Chapter 1 Notes/Homework
Our Very, Very Ordinary Location
- Earth- an average size planet in an average-sized orbit. -The Sun- a slightly above-average size star. -Our location in the Milky Way Galaxy- neither near the center nor near the outskirts. -Our Galaxy-neither unusally big nor small
Star Cluster
-A collection of hundreds to millions of stars gravitationally bound (or not) orbiting (or inside) a galaxy. -10 light years = 10 to 14km.
Galaxy
-A great island of billions of stars and gas, all held together by gravity and orbiting a common center. - 100,000 light years = 10 to 18km
Solar (Star) System
-A star and all the material that orbits it, including its planets and moons, asteroids, and comets. -Light crossing time: 10 hours (Earth-Sun: 8.3 minutes) 10 to 10 km
Nebula
-An interstellar cloud of gas within a galaxy. ~10 light years = 10 to 14km
continued
-At great distances, we see objects as they were when the Universe was much younger. Appearance of object is effectively ":frozen in time" while the ligh from the object is transiting space, so more distant objects appear younger to us.
The Age of the Universe
-Current Age of Universe ~ 14 billion years. -Sun's Age ~ 4.5 billion years
How can we know what the universe was like in the past?
-Light travels at a finite speed (300,000 km/s). Destination Light travel time Moon 1 second Sun 8 minutes Next nearest 4.3 years star Andromeda 2.5 million years Galaxy -Thus, we see objects as they were in the past: The farther away we look in distance, the further back we look in time.
Are we ever sitting still?
-NO! No place in the Universe is "at rest". -We can't even define what "at rest" means.
Distance Units and Astronomy
-Planets: kilometers (km) (1km~0.6 mile) -i.e., Earth's circumference is ~40,000 km. -Solar System: Astronomical Unit (AU) -averge Earth-Sun distance =150 million km -Venus is 0.7 AU from Sun, Mars at 1.5 Au (and of course, Earth is 1.0 AU from Sun, by definition). -Stars, Galaxies, Universe: light year (ly) - 9.46 trillion km (distance light travels in 1 year).
Rotation vs. Revolution
-Rotate - spinning of an object about its own axis (e.g., a spinning top) - Earth spins on its axis once per day -Revolve - movement of an object around another object (e.g., a ball tied to a string swung around your head) - orbit of the Earth around the Sun every 365 days -The Earth orbits (revolves) around the Sun once every year 108,000 km/hr, or 30 km/s... -Our Sun moves relative to the other stars ... ~70,000 km/hr, or ~20 km/s -Our Sun and local stars orbit around the center of the Milky Way Galaxy every 230 million years. 800,000 km/hr, or 220 km/s... -Galaxies have orbital motions in clusters -All of this together with the expansion of the Universe -Several hundred to few thousand km/s
How large is the Solar System?
-Shrink everything down by a factor of 10 billion. 1:10 billion (10 to 10) scale - the Sun is the size of a grapefruit -Jupiter is the size of a marble -Earth is the size of tip of a ball point pen. -If the Sun is a grapefruit, Neptune is a small pebble located somewhere several city blocks away! -Our Solar Sytem is almost entirely empty space.
How big is the Universe?
-The Milky Way is one of about 100 billion (10 to 11) galaxies. -10 to the 11 stars/galaxies x 10 to 11 = 10 to 22 stars. -There are as many stars as grains of (dry) sand on all Earth's beaches.
Rank the following items according to their size (diameter) from left to right, from largest to smallest.
-The Universe -The Local Supercluster -The Local Group -The Milky Way Galaxy -Our Solar Systen -The Sun -Jupiter -Earth
How do our lifetimes compare to the age of the universe?
-The cosmic calendar: a scale on which we compress the history of the universe into 1 year. -The Big Bang occurred on January 1 on this calendar, ~14 billion years ago. -1 month=~1 billion years. - 1 day = ~40 million years. -Matter condenses, and galaxies form about a billion years later - late January/ early February. -Sun, Earth, solar system form about 4.5 billion years ago-early September. -Simple single cell organism appear on Earth in late September. -Life on earth greatly increases in varity during the Cambrian Period in mid-December. -Dinosaurs dominate Earth shortly after Christmas. -Dinosaurs go extinct 4 days later. -Early human ancestors evolve when the New Year's party gets started. -Modern humans (Homo Sapiens) arrive as the Ball begins to drop in Times Square. -Humans begin farming 25 seconds before midnight. -Egyptians built the pyramids 11 seconds before midnight. -Our modern view of the solar system was established by Kepler and Galileo 1 second before midnight. -Typical college student born 0.05 (1/20th) seconds before midnight.
Rank the following items that describe distances from longest distance to shortest distance.
-The distance from the Milky Way Galaxy to the Andromeda Galaxy. -The distance from the Sun to the center of the Milky Way Galaxy. -The distance from Earth to Alpha Centauri. -One light year. -The distance across our solar system (to Neptune) -The average distance from Earth to the Sun -One astronomical unit (AU)
A Universe in motion
-We are not "sitting still." -We are moving with the Earth and not just in one direction. -The Earth rotates around its axis once every day. ~1500 km/hr in Alabama (0.4 km/s)
To our best knowledge, the age of the Universe is about
14 billion years.
How large is the Galaxy?
1:10 to the 19 (20 quintillion) scale - equivalent to the Milky Way Galaxy being as big as a football field. Sun is now the size of an atom.
How far is a light year?
A light year (or parsec, where 1 parsec = 3.26 light years) is a unit of distance, not a unit of time.
Planets
A moderately large object which orbits a star; it shines by reflected optical light from its host star. Planets may be rocky or gaseous in composition.
Comet
A relatively small and icy object that orbits a star. It may or may not have a tail (most do not).
Asteroid
A relatively small and rocky object that orbits a star.
Moon/Satellite
A rocky or icy object that orbits a planet.
How far away is the nearest star (if the Milky Way Galaxy is the size of a football stadium and the Sun is at the 25 yard line)?
A. 4 millimeters away
Universe
All matter and energy. Everything within and between galaxies. >10 to the 10 (>10 billion) light years = 10 to the 23km.
If our Solar Syetem were made smaller such that the Sun was the size of a softball, which of the following would best describe how large a region our Solar System would occupy (out of the orbit of the planet Neptune)?
An area a little larger than The Quad on the University of Alabama campus.
How large is the observable Universe (if the Milky Way Galaxy is the size of a football field)?
C. the size of the Pacific Ocean
On the cosmic calendar, when did modern humans appear?
D) 1—2 minutes before midnight on December 31
How far away is the nearest star if the Sun is the size of a grapefruit in Washington DC?
D. in California
An astronomical unit (AU) is
Earth's averafe distance from the Sun.
Consider our "cosmic address" as discussed in class. From smallest scale to largest scale it is
Earth, Solar Systen, Milky Way Galaxy, Local Group, Local Supercluster, Universe
Consider our "cosmic address" as discussed in class. From smallest scale to largest scale it is __________
Earth, solar system, Milky Way Galaxy, Local Group, Local Supercluster, universe;
Match the words universe
On average, galaxies are getting farther apart with time, which is why we say our universe is expanding.
Match the word. Milky Way Galaxy
Our entire solar system orbits around the center of the Milky Way Galaxy about once every 230 million years.
Match the word solar system
Our solar systen is moving toward the star Vega at about 70,000 km/hr
Match the words Local Group
The Milky Way and Andromeda galaxies are among a few dozen galaxies that make up our Local Group
Match the word Rotates
The Sun appears to rise and set in our sky because Earth rotates once each day.
Consider two galaxies of about the same age that are at different distances from us. Which of the two will appears younger to us?
The galaxy that is furthest from us.
How could one best describe the Sun/Earth's place in our Universe?
There is nothing particularly noteworthy about the Earth, the Sun, or the Milky Way Galaxy in terms of its size or location.
Match the word orbits
You are one year older each time Earth orbits about the Sun,
An object viewed in a telescope that is two million light years from you will appear to be ...
as it was two million years ago.
An advertisement for an electrical appliance says the item is light-years ahead of its time. This does not make sense because
it uses "light-years" to discuss time, but a light-year is a unit of distance, not time.
The Earth completes one revolution around the Sun every
one year.
The age of our solar system is about....
one-third of the age of the universe.
The contents of our Solar System include
the Sun and all the objects that orbit it.
The estimated number of stars in the universe is about the same as:
the number of grains of sand on all the beaches on Earth.
Which is largest?
the size of a typical galaxy
Our Universe is composed of...
the sum total of all matter and energy.
Galaxy A and Galaxy B are two galaxies that are far away. If Galaxy A is one-third as distant as Galaxy B then
we are seeing Galaxy A as it looked at a later time in the history of the universe than Galaxy B.
Star
~10 to the six (1 million) km diameter. -light crossing time: 3 seconds. -Hot gaseous objects generating heat and energy by fusing elements in their cores.