Astronomy Part 2

2. Astronomy Part 2 • By Sahithi And Morgan

3. 2.1 Formation of the sun and the planets The Nebular Hypothesis was that our Solar System formed from a spinning cloud of gas and dust. This nebula was drawn together by gravity. As particles began to come together in the center, it released kinetic energy and gravity increased. Today's planets were caused by the collision and collection of particles. This process is called accretion. This process first created Planetesimals. Planetesimalsare nothing but baby planets or beginning planets.

4. 2.2 Minor Members of our Solar System There are three types of minor members in our solar system, Asteroids, Meteors and Comets. Asteroids are small, rocky bodies that orbit the sun. Asteroids mainly lie between Mars and Jupiter. This ring of Asteroids divide the inner and the outer planets. Asteroids didn’t become planets due to the gravitational pull of Jupiter.

5. 2.2 Minor Members of our Solar System Meteors are a chunk of space debris that enters Earth's atmosphere and burns up, creating a streak of light. Meteors are the ones that are in the atmosphere. Meteoroids are a chunk of space debris, smaller than Asteroids, that hasn’t yet reached the Earth's atmosphere. Meteorite is a large meteoroid that strikes the Earth's surface. These are all the same thing except that they are based on their location. Remember, if it hits the earth, it's meteorite, if it doesn’t hit the earth, its meteor-WRONG.

6. 2.2 Minor Members of our Solar System Halley’s Comet Comets are small, icy objects that have very elliptical orbits around the sun. Comets are also called dirty snowballs. Comets may have brought water and other materials when in collision. A comet's tail always points away from the sun due to solar wind. There are two types of comets: Short period and Long period. Short period comets come from the Kuiper Belt and Long period comets come from the Oort Cloud. Both of these are located outside the orbit of the planet Neptune. One example of a comet is the Halley’s Comet. It is expected to appear again in 2061.

7. 2.3 & 2.4 Revolutions and Rotations of the Earth Geocentric Model Johannes Kepler The Geocentric Universe: The ancients believed that the universe revolved around Earth. The word "Geo" in Geocentric means Earth and the word "Centric" means center. Hence, Earth centered. The Heliocentric Universe: About 1500 years later, Nicolaus Copernicus made a model of the universe that placed the Sun in the center. The word "Helio" in Heliocentric means the sun. Johannes Kepler later perfected it with his 3 laws of Planetary Motion. The three laws were that the planets orbit in ellipses and not in circles, Planets orbit faster when closer to the Sun and Calculated the time it takes a planet to orbit.

8. 2.3 & 2.4 Revolutions and Rotations of the Earth Earth's Revolution- A year has 365.24 days. The Leap Year makes up the .24 of the day from the four years. Perihelion is the point where the Earth is closest to the Sun. Aphelion is the point where the Earth is farthest from the Sun. Earth's Rotation- Earth rotates on its Axis, an imaginary line through the center of Earth from pole to pole. One rotation takes 24 hours (1 day). Everything in the sky appears to rise from the East and set in the West.

9. 2.5 The Precession of the Earth's Axis Earth's axis is tilted about 23.5 degrees and does not remain stationary. The axis wobbles very slowly like a top. This wobble is called Precession. The cause of the precession is the bulge at the equator of the Earth. Earth is not a perfect sphere, it is slightly fatter at the equator. Hence, the Earth is called an Oblate Spheroid. The angle of the axis also varies slightly. This type of wobble is called Nutation.

10. 2.6 Seasons

11. 2.6 Seasons • Four Seasons- Winter, Spring, Summer and Fall • Seasons are NOT caused by how close the Earth is to the Sun. • Solstice is when the Sun reaches the highest or lowest point in the sky at noon, marked by longest and the shortest days. • Summer: June 20/21 • Winter: December 21/22 • Equinox is the time or date(twice a year) at which the Sun crosses the celestial equator, when day and night are equal. • Vernal: March 20 • Autumnal: September 22/23

12. 2.7 & 2.8 Moon and its Phases Moon is less dense and less massive than the Earth. Gravity in the Moon is 1/6 of the gravity in the Earth. The moon revolves around Earth every 27.3 days. The moon also rotates the same amount of days. Due to this, we only see one side of the Moon. There is no atmosphere but there are different types of surfaces on the Moon. • Craters: Large, bowl-shaped cavities caused by impacts, such as asteroids • Maria: Large, level basalt plains on the surface of the moon, appearing dark by contrast with highland areas • Terrae(highlands): Light-colored, rough upland or mountain regions • Regolith: The layer of loose rock and dust that covers the surface

13. 2.7 & 2.8 Moon and its Phases Waxing: Illuminated area is “growing” right to left Waning: Illuminated area is “growing” right to left Gibbous: greater than half Crescent: less than half The Phases of the Moon is caused by the Sunlight and the Earth’s position. Waning Waxing

14. 2.9 Eclipses Solar Eclipse: Moon is b/w Earth and Sun. This type of eclipse always occurs during a new moon. Only one small area on Earth is visible. There are three types: • Total Solar Eclipse: Sun is fully covered by the Moon • Annular Solar Eclipse: Sun and Moon are lined up but the Moon looks smaller than the Sun • Partial Solar Eclipse: Sun is partially covered by the Moon since they aren’t all lined up.

15. 2.9 Eclipses Lunar Eclipse: Earth is b/w Moon and Sun. This type of eclipse always occurs during a full moon. This eclipse can only be seen by people on side of the Earth that is facing the Moon. Eclipses don’t happen every month b/c the Moon’s orbit is a bit off. Umbra: Total shadow Penumbra: Partial shadow

16. THE END! 