STRUCTURE OF THE UNIVERSE MIDTERM 186 terms
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186 Terms
Order these: solar system, universe, local group, supercluster, galaxy cluster, planet
Planet, solar system, galaxy, local group, galaxy cluster, supercluster, universe
Is Earth located in a galaxy cluster?
No
The Milky Way has over _______ stars.
100 billion
One astronomical unit is equal to ______.
the distance between the Earth and Sun
What is a light-year?
the distance light travels in one year, about 10 trillion km
The farther we look in distance, ______.
The further we look back in time
What's a star?
A large, glowing ball of gas that generates heat and light through nuclear fusion in its core.
What's a planet?
A moderately large object that orbits a star and shines primarily by reflecting light from its star
What's an exoplanet?
a planet orbiting a star other than the sun
What's a moon?
a natural satellite that orbits a planet
What's an asteroid?
a relatively small and rocky object that orbits a star
What's a comet?
A relatively small and ice-rich object that orbits a star
What's a small solar system body?
An asteroid, comet, or other object that orbits a star but is too small to qualify as a planet or dwarf planet
What's a world?
In the context of astronomy, any planet, dwarf planet, moon, or small body that we could imagine visiting.
What's a star system?
A star (sometimes more than one) and any planets and other materials that orbit it
What's a galaxy?
A great island of stars in space, containing a few million to a trillion or more stars, all held together by gravity and orbiting a sommon center
What's a galaxy group/cluster?
A collection of galaxies bound together by gravity
What's the difference between a galxy cluster and galaxy group?
Small collections (up to a few dozen galaxies) are generally called groups, while larger collections are called clusters.
What's a supercluster?
A gigantic region of space in which many groups and clusters of galaxies are packed more closely together than elsewhere in the universe.
What's a universe?
The sum total of all matter and energy—that is, all galaxies and everything between them.
What's the observable universe?
The portion of the entire universe that can be seen from Earth, at least in principle.
What's rotation?
The spinning of an object around its axis
What's revolution or orbit?
The orbital motion of one object around another due to gravity
What's expansion?
The increase in the average distance between galaxies as time progresses.
What's the boundary of the observable universe and why?
14 billion lightyears because the universe is 14 billion years old
The sun outweighs all the planets combined by a factor of ____.
Nearly 1000
What's the nearest star to the sun?
Alpha Centauri
On the one to ten billion scale, if the sun is in Washington DC, where is Alpha Centuri?
California
Convenient interstellar travel remains within/beyond/well beyond our present technology?
Well beyond
The number of _____ is comparable to the number of stars in the universe.
grains of sand on Earth's beaches
Do stars go through life cycles?
Yes
What is a supernova?
the death of a star
Do galaxies recycle?
Yes
Where does most of the material from which we and our planet come from?
Stars that lived and died before the birth of our Sun
If the history of the universe was a year, when would did early hominids begin to walk upright?
12/31 at 9pm
If the history of the universe was a year, when did the Milky Way form?
February
If the history of the universe was a year, when did Earth form?
September 3
All the planets rotate clockwise except for ___ & ____.
Venus & Uranus
All the planets orbit the sun counterclockwise or clockwise?
Counterclockwise
The Earth is tilted how many degrees?
23.5 (in reference to the ecliptic plane)
Stars in our local solar neighborhood move ___.
randomly
Do we rotate around the center of our galaxy?
yes
Virtually every galaxy outside the Local Group is moving toward/away from us?
Away
The more distant the galaxy, the slower/faster it appears to be moving?
Faster
What's the distance of a light second?
300,000
What do we multiply kms by to get miles
.6214
If the Sun were the size of a large grapefruit, how large would Jupiter be?
A marble
If the Sun were the size of a large grapefruit, how large would the Earth be?
Ball point
If the Sun were the size of a large grapefruit, how far would the Earth be?
15 meters
If the sun were the size of a large grapefruit, how far would Pluto be?
600 meters
The Voyager 2 Spacecraft is on its way out of our solar system at a speed of about 50,000
kilometers per hour. It will reach the distance of the nearest star system (beyond our solar
system, Proxima Centauri aka: Alpha Centauri C) in about ________ years.
10,000
Someday we may build spaceships capable of traveling a light-year in only a decade. TRUE/FALSE
TRUE
NASA will soon launch a spaceship that will photograph our Milky Way Galaxy from beyond its halo. MAKES SENSE/DOESN'T MAKE SENSE
DOESN'T MAKE SENSE
How many stars can you see with the naked eye?
2000
What's a constellation
A region of the sky with well defined borders
Are the stars in a constellation close to each other?
Not necessarily
Why is the celestial sphere a useful illusion?
It allows us to map the sky as seen from Earth.
What are the two special points in the celestial sphere?
North celestial pole and south celestial pole
What are the two special circles on the celestial sphere?
Celestial equator and ecliptic plane
What's galactic plane?
Plane of the Milky Way's disk
What's the altitude of the zenith?
90 degrees
Define angular size.
The angle it appears to span in your field of view.
Why do the moon and Sun have the same angular size even though the sun is 400 times larger?
Because the sun is about 400 times farther away.
Describe the relation between degrees, arcminutes, and arcseconds.
Each degree has 60 arcminutes, each arcminute has 60 arcseconds.
If given angular size and distance can we determine physical size?
yes
If the earth rotates from west to east, which way does the celestial sphere appear to rotate?
East to west
Why do we always see some stars?
They are circumpolar and their daily circle is always above the horizon.
Does the sky vary with longitude?
no
Why do we never see some stars?
Their daily circle is entirely below the horizon.
Latitude measures north/south or east/west position?
North/south
Longitude measures north/south or east/west position?
East/west
Is the altitude of the celestial pole in your night sky equal to your latitude?
Yes
The suns location along the ____ determines ____.
ecliptic & which constellations we see at night
What causes seasons?
The Earth's tilt
When is the sun highest in the sky?
Summer solstice
When are day and night equal lengths?
Equinox
When does the sun rise at due east and set at due west?
Equinox
When is the Earth closest to the Sun?
January
Why are seasons more extreme in the northern hemisphere?
More land
Define precession
a gradual wobble that alters the orientation of Earth's axis in space
Does precession change the amount of the tilt?
Nah
What does precession impact?
It changes the points in Earth's orbit at which the solstices and equinoxes occur and the constellations we see
How long is the Earth's cycle of precession?
26,000 years
How long is the lunar cycle?
29.5 days
Which is new moon?
Between earth and sun
Which is full moon?
When earth is between the sun and the moon
When does full moon rise?
Around sunset
When does first quarter moon rise?
Around noon
When does third quarter moon rise?
Around midnight
The moon rotates on its axis in the same amount of time ____.
It takes to orbit the earth
What can we see during a solar eclipse?
The sun's corona
Why do we not have a lunar and solar eclipse every month?
Because the moon's orbit is slightly inclined (about 5 degrees from the ecliptic)
What are nodes?
The point where the moon's orbit crosses the ecliptic plane
Define saros cycle
A period of 18 years, 11 days, and 8 hours used in astronomy to predict eclipses
What causes eclipses?
Shadows/blocking
Which planets are easy to find with the naked eye?
Mercury, Venus, Jupiter, Mars, Saturn
What is stellar parallax?
The apparent shift in position of a nearby star
Why is stellar parallax rather small?
Because nearby stars are far away
Who initially proposed the idea that the Earth goes around the Sun?
Aristarchus
Are there more circumpolar stars in the US or North Pole?
North Pole