Intro to AstronomyIntro to Astronomy

Ch 26Ch 26

Value of AstronomyValue of Astronomy

Astronomy:Astronomy: the scientific study of the universe the scientific study of the universe

Scientists who study the universe are called Scientists who study the universe are called astronomersastronomers

In the process of observing the universe, astronomers In the process of observing the universe, astronomers have made exciting discoveries, such as new planets, have made exciting discoveries, such as new planets, stars, black holes, and nebulas. stars, black holes, and nebulas.

By studying these objects, astronomers have been able By studying these objects, astronomers have been able to learn more about the origin of Earth and the to learn more about the origin of Earth and the processes involved in the formation of our solar system.processes involved in the formation of our solar system.

Astronomers may also learn how to protect us from Astronomers may also learn how to protect us from potential catastrophes, such as collisions between potential catastrophes, such as collisions between asteroids and Earth.asteroids and Earth.

Organization of the UniverseOrganization of the UniverseGalaxy Galaxy a collection of stars, dust, and gas bound together a collection of stars, dust, and gas bound together

by gravityby gravity

The solar system includes the sun, Earth, the other The solar system includes the sun, Earth, the other planets, and many smaller objects such as asteroids and planets, and many smaller objects such as asteroids and comets.comets.

The solar system is part of a galaxy.The solar system is part of a galaxy.

The galaxy in which the solar system resides is called The galaxy in which the solar system resides is called the the Milky Way galaxyMilky Way galaxy..

The nearest part of the universe to Earth is our solar The nearest part of the universe to Earth is our solar system.system.

Measuring Distances in the Measuring Distances in the UniverseUniverse

Astronomical UnitAstronomical Unit the average distance between the average distance between the Earth and the sun; approximately 150 million the Earth and the sun; approximately 150 million kilometers (symbol, AU)kilometers (symbol, AU)

Astronomers also use the speed of light to Astronomers also use the speed of light to measure distance.measure distance.

Light travels at 300,000,000 m/s. In one year, Light travels at 300,000,000 m/s. In one year, light travels 9.4607 x 10light travels 9.4607 x 101212 km. This distance is km. This distance is known as a known as a light-yearlight-year..

Aside from the sun, the closet star to Earth is 4.2 Aside from the sun, the closet star to Earth is 4.2 light-years away.light-years away.

Observing SpaceObserving Space

Electromagnetic SpectrumElectromagnetic Spectrum all of the frequencies all of the frequencies or wavelengths of electromagnetic radiation.or wavelengths of electromagnetic radiation.

Light, radio waves, and X rays are all examples Light, radio waves, and X rays are all examples of electromagnetic radiation.of electromagnetic radiation.

The radiation is composed of traveling waves of The radiation is composed of traveling waves of electric and magnetic fields that oscillate at fixed electric and magnetic fields that oscillate at fixed frequencies and wavelengths.frequencies and wavelengths.

Invisible Electromagnetic RadiationInvisible Electromagnetic Radiation

Invisible wavelengths cannot be seen by the human eye. Invisible wavelengths cannot be seen by the human eye. They include infrared waves, microwaves, radio waves, They include infrared waves, microwaves, radio waves, ultraviolet rays, X rays, and gamma rays, and are ultraviolet rays, X rays, and gamma rays, and are detected only by instruments.detected only by instruments.

In 1852, a scientist named Sir Frederick William In 1852, a scientist named Sir Frederick William Herschel discovered Herschel discovered infraredinfrared, which means “below the , which means “below the red.”red.”

Infrared is electromagnetic radiation that has waves Infrared is electromagnetic radiation that has waves longer than waves of visible light. longer than waves of visible light. Ultraviolet Ultraviolet means means “beyond the violet” and has wavelengths shorter than “beyond the violet” and has wavelengths shorter than waves of visible light.waves of visible light.

Objectives 26.2Objectives 26.2 DescribeDescribe two lines of evidence for Earth’s two lines of evidence for Earth’s

rotation.rotation.

ExplainExplain how the change in apparent positions of how the change in apparent positions of constellations provides evidence of Earth’s constellations provides evidence of Earth’s rotation and revolution around the sun.rotation and revolution around the sun.

SummarizeSummarize how Earth’s rotation and revolution how Earth’s rotation and revolution provide a basis for measuring time.provide a basis for measuring time.

ExplainExplain how the tilt of Earth’s axis and Earth’s how the tilt of Earth’s axis and Earth’s movement cause seasons.movement cause seasons.

Movements of EarthMovements of Earth

rotation rotation the spin of a body on its axisthe spin of a body on its axis

Each complete rotation takes about one day.Each complete rotation takes about one day.

The Earth rotates from west to east. At any The Earth rotates from west to east. At any given moment, the hemisphere of Earth that given moment, the hemisphere of Earth that faces the sun experiences daylight. At the same faces the sun experiences daylight. At the same time, the hemisphere of Earth that faces away time, the hemisphere of Earth that faces away from the sun experiences nighttime.from the sun experiences nighttime.

These movements of Earth are also responsible These movements of Earth are also responsible for the seasons and changes in weather.for the seasons and changes in weather.

Rotating EarthRotating Earth

The Foucault PendulumThe Foucault Pendulum

In the 19th century, the scientist Jean-Bernard-Leon In the 19th century, the scientist Jean-Bernard-Leon Foucault, provided evidence of Earth’s rotation by using Foucault, provided evidence of Earth’s rotation by using a pendulum.a pendulum.

The path of the pendulum appeared to change over time. The path of the pendulum appeared to change over time. However, the path does not actually change. Instead, However, the path does not actually change. Instead, the Earth moves the floor as Earth rotates on its axis.the Earth moves the floor as Earth rotates on its axis.

The Coriollis EffectThe Coriollis Effect

The rotation of Earth causes ocean currents and wind The rotation of Earth causes ocean currents and wind belts to curve to the left or right. This curving is caused belts to curve to the left or right. This curving is caused by Earth’s rotation and is called the by Earth’s rotation and is called the Coriolis effectCoriolis effect..

The diagram below shows the The diagram below shows the Earth’s OrbitEarth’s Orbit

The Revolving EarthThe Revolving Earth

revolution revolution the motion of a body that travels the motion of a body that travels around another body in space; one complete trip around another body in space; one complete trip along an orbitalong an orbit

Even though you cannot feel Earth moving, it is Even though you cannot feel Earth moving, it is traveling around the sun at an average speed of traveling around the sun at an average speed of 29.8 km/s.29.8 km/s.

Each complete revolution of Earth around the Each complete revolution of Earth around the sun takes 365 1/4 days, or about one year.sun takes 365 1/4 days, or about one year.

The Revolving Earth Cont.The Revolving Earth Cont.

perihelion perihelion the point in the orbit of a planet at which the the point in the orbit of a planet at which the planet is closet to the sunplanet is closet to the sun

aphelionaphelion the point in the orbit of a planet at which the the point in the orbit of a planet at which the planet is farthest from the sunplanet is farthest from the sun

An An ellipse ellipse is a closed curve whose shape is determined is a closed curve whose shape is determined by two points, or foci, within the ellipse. In planetary by two points, or foci, within the ellipse. In planetary orbits, one focus is located within the sun.orbits, one focus is located within the sun.

Earth’s orbit around the sun is an ellipse. Because its Earth’s orbit around the sun is an ellipse. Because its

orbit is an ellipse, Earth is not always the same distance orbit is an ellipse, Earth is not always the same distance from the sun.from the sun.

Constellations and Earth’s MotionConstellations and Earth’s Motion

Evidence of Earth’s RotationEvidence of Earth’s Rotation A A constellationconstellation is a group of stars that are organized in a is a group of stars that are organized in a

recognizable pattern. Over a period of several hours, recognizable pattern. Over a period of several hours, the constellations appear to have changed its position in the constellations appear to have changed its position in the sky. The rotation of Earth on its axis causes the the sky. The rotation of Earth on its axis causes the change in position.change in position.

Evidence of Earth’s RevolutionEvidence of Earth’s Revolution Earth’s revolution around the sun is evidenced by the Earth’s revolution around the sun is evidenced by the

apparent motion of constellations. apparent motion of constellations.

Thus different constellations will appear in the night sky Thus different constellations will appear in the night sky as the seasons change.as the seasons change.

The diagram below shows how the The diagram below shows how the constellations move across the sky.constellations move across the sky.