Astronomy 101 The Solar System Tuesday Thursday 2

Astronomy 101 The Solar System Tuesday, Thursday 2: 30 -3: 45 pm Hasbrouck 20 Tom Burbine tomburbine@astro. umass. edu

Course • Course Website: – http: //blogs. umass. edu/astron 101 -tburbine/ • Textbook: – Pathways to Astronomy (2 nd Edition) by Stephen Schneider and Thomas Arny. • You also will need a calculator.

Office Hours • Mine • Tuesday, Thursday - 1: 15 -2: 15 pm • Lederle Graduate Research Tower C 632 • Neil • Tuesday, Thursday - 11 am-noon • Lederle Graduate Research Tower B 619 -O

Homework • We will use Spark • https: //spark. oit. umass. edu/webct/logon. Display. d owebct • Homework will be due approximately twice a week

HW #3 (due today) • 10 questions • In Assessment in Spark

Hw #4 (due Monday) • Under Assessments in Spark

Exam #1 • Next Thursday • Material we cover today will be on the exam

New Discovery • http: //www. cnn. com/2009/TECH/space/09/16/ne w. rocky. planet/index. html

Nicholas Copernicus (1473 -1543) • Copernicus came up with a model that the Earth revolves around the Sun • Similar to what Aristarchus (310 – 230 BC) thought 2000 years before • However, Copernicus’ models did not match observations since he wanted everything to arouind in perfect circles

Tycho Brahe (1546 -1601) • Tycho Brahe was the greatest naked eye observer of all time • He lived before the invention of the telescope • His observations of the alignment of Jupiter and Saturn occurred two days later than when predicted by Copernicus • Tycho came up with a model where the planets orbit the Sun but the Sun orbits Earth

Johannes Kepler (1571 -1630) • Tried to match circular orbits to Tycho’s data • Couldn’t do it • Because Tycho’s observations were so good, Kepler had to come up with a new model

Kepler was trying to match an orbit to Tycho’s observations of Mars • “If I believed that we could ignore these eight minutes of arc, I would have patched up my hypothesis accordingly. But, since it was not permissible to ignore, those 8 minutes pointed to the road to a complete reformation in astronomy. ” • Kepler came up with his 3 laws of planetary motion

Kepler’s st 1 Law • The orbit of each planet about the Sun is an ellipse with the Sun at one focus (there is nothing at the other focus)

Differences between ellipses and circles

Eccentricity (e) • e = distance between the two foci/length of major axis • e of circle is 0 • The larger e becomes, the more eccentric the orbit

Definitions • Perihelion – planet closest to the Sun • Aphelion – planet farthest from the sun • Semimajor axis (a) – the average of a planet’s perihelion and aphelion distances

Kepler’s nd 2 law • As a planet moves around its orbit, it sweeps out equal areas in equal times. • This means that the planet travels faster when it is nearer the Sun and slower when it is farther from the Sun

• http: //surendranath. tripod. com/Applets/Dynamics/ Kepler/Kepler 1 Applet. html

Kepler’s rd 3 Law • More distant planets orbit the Sun at slower average speeds, obeying the precise mathematical relationship p 2 = a 3 where p is a planet’s orbital period in years and a is the average distance from the Sun in astronomical units (AU).

Calculations • The period for the Earth to go around the Sun is 1 year • The average distance of the Earth to the Sun is 1 Astronomical Unit (AU)

How long does it take Jupiter to go around the Sun • If Jupiter is 5. 2 Astronomical Units from the Sun, how long does it take Jupiter to go orbit the Sun once • p 2 = a 3 = 5. 23 = 140. 6 • p = √ 140. 6 = 11. 9 years

Another example • Mercury is 0. 4 Astronomical Units from the Sun. • How long does it take Mercury to orbit the sun once? – A) 1 year – B) 3 months – C) 9 months – D) 5 years

The calculation • p 2 = a 3 = 0. 43 = 0. 064 • p = √ 0. 064 = 0. 25 years

• An asteroid takes 8 years to go around the Sun • How far is the asteroid away from the Sun? – A) 1 AU – B) 3 AU – C) 4 AU – D) 8 AU

The calculation • a 3 = p 2 = 82 = 64 • a = (64)1/3 = 4 AU

You can calculate a planet’s orbital speed • Since you know a planet’s orbital distance • And you know its orbital time • You can calculate a planet’s average orbital speed

Orbits • • all the planets orbit the Sun in a counterclockwise direction (but they do not orbit it at the same rate). The Earth rotates counterclockwise

Arguments against the Sun being the center of the solar system • 1) If the Earth was moving, objects such as birds and clouds would be left behind as the Earth moved • 2) The heavens must be perfect and unchanging. Noncircular orbits do not fit this model • 3) Stellar parallax would be observable

Galileo Galilei (1564 -1642) • He was able to figure out answers to these arguments • 1) Things in motion tend to remain in motion. • 2) He used a telescope to see sunspots on the Sun and features on the Moon. • 3) Galileo found that stars were more numerous and more distant than imagined

He also • He discovered the moons of Jupiter and saw that they were orbiting Jupiter • Proving that bodies could orbit other bodies besides the Earth

Galileo also found that Venus orbited the Sun

Who came up with the first understanding of how gravity and forces really work?

Isaac Newton (1642 -1727)

http: //www. hulu. com/watch/63319/cosmos-the-harmony-of-the-worlds

Any Questions?