Stars/Galaxies Exam 1 Study Guide

Scientific Method

Ask question → hypothesis → prediction → observation

Hypothesis

proposed explanation made on basis of limited evidence as a starting point for further investigation

Law

Describes what happens (one sentence)

Theory

group of linked hypotheses on broad topic that had rigorous testing - Explains why or how (multiple sentences)

Hallmarks of good science

Skepticism, disprove instead of prove, falsifiability, pattern is just a pattern, data over ideas, include all data, precise predictions, clearly defined scope

Clearly defined scope

When does it work, when does it not work?

Prediction

One specific test of hypothesis

Falsifiability

Is there a way to tell if something could be false (limits to subjects we can get data on)

Pseudoscience

Does not follow rules of science, exploits cognitive bias

Model

group of linked hypothesis that are often represented visually

1 astronomical unit (AU)

93 million miles (average distance between earth and sun)

Speed of light

300,000 km/s

Light year

distance light travels in a year

Order of planets

Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune (My very educated mother just served us nachos)

Cosmic Calendar

Shrunken history of universe to one year

Universe age

13.8 billion years

Solar system age

4.5 billion years

Milky Way

Spiral galaxy that Earth lives in

Local Group

Neighboring group of galaxies such as Andromeda Galaxy or Milky Way

Physical scales and timescales

Celestial Sphere

Imaginary sphere around earth that stars appear to lie on

Zenith

top of the sky

Horizon

where sky meets ground

Meridian

Line on a sundial that the sun crosses which represents noon (North - south line)

Gnomon

raised stick which cast a shadow in a sundial to show time

Celestial Equator

projection of Earth’s equator onto the sky

Celestial Poles

Projection of north/south pole into the sky

Ecliptic

Path of Earth orbit around the sun

Moon’s tilt

5 degrees relative to earth’s path around sun (ecliptic)

Earth’s tilt

23.5 degrees

Precession

Earth’s axis turns like a top, cycle is 26,000 years

Retrograde Motion

Planet sometimes appear to move backwards relative to background stars (drift westward instead of east)

Ptolemy’s Geocentric Model

Model where planets and sun orbits around Earth

Copernicus’ Heliocentric Model

Model where planets orbits around the sun

Galileo Observations

Observed moon, Jupiter, milky way, and Venus with telescope

Galileo’s moon discovery

Moon had craters and not perfectly spherical, disproving ptolemy’s idea all objects are perfectly spherical

Galileo’s Jupiter discovery

Jupiter had 4 moon’s, doubt on Ptolemy’s idea everything goes around Earth

Galileo’s Milky Way discovery

More stars in galaxy than previously thought, universe bigger than we thought, why do we think we live in center of it

Galileo’s Venus discovery

Found that Venus had phases like moon, saw full moon, disproved Ptolemy’ idea Venus had only crescent and new phases due to it being in front of sun

Seasons

Caused by tilt of Earth, more sunlight time and more direct intense sunlight in summer

Sidereal day

One rotation of the earth (23 days and 56 minutes)

Solar day

Time it takes for the sun to reach highest point in the sky (24 hour day)

Seven day week

Based on 7 planet gods and biblical story of creation (Judeo-Christian)

Sidereal month

one orbit of moon around the Earth (27.3 day)

Synodic Month

One cycle of lunar phases (29.5 days)

Sidereal year

one orbit of Earth around the sun (365.24 days)

Tropical year

one cycle of seasons

Lunar phases

New, waxing crescent, first quarter, waxing gibbous, full, waning gibbous, third quarter, waning crescent (bright side left to right)

Lunar Eclipse

When Earth is between sun and moon, full moon and crossing ecliptic

Solar Eclipse

When moon is between sun and earth, new moon and crossing ecliptic

Kepler’s First Law

orbit of each planet is an ellipse with the sun at one focus of the two focuses

Kepler’s second law

Planets sweep out equal areas in equal times (planets move faster when closer to the sun)

Kepler’s third law

p² = a³, p is orbital period, a is average distance from the sun, shows how long a planet takes to orbit (farther away = longer orbit compared to planet closer to sun) Only works for objects orbiting sun

Speed

Distance divided by time

Velocity

Speed and direction

Acceleration

Any change in velocity (speed or direction)

Force

A push or a pull

Mass

amount of stuff in an object

Weight

Force from things that are holding you up, force of gravity on an object by a planet/moon

Newton’s first law

Law of inertia, object’s velocity does not change unless there is a net force acting on it (continues to do something unless force acts upon it)

Newton’s second law

Net force = mass x acceleration

Net force

total force acting on an object

Newton’s third law

If an object pushes or pulls a second object, the second object pushes or pulls back with an equal force in the opposite direction

Newton’s Law of Gravitation

F1 = F2 = G(m1xm2/r²), calculates gravitational force between two objects, double mass = double force, double distance = down ¼ force

Newton’s modifications to Kepler's 1st law

planets and sun orbits their center of mass that lies at common focus of both ellipses (orbits center of mass of two body system, larger objects closer to center of mass thus move less)

Newton’s modifications to Kepler’s 3rd law

p² = (4pi²/G(m1+m2))a³, can use to describe orbit of any object around another object, also can be used to calculate mass of object

Escape velocity

object will escape Earth’s orbit permanently at an initial speed greater than 11 km/s

Orbit velocity

object will orbit Earth on circular path at an initial speed of 8 km/s forever

Solstice

Longest day/night of year, June 20/21, Dec 21/22

Equinox days

12 hour night/day, March 20, Sept 22/23