1. Solar System Astronomy

2. Solar System Astronomy Vocabulary Coriolis Effect: the tendency of matter moving across Earth’s surface to be deflected from a straight-line path. Eccentricity: the out-of-roundness of an ellipse. Eclipse: when either the Moon passes between Earth and the Sun or the Moon is in Earth’s shadow. Ellipse: a closed curve around two fixed points; called foci. The orbits of all planets around the Sun are ellipses. Focus (foci): one of the two fixed points is an ellipse. Foucault pendulum: a freely swinging pendulum whose path appears to change over time in a predictable manner; provides evidence of Earth’s rotation. Geocentric Model: any celestial model that has Earth at its center. Heliocentric Model: any celestial model that has Sun at its center. Jovian planets: Planets which are similar to Jupiter. Moon: the natural satellite of the earth, visible (chiefly at night) by reflected light from the sun. Revolution: the movement of one body around another. Rotation: the turning of an object on its own axis. Solar System: includes our Sun, the nine planets, and many Moons, and all the other objects that revolve around the Sun. Terrestrial planets: planets which are most similar to Earth. Tides: cyclic fluctuations in coastal water levels caused by gravitational forces between Earth, Sun, and Moon.

3. Our Solar System A solar system is any single star and all of the objects that revolve, or orbit, around it. Our solar system includes: –Eight planets (p. 15 ESRT) –Two main asteroid belts (one between Mars and Jupiter, one out past Neptune). Asteroid - rocky objects that orbit the sun –Comets - spheres of ice that are only visible when they are close to the sun –Meteor - small solid particles that burn off as they pass through Earth’s atmosphere (shooting star) Our solar system is heliocentric (“sun-centered”) Humans used to believe that all objects revolved around Earth. This was incorrect and is called geocentric (“Earth-centered”)

4. Heliocentric vs. Geocentric Helios (/ ˈ hi ː li. ɒ s/; Ancient Greek: Ἥ λιος Hēlios; Latinized as Helius; Ἠ έλιος in Homeric Greek) was the personification of the Sun in Greek mythology. geo- of or relating to the earth. "geocentric“ geology: the science that deals with the earth's physical structure and substance, its history, and the processes that act on it.

5. Solar System Data – p. 15 ESRT p. 15 ESRT shows the major objects in our solar system, organized by distance from the sun, and data associated with each object Highlight the line between Mars and Jupiter. This represents where the major asteroid belt is. It also separates the Jovian planets from the Terrestrial planets. Label the two groups of planets: –Terrestrial (“like Earth”) Planets – Mercury, Venus, Earth, Mars Smaller (less mass, smaller diameter) More dense (mostly made of solids) –Jovian (“like Jupiter”) Planets – Jupiter, Saturn, Uranus, Neptune Larger (more mass, bigger diameter) Less dense (mostly made of gas) Which planet has the longest day? –Venus Which planet has the longest year? –Neptune Which planet has the largest volume? –Jupiter Which planet would float in water? –Saturn There is an asteroid belt between Mars and Jupiter. How far from the sun is this? –227.9 – 778.4 million km

6. Revolution Revolution – one object’s movement around the other. –Ex: the moon revolves around Earth the Earth revolves around the sun One revolution of Earth is 365.26 days long. This is the time it takes for Earth to travel one time around the sun. As one object revolves around another it travels in an oval shaped path. This oval shaped path is called an ellipse. Ellipses can be almost round or pretty flat. Eccentricity measures how round or flat an ellipse is. –Rounder orbits are less eccentric (numerical values are smaller - closer to zero) –Flatter orbits are more eccentric (numerical values are larger - closer to one) less eccentric more eccentric

7. Calculating Eccentricity of an Ellipse Eccentricity = distance between foci length of major axis One of the focus points (foci) is the object that is being orbited (ex: the sun is one of the foci for Earth’s orbit). The other is an imaginary spot in space. The major axis is the line drawn straight through both foci to the edge of the ellipse. The major axis will always be larger than the distance between the foci. When we divide a smaller number by a larger number we always get a decimal. –Larger numbers represent more eccentric ellipses (flatter ovals) –Smaller numbers represent less eccentric ellipses (rounder ovals) Calculate the eccentricity for each ellipse. Show your work: ecc. = _3.3 cm__ = 0.485 ecc. = _2.2_cm_ = 0.400 ecc. = _1.5 cm__ = 0.385 6.8 cm 5.5 cm 3.9 cm UNITS CANCEL OUT – ECCENTRICITY VALUES HAVE NO UNITS!

8. Orbital Velocity Earth’s orbital path around the sun is an ellipse (oval, not round). Because of this, Earth is sometimes closer to the sun (perihelion) and sometimes farther (aphelion) from the sun. These differences in distance directly affect the gravitational pull of the sun on the Earth. –When the sun is closer (perihelion) there is a stronger gravitational pull –When the sun is farther (aphelion) there is a weaker gravitational pull This change in gravity affects the speed that the Earth moves in it’s orbit (orbital velocity) –Stronger gravity = faster velocity –weaker gravity = slower velocity Objects closer to us look bigger (farther look smaller) – apparent size Make a t-chart showing these variables: