Unit II Astronomy

Our Solar System Early astronomers used to think that the sun, stars and other planets orbited a stationary Earth – geocentric view (Earth centered) Most planets moved toward the east Mars does not move toward east, called retrograde motion

Formation of Our Solar System Theory as to how our solar system formed Interstellar clouds exist between stars Contain gases mostly helium and hydrogen Density is very low but gravity can cause cloud to condense and form stars or planets

Formation of Our Solar System At first collapse is slow, then it speeds up Cloud becomes more dense at its center The cloud will flatten and becomes a rotating disk with dense concentrations at the center

Formation of Our Solar System When the cloud slowed, the material started to condense and form larger bodies More and more stuck together to form planetesimals planetesimals hit each other, some were destroyed and others stuck together

Formation of the Solar System Jupiter was the first planet to form in the outer solar system grew larger as it attracted more planetesimals Saturn and other planets formed but could not be as large since Jupiter had most of materials Inner planets are rocky while outer planets are gaseous – sun may have gas from inner area

Big Bang Theory The universe is expanding The big bang theory refers to an expansion of space with matter Means the universe had a beginning

Steady-State Theory The universe has always looked this way States new matter is created as the universe is expanding Reason why the overall density of the universe is not changing More evidence supports the Big Bang Theory

Our Solar System In 1543 Polish scientist Copernicus stated the heliocentric view (sun centered) - not well accepted at first Earth and the other planets orbited the sun helped explain retrograde motion since the closer planets would revolve more quickly than the outer planets

Kepler’s Laws 1 st law - planets revolved around the sun in an ellipse rather than a circle 2 nd law – an imaginary line sweeps out from the sun to all of the planet equal amounts of area in equal amounts of time 3 rd law – mathematical relationship between a planet’s ellipse and its orbital period

Earth 3 rd planet from the sun Axis is tilted which creates our seasons – determines the amount of solar radiation impacting Earth’s surface

Precession Precession is the change in direction of the axis, but without any change in tilt Does not affect seasons as long as it stays 23.5 degrees Takes about 26,000 years to go through one precession

Nutation Nodding around the precessional axis Change in angle ½ degree either way Occurs over an 18 year period and due to the moon Very slightly increases or decreases the amount of seasonal effects

Barycenter The point between two objects where they balance each other Ex. When a moon orbits a planet, both bodies actually orbit a point that lies outside the larger body (primary) Moon orbits the earth approximately 1,710 km below the surface of the Earth where their masses balance

The Sun not stationary in our solar system Actually moves as the planets tug on it, causes it to orbit the solar system’s barycenter Never goes too far from the solar system barycenter Much larger than any of the planets

Sun-Earth-Moon System Sun provides light and warmth, source of energy that fuels our society Moon raises tides and goes through phases that light up our sky Calendars are based on the motions of sun and moon

Daily Motions Sun rises in the east and sets in the west due to Earth’s rotation Earth rotates once every 24 hours or 15° per hour Can be shown by Foucalt pendulum that swings in a constant direction

Day Length length of a day takes a little longer than the time it takes the Earth to rotate on its axis once As it is rotating it is also moving along its orbit Time period from sunrise to sunrise or sunset to sunset is called a solar day Timekeeping is based on solar day

Earth’s Tilt Annual change is season is due to Earth’s movement around the sun The plane in which the Earth orbits the sun is called the ecliptic Earth’s axis is tilted 23.5° relative to the ecliptic For 6 months the Northern Hemisphere is tilted toward the sun and the other 6 months the Southern Hemisphere is tilted toward the sun

Summer Solstice around June 21 st sun is directly overhead of the Tropic of Cancer which is at 23.5° north latitude maximum daylight hours in Northern Hemisphere and the least amount of daylight in Southern hemisphere

Winter Solstice Sun is directly over the Tropic of Capricorn at 23.5° south latitude around December 21 st daylight in the Northern Hemisphere is at a minimum and at a maximum in the Southern Hemisphere

Equinoxes Both hemispheres receive equal amounts of sunlight sun is directly overhead of equator autumnal equinox is September 21 st vernal (spring) equinox is March 21 st

Equatorial Bulge Difference in Earth’s diameter between the equator and the poles Due to centripetal force in motion A rotating body will form an oblate spheroid instead of a sphere

Composition of the Sun The sun is 70.4% hydrogen and 28% helium by mass Contains a small amount of several other elements largest object in our solar system – both in size and mass - more than 99% of all the mass in the universe

Solar Interior core of the sun where pressure and temperature are very high – fusion occurs Fusion is the combining of smaller nuclei into a larger nuclei (nuclei is plural of nucleus) Fusion is the process that produces the radiant energy of stars Fission is the opposite – splitting of larger nuclei into smaller nuclei

Sun’s Energy Radiation – transfer of energy by electromagnetic waves Takes about 8 minutes to reach the Earth Energy is transferred from the sun to the Earth by electromagnetic waves (radiation)

Sun’s Energy cont. Most of the energy that reaches the Earth is either infrared or visible light When sunlight enters the Earth’s system it can be absorbed or reflected ml ml Global energy balance

Solar Wind Gas flows outward of the corona to form the solar wind charged particles or ions flow through the solar system Earth’s magnetic field deflects the particles

Electromagnetic Radiation Electromagnetic radiation is electric and magnetic disturbances traveling through space as waves The human eye can only detect a small range called visible light Includes infrared and ultraviolet radiation, radio waves, microwaves, x rays and gamma rays

Electromagnetic Radiation classified by wavelengths or frequency A wavelength is the distance between peaks on a wave Longer wavelength = lower frequency Shorter wavelength = higher frequency

Electromagnetic Radiation All types of electromagnetic radiation travel at the speed of light, their wavelengths and frequencies are different

The Moon one of the largest in the solar system radius is about 27% of the Earth Most moons are much smaller in relation to the planet they orbit moon is also relatively far away from the Earth than other moons, only inner planet moon

Surface of the Moon moon does not reflect much of it sunlight Has no atmosphere Temperatures can be as warm as 127°C or as cold as -173°C

Phases of the Moon new moon occurs when the moon is in- between the Earth and the sun moon appears dark since the “sunny” side is not facing us

Phases of the Moon cont. moon continues to orbit we see more and more – waxing less than half - waxing crescent more than half - waxing gibbous

Phases of the Moon cont. As we see less and less of the moon - waning Waning gibbous - more than half of the moon Waning crescent - less than half of the moon

Synchronous Rotation same side of the moon faces the Earth all the time moon spins exactly one time as it orbits the Earth – synchronous rotation Probably due to Earth’s gravity

Tides moon pulls on the Earth which causes tides ocean will rise and fall every 12 hours sun also pulls on the Earth but not as much as the moon

Tides When the sun and moon align we have spring tides - higher than normal When the moon is at a right angle to the sun- earth line there are neap tides - lower than normal

Moon not always the same distance from the Earth perigee is when the moon is closest to the Earth apogee is when the moon is farthest away from the Earth

Lunar Eclipse occurs when the moon passes through the Earth’s shadow Can only occur at a full moon When is the next lunar eclipse that we will be able to see?

Solar Eclipse when the moon passes between the sun and the Earth and blocks our view of the sun does not occur every month since the moon is tilted at a 5°angle to the ecliptic Usually the moon is slightly north or south

Hertzsprung-Russell Diagram Each star has a specific mass, luminosity, magnitude, temperature and diameter Can be graphed on a H-R diagram About 90% of stars are on the main sequence from the upper left to the lower right of the diagram

Hertzsprung-Russell Diagram cont. The upper left are the hot, luminous stars and the lower right are the cool, dim stars The large, cool, luminous stars are called red giants – upper right corner The small, dim, hot stars are called white dwarfs - lower left corner