4.4 – 4.5

The Sun (Sol) closest star to the earth made mostly of hydrogen and helium spins in a circle about once a month about 93 million miles from earth The sun has many layers Granule “Bubble” of rising plasma that gives a speckled look to the sun’s surface 1. core hottest portion of the sun about 27,000,000 F

2. photosphere visible portion of the sun It’s name means the “sphere of light” Most of the photosphere is about 10,000 F It is the surface of the sun. sunspots spots on the photosphere that are cooler than the rest of the sun Sunspot Granule

solar eclipse occurs when the moon passes between the Earth and Sun 3. chromosphere part of the sun’s atmosphere closest to the surface called the “sphere of color” usually pink or orange in color spicules spikes of hydrogen gas from the chromosphere

solar prominences huge loops of cooler gas that erupt and rise thousands of miles above the sun’s surface solar flare large explosion on the sun’s surface caused by a change in the sun’s magnetic field can actually be powerful enough to disrupt radio and electrical power on the earth

Solar Prominence Solar Flare

hottest region of the sun’s atmosphere 4. corona hottest region of the sun’s atmosphere reaches temperatures of 6,000,000 F Solar winds Particles that escape from the corona and fly through space at about 2 million mph Our magnetic field protects us from solar winds

Long-distance measurements light year the distance light travels in one year 186,000 miles per second 5.9 trillion miles per year Proxima centari is about 4.2 light years from earth The milky way is about 100,000 light years across

Star Magnitude magnitude brightness of a star absolute magnitude how much light the star produces the brightness of a star when measured up close apparent magnitude the brightness of a star as it appears from earth

In addition to magnitude, stars are often classified by color. the hotter the star the brighter it will appear four major colors reds – 5,000 F yellows – 10,000 F whites – 20,000 F blues – 40,000 F

Stellar Siblings Giants and Dwarfs The Sun is an average size star Giants can reach 150,000,000 miles across Dwarfs can be as small as 12 miles across Stellar Siblings Binary stars Two stars that travel around each other and appear as one star

Stellar explosions Optical double Two stars that appear to be close from earth but are actually far apart Stellar explosions Nova When a star flares up to many times its original brightness Supernova When a star actually explodes and becomes extremely bright then dark

Early ideas in astronomy Ancient astronomers spent hours studying the night skies without the aide of telescopes. They observed five “stars” moving independently of the other stars in the sky. The “stars” were given the name planets. Astronomers in ancient Greece discovered the earth is not flat but round. Planets Means “wanderers” Claudius Ptolemy Proposed a geocentric theory (150 AD) Earth centered universe

Nicolaus Copernicus (1530 AD) He introduced the Heliocentric theory Sun centered solar system He stated that all planets orbit or revolve around the sun in perfect circles. Copernicus was ridiculed and much of his work was rejected in favor of the work of Ptolemy and Aristotle Galileo Scientist who made great improvements to the telescope He provided support to Copernicus after observing that Jupiter’s moons orbit Jupiter

Geocentric and Heliocentric models

Oval pattern that the planets travel around that contain 2 foci Johannes Kepler German astronomer that said his goal was “finding mathematical harmonies in the mind of the Creator” Kepler said that planets orbit the sun in an ellipse instead of a circle Ellipse Oval pattern that the planets travel around that contain 2 foci Foci (plural for focus) 2 central points within the ellipse

Kepler used his understanding of math and astronomy to produce three laws of planetary motion First law Every planet orbits the sun in an ellipse, with the sun as one of the foci of the ellipse and an empty point in space as the other Second law As a planet moves closer to the sun, it travels faster, and as it moves farther away it slows down

Measurement of the distance between the earth and the sun Third law Shows the relationship between a planet’s distance from the sun and the time it takes the planet to complete one orbit He realized that a planet must be further away from the sun if it takes longer to orbit, and Kepler used astronomical units to measure that distance Astronomical unit Measurement of the distance between the earth and the sun The inner planets travel around the sun at a much faster pace than do the outer planets Mars is 1.5 AU from the sun Saturn is 9.5 AU from the sun

Sir Isaac Newton Kepler described what planets do, but he did not know why. Newton answered that question with his discovery of gravity and the law of universal gravitation. Gravity The force of attraction that exists between any two objects Law of universal gravitation The strength of the gravitational force between two objects depends on their masses and the distance between them Gravity holds the planets in their orbit as they circle around the sun

Study This Solar Flare Corona Solar Wind Light year Solar prominence Solar Flare Corona Solar Wind Light year Speed of light in miles/sec and miles/year Proxima centauri Absolute magnitude 4 Galaxies Constellation Nebula North Star Axis of Rotation Ursa Major Big Dipper Cassiopeia Perseus Cygnus Gemini Orion Betelgeuse Rigel Canis Major Southern Cross Sirius Sun Core Distance from the earth to the sun Photosphere Solar Eclipse Chromosphere

Study This Apparent magnitude Giant Dwarf Binary star Optical Double Nova Supernova Planet Ptolemy Copernicus Galileo Kepler Ellipse Isaac Newton Gravity