ASTRONOMY Dr. White Mrs. Griffin

Learning from Light: The Big Bang Objective: Explain the origin of the universe according to the Big Bang theory

Review purposes only A.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

Review purposes only 3. Wavelength varies indirectly with energy content 4. ROYGBIV, which is more energetic red or violet? Observe an exploded star at different wavelengths.Observe an exploded star at different wavelengths. Vis.

Review purposes only B. 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

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 billion galaxies D.Many shapes exist

The Universe A.Includes all visible galaxies B.Age thought to be billion years old C.‘Big Bang’ is best theory of formation 1.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

A look at our nearest neighbor in Space The Moon Free powerpoints at

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

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

More daylight hours, more direct sunlight Northern Hemisphere Summer

SOLSTICES SUMMER, JUNE 21 WINTER, 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?

EQUINOXES VERNAL, MARCH 21 AUTUMNAL, 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 solar days Elliptical orbit (plane of the ecliptic) Perihelion million miles (Jan. 4) Aphelion million miles (July 5) 93 million miles average distance

Time Standard Time The International Date Line Daylight Savings Time Year = 365 1/4 days or 365 days 5 hrs. 48 min seconds Solar Day = 24 hours on average. Changes slightly with the elliptical orbit around the sun.

360 o / 24 hr. = 15 o standard zones (7.5 o 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/d Stars having a small d show a small v Stars 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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