Astronomy 1020-H Stellar Astronomy Spring_2016 Day-8

Course Announcements SW-2 … will download scores on Monday. SW-3 & 4 will be due soon-ish. 1 st set of Dark Sky observing nights: Mon. Feb. 8 – 7:30pm at the observatory. Tues. Feb. 9 is the weather backup if both are cancelled.

Why does the sky change over the course of a year? As we orbit the sun the direction opposite the sun changes and we only see the stars when the sun is not up

Color-Card Question Basic Motions & Ancient Astronomy: Seasonal Sky Analogy Apparent Motion of the Sun

Kepler’s First Law: The orbit of a planet about the Sun is an ellipse with the Sun at one focus.

Kepler’s Second Law: A line joining a planet and the Sun sweeps out equal areas in equal intervals of time.

According to Kepler’s second law, a planet with an orbit like Earth’s would: A. move faster when further from the Sun. B. move slower when closer to the Sun. C. experience a dramatic change in orbital speed from month to month. D. experience very little change in orbital speed over the course of the year. E. none of the above.

Kepler’s THIRD LAW The size of the orbit determines the orbital period planets that orbit near the Sun orbit with shorter periods than planets that are far from the Sun a 3 AU = P 2 years

Kepler’s THIRD LAW The size of the orbit determines the orbital period planets that orbit near the Sun orbit with shorter periods than planets that are far from the Sun p = 1 year p = ~ 12 years

Kepler’s THIRD LAW The size of the orbit determines the orbital period planets that orbit near the Sun orbit with shorter periods than planets that are far from the Sun MASS DOES NOT MATTER Both have p = 1 year

Which of the following best describes what would happen to a planet’s orbital speed if it’s mass were doubled but it stayed at the same orbital distance? A. It would orbit half as fast. B. It would orbit less that half as fast. C. It would orbit twice as fast. D. It would orbit more than twice as fast. E. It would orbit with the same speed.

Color-Card Question Renaissance Astronomy Kepler’s 3 rd Law

Newton’s First Law of Motion A body remains at rest or moves in a straight line at a constant speed unless acted upon by an outside (net) force. A rockets will coast in space along a straight line at constant speed. A hockey puck glides across the ice at constant speed until it hits something

Newton’s Second Law of Motion (net)Force = mass x acceleration or F net = m x a Acceleration is the rate of change in velocity – or how quickly your motion is changing. Three accelerators in your car!!