unit 3 astronomy

What was Isaac Newton known for?

first to formulate and test the law of universal gravitation

law of universal gravitation

every object in the universe attracts every other object

what did newton show

gravity and inertia keep planets in orbit

what is newton known for connecting

falling on apples on earth to the same force that keeps planets moving

what is the gravitational force exerted on other objects by an object directly proportional to

the masses of the objects

what is the gravitational force exerted on other objects by an object INVERSELY proportional to

the square of the distance between the objects centers

when a rock falls off a cliff, what is pulled

the earth toward the object

what has the most gravitational pull in our solar system

the sun

what happens when two objects come closer to each other

more gravitational attraction

what is the universal gravitational constant (g)

value that determines the strength of the gravitational force between any two objects in the universe, based on their masses and the distance between them

what happens since earths mass and radius dont change

the gravitational force you feel on earth's surface is always proportional to your mass

what is gravitational field strength (g)

how much force gravity pulls on each kilogram of mass

ways to think about gravitational field strength (g)

acceleration and force per mass

g on earth

9.8 m/s^2

what is mass

amount of matter in an object, same everywhere in the universe

what is weight

gravitational force acting on an object, changes depending where you are

how to calculate weight

mass x g

what does your weight depend on

gravitational field strength where you are

what percent of gravity do astronauts in the iss experience (compared to earth)

90%

what is johannes kepler known for

discovered three laws that describe planetary motion, laws helped prove that planets orbit the sun

what did astronomers believe before kepler

planets move in perfect circles

what is keplers first law

the law of ellipses, all planets orbit the sun in elliptical paths with the sun at one focus of the ellipse

what is an ellipse

oval where the sum of the distances to the foci from any point on it remains constant

what does focus on an ellipse refer to

two special points on the inside

what is the semi-major axis

half of the longest diameter (distance line)

what is the semi-minor axis

half of the shortest diameter

what is the center of an ellipse

midpoint of the foci

what is eccentricity

measure of how stretched an ellipse is between 0 and 1

what is the focal distance

distance between the center and either focus

where is the sun on an ellipse

one of the foci

what is the foci that isnt the sun

nothing

what is perihelion

point in a planets orbit when its closest to the sun

what is aphelion

point in a planets orbit where its furthest from the sun

what follows an elliptical path

any object orbiting another

how come we only see halley's comet occasionally

has a very high eccentricity, takes 76 years to complete an orbit

what is keplers second law

a line connecting a planet to the sun sweeps out equal areas in equal times

what does sun-induced speed changes keep equal

swept areas

what does higher eccentricity do related to perihelion and aphelion

larger speed difference

what would happen if an orbit equaled 0

planet always orbits at same speed

what is conservation of angular momentum

speed of orbiting is conserved if no external forces

what is angular momentum equal to

mass x speed x distance

why is Halley's Comet only visible for such a short time if its orbit takes 76 years

it's closer to the sun

why does the conservation of angular momentum cause planets to move faster when closer to the sun

to keep the product of mass x speed x distance the same through velocity

why must speed decrease when distance increases and vice versa according to conservation of angular momentum

to always stay the same for an orbiting body (the law)

what is the astronomical unit (au)

measurement of distances in our solar system using the average distance between the earth and the sun

what is one au equivalent to

the average distance from the earth to the sun

what's the point of using au

simplicity, easier to compare distances relative to earth, standard unit in astronomy, scaled to our solar system

what is keplers third law

the square of a planets orbital period is proportional to the cube of its semi-major axis

what is a simple summary of keplers third law

the farther a planet is from the sun the longer it takes to orbit following a mathematical pattern

What is an orbital period

Time in earth years that it takes a planet to make a revolution around the sun

What is earths orbital period

365.25 days (one year)

Why do planets with larger orbital periods have higher aus

Longer paths and slower speeds

What does keplers third law work for

Any object orbiting another

how do we determine if an exoplanet orbiting another star is in the habitable zone

measuring orbital period by observing repeated transits or wobbles

how can we measure the mass of the star

measuring period or distance of any planet

What is t in t^2=a^3

orbital period in earth years

what is a in t^2=a^3

semi-major axis in AU

What happens to gravitational force if you double the distance between two objects

It becomes 1/4 as strong

why does the gravitational force become 1/4 as strong with a doubled distance

you are squaring the change in distance and then inverting it to find the change in force

what does g represent

gravitational field strength

you have a mass of 60 kg on earth, how much would you weigh on the moon? (g= 1.6n/kg)

96N (60x1.6)

What planet has the most circular orbit in our solar system

Venus