Astronomy

Aphelion

The furthest point from the Sun

Perihelion

The closest point to the Sun

Epicycles

The circular orbit of a planet, the center of which revolves around Earth in a sphere.

Geocentrism

The belief that the solar system revolves around the Earth.

Heliocentrism

The belief that the Sun is the center of the solar system.

Kepler's First Law

Planets orbit the Sun in nearly circular ellipses with the Sun at one of the foci of the ellipse.

Kepler's First Law is Eccentricity = c/a. What are c and a?

c= distance from Sun to center, a= semi-major axis

What is Eccentricity=c/a on a scale of?

0-1

Eccentricity

The range of ellipse shape ranging from circular to ovoid

A planet starts speeding up after...

Aphelion

When a planet is closer to the Sun, is is moving ________.

Faster

Why do planets move faster when they are closer to the Sun?

The force of gravity is greater

Why do planets start speeding up after Aphelion?

The distance between the planet and the Sun is decreasing; it is closer to the Sun, so it's faster because the force of gravity is greater. The direction of forces are similar.

Kepler's First Law: What is e equal to and what does it imply?

0; perfect circle

Kepler's Second Law

A line between the Sun and the planet sweeps equal areas in equal times.

Kepler's Second Law explained

The planet's speed increases as it approaches the Sun and decreases as it recedes.

Kepler's Third Law

The square of a planet's orbital period is directly proportional to the cube of the orbit's semi-major axis.

Kepler's Third Law equation

T^2=a^3

T^2=a^3: What are T and a?

T= orbital period (how long it takes to complete a revolution), a= orbital radius

Kepler's Third Law establishes a relationship between...

The time taken by a planet to complete one revolution and its distance from the Sun

The closer a planet is to the Sun...

The faster it completes its revolution around the Sun.

Aliens have come to the Solar System and moved Venus to outside of Mars's orbit! How has Venus's orbital period changed? Why?

Venus's year will lengthen because it is farther from the Sun.

Kepler's First Law: If you move the foci closer together, it becomes more...

Circular

Length of year of 9 AU

27

Length of year of 0.5 AU

0.35

Ptolemy

Heavy in the geocentric model. The geocentric model did not account for the retrograde motion of planets, which Ptolemy attempted to account for with epicycles.

Ptolemy time period

100-170 AD

Nicolaus Copernicus

Published a heliocentric model of the solar system.

Copernicus time period

1473-1543

Tycho Brahe

Proposed a sort of hybrid-system where Earth was the center of the Solar System, the Moon revolved around Earth, and the Sun revolved around the Earth, but all the other planets revolved around the Sun. His data was later used to help prove the heliocentric model.

Brahe time period

1546-1601

Whose model is this?

Ptolemy

Whose model is this?

Copernicus

Whose model is this?

Brahe

Circumpolar key constellation

Big Dipper

Autumn key constellation

Cassiopeia

Winter key constellation

Orion

Spring key constellation

Ursa Major

Summer key constellation

Summer Triangle

Aliens have swapped Jupiter and Mercury. Jupiter's orbital period is now 0.24 years. How far is Jupiter from the Sun? a^3=T^2

0.386

Horizon's coordinate system is based on...

The observer's location

Orbits are very nearly...

Circular

___ out of 8 planets rotate in the same direction as the Sun

6

Terrestrial Planet

Small in mass, close to the Sun, made of metal and rock, few moons and no rings

What are the terrestrial planets?

Mercury, Venus, Earth, Mars

Jovian Planet

Large mass and size, far from the Sun, made of hydrogen, helium, and hydrogen compounds, rings and many moons

What are the jovian planets?

Jupiter, Saturn, Uranus, Neptune

Asteroid

Small, rocky objects that orbit the Sun, made of metal and rock, most orbit in the asteroid belt between Mars and Jupiter

Comet

A celestial object consisting of a nucleus of ice and dust and, when near the sun, a tail of gas and dust particles pointing away from the sun; ice-rich, many are found in the Kuiper belt beyond Neptune's orbit

Oort Cloud

A distant, spherical region that contains icy objects like comets

Uranus's odd tilt

Uranus rotates nearly on its side compared to its orbit, and its rings and major moons share this sideways orientation

Earth's relatively large moon

Our own Moon is much closer in size to Earth than most other moons in comparison to their planets

Nebular Hypothesis

The idea that a spinning cloud of dust made of mostly light elements, called a nebula, flattened into a protoplanetary disk and became a solar system

Nebular Hypothesis: Heating

Gravity pulls nebular material, converts potential energy to kinetic energy, then to thermal energy as particles crash together

Nebular Hypothesis: Spinning

As mass collects near center, speed of rotation increases

Nebular Hypothesis: Flattening

As particles collide, they continue to grow, and the cloud flattens into a disk

Why are there two types of planets?

Location. Terrestrial planets formed in front of the frost line. T Tauri winds blew gaseous material outside of the frost line, giving Jovian planets more material to form from.

Order of the planets and other objects in our solar system

Sun, Mercury, Venus, Earth, Mars, Asteroid Belt, Frost Line, Jupiter, Saturn, Uranus, Neptune

Within the Frost Line

Rocks and metals condense, hydrogen compounds stay gaseous

Beyond the Frost Line

Hydrogen compounds, rocks, and metals condense

Accretion

Growth through collision

Planetesimals

Early seeds that would grow to become planets

Accretion Process

Early in the accretion process, there are many relatively large planetesimals on crisscrossing orbits. As time passes, a few planetesimals grow larger by accreting smaller ones, while others shatter in collisions. Ultimately, only the largest planetesimals avoid shattering and grow into full-fledged planets.

Outer planet formation

The outer planets formed beyond the frost line where hydrogen compounds could condense. Particles that were present were ice, metals, and rock. The cores accreted rapidly into large clumps of ice and rock. They grew larger faster. They captured a large amount of hydrogen and other gases from the surrounding nebula with their enormous gravity.

Outer planet moon formation

The moons around large planets formed in much the same way as the smaller planets around the Sun

Azimuth

The distance along the horizon measured clockwise from the north point of the horizon.

Cardinal directions

Cardinal directions are points on a compass that help locate where things are. The four cardinal directions are North, South, East, and West.

Zenith

The point directly above (90 degrees) above your head.

Nadir

The point directly below (-90 degrees) below your feet.

Horizon

The point where the sky meets the ground at zero degrees.

Altitude

Altitude is the height of something above the horizon.

Celestial meridian

A celestial meridian is a made up circle that crosses from north to south in the sky.

Transit

The movement of a celestial body like meteors or planets across the sky.

Solar noon

Solar noon is when the Sun looks like it’s at the highest point in the sky.

Why do meteor showers occur?

Meteor showers occur when the Earth passes through a trail of comet debris while orbiting the Sun.

Why are meteor showers predictable?

Meteor showers are predictable because the Earth passes through comet orbits at the same time each year.

What are many meteor showers named after?

The constellation the meteors appear to emanate from in the night sky

Trans-Neptunian Object

An icy body beyond the orbit of Neptune

Kuiper Belt

A large region beyond the orbit of Neptune that contains millions of icy bodies

Asteroid Belt

A region that includes many asteroids, located in between Jupiter and Mars

The Scattered Disk

The Scattered Disk is a region far beyond the main part of the Kuiper Belt. There are many objects that have been scattered by Neptune here.

A planet is defined as a celestial body that...

Orbits a star, big enough to have enough gravity to force it into a spherical shape, big enough that its gravity cleared away any other objects of a similar size near its orbit around the Sun

Mercury atmosphere description

Mercury has a thin exosphere made up of atoms blasted off the surface by the solar wind and striking meteoroids

Venus atmosphere description

The atmosphere is mostly carbon dioxide. Venus has the hottest surface in the Solar System, apart from the Sun

Earth atmosphere description

Earth has an atmosphere that consists of 78% nitrogen, 21% oxygen, and 1% other gases such as argon, carbon dioxide, and neon

Mars atmosphere description

Mars has a thin atmosphere made up mostly of carbon dioxide, nitrogen, and argon gases

Jupiter atmosphere description

Jupiter has three distinct cloud layers in its skies. The top cloud is made of ammonia ice, the middle layer is made of ammonium hydrosulfide crystals, and the innermost layer is made of water ice and vapor

Saturn atmosphere description

Winds in the upper atmosphere reach 1,600 feet per second. Saturn is blanketed with clouds that look like faint stripes, jet streams, and storms

Uranus atmosphere description

Uranus' atmosphere is mostly hydrogen and helium, with a small amount of methane and traces of water and ammonia

Neptune atmosphere description

Neptune's atmosphere is made up mostly of hydrogen and helium with just a little bit of methane

Pluto atmosphere description

Pluto has a thin, tenuous atmosphere that expands when it comes closer to the Sun and collapses as it moves farther away

Co-formation hypothesis

The Moon formed in orbit around Earth at the same time as the Earth formed

Capture hypothesis

The Moon formed somewhere else in the solar system with less iron, and was captured by Earth's gravity and began to orbit around the Earth

Fission hypothesis

Early molten Earth spun so fast that material spewed off and formed the Moon

Giant impact hypothesis

When the Earth formed, a nearby newly-formed object half as wide as Earth collided with it. A fraction of the debris from the crust and mantle (from both Earth and the colliding object) spewed into orbit around Earth and accreted to form the Moon

Which Moon formation hypothesis is widely accepted?

Giant impact

Evidence for giant impact hypothesis

Density, composition, the Moon's orbital plane

The Moon orbits the Earth at a ___ degree tilt relative to the planets’ orbits around the Sun.

5

Total Solar Eclipse

Observers in the narrow path of totality (up to 200 miles wide) get the chance to experience daytime darkness and a magnificent view of solar corona

Total Solar Eclipse duration

7.5 minutes