Astro 200 - Midterm 1

Star

ball of hot gas (plasma, actually) that generates energy via a process called nuclear fusion in its core. The Sun is a star.

Planet

an object large enough to be spherical in shape and dominant in its orbit around a star.

Moon (or satellite)

a celestial body that orbits a planet.

Asteroid

a small celestial body made up mostly of rocks and metals in orbit around the Sun or another star.

Comet

a small celestial body made up mostly of ices in orbit around the Sun or another star.

Solar System / Star System

a system of planets and other celestial bodies orbiting a star (or

sometimes a system with more than one star).

Nebula

an interstellar cloud of gas and dust.

Galaxy

a collection of millions to hundreds of billions of stars, and interstellar gas and dust, held together by their mutual gravitational attraction.

Universe

The sum total of all matter and energy; that is, everything within and between all galaxies

Our cosmic address is our

location in the Universe

Earth is the _________ planet from the Sun in our Solar System,

third

The milky way galaxy has somewhere between ___________ and ________________ stars

100 billion and 400 billion stars

The astronomical unit (AU) is

the average distance between the Earth and the sun (approximately 149 million kilometers or 93 million miles)

A lightyear (ly) is

the distance light travels in one year (9 trillion kilometers, or 6 trillion miles, or 63,000 AU)

The universe is _____________ years old

13.8 billion

The cosmic calendar is a way of

fitting the history of the universe into one calendar year

On the cosmic calendar, each month is __________________ years, an

1.15 billion years

On the cosmic calendar, January 1st marks

the big bang

On the cosmic calendar, each day is

38 million years

On the cosmic calendar, each second is

444 years

On the cosmic calendar, the first stars formed on

January 10th

On the cosmic calendar, the milky way formed on

March 15th

On the cosmic calendar , the solar system formed on

August 31st

Carl Sagan stated "We live on an insignificant planet, of a humdrum star, lost in a galaxy, tucked away in some forgotten corner of a universe", this is the principle of _______________

mediocrity

An extrasolar planet is

a planet orbiting another star, rather than the sun

A habitable world is one that

has conditions suited for life

The three necessary ingredients for life are

a liquid medium (water ideally), organic molecules (contain carbon), and energy

We've discovered subsurface bodies of liquid water throughout our Solar system, including on

Jupiter's moon Europa and Saturn's moon Enceladus

The largest moon in our solar system, the only moon with its own magnetic field is

Jupiter's moon Ganymede

The second largest moon in our solar system, the only moon with its own atmosphere is

Titan

Titan has lakes of

methane, ethane, and ammonia

Our best hope of detecting life on extrasolar planets is by

listening to radio signals emitted by other civilizations

The search for extrasolar radio signals is called

ExtraTerrestrial Intelligence (SETI)

The search for life in the universe is often described by the word

astrobiology

Constellations have been formalized not to represent just the shapes and patterns of the ancients, but

specific regions of the skt

There are ___ constellations covering the entire night sky

88

In the northern hemisphere, modern constellations are based on

Greco-roman constellations

An asterism is a

pattern of stars that is either a subset of a constellation or made up of stars from different constellations

The Big Dipper is an __________________ contained in the constellation Ursa Major.

asterism

Latitude is measured as ___________ from the equator to the north pole, and ____________ from the equator to the south pole

positive; negative

The zero line of longitude is called the

prime mieridian

Los Angeles' coordinates are

34 N , 118 W

When you are observing the night sky, the point directly above you is your

zenith

When you are observing the night sky, the point directly below you is your

nadir

When you are observing the night sky, where the sky meets the earth is your

horizon

When you are observing the night sky, the imaginary line extending from the north to the south passing through your zenith is your

meridian

In an altitude-azimuth system, altitude is measured as degrees from the

horizion

In an altitude-azimuth system, it's ________ degrees at the horizon _______ degrees at the point directly above you (zenith).

0 , 90

Azimuth is measured using ___________direction

cardinal direction (north northeast, south, etc)

North is ____ azimuth

0 degrees

East is _______ azmiuth

90 degrees

South is ________ azimuth

180 degrees

West is _________ azimuth

270 degrees

Angular size is

the size, in degrees, of an object in the night sky

Angular distance is

the distance in degrees, separating two objects

The celestial sphere

is an imaginary sphere surrounding Earth to which the stars are attached

The celestial equator is a projection of

earth's equator onto the celestial sphere

When viewed from the north pole, the earth rotates

counter-clockwise (west to east)

From our view, the Sun, and the Moon, the stars rotate

east to west

During the year, the Sun moves along a path called the ____________ on the celestial sphere

ecliptic

The ecliptic path is tilted _______ to the celestial equator

23.5 degrees

Earth's rotation axis is tilted with respect to the plane of its orbit around the Sun, this plane is called the

ecliptic plane

What is a circumpolar star?

a star that always remains above your horizon

If you're at one of the poles, then every star you see will be ____________, and will rise and set

circumpolar

If you're at the equator, then every star will rise and set, and no star will be

circumpolar

The higher the ________________, the larger the circle of circumpolar stars

latitude

Sidereal means

with respect to or relative to the stars

A solar day is

the time interval between the Sun's full circuit of the sky, when it's returned to the same position it was the day before

A solar day is exactly _________ hours long

24

A sidereal day measures

the interval when a star appears exactly in the same place after a full circuit of the sky

The reason we have 7 daysin a week is because of

the 7 visible planets

Earth's seasons are caused by

the tilt of its axis with respect to the ecliptic

Moving from the spring equinox to the summer solstice (June 20 to 21, the length of the day ________________, and the length of the night ________________

increase; decreases

At the spring or vernal equinox (March 20 or 21), we have __________ hours of daylight, and _______ hours of darkness

12

At the equinoxes we have __________ daylight and darkness

equal

The northern hemisphere receives the most direct sunlight on

the June solstize

The Ishango bone from Africa shows ancient markings corresponding to the horns of the crescent moon, this was used to

predict the seasons

Mayan astronomers were able to predict _______________ throughout the year

the times of sunrise and sunset

Thaleus of Miletus sought __________ explanations for phenomena

natural

Plato developed the idea of

the perfection of the heavens, and the imperfect earth at the center of the universe

__________________ first proposed the heliocentric view of the universe

Aristarchus

Heliocentrism is

The belief that the sun was the center of the solar system and that the earth rotated around it

Geocentrism is

the idea that Earth is the center of the Universe

Eratosthenes calculated

the circumference of the earth using shadows to cast on the ground in two cities

According to Aristotle, motion in the heavens was on ______ circles upon ______________ spheres

perfect

According to Aristotle, motion on earth requires a

constant pushing forth

According to Aristotle, heavier objects

fall to the ground faster than lighter objects

According to Aristotle, the heavens begin somewhere between the

Earth and the moon

According to Aristotle, ________ was stationary

the earth

Aristotle believed earth was stationary because, ______ _______________ had not been observed for any stars

stellar parralax

Despite using a heliocentric model, Copernicus still used ________ _____ for planetary orbits

perfect circles

According to the Copernican model, planets farther from the sun move ________ compared to the planets closer in

slower

Kepler's first law of motion

he planets orbit the Sun in elliptical orbits with the Sun at one focus of the orbit.

Keplers second law of motion is that

the planets sweep out equal areas of their orbits in equal time, moving faster when they're closer to the Sun and slower when they are farther.

Kepler's third law

the period of a planet's orbit (the time it takes to go once around the Sun) is related to the length of its semimajor axis (its average distance from the Sun)

According to Kepler's third law, any object orbiting the Sun that has a semimajor axis of 1 AU (the Earth, comets, asteroids, etc.) will take exactly ___________ to orbit the sun

1 year

For an object that orbits the Sun, the point at which it is closest to the Sun is called its

perihelion

For an object that orbits the Sun, the point at which it is farthest from the Sun is called its

aphelion.

Speed is a scalar quantity, and is just one number. Velocity is however a vector quantity including both

magnitude (the speed) and direction

Acceleration is a change in

velocity