HUGE NEWS – Discovery of Gravitational Waves!
Washington site
Louisiana site
Laser Interferometer
Gravitational-Wave
Observatory (LIGO)

HUGE NEWS – Discovery of Gravitational Waves!
E = mc 2
Washington site
Louisiana site
Energy released as gravitational waves equal to mass-energy of 3 solar masses
(about 10 31 kg)
Recall: Converting
0.1 kg to energy gives you this:

Average: 68.2% Scores available on Blackboard
High: 100%
Exam #1 likely to be most difficult exam.
You can see your exam by visiting office hours.

A hot solid (like a piece of metal or rock) gives off a light spectrum like… – see images below – A, B, C from top to bottom:
Blackbody (thermal) radiation

The Moon does not rotate.
- Wrong! The Moon rotates once every month (29.5 days).
The unseen far side of the Moon is always dark.
- Wrong! Far side of the Moon gets as much sunlight as the side facing us over the course of a month.
You can’t see the Moon during the day.
- Wrong! The Moon is often up during the day.
The Moon phases are caused by the Earth’s shadow.
Wrong! No phase is caused by Earth’s shadow. The phases are caused by different illuminations of the side of the Moon facing Earth.

 Half of Moon is illuminated by Sun and half is dark at all
times.
 The phase of the Moon depends on what fraction of the lit half is visible from Earth .
 There is no “dark side of the Moon” – this is a misnomer
 There is a “back side of the Moon” which never faces Earth
Earth’s shadow does not cause Moon phases!

It takes the Sun ~30 days to move through one zodiac constellation. But all stars plus Sun rise and set each day because of Earth’s rotation. STARS ARE NOT “FIXED” IN
THE NIGHT SKY!

The angular momentum of a planet around the Sun
A) is greatest when the planet is nearest the Sun.
B) is greatest when the planet is farthest from the Sun.
C) is always the same regardless of where the planet is in its orbit.
D) is proportional to the square of the period of the planet around the Sun.
Angular momentum (m *v *r) is conserved
 it is always a constant value

• We can learn more about a world like our
Earth by studying it in context with other worlds in the solar system.
• Stay focused on processes common to multiple worlds instead of individual facts or trivia specific to a particular world.
• In general, we want to answer the question
“why” rather than “how many” or “how far”.

 There currently are eight major planets (sorry,
Pluto, Planet 9) with nearly circular orbits orbiting the Sun in the same direction .
 Pluto and Eris and other “dwarf planets” are smaller than the major planets and have more elliptical orbits.

Sun and planet sizes to scale, but distances are not

Planets are very tiny compared to distances between them.
Again, the Sun is the size of a grapefruit.
Jupiter is the size of a marble, Earth is the tip of a ball-point pen

•
Over 99.9% of solar system’s mass
• Made mostly of hydrogen/helium gas + 1% heavier elements
• Converts 4 million tons of mass into energy each second via
E = mc 2 by the fusion process

Radius of Sun = 109 R
Earth distances
= ~2 Earth-Moon

Mercury
Venus
Earth
Mars

•
Made of metal and rock; large iron core
• Desolate, cratered; long, tall, steep cliffs
• Extremely tenuous, almost non-existent atmosphere

Largest day/night swing in temperature in the Solar System : 520 K

Surface similar in appearance to Earth’s
Moon.

•
Nearly identical in size to Earth; surface hidden by clouds
• Hellish conditions due to an extreme greenhouse effect
• Even hotter than Mercury: 733 K, day and night

A Venusian day lasts longer than a Venusian year!
Rotation speed only 6.5 km/hr – a moderate walking pace

Actual view of Venus’s surface by Soviet lander Venera 13 before it was crushed after 127 minutes by the 89 Earth atmosphere pressure.
Thunder and lightning was detected.

Earth and Moon with sizes shown to scale
(Moon about ¼ diameter of Earth) •
An oasis of life
• The only surface liquid water in the solar system
• A surprisingly large moon

•
Looks almost Earth-like on surface, but thinner atmosphere.
• Giant volcanoes, a huge canyon, polar caps, more
• Water flowed in distant past; could there have been life?

More comfortable than Tuscaloosa in summer, not so nice in winter.

Mount Olympus – 3 times higher than Mt. Everest, 600 km across.
The largest volcano known in the Solar System.

Viking - 1977

Viking - 1977
Mars Global Surveyor - 2001

Galle crater on Mars

Moons of Mars gravitationally locked in a 1:1 resonance
Densities 1.76 g/cm 3 and 1.9 g/cm 3 , like asteroids – captured?

A view from Viking 1

A view from Pathfinder
Sunset on Mars

not
A) they have few/no Moons
B) they have similar composition as the Sun
C) they all orbit in the same direction around the Sun
D) they all have nearly circular orbits

not
A) they have few/no Moons
B) they have similar composition as the Sun
C) they all orbit in the same direction around the Sun
D) they all have nearly circular orbits
Sun is 99% hydrogen/helium, planets made nearly all of heavier elements (C, O, Si, Fe, etc.)

Jupiter
Saturn
Uranus
Neptune

• Much farther from Sun than inner planets
• Mostly hydrogen/heli um; no solid surface
• 300 times more massive than Earth
• Many moons, rings

Much less dense than inner rocky planets (because it is mostly gas).

Jupiter harbors many moons, including four large
“Galilean” moons shown here.

• Giant and gaseous like Jupiter
• Spectacular rings
• Many moons, including cloudy Titan

Only 2/3 as dense as water!

Rings are
NOT solid ; they are made of countless small chunks of ice and rock, each orbiting like a tiny moon.
Artist’s conception

• Smaller than
Jupiter/Saturn; much larger than Earth
• Made of H/He gas and hydrogen compounds
(molecules - H
2
O,
NH
3
, CH
4
)
• Extreme axis tilt
• Many moons and a faint ring system
• Excess methane gives bluish color

Uranus spins on its side – rotational axis points toward Sun

~42 years of continuous daylight followed by
~42 years of continuous night at the poles.

• Similar to
Uranus (except for axis tilt)
• Many moons
(including
Triton) and a faint ring system

A) gas giants have many moons
B) gas giants are made mostly of H/He and hydrogen compounds
C) gas giants have rings
D) all of the above

A) gas giants have many moons
B) gas giants are made mostly of H/He and hydrogen compounds
C) gas giants have rings
D) all of the above