Stars Galaxies Midterm

AU (astronomical unit)

Earth’s avg distance to the Sun (approximately 93 million miles/150 million km)

• doesnt depend n where earth is in elliptical orbit

Nuclear force binds ______

neutrons and protons together

Protons

positively charged particles in an atom's nucleus that help determine an element's identity.

Neutron

A subatomic particle found in the nucleus of an atom, with no electric charge and a mass slightly greater than that of a proton.

Electron

A negatively charged subatomic particle that orbits the nucleus of an atom, playing a key role in chemical bonding and reactions.

mega, kilo, centi, milli, etc

How long does it take light to travel to earth from the moon?

1 second

If something is 2000 light years away, how old do we see it when it reaches earth?

2000 years old

Order the beginning of the universe

Hypothesis

attempt @ explanation

Law

all samples meet same outcome (i.e. gravity); generalization

Fact

Statement significant to 1 thing

ex. the sky is blue

Theory

explains why & how; deeper than law

ex. Theory of relativity explains deeper gravity

Where would you see the most stars, north pole, south pole, equator?

Equator

Eclliptic

apparent path of constellations in the sky

How do we know Earth is round?

1. Photos from space

2. Ships pass over the horizon

3. Round shadow on moon

   1. N star moves to zenith as you move north

Ptolemaic vs Copernican model

Ptolemaic: geo-centric> stars orbit Earth

• used complex epicycles to justify orbits

Copernican: helio-centric> earth orbits sun

• still used complex epicycles to justify retrograde motion

• circular orbits (not elliptical)

Phases of venus

observed by Galileo; justified helio-centric models because you cant see a full venus in a geo-centric (has to be opposite Earth in orbit)

• went through all phases (could only happen in helio-centric)

What did Galileo prove when he observed jupiter’s moons?

Observed moons orbitting jupiter; proved things could orbit obj other than Earth

Why are lunar eclipses more pop than solar eclipses?

shadow of earth is bigger than shadow of moon (wider path)

Tycho Brahe & Kepler

Brahe: measured sky & planets; observation only; hired Kepler & kept work from him to keep the fame

Kepler: mathmatically predicted motion of planets using brahe’s observations

• proved helio-centric modelKe

Kepler’s Laws

1. planets orbit the sun in elliptical orbits; Sun is also 1 of the foci

2. line joining planets to sun sweeps out in equal space, equal time

3. P²=a³ (linear relationship)

Eccentricity

how elliptical orbit is; higher eccentricity, more elliptical

Perihelion & Apehelion

Perihelion: closest to sun in orbit (fastest)

Apehelion: furthest from sun in orbit (slowest)

Orbital period vs rotational period (earth)

Orbital period: 365.25 days (1 revolution)

Rotational period: ~24 hr

Newton’s laws

1. every obj will stay in motion unless acted upon by equal and opp force

2. change in motion is prop to and in direction of force acting on it (i.e. heavier rocket needs more force to produce same acceleration)

3. For every action there is an equal and opp reaction (i.e. gun recoils when bullet is shot)

Asteriods & comets

Asteriods: reminents of Big bang, lie between mars and jupiter (asteriod belt is very empty)

Comets: high eccentricity

What happens if you shoot a bullet at orbital speed around earth (8 km/s)?

It orbits in a circle, 11 km/s escape velocity

Discovery of Neptune

william herschel thought uranus’ orbit had a discrepancy, turned out to be grav pull from neptune

• confirmed newton’s theory of grav A

ascension vs declination

Asension: longitude (right to left)

Declination: latitude (up and down)

• starts from vernal equinox (where celestial equator meets eclliptic)W

Where does the prime meridian go through?

Greenwich england (0,0)

Why are summer days hotter

days are longer, sun gets higher in sky (NOT because earth is closer to sun)

What happens @N and S pole because of the tilt of earth’s axis?

Spend ½ year in daylgith, ½ in night

ex. S pole spends 24 hours light in winter, N 24 dark

Solar vs Sidereal day

Solar: day as measured by position of sun on earth (24 hr)

Sidereal: day as measured by rotation of stars across meridian (23 hr and 56 min)

Does the moon rotate

Yes; the moon is tidally locked to earth (see relativly the same side); helps keep axis in check

Phases of the moon

Why did Copernicus formulate a new model of the universe?

Ptolemaic model needed adjustments to predict the position of the planets

Motions described by geocentric model were too complex with use of epicycles & deferents

How does the path of the season change with the seasons?

Earth’s axis is tilted with respect to the solar ecliptic> sun gets lower in winter in N hemi