent

new moon

crescent

waning Moon

waxing Moon

SUN

The Reason For the Seasons

Seasons Misconception• Many people carry the misconception that the

seasons are due to the distance of the Earth from the Sun. However, consider the following facts:

– The Earth’s orbit around the Sun is nearly a perfect circle. The Earth is slightly closer to the Sun in January and farther from the Sun in July.

• Perihelion (closest to the Sun) is around January 3 when Earth is about 91,405,436 miles from the Sun.

• Aphelion (farthest from the Sun) is around July 4 when Earth is about 94,511,989 miles from the Sun.

What Causes Earth’s Seasons?

• Earth’s axis is tilted 23.5 degrees – it always points in the same direction (Polaris, the North Star) as we orbit our Sun once a year

• This tilt causes the hemispheres to alternate in the amount of our Sun’s light and heat they receive through the year

http://www.lpi.usra.edu/education/skytellers/seasons/about.shtml

More daylight hours, more direct sunlight

Northern Hemisphere Summer

http://www.lpi.usra.edu/education/skytellers/seasons/about.shtml

SOLSTICESSUMMER, JUNE 21WINTER, DECEMBER 21

Where are the overhead rays of the sun on these days?

Which parts of the earth are in darkness and light? For how long?

Tropic of Cancer at 23.5º N Tropic of Capricorn at 23.5º S Arctic Circle (66.5 º N)Antarctic Circle (66.5º S)

Notice these four important parallels.

Where do they occur? Why?

EQUINOXESVERNAL, MARCH 21AUTUMNAL, SEPTEMBER 21

Rotation of the Earth

• Rotate west to east or ‘counter-clockwise’ (when viewed from the North Pole)– sunset and sunrise

• Rotation period is 24 hours per solar day (23 hours 56 minutes with respect to other stars)

Revolution of the earth• Period of revolution is 365.25 solar days

• Elliptical orbit (plane of the ecliptic)

Perihelion - 91.5 million

miles

(Jan. 4)

Aphelion - 94.5 million

miles

(July 5)

93 million miles average distance

TimeStandard Time

The International Date Line

Daylight Savings Time

Year = 365 1/4 days or 365 days 5 hrs. 48 min. 45.685 seconds

Solar Day = 24 hours on average. Changes slightly with the elliptical orbit around the sun.

360o / 24 hr. = 15o standard zones (7.5o E and W from standard meridian)

Standard Time

International Date Line

Cross W to E - gain day; E to W - lose day

International Date Line

A day is 24 hours, but a date

lasts for 48 hours!

At any given time on earth, except

Greenwich noon, there are two dates on the

planet. The new date starts at the IDL when midnight crosses the IDL and moves westward around the planet for 24 hrs. displacing the old date. Then it fades out as the “old” date for 24 hrs.

Key Points• Size and Shape of Earth.• Latitude and Longitude• Explain the basic earth-sun relationships.• Equinoxes, solstices and the relationship among

– seasons– the latitude of the sun’s direct rays, and – the intensity of solar radiation received– changes in Daylight and Darkness

Barycenter & Precession

• Precession – movement (wobble) of the axis of rotation of an astronomical body (the axis slowly traces out a cone); for the earth it occurs once every 26,000 years of earth motion.

Precession “Wobble Cone” (P)

Nutation “Wobble Cone Wiggle” (N)

Rotational Axis {R}

Barycenter

• Barycenter – common center of mass around which 2 bodies revolve.

Hubble’s Law

H = v/dStars having a small d show a small vStars having a large d show a large v

OR

Nearer stars are moving away more slowly (smaller red shifts) More distant stars are moving away more rapidly (larger red shifts)

Kepler’s Laws Of Planetary Motion

• In astronomy, Kepler's laws of planetary motion are three scientific laws describing orbital motion, originally formulated to describe the motion of planets around the Sun.

• Kepler's laws are:

– The orbit of every planet is an ellipse with the Sun at one of the two foci.

– A line joining a planet and the Sun sweeps out equal areas during equal intervals of time.

– The square of the orbital period of a planet is directly proportional to the cube of the semi-major axis of its orbit.

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