AST Final Study Guide

galaxy

a gravitationally-bound system that consists of stars, gas, dust, and dark matter; contains billions of solar systems

solar system

a gravitationally-bound system made up of a star (or 2+) and all the planets, moons, comets, asteroids, dwarf planets, gas, and dust that orbit it

What type of galaxy is the Milky Way?

a spiral galaxy

space scale from smallest to largest

Earth → our solar system → Milky Way Galaxy → Local Group → Virgo Supercluster → Laniakea Supercluster → universe

How far is the closest star to the Sun?

Proxima Centauri; 4.2 light years

What is the diameter of the Milky Way Galaxy?

100,000 light-years

What is the diameter of the Laniakea Supercluster?

350 million light-years

hypothesis

an idea that can explain a phenomenon

theory

a hypothesis that tests have failed to disprove

physical law

a theory that has been very well tested and is of fundamental importance

steps of the scientific method

start with an observation or idea → suggest a hypothesis → make a prediction → perform a test, experiment, or additional observation → if the test supports the hypothesis, make more predictions and test them; if it doesn’t, revise your hypothesis or make a new one

scientific method definition

a systematic way of testing new ideas

celestial sphere

a projection of Earth’s poles and equator into space; rotates around the north and south celestial poles

ecliptic

the plane in which the Earth orbits the Sun; from our perspective, the Sun’s apparent path across the sky over a year

meridian

an imaginary circle on the celestial sphere that passes through the north and south poles

zenith

as an observer, the point straight above your head

What is the angle of the ecliptic?

inclined 23.5 degrees to the celestial equator

circumpolar

celestial objects that remain above the horizon (so visible) at all times for a specific location on Earth

What causes seasons on Earth?

the axial tilt (the 23.5 degrees of the axis with respect to the ecliptic); in summer, the angle of sunlight is more direct, so energy is more concentrated and days are longer

summer solstice

the Sun reaches its highest point above the ecliptic; longest day

autumnal equinox

the Sun ins on the celestial equator; equal hours of day and night

winter solstice

Sun reaches its lowest point above the ecliptic; shortest day

vernal equinox

Sun is on the celestial equator; equal hours of day and night

What are the phases of the moon in order?

new moon, waxing crescent moon, first quarter, waxing gibbous moon, full moon, waning gibbous moon, third quarter, waning crescent moon

cosmological principle

the assumption that the physical laws that apply here on Earth apply everywhere else in the Universe; there is nothing special about our place in the Universe; the universe is homogenous (galaxies are distributed similarly everywhere) and isotropic (looks the same to all observers regardless of the direction they’re looking)

What did Copernicus do?

thought of a heliocentric (Sun-centered) solar system; explained retrograde motion; determined planets’ distances from the Sun relative to the Earth-Sun distance

What did Rømer do?

he was the first to measure the speed of light (300,000 km/s); did this by observing the eclipses of Jupiter’s moon

What did Galileo do?

first to use a telescope for astronomy; discovered the phases of Venus and the 4 largest moons of Jupiter; controversial w church bc he provided evidence that our solar system is heliocentric

luminosity

the amount of light emitted by a star

What determines the observed brightness of a star?

both luminosity and distance

How is a star’s brightness measured?

in magnitudes; brighter objects have smaller magnitudes

Newton’s first law of motion

an object in motion stays in motion and an object at rest stays at rest unless acted upon by a net force

Newton’s second law of motion

the acceleration of an object is directly proportional to the magnitude of the net force acting on it, and inversely proportional to the object’s mass

Newton’s second law equation

F = ma (net force equals mass multiplied by acceleration)

Newton’s third law

for every action in nature, there is an equal and opposite reaction

How do Newton’s second law relate to gravity?

they both explain why planets orbit the Sun

law of gravity

the strength of the gravitational force between two objects depends on the objects’ mases and the distance between them

Inverse Square Law equation

F_grav = G * ((m₁*m₂)/r²) ; (G - universal gravitational constant; m - masses; r -separation distance)

Kepler’s first law of motion

the orbits of the planets around the Sun are ellipses; the Sun is at one focus

eccentricity

the shape of an orbit; the greater it is, the more elongated the ellipse

Kepler’s second law

the law of equal areas; the line between the Sun and each planet sweeps out equal areas in equal times; planets go faster the closer they get to the Sun

Kepler’s third law

the period² of the planet’s orbit in years is equal to the semimajor axis³ in AU; distant planets take longer to orbit the Sun and travel at slower speeds

How do orbits work?

an object in orbit around something is constantly falling toward it but constantly missing

What is gravity’s role in orbits?

it provides the centripetal force that holds a satellite in its orbit; it also changes the direction and speed of planets

What did Apollo astronauts do?

collected rocks from the moon that contained gas bubbles, evidence of volcanic activity

Kepler telescope

monitored the brightness of 150,000 main-sequence stars and found many exoplanets

James Webb Space Telescope

infrared telescope and replacement for Hubble

Transiting Exoplanet Survey Satellite (TESS)

identified 5,840 exoplanet candidates, meant to be followed by JWST

LUVOIR

proposed telescope designed to study and search for habitable exoplanets and investigate the early universe

What is light?

an electromagnetic wave; doesn’t require a medium to travel through

electromagnetic spectrum

the full range of electromagnetic radiation, organized by wavelength/frequency

What is the relationship between energy, wavelength, and the speed of light?

higher frequency/shorter wavelength means more energy; wavelength = speed/frequency; the speed of light is constant

Which wavelengths of light are the most energetic?

gamma rays are the most, then x-rays, then ultraviolet

Does a photon of red or blue light carry more energy?

blue

Which wavelengths of light are the least energetic?

Radio is the least, then TV, cell phone, microwave, and infrared

What are CCDs?

charge-coupled devices; digital detectors that contain an array of pixels. photons strike the pixels to create electric charges that are read by a computer to form an image

refraction telescopes

use lenses to collect and focus light; primary lens bends the light

reflecting telescopes

use mirrors to collect and focus light

radio telescopes

large collecting areas to catch radio waves

interferometric arrays

combine the signals from many telescopes; acts as one large telescope to improve resolution

space-based telescopes

avoid problems with the atmosphere ex. Hubble and Chandra X-ray Observatory

adaptive optics

help correct for atmospheric distortion

How do protostars form?

molecular clouds (mostly hydrogen and dust) experience self-gravity and eventually collapse

How do stars form?

more material falls on the protostar, making it more compact and causing the interior temperature and pressure to rise; they increase until nuclear fusion of hydrogen into helium is possible; once the reaction occurs a star is born

brown dwarfs

protostars that never begin nuclear fusion

angular momentum

how a spinning sphere becomes a flattened, rotating disk; remains constant as the rotation of a dust cloud speeds up

main-sequence stars

90% of all stars; lie along a region on the H-R diagram from upper left (high temperature, high luminosity) to lower right (low temperature, low luminosity); mass of the star determines all of its characteristics

post-main-sequence star

a star that has exhausted the hydrogen fuel in its core and is evolving beyond the main sequence; the fusion process slows down and the balance between gravity and pressure is disrupted

What is the final fate of a high-mass star?

higher temperature and pressure means these stars burn their fuel more quickly and have shorter life-spans; ends in a huge explosion called a Type II supernova

What happens to low-mass stars over time?

they burn through their nuclear fuel more slowly and have longer lifetimes than high-mass stars; evolve from main sequence → red giant → planetary nebular → white dwarf

primary atmospheres

new planets are formed with them; consist mainly of hydrogen and helium; all terrestrial bodies lose them due to: proximity to the Sun, high gas speeds, and low planetary gravity

secondary atmospheres

acquired later by comet/asteroid impacts and volcanism releasing gases

volatile

a material that turns into a gas at relatively low temperatures

doppler/radial velocity method

method to detect exoplanets by measuring the Doppler effect (redshift as moves away, blueshift as approaches) on a star to infer the presence of a planet orbiting it

transit method

method to detect exoplanets by observing a dip in a star’s brightness which would be caused by a planet crossing in front of it

gravitational lensing method

method to detect exoplanets by looking for a light bending effect of the star by the planet’s gravity

direct imaging method

method of detecting exoplanets by taking pictures and blocking the bright light from a star to enhance the light coming from a planet

How many exoplanets have been confirmed?

5,885

How do lunar tides work?

the Moon’s gravity pulls harder on the side of Earth that is closer, stretching it; they also affect the solid part of Earth and cause friction which generates heat in the interior

spring tides

when the Sun, Moon, and Earth are in a line; above-average tide

neap tides

when the Sun, Earth, and Moon form a right angle; solar and lunar tides partially cancel each other

What processes shape planetary surfaces?

impact cratering, tectonism, volcanism, erosion

greenhouse effect

sunlight hits ground, which radiates infrared radiation back to space, but greenhouse gases trap some of them and send them back to the ground, heating it further

What is the importance of CO₂ over geologic history?

most of Earth’s is stored in rocks, so Earth won’t have a natural runaway greenhouse effect

troposphere

layer where most human life exists; mainly water vapor; temp/pressure decrease as altitude increases

stratosphere

layer above troposphere; temp increases as altitude increases; absorbs UV light and protects life on Earth

mesosphere

layer above stratosphere; temp decreases as altitude increases; upper section is coldest part of atmosphere

thermosphere

layer above mesosphere; temperature increases as altitude increases; UV radiation and solar wind can ionize atoms

ionosphere

layer above thermosphere; electrically charged layer of plasma

What is the order of layers of Earth’s atmosphere?

troposphere, stratosphere, mesosphere, thermosphere, ionosphere

Mars’s atmosphere

thinner due to low gravity; has extreme temperature variations and weather;

Venus’s atmosphere

more than Earth; runaway greenhouse effect because water vapor and carbon dioxide aren’t trapped on the planet; 96% carbon dioxide

Mercury’s atmosphere

practically none due to high temperature and low gravity

the Moon’s atmosphere

practically none due to low gravity

primary (p) waves

longitudinal, like sound waves, and pass through solids and liquids

secondary (s) waves

transverse, like water waves, and can’t pass through liquids

gas giants

Jupiter and Saturn; contain primarily hydrogen and helium

ice giants

Uranus and Neptune; contain more water ice and other ices

Jupiter’s atmosphere

lower layers have water clouds, middle layers have deeper clouds of ammonium hydrosulfide, and upper layers have colorful clouds and are mostly made of ammonia ice crystals; Great Red Spot

Saturn’s atmosphere

lower gravity leads to thicker cloud layers; consists of just ammonia ice, troposphere, a haze, and stratosphere