Earth Science

1. Earth Science Chapter 9 Earth in Space and Beyond

2. Earth in the Universe • Because the Universe is so large, the speed of light (186,000 miles/sec) is used to measure distances in space. • A light year is the distance light travels in 1 year (6 trillion miles). • Polaris is about 300 light years away. • The farthest known star system is about 12 billion light years away.

3. Earth in the Universe • A galaxy is a system of billions of stars. • Three types of galaxies: • Spiral galaxies - shaped like pinwheels with huge spiral arms. • Elliptical galaxies – look like blobs with no spirals and can be circular or flattened. • Irregular galaxies – have no definite shape.

4. Earth in the Universe

5. Earth in the Universe • Milky Way Galaxy • Spiral galaxy rotating counterclockwise • 230 million years per revolution around center • 100,000 light years across • 15,000 light years thick • Sun is on one arm 30,000 light years from nucleus

6. Earth in the Universe

8. Earth in the Universe • Sun • Mass is about 33,000 times Earth’s • Diameter is about 109 times Earth’s • Temp is about 6,000 K at surface and at surface and 12 million K at center • Average star (mass, diameter, and density) • Composed primarily of hydrogen and helium • About 5 billion years old (5 billion years left) • Sunspots are regions of cooler gas at surface

10. The Solar System • Solar system – includes Sun, 8 planets, many moons & all that revolves around Sun • Formed about 5 billion years ago from a giant cloud of gas and debris • The type of planet formed depends on conditions such as temp. and substances (rock fragments, ice crystals, gases) which exist at such distance. • Gravity caused planets to be layered according to density differences in their materials.

11. The Solar System • The characteristics of planets are affected by each planets distance from the Sun. • Terrestrial planets - planets made primarily of rock formed near the Sun where its heat drove off ices & gases. • Mercury, Mars, Earth, and Venus • Small dense planets which suggests that they primarily solid • Hard rocky surface with craters, canyons, and volcanoes

12. The Solar System • Jovian planets - far from the Sun, where temps. are low, planets retained volatile substances resulting in planets made primarily of gas (gas giants). • Jupiter, Saturn, Uranus, and Neptune • Large very low density planets which suggests they are primarily gas • Solid cores buried beneath atmospheres tens of thousands of kilometers thick.

14. Origin and Fate of the Universe • Doppler effect – a change of light or sound wavelengths as a source moves towards or away from the observer. • Light waves speeding away through space will stretch into longer wavelengths (red-shift). • Light waves speeding toward us will be squeezed into shorter wavelengths (blue-shift). • The red-shift is proof that the universe is expanding as all galaxies display the red-shift and are therefore moving away from us.

15. Deep Space Phenomena • Big Bang – powerful explosion of an incredibly dense mass that produced the expanding Universe that exists today. • Occurred 15 – 20 billion years ago • All matter in the Universe was concentrated in a single atom. • After explosion clouds of hydrogen and helium began to form, which led to the beginnings of galaxies and stars.

16. Deep Space Phenomena

17. Deep Space Phenomena • Formation of stars • Stars begin as nebula (huge masses of dust and hydrogen gas). • A nebula is compressed by gravitational forces and nuclear fusion begins. • Hydrogen is fused into helium and energy is released. • Some energy is released as light and a star is born.

20. Deep Space Phenomena • A pattern was discovered that allows stars to be compared by brightness and color. • Each point on an H-R diagram represents a star whose brightness (absolute magnitude) and color temperature (spectral type) have been determined. • Stars start out in the Main Sequence and as the core cools, they move into the giant category. • As the stars continues to collapse they become very small and very hot white dwarfs.

22. Celestial Observations • Celestial sphere – The imaginary sphere on which all objects in the sky seem to be located. • The horizon is where the sphere meets Earth. • The zenith is the point directly overhead. • The altitude is the distance above the horizon. • The azimuth is the distance in degrees measured clockwise from due north.

25. Celestial Observations • All celestial objects appear to move from E to W across sky due to Earth’s rotation. • Long-exposure photos of stars show that the stars form arcs called star trails. • Circumpolar stars & constellations • Located between the northern horizon & Polaris • Never set • Appear to move in counterclockwise circles

27. Celestial Observations • Constellations change slowly as Earth orbits the Sun. • Earth takes a year to go once around the Sun, thus darkened portion of Earth is pointed toward different directions throughout the year. • If you follow a specific constellation on successive evenings, it will rise about 4 minutes earlier every night.

30. Celestial Observations • Planetary motions • Planets also move from E to W across sky • Over long periods of time the planets seem to change position relative to the stars around them. • Planets don’t shift as much as the stars, thus the planets actually move eastward relative to the star fields behind them.

31. Models to Explain Celestial Motions • Geocentric model • Suggested by Ptolemy 2000 years ago • Earth is stationary (not rotating or revolving) and all celestial objects move around it at fixed distances from it. • Widely accepted because it explained all of the daily motions of the Sun, planets, & stars. • The retrograde motion (backwards) of some planets was explained by showing they move in small circles called epicycles.

33. Models to Explain Celestial Motions • Heliocentric model • Suggested by Copernicus in the early 16th century. • Model used at present time • Earth and planets revolve around the Sun and Earth rotates on its axis. • The apparent retrograde motion of some planets is caused by the fact that each planet revolves around the Sun at a different speed.

35. Orbital Forces • Kepler’s Laws of Planetary Motion • The orbits of the planets around the Sun are ellipses, with the Sun at one foci. • Planets travel in closed curves called ellipses. • The center of the ellipse consists of two fixed points, called foci.

36. Orbital Forces • Eccentricity is the out of roundness of an ellipse (e = d/L). eccentricity = distance between foci length of major axis d L

37. Orbital Forces • An imaginary line joining a planet to the Sun will sweep over equal areas in equal periods of time. • A planet travels fastest and farthest when it is nearest the Sun (perihelion). • A planet travels slowest and covers the least distance when it is farthest from the Sun (aphelion).

39. Orbital Forces • The square of any planet’s orbital period is proportional to the mean radius of its orbit cubed. • The period of a planet equals its year. • The farther a planet is from the Sun the larger its orbit and the longer its period.

40. Orbital Forces • Newton’s Universal Law of Gravitation • The gravitational force between any two objects is in the Universe is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers. • As the masses increase, the gravitational force increases. • As distance between the objects increases, gravitational force between them decreases.

41. Earth’s Rotation • Evidence of Earth’s rotation • Foucault Pendulum • A swinging pendulum changes its direction of motion in a predictable manner as Earth rotates under it. • The rate of change in the direction of a pendulum on Earth depends on its latitude. • At the equator it is 0 deg/hour. • At the poles it is 15 deg/hour. • At our latitude it is 10.5 deg/hour.

44. Earth’s Rotation • Motions of the sun • Due to Earth’s rotation, the Sun appears to move E to W at a rate of 15 degrees per hour. • Because Earth’s axis is tilted at 23.5 degrees, the latitude at which direct rays strike Earth’s surface changes in a cyclic pattern. • Seasonal changes are caused by: • Tilt of Earth’s axis • Parallelism of Earth’s axis • Revolution around the sun

47. Moon and Its Effects • The Moon, like all celestial objects, appears to move from E to W across the sky. • As the Moon makes one revolution around Earth, it also makes one rotation on its axis. • The same side of the Moon is always facing Earth.

48. Moon and Its Effects • Because Earth orbits the Sun as the Moon revolves around Earth, the Moon must actually travel farther than one revolution to complete a cycle of phases. • 27 1/3 days to complete one revolution around Earth (sidereal month) • 29 1/2 days to complete a cycle of phases (synodic month)

49. Moon and Its Effects • The shape of the Moon’s orbit is elliptical • Its closest distance from Earth (perigee) is about 356,000 km • Its farthest distance from Earth (apogee) is about 407,000 km • The position of the Moon with respect to the Sun and Earth is responsible for Earth tides, Moon phases, and eclipses.

50. Tides • The cyclic changes in Earth-Moon Sun alignments are responsible for cyclic fluctuations in the high and low tides of oceans and other large bodies of water. • Tides fluctuate throughout the course of the day as well as the month. • Every day large bodies of water experience two cycles of high tides and two cycles of low tides.