AIM: What is Astronomy? Do Now: Answer the following question in your notebook. Where is the sun in our solar system? What percent of our Solar System’s mass is occupied by the Sun? The sun makes up about 99% of our solar systems mass.

I. Astronomy is the science that studies the universe and all objects in it. **Apparent motion= what an object appears to be doing, not what it is actually doing** Why do some objects appear to be moving in space?

II. Two Views: Geocentric: - Earth is motionless at the center of the universe; all planets including the sun revolve around it. Heliocentric: - Sun is the center of the solar system; all planets revolve around it. (Simple explanation) Which one is true? Heliocentric

III. Planetary Motion - Johannes Kepler made observations of objects in the night time sky. In doing this he discovered that: 1. The path of each planet around the sun is an ellipse (oval-shape), with the sun as one focus. - a focus is an object that a planet moves around.

Focus 1 Focus 2 Major Axis Eccentricity = Distance between the foci Length of the major axis - Eccentricity measures the ellipse and describes it’s shape. ESRT Cover

Eccentricity = 1 (a line) Eccentricity = 0.5 Eccentricity = 0 (a circle) FF FF F From the back table take an Ellipse worksheet from the top bin and a ruler Most Eccentric Least Eccentric - Eccentricity can described a planets ellipse as:

2. The closer a planet is to the Sun (foci) the faster it revolves. Faster Slower

Astronomical unit (AU) - it is about 150 million kilometers. - is the average distance between Earth and the sun. Light Year - the distance light travels in one year. IV. Measurement in Space

V. Gravitational Force In which diagram does the star have the greatest gravitation force? The greatest mass and least distance increases as distance between objects decrease. (closer together = stronger force) increases as mass increases. (more mass = more force)

VI. Other Motion: Retrograde Motion is the apparent westward motion of planets as compared to the background stars.

Closure: - Obtain an “Intro to Astronomy” worksheet (back top bin) -Using your ESRT and the notes answer the questions. Focus 1 Focus 2 Major Axis Eccentricity = Distance between the foci Length of the major axis