Astronomy - Week 3

Tycho Brahe

Danish nobleman who surveyed the sky without a telescope and observed a supernova (___ ‘s star) in 1522

Johannes Kepler

Who did Brahe hire as an assistant for his mathematical analysis?

elipse

unlike a circle, it is not defined by a single central point but rather two foci. has a long radius called the semi major axis and a short radius called the semi minor axis.

Keplers first law

states that each planet moves around the sun in an orbit that is an ellipse, with the sun at one focus of the elipse

Keplers second law

states that the straight line joining a planet and the sun sweeps out equal areas in space in equal intervals of time. means that the planet moves faster when it is closer to the sun and slower when it isnt.

Keplers third law

the most mathematical law- the square of a planets orbital period is directily proportional to the cube of the semi major axis of its orbit

universal law of gravitation

a short equation which says that there is a force between any two masses

acceleration of gravity

___of the earth, moon, or other astrinomical body does not depend of the mass of the dropped object.

the only requirment for gravity to act on an object

the object has mass (i.e it physically exists) and there is another object with mass anywhere in the universe

object moves too slow

object doesnt orbit and falls back to earth

object moves too fast

object doesnt orbit and escapes earths gravity

object moves just right

object is on a closed orbit and this just right speed is 17500 miles per hour (8 km/s)

Edmun Halley

who tracked part of the orbit of a comet and predicted when it would return using Newton’s laws of motion? He was exactly correct.