Astronomy Notes

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gravitational potential energy

on earth, GPE depends on:

-objects mass

-strength of gravity

-distance object could potentially fall

in space an object or gas cloud has more gravitational energy when it is spread out than when it attracts.

- a contracting cloud converts gravitational potential energy to thermal energy.

Energy

-energy can be neither created nor destroyed

-energy can change form or be exchanged between objects

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conservation before energy

conservation of angular momentum

-angular momentum conservation also explains why objects rotate faster as they shrink in radius

velocity gets bigger as radius gets smaller

velocity gets smaller as radius gets bigger

how can orbits change?

-friction: atmospheric drag, or tidal flexing of a “fluid” object

-a gravitational encounter

orbits

-ellipses are not the only orbital paths. Orbits can be:

-bound(ellipses)

-unbound

-parabola

-hyperbola

the type of orbit depends on the energy of the object at the start of its trajectory

escape velocity

-if an object gains enough orbital energy, it may escape (change from a bound to unbound orbit)

-escape velocity from earth = 11 km/s from sea level (about 40,000 km/hour)

how does gravity cause tides

-moons gravity pulls harder on near side of earth then on far side

-difference in moons gravitational pull stretches earth

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chapter 10.2 Radiation tells us the temperature, size and composition of stars

properties of matter, THEN

Democritus (470-380 B.C)

“Atoms”meaning; indivisible

all matter made up of 4 elements: fire water earth air

Properties of matter, NOW

“atoms” are divisible

many more elements.

Periodic table

Parts of an atom

- Nucleus: proton + charge, neutron no charge, electron – charge

- Mass of proton is almost same as mass of neutron

- Mass of electron is about 1/2000th of the mass of the proton

- Helium atom = 2 protons, 2 neutrons, and 2 electrons

Atoms act like a mini solar system

Nuclear density- a teaspoon of material as dense as the matter in an atomic nucleus would weigh 2 billion tons

Magnify atom 1 trillion times, would be a grape seed but have force on it from 4.5 football fields away

Electron orbits- electron orbits in the electron cloud are restricted to very specific radii and energies

Radial velocity ( Doppler method, wobble method)

Transit method

Direct imaging

THE SUN

Never look directly at the sun