Chelsea Esposito Notes

Chapter 1

Our place in the Universe

Star – a large, glowing, ball of gas that generates heat and light through nuclear fusion.

Planet- A moderately large object that orbits a star. It shines by reflecting light. Planets may be rocky,
icy, or gaseous.

Moon (or satellite) - An object that orbits a planet

Asteroid- A relatively small and rocky object that orbits a star.

Comet- A small and icy object that orbits a star

Nebula- an interstellar cloud of gas and/or dust

Galaxy- a great island of starts in space, all held together by gravity and orbiting a common center.

-Andromeda is our closest galaxy

How did we come to be?

Birth of universe: the expansion of the universe began with a hot and dense Big Bang. One region of
the universe has expanded with time. The universe continues to grow but, on a smaller scale gravity
has pulled matter together to make galaxies.

Galaxies as Cosmic Recycling Planets: The early universe contained only two chemical elements:
hydrogen and helium. All other elements were made by starts and recycled from one stellar
generation to the next with in galaxies like our Milky Way.

Life Cycles of Stars: Many generations of starts have lived and died in the MW.

Earth and Life: By the time our SS was born, 4.5 billion years ago, about @5 of the original hydrogen
and He had been converted into heavier matter.

How can we know what the universe was like in the past?

Light travels at a finite speed: 300,000 km/s

Thus, we see objects as they were in the past. The farther away we look in distance, the further back
we look in time.

Light year- the distance light can travel in one year, about 10 trillion km (6 trillion miles). At great
distances, we see objects as they were when the universe was much younger.

Can we see the entire universe?

No. There may be things from farther away and the light has no reached us.

How big is the universe?

The MW is about 100 billion galaxies. 10^11 stars/galaxy x 10^11 galaxies = 10^22

It has as many stars as grains of sand on the of Earth’s beaches.

How is the Earth moving?

Contrary to our perception, we are not “sitting still”. We are moving with the Earth. Earth rotates
around its axis once every day. At typical relative speeds of more than 70,000 km/hr. Starts are so far
away that we cannot easily notice their motion.

Do galaxies move?

Galaxies are carried along with the expansion of the universe. How did Hubble figure it out?

Are we ever sitting still?

No. Everything is always expanding, rotating, or growing.

CHAPTER 2

The Celestial Sphere

Starts at different distances all appear to lie on the celestial sphere. The ecliptic is the Sun’s apparent
path. The 88 official constellations cover the celestial sphere.

The Milky Way

A band light that makes a circle around the celestial sphere. What is it? Our view into the galaxy.

An objects altitude (above horizon) and direction (along horizon) specify its location in our local sky.

Zenith- the point directly overhead

Horizon- all points 90 degrees away from the Zenith

CHAPTER 4

Making Sense of the Universe: Understanding Motion

Energy and Gravity

How do we describe motion?
How is mass different from weight?

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Speed: Rate at which objects move

Speed = distance/time (units of m/s)

Velocity: speed and direction

Acceleration: Any change in velocity. Units of speed/time (m/s^2)

Acceleration of Gravity

All falling objects accelerate at the same rate (not counting friction of our resistance.)

On Earth g ≈ 10 m/s^2 : speed increases 10 m/s, with each second of falling

Acceleration of Gravity (g)

Galileo showed that g is the same for all falling objects, regardless of their mass.
Momentum = m x V
A net force changes momentum which generally means an acceleration ( Δ in velocity)
The rotational momentum of a spinning or orbiting object is known as angular momentum

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Mass – amount of matter in an object

Weight- the force that acts on an object

On the moon, your weight is less, your mass is the same

Why are astronauts weightless in space?

-There is gravity in space

-weightlessness is due to a constant state of free-fall

Mass= quantity of matter

Weight= force acting on mass

4.2 Newton’s Laws of Motion

How did Newton change our view of the universe?

What are Newton’s three laws of motion?

How did Newton change our views of the Universe? Newton 1642-1727

- He realized the same physical laws that operate on Earth also operate in the heavens -> one
universe

- Discovered laws of motion and gravity

- Much more: experiments with light, first reflecting telescope, calculus.

Newton’s Three Laws

1st: an object moves at constant velocity unless an Earth force acts to change its speed or direction.

2nd: force = mass x acceleration

3rd: For every force, there is always an equal and opposite reaction force.

Is the force that Earth exerts on you longer, smaller, or the same as the force you exert on it?

Earth and you exert equal and opposite forces on each other.

4.3 Conversation Laws in Astronomy

- What keeps a planet rotating and orbiting the sun?

- Where do objects get their energy?

Conservation of Momentum?

The total momentum of interacting objects cannot change unless an external force is acting
on them.
Interacting objects exchange momentum through equal and opposite forces.

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What keeps a planet rotating and orbiting the sun?

Angular Momentum

Am = mass x acceleration

Where do objects get their energy?

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Energy makes matter move.
Energy is conserved, but it can…
o Transfer from one object to another
o Change in form.

Basic types of energy
- Kinetic (motion)
- Radiation (light)
- Stored or potential

Energy can change type but cannot be destroyed.

Thermal Energy: The collective kinetic energy of many particles.
- Thermal energy is related to temperature but it is not the same.
- Measure of the total kinetic energy of all the particles in a substance. It, therefore, depends
on both temperature AND density.

Gravitational Potential Energy

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on Earth , it depends on…
an objects mass (m)
strength of gravity (g)
-distance an object could potentially fall.

The Force of Gravity

-Universal Law of Gravitation

1. Every mass attracts every other mass

2. Attraction is directly proportional to the product of their mass.

How does Newton’s law of gravity extend Kepler’s Laws?

Kepler’s finest two laws apply to all orbiting objects, not just planets.
Ellipses are not the only orbital paths.

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Newton’s version of Kepler’s 3rd law: If a small object orbits a larger one and you measure the
orbiting object’s orbital period AND average orbital distance.

How do energy and gravity together allow us to understand orbits?

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Total orbital energy (grav. + kinetic energy) stays constant if there is no external force.
Orbits cannot change spontaneously.

Changing an Orbit

è What can make an object gain or lose orbital en?
o Friction or atmospheric drag
o A gravitational encounter

Escape Velocity
- If an object gains enough orbital energy, it may escape (change from a bound to unbound
orbit).
- Escape velocity from Earth

Tide s

The moon’s gravity pulls harder on near side of Earth than on far side.
The difference in the moon’s grav. Pull stretches the Earth.
Size of the tide depends on the phase of the moon.

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Tidal Friction

-Tidal friction gradually slows Earth’s rotation (and makes the moon get father from Earth).

- Moon once orbited faster (or slower), t.f. caused it to “lock” in synchronous rotation.

CHAPTER 6

-closer to the sun, the faster the orbit

- Planetecimal - little pieces of a planet

Breif Tour

The solar system exhibits clear patterns of composition and motion.

These patterns are far more important and interesting than numbers, names, and other trvia.

Planets fall into two categories

small, rocky terrestrial planets
large, hydrogen-rich jovian planets

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Asteroids and comets populate the solar system

found throughout, but are concentrated in 3 distinct regions.

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Several notable exceptions to these trends stand out.

some planets have unusual axis tilts, unusually large moons, or moons of unusual orbits
Planets are very tiny compared to the distances between them.

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SUN

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Over 99.8% of solar system’s mass
Made mostly of gas (H/He) (plasma)
Converts 4 million tons of mass into energy each second.

Mercury

- Made of metal and rock; large iron core

- Desolate, cratered; long, tall, steep cliffs.

- Very hot and very cold, day 475 degrees Celsius, night -170 degreeds Celsius

Venus

Nearly identical in size to Earth; surface hidden by clouds
Hellish conditions due to an extreme green-house effect
Even hotter than Mercury: 470C, day and night

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Earth

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an oasis of life
only surface with liquid water in the ss
a surprisingly large moon

Mars

Looks almost Earth-like
Giant volcanoes, a huge canyon, polar caps, and more
Water flowed in the distant past; could there have been life?

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Jupiter

much farther from the sun than inner planets
4 moons
o Io: active volcanoes
o Europa: possible subsurface ocean
o Ganymede
o Callisto

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Saturn

Giant and gaseous like Jupiter
Spectacular rings
Many moons
Its rings are not solid
Cassini launched ’97, landed in ‘04

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Uranus

Smaller than Jupiter and Saturn
Made of H/He

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Neptune

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Axis tilt

Pluto & other Dwarves

To small to clear an orbital path to be considered a planet.

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6.2 Clues to the Formation of Our Solar System

What features of our solar system provide clues to how it formed?

Motion of large bodies
o All in same direction & plane

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Swarms of small bodies

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Many rocky asteroids and icy comets populate the solar system
Oort Cloud, Kuiper belt, asteroid belt

Notable Expectations

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unusual axis tilts

Nebular Theory

Unusual axis tilts

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Nebular Theory

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Our ss formed from a giant cloud of interstellar gas.
(nebular = cloud_

6.3 Birth of SS

Galactic Recycling

Elements that formed planets were made in starts and then recucled through interstellar
space.
We can see stars forming in interstellar gas clouds.

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Conservation of Angular Momentum

Heating, Spinning faster, Flattening

-like a ballerina bringing in her arms during a spin

Formation of Terrestrial Planets

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small particles of rock and metal were present inside the frost line.
Planetesimals of rock and metal built up as these particles collided.
Gravity eventually assembled these planetesimals into terrestrial planets.

Tiny solid particles stick to create planetesimals.

Accretion of Planetesimals

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Many smaller objects collected into just a few larges ones.

Formation of Jovian Planets

Ice could form small particles outside the frost line.
Larger planetesimals.-

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