ASTR Exam 1

Earth's Cosmic Address

Earth, Solar System, Milky Way Galaxy, Local Group, Local Super Cluster

solar system

the sun and all of the planets and other bodies that travel around it

galaxy

an island of stars in space all held together by by gravity and orbiting a common center

The Milky Way

-the galaxy our solar system is in

-relatively large, one of the two largest in our local group

Where is our solar system located within the Milky Way Galaxy?

a little over halfway from the galactic center to the edge of the galactic disk

local group

-the group of about 40 galaxies that the Milky Way belongs to

-located on outskirts of our local supercluster (Laniakea)

Galaxy cluster

cluster of galaxies

superclusters

-largest known structures in the universe

-region where galaxies and galaxy clusters are more tighly placed

universe

The sum total of all matter and energy; that is, everything within and between all galaxies along with all of the different structures (planets, galaxies, stars, superclusters, voids, etc)

Astronomical Unit

-average distance of Earth from the Sun

- 1 AU = 150 million km

-mainly used for distances in our solar system

Light year

-distance light travels in one year

- 1 ly = 10 trillion km

-used to describe distances of stars and galaxies

in what way do we "look back in time" when observing space?

-since certain objects in space are so far away it can take light years to reach us

- however many ly away = how many years ago from the present we are seeing something

- Ex. Andromeda is 2.5 mil ly away so we see it as it was 2.5 mil years ago

why are snapshots of galaxies pictures of space and time?

- the shape of galaxies give them a far and near side which are different ly lengths

- allows us to see different parts of a galaxy over a spread out time period

- In Andromeda galaxy the light we see from the far side left 100,000 years before the light on the near side

observable universe

-The portion of the entire universe that can be seen from Earth, at least in principle

-The observable universe is probably only a tiny portion of the entire universe.

-14 billion ly

-anything further than 14 billion of ly technically does not exist yet

what can the number of stars in the observable universe be compared to on Earth

counting every grain of sand on every beach on Earth

universe is expanding principle

-means distances between galaxies increase with time

-implies galaxies were once close together in the past

the big bang

-name of the event thought to mark the birth of the universe

-starting point of the universe's expansion

what happens when gravity overpowers the universe's expansion

forms galaxies and galaxy superclusters

-the gravitational pull of these does not expand with the universe and stays constant in size

how do stars and planets form?

Space stuff (dust, gas etc) is pulled together by gravity and forms a tight clump

when do stars "die"

when they exhaust their usable fuel from fusion

supernova

-a massive explosion that occurs when a star dies

-returns matter to space becoming parts of new clouds of gas and dust allowing new stars to be born

what were the two main chemical elements present in the early universe

hydrogen and helium

why are people "star stuff"?

because we are made of elements that were manufactured by the deaths of stars

what way does Earth rotate around its axis?

counterclockwise (west to east)

rotation

The spinning of Earth on its axis

-one rotation a day

orbit

The path of an object as it revolves around another object in space

-one year around Sun

ecliptic plane

The plane of Earth's orbit around the Sun

what is the tilt of Earth's axis?

23.5 degrees

what is axis tilt?

the amount by which a planet's axis is tilted with respect to a line perpendicular to the ecliptic plane

what way does Earth orbit the Sun?

counterclockwise (west to east)

why don't we see other stars racing in the sky?

-they are so far away their movement is not noticeable

-everything in the galaxy is still moving relative to one another

dark matter

matter that emits no light at any wavelength

-makes up most of space

dark energy

name given to energy that could be causing the expansion of the universe to accelerate

how do galaxies move relative to one another in the local group?

-galaxies either move towards or away from us

-some orbit other galaxies

how did we determine the age of the universe?

We based it on how quickly it is expanding

-exponential expansion

is there a center to the universe?

no

how does astronomy affect human history?

revolutions in astronomy have gone hand in hand with revolutions in science and technology that have shaped modern life

how many stars are visible to the naked eye on a moonless night away from city light?

2,000 stars

constellations

patterns in the sky that have been given names throughout history

what purpose do constellations serve for astronomers?

depict regions of the sky with self-defined borders

are stars in constellations close together

no they just appear close because of human's lack of depth perception

celestial sphere

the imaginary sphere on which objects in the sky appear to reside when observed from Earth

important points on the celestial sphere

-North Celestial Pole

-South Celestial Pole

-Celestial Equator

-Ecliptic

North Celestial Pole

point directly over Earth's North Pole

South Celestial Pole

point directly over Earth's South Pole

Celestial Equator

projection of Earth's equator into space, makes a complete circle around the celestial sphere

ecliptic

the path the Sun follows as it appears to circle the celestial sphere annually

-crosses at 23.5 angle due to Earth's tilt

features of the local sky

-horizon

-zenith

-meridian

horizon

boundary between Earth and sky

zenith

point directly overhead

meridian

imaginary half circle scratching from horizon due south through the zenith to the horizon due north

what do you need to pinpoint objects in the local sky?

-direction along horizon (azimuth)

-altitude above horizon

azimuth

An angle measured from due north clockwise

-N = 0 degrees

-E = 90 degrees

-S = 180 degrees

W = 270 degrees

altitude

angle above the horizon

angular size

angle an object appears to span in your field of view

can you use angular size to tell the true size of an object?

no

angular distance

angle that appears to separate objects

what is the angular size used to find?

apparent size

what is the angular distance used to find?

measure distance between stars

what direction do the stars appear to move through our sky?

east to west

circumpolar stars

stars that never set

where do stars rise and set?

rise in the east and set in the west

Does the sky vary with latitude or longitude?

latitude

why does latitude effect the constellations we see?

because it impacts where our horizon is

what is the altitude of the celestial pole equal to?

your latitude

why does the night sky change throughout the year?

because Earth changes position in its orbit

In what direction does the Sun appear to move through our sky?

east to west (westward)

what determines what constellations we see at night?

the Sun's apparent location along the ecliptic

during a zodiac's paired month can you see that constellation?

-no because it is where the Sun is located so it is only visible in the daytime sky

-instead we see opposite constellations

what causes the seasons?

the tilt of Earth's axis

- causes sunlight to fall differently on Earth at different times

does Earth's tilt direction ever change

No, always pointed towards Polaris

When is the NH tipped toward and away from the Sun

toward in June and away in December

When is the SH tipped toward and away from the Sun

toward in December and away in June

Earth's orientation in June

sun hits at steep angle for NH and shallow angle for SH

what season does a steep angle cause

Summer

-More concentrated light, makes it warmer

-Means the Sun follows a longer and higher path through sky, more hours of daylight, more time to be warmed by Sun

what season does a shallow angle cause

Winter

Sunlight is less concentrated

Sun follows a shorter, lower path through sky

Earth's orientation in December

sunlight hits Earth at steep angle in SH and shallow angle in NH

When are the NH and SH illuminated equally

March and September

-mark the transitional seasons

what season is March in the NH

spring

what season is March in the SH

fall

what season is September in the NH

fall

what season is September in the SH

spring

what would happen if Earth did not have an axis tilt

there would be no seasons

June solstice

-summer solstice for NH

-winter solstice for SH

-June 21

-NH tipped most directly toward Sun and receives most direct sunlight

December solstice

-winter solstice for NH

-summer solstice for SH

-December 21

-NH receives least direct sunlight

March equinox

-spring/vernal equinox in NH

-fall/autumnal equinox in SH

-March 21

-NH goes from being slightly tipped away from Sun to being tipped slightly toward Sun

-winter to spring NH

-summer to fall SH

September Equinox

-fall/autumnal equinox in NH

-spring/vernal equinox in SH

-September 22

-NH first starts to tip away from the Sun

-summer to fall NH

-winter to spring SH

what do solstice and equinox dates depend on?

where we are in leap year cycle

what is the purpose of leap years

to keep solstices and equinoxes around the same dates

-add one day (Feb 29) every 4th year

when do equinoxes occur?

-On the two days of the year which the Sun rises precisely due east and sets precisely due west

-When sun is above and below horizon for equal time-12 hours

when does the June solstice occur?

-the day in which the Sun follows its longest and highest path through NH sky

-Shortest and lowest for SH

-Day when Sun rises and sets farther to the north of due east and due west

-NH has longest hours of daylight and Sun rises highest in the midday sky

when does the December solstice occur?

-When the Sun rises and sets farthest to the south

-the NH has its shortest hours of daylight and lowest midday Sun

-SH has longest hours of daylight and Sun rises highest in midday sky

What do solstices and equinoxes mark?

first day of a season

what does the June solstice mark

-NH: first day of summer

-SH: first day of winter

what does the December solstice mark

-NH: first day of winter

-SH: first day of summer

what does the March equinox mark

-NH: first day of spring

-SH: first day of fall

what does the September equinox mark

-NH: first day of fall

-SH: first day of spring

how does latitude affect seasons?

-higher latitudes have more extreme seasons

-equator regions do not have 4 seasons, only rainy and dry ones

why does latitude affects seasons?

-NH has more land and less ocean which allows it to heat and cool more easily leading to extreme seasons

-SH has more ocean which moderates its climate

precession

the gradual wobble of the axis of a rotating object around a vertical line