Ch 26. Astronomy The scientific study of the universe Scientist who study the universe are called what? Astronomers What are some important things astronomers.

Ch 26

AstronomyThe scientific study of the universe

Scientist who study the universe are called what?Astronomers

What are some important things astronomers do?Discover new stars, galaxies, planets, & black

holesProtect Earth against objects that may hit us

The UniverseGalaxy – a collection of stars, dust, and gas

bound together by gravity.Our solar system is part of what galaxy?

Milky-Way GalaxyWhat are some things found in our solar

system?EarthSunOther planetsSmall asteroids and comets

Measuring Distances in Spaceastronomical unit the average distance

between the Earth and the sun; approximately 150 million kilometers (symbol, AU)

Astronomers also use the speed of light to measure distance

Light travels at 300,000,000 m/s. In one year, light travels 9.4607 x 1012 km. This distance is known as a light-year.

Earth’s RotationRotation – The spin of a body on its axisDoes the Earth rotate from west to east or

east to west?West to east

At any given time, Earth’s hemisphere facing the sun is experiencing daylight and the Earth’s hemisphere away from the sun is experiencing night time.

Earth’s Rotationperihelion the point in the orbit of a planet

at which the planet is closet to the sunaphelion the point in the orbit of a planet at

which the planet is farthest from the sunEarth’s orbit around the sun is an ellipseAn ellipse is a closed curve whose shape is

determined by two points, or foci, within the ellipseEarth is not always the same distance away from

the sun

Earth’s Orbit

The Revolving EarthRevolution – the motion of a body that travels

around another body in space; one complete trip along an orbitEarth’s revolution around the sun causes seasons to

occur.At what speed does the Earth travel around

the sun?29.8 km/s

How long does it take Earth to orbit the sun? Be specific!365 ¼ days ~ 1 year

The Foucault PendulumHow did we figure out the Earth was

spinning?A brilliant man used a pendulum!

Jean-Bernard-Leon Foucault – scientist who provided evidence of Earth’s rotation by using a pendulum

http://www.youtube.com/watch?v=S2id35aQH0s

The Coriollis EffectThe rotation of Earth causes ocean

currents and wind belts to curve to the left or right.

This curving is caused by Earth’s rotation and is called the Coriolis effect.

Earth’s RotationQuestion: What’s one way we can prove the

Earth is rotating?As the night passes, the constellations move in

the sky. (Earth’s rotation)Earth’s revolution around the sun is evidenced

by the apparent motion of constellations.Thus different constellations will appear in the

night sky as the seasons change. (Earth’s revolution)

Constallationconstellation - a group of stars that are

organized in a recognizable pattern.As the night goes on, constellations appear to

change positions in the sky – this is caused by the rotation of the Earth.

Measuring TimeEarth’s rotation = one day (about 24 hours)Earth’s revolution = one year (about 365 ¼ days)

Moon’s revolution = 29.5 dayscalendar - a system created for measuring long

intervals of time by dividing time into periods of days, weeks, months, and years.

Question: Why do we have a leap year?Since a year has an extra ¼ day, every 4 years we

add a day to the month of FebruaryWho revised the calendar to account for the extra

day every four years? – Julius Ceaser

Measuring Time con’t.The modern calendar was created by Pope Gregory

XIII – much like the acient ROMANSTime Zone – 24 different time zones. The zone to

the east is an hour later than the zone on the west.Each time zone is about 15 degrees apart

International Date LineInternational Date Line was established to prevent

confusion about the point on Earth’s surface where the date changes.

The line runs from north to south through the Pacific Ocean. The line is drawn so that it does not cut through islands or continents.

Measuring Time con’t.Daylight Savings Time - Because of the tilt

of Earth’s axis, daylight time is shorter in the winter months than in the summer months

Season’sEarth’s axis is tilted at 23.5˚.Question?? Earth’s axis always points

towards what?? – North StarChanges in the angle at which the sun’s

rays strike Earth’s surface cause the seasons.

Equinoxesequinox the moment when the sun

appears to cross the celestial equator- at an equinox, the sun’s rays hit the Earth’s

equator at a 90 degree angle.Night and day light are appx. Equal

everywhere on Earth.

The autumnal equinox occurs September of each year and marks the beginning of fall in the Northern Hemisphere.

The vernal equinox occurs on March 21 or 22 of each year and marks the beginning of spring in the Northern Hemisphere.

The Season’s con’tsolstice the point at which the sun is as far

north or as far south of the equator as possible

The summer solstice occurs on June 21 or 22 of each year and marks the beginning of summer in the Northern Hemisphere.Most daylight in the summer solstice!!!!

The winter solstice occurs on December 21 or 22 of each year and marks the beginning of winter in the Northern Hemisphere.