Astronomy 101 The Solar System Tuesday, Thursday 2:30-3:45 pm Hasbrouck 20 Tom Burbine

Course Course Website: – Textbook: –Pathways to Astronomy (2nd Edition) by Stephen Schneider and Thomas Arny. You also will need a calculator.

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

Homework We will use Spark owebcthttps://spark.oit.umass.edu/webct/logonDisplay.d owebct Homework will be due approximately twice a week

Exam #1 Average was 85 Grades ranged from 40s to 100s

HW #5 Due Thursday

A hypothesis is an educated guess, based on observation. Usually, a hypothesis can be supported or refuted through experimentation or more observation. A hypothesis can be disproven, but not proven to be true. A scientific theory summarizes a hypothesis or group of hypotheses that have been supported with repeated testing. A theory is valid as long as there is no evidence to dispute it. Therefore, theories can be disproven. A law generalizes a body of observations. At the time it is made, no exceptions have been found to a law.

assume all mass is concentrated in the center of a body

F = G M 1 M 2 r 2 The value of G was determined by Henry Cavendish between G = 6.67 x m 3 /(kg  s 2 ) calculate-the-gravitational-constant-like-cavendish- did/ calculate-the-gravitational-constant-like-cavendish- did/

What is the attraction of two people in this room? F = G M 1 M 2 r 2 Say their masses are both 100 kg Their distances are 10 meters apart F = 6.67 x m 3 /(kg  s 2 ) * 100*100 kg 2 /(10*10 m 2 ) F = 6.67 x N = N Remember the person weighs 980 N

F = G M 1 M 2 r 2 How would the force between the two people change if they were only 5 meters apart instead of 10 meters? A) Stay the same B) Double (Increase by a Factor of 2) C) Quadrupul (Increase by a Factor of 4) D) halve (decrease by a factor of 2)

F = G M 1 M 2 = G M 1 M 2 = 4 G M 1 M 2 (r/2) 2 r 2 /4 r 2 How would the force between the two people change if they were only 5 meters apart instead of 10 meters? A) Stay the same B) Double (Increase by a Factor of 2) C) Quadrupul (Increase by a Factor of 4) D) halve (decrease by a factor of 2)

Acceleration of gravity (g) M is the Earth’s mass F = ma = G Mm r is the Earth’s radius r 2 m is the mass of an object F is the force a is the acceleration a = G M r 2 g = a = G M r 2

Acceleration of gravity (g) M is the Earth’s mass g = G M r is the Earth’s radius r 2 g = 6.67 x m 3 /(kg  s 2 ) * (6.0 x kg) (6.4 x 10 6 m) * (6.4 x 10 6 m) g = 9.8 m/s 2

Gravitational acceleration Gravitational acceleration is different on different planets because they have different sizes and masses Gravitational acceleration (on Moon) = 1.6 m/s² (0.165 g) Gravitational acceleration (on Jupiter) = 24.8 m/s² (2.53 g)

Experiment on the Moon

How things fall Heavy and light objects fall at the same rate The heavy object does not fall faster (as long as there is no air resistance) g = G M (does not depend on mass of object) r 2

How does gravity work? Gravity distort space-time einsteins-messengershttp:// einsteins-messengers

Escape velocity Velocity above this will allow an object to escape a planet’s gravity For Earth: v = square root[(2 x 6.67 x m 3 /(kg  s 2 ) x (6.0 x kg)] (6.4 x 10 6 m) v = square root [1.25 x 10 8 m 2 /s 2 ] v = 11.2 x 10 3 m/s = 11.2 km/s v

Escape velocity Escape velocity is different on different planets because they have different sizes and masses Escape velocity (on Moon) = 2.4 km/s Escape velocity (on Jupiter) = 59.5 km/s

What causes tides on earth? Moon pulls on different parts of the Earth with different strengths khttp:// k

Forces on Water Average Force on 1 kg water on Earth from Moon F = G M m = 6.67 x m 3 /(kg  s 2 ) * (7.35 x kg) * (1 kg) r 2 (3.84 x 10 8 m) 2 F = 3.33 x N Force of 1 kg on water on near-side of Earth from Sun F = G M m = 6.67 x m 3 /(kg  s 2 ) * (7.35 x kg) * (1 kg) r 2 (3.84 x 10 8 m x 10 6 m) 2 F = 3.44 x N Difference in forces is 1.1 x N Called Tidal Force

Tidal force arises because the gravitational force exerted on one body by a second body is not constant across its diameter Water flows so this tidal force causes the tides that are seen on Earth

Effects on tides due to Sun Sun exerts a stronger gravitational force on the Earth But since farther away, the differential force from one side of the Earth to the other is smaller Sun’s tidal effect is about one-half that of the Moon

Forces on Water Average Force on 1 kg water on Earth from Sun F = G M m = 6.67 x m 3 /(kg  s 2 ) * (2 x kg) * (1 kg) r 2 (1.5 x m) 2 F = x N Force of 1 kg on water on near-side of Earth from Sun F = G M m = 6.67 x m 3 /(kg  s 2 ) * (2 x kg) * (1 kg) r 2 (1.5 x m x 10 6 m) 2 F = x N Difference in forces is 5.0 x N due to Sun Difference in forces is 1.1 x N due to Moon

Remember Force downwards is 9 Newtons on 1 kg of water Water won’t be pulled off Earth Water can flow

Shoemaker-Levy 9 Comet that hit Jupiter Jupiter-orbiting comet Broken apart by tidal forces Discovered in 1993 Hit Jupiter in 1994

Roche Limit The smallest distance at which a natural satellite can orbit a celestial body without being torn apart by the larger body's gravitational force (tidal forces). The distance depends on the densities of the two bodies and the orbit of the satellite. If a planet and a satellite have identical densities, then the Roche limit is times the radius of the planet. Jupiter's moon Metis and Saturn's moon Pan are examples of natural satellites that survive despite being within their Roche limits

Why is the Roche Limit important? Comet Shoemaker-Levy 9's decaying orbit around Jupiter passed within its Roche limit in July, 1992, causing it to break into a number of smaller pieces. All known planetary rings are located within the Roche limit

The first impact occurred at 20:15 UTC on July 16, 1994 Fragment A of the nucleus slammed into Jupiter's southern hemisphere at a speed of about 60 km/s. Instruments on Galileo detected a fireball which reached a peak temperature of about 24,000 K, compared to the typical Jovian cloudtop temperature of about 130 K, before expanding and cooling rapidly to about 1500 K after 40 s.

Has this happened before? Ganymede

Any Questions?