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Earth Sun Star & Universe Intro to Astronomy

This Chapter covers Earth Sun Star & Universe Intro to Astronomy

Field View

the visible area in an image, usually given as the diameter or a region

Astronomy is sometimes known as?

the science of big numbers

scientific notion

a way to write big or small numbers without using lots of zeros

solar system

consists of the sun, family of planets, asteroids, moons and comets


small spherical nonluminous bodies that orbit a star and shine by reflected light

Venus is the size of?


how big is mercury?

just over 1/3 of the earths diameter

the sun is a?


describe the sun

self luminous
ball of hot gas
generates own energy

astronomical unit (AU)

average distance from the earth to the sun = to
1.5 x 10(8)

what is the average (AU) from Venus to the sun

about 0.72 (AU)

what is the average (AU) from mercury to the sun

about 0.39 (AU)

why are distances averages?

because the orbits of the planets are not perfect circles

how long does it take light from the sun to reach earth?

Eight minutes

how long does it take light from the sun to reach neptune?

Four hours

what star is the only visible one?

the sun

how many stars are there?


light year (ly)

the distance that light travels in one year
roughly 10(3) km or 63,000 (AU)
light year is a distance not a time

what is the closest star to the sun?

Alpha Centauri

how many (ly) is Alpha Centauri from earth?

4.2 (ly)


great cloud of stars, gas and dust held together by the combined gravity of all of its matter
contains our solar system, billions of stars, planets that orbit them, billions of planetary system

how many stars does a galaxy contain?

some over 100 billion

what is the (ly) diameter of galaxies?

1500 to over 300,000 (ly) in diameter

milky way

hazy band of light that circles the sky, produced by the combined light of billions of stars in our milky way galaxy

milky way galaxy

the spiral galaxy containing the sun; visible at night as the milky way

spiral arms

long, spiral patterns of bright stars, star clusters, gas and dust that extends from the center to the edge of the disk of spiral galaxies


includes all galaxies, stars, planets, our own galaxy and our solar system

how old is the universe?

Fourteen billion years old

when was there light?

Four hundred million years ago, when gravity pulled some of the gases together and formed the first stars

why study astronomy?

to answer:
what are we?
how do we know?

what do we live on?

a planet

why do scientists use the metric system?

simplifies calculations

how long does it take earth to orbit the sun?

one year

how big is the moon compared to earth?

1/4 the diameter of earth

how big is the sun compared to earth?

one hunderd & nine times larger than earth

what is the (AU) from mars to the sun?

1.5 (AU)

how many (ly) in diameter is our galaxy?

Eighty thousand (ly)

Name the event that caused our universe to begin about 14 billion years ago

big bang theory

Big Bang Theory

Four hundred million years after the big bang universe filled with hot gas
cooled & galaxies began to form
stars began to shine

when did the sun and planets of our solar system form?

4.6 billion years ago

where did life begin?

on the ocean floor after the earth formed but did not emerge onto land until 400 million years ago

when did dinosaurs evolve?

Four hunderd million years ago & went extinct 65 million years ago

when did humanlike creatures develop on earth?

Four millions years ago

when did human civilization develop?

about 10,000 years ago

why are light years more convenient than miles, kilometers or astronomical units for measuring certain distance?

because the distance is to large to express

why is it difficult to detect planets orbiting other stars?

because they are to small, to faint and to close to the glare of their star to be easily visible

what does the size of the star image in a photograph tell you?

the stars brightness not its actual size

what is the difference between the milky way and the milky way galaxy?

the milky way galaxy is our galaxy and the milky way is the combined light of billions of stars in our milky way galaxy

how does astronomy help answer the question “what are we”?

it helps us to learn how we fit into the history of the universe

how does the scientific method give scientists a way to know about nature?

it is a general way of testing and refining ideas to better describe how nature works