Life in the Universe

Frank Drake spent many years looking for life in the universe. It is a more difficult problem to find intelligent life, which was the objective of the SETI project. In ancient times the search spread from South America to the North, and from West Eurasia to the East. The contact between Columbus and the natives was October 12, 1492. Russia and the U.S. started exploring in the 1960’s to search for life outside of Earth, but even 50 years later there is still no evidence. Alan Boss started his study of the formation of the solar system under the guidance of Stanton Pearle at UCSB in 1975, which ended in 1979, and also started Theoretical Planetology in that same year. Michel Mayor and Didier Queloz discovered the first extrasolar planet in 1995. The Kepler spacecraft was sent in March 2009 to search for these planets. President George W. Bush had announced on January 14, 2004 of the intention to put a man on Mars. NASA currently has an active rover program to study Mars but there is still no evidence of life.

Chapter 2.1

What does the universe look like? With the naked eye we can see over 2000 stars as well as the Milky Way. A constellation is a region of the sky, with over 88 constellations filling the sky. Stars at different distances all appear to lie on the celestial sphere. The ecliptic is the sun’s apparent path through the celestial sphere. The 88 official constellations cover the celestial sphere. The Milky Way is a band of light that makes a circle around our celestial sphere. It is our view into the plane of our galaxy. An object’s altitude( above horizon) and direction(along the horizon) specify its location in our local sky. Zenith(point directly overhead), horizon(all points 90 degrees from zenith.) You measure the sky using angles. One degree is equal to 60 arc minutes, and one arc minute is equal to 60 arc seconds. Angular size= physical size x 360 degrees/ 2 pi x distance. An object's angular size appears smaller if it’s farther away. Why do stars rise and set? Earth rotates west to east, so stars appear to circle from east to west. Stars near the north celestial pole are circumpolar and never set. We cannot see stars near the south celestial pole. All other stars(the sun, moon, planets) rise in the east and set in the west. The constellations we see depend on latitude because your position on Earth determines which constellations remain below our horizon. Time of the year determines the location of the sun in the sky. The sky varies with latitude but not longitude . Your altitude is equal to the altitude of the celestial pole.

Chapter 2.2

Seasons depend on how the Earth’s axis affects the directness of sunlight. Axis tilt changes the directness of sunlight during the year. The sun’s altitude also changes with the seasons. The sun’s position at noon in the summer is high due to more direct sunlight, and is low at noon in the winter due to less direct sunlight. The real reason for seasons is that Earth’s axis points in the same direction(Polaris) all year round, so orientation to the sun changes as the Earth orbits the sun. Distance doesn’t matter because the variation of Earth’s distance to the sun is small, only about three percent, which is overwhelmed by the tilt of the axis. There are four special points that mark the progression of the seasons, the summer solstice(sun is at its highest path, and rises and falls at the most extreme north of the sky due east), the winter solstice(sun is at its lowest path, and rises and falls as its most extreme north due east), and the spring and fall equinox, in which the sun rises precisely due east and sets precisely due west. Seasonal changes, however, are more extreme at high altitudes. The axis’ tilt is 23.5 degrees, but precesses every 26,000 years, meaning Polaris won’t always be the North Star.

Chapter 2.3

Lunar phases are a consequence of the Moon’s 27.3 day orbit around Earth. Half of the Moon is illuminated by the sun, the other half is dark. We see a changing combination of bright and dark faces as it orbits the Earth, but we only see one side of the Moon due to synchronized rotation, where the Moon rotates exactly once with each orbit. Eclipses are caused when the sun and Moon cast shadows. When either passes through each other’s shadow we have an eclipse. Lunar eclipses can only occur during the full moon. In order for an eclipse to occur, the must either be a full moon for a lunar eclipse or a new moon for a solar eclipse, and the Moon must be at or near one of the two points in its orbit where it crosses the ecliptic plane.

Chapter 2.4

Retrograde motion occurs when we pass up a planet and it seems to go backwards, going from east to westwards, also called a parallax.