Astronomy Ch15-21 Study Guide

3.8 × 10²⁶ watts

How much energy does the Sun produce every second?

Kelvin-Helmholtz contraction

Gravitational contraction converts potential energy into heat; occurs when the surface of a star or a planet cools

main fusion process in the Sun

Proton-Proton Chain occurring in the core

details of p-p chain

4 hydrogen nuclei fuse → 1 helium-4 nucleus. Requires minimum temperature of 10 million K

details of hydrostatic equilibrium

Gravity (2 × 10³⁰ kg) pulls inward; pressure from fusion pushes outward; forces balance → Sun stable for ~10 billion years

helioseismology

study of pulsations or oscillations of the Sun in order to determine the characteristics of the solar interior via Doppler shifts (red/blue); can detect activity on opposite side of Sun

why are neutrinos important

rate of _ indicates energy production; 35 million billion pass through 1 m² of Earth every second

luminosity

rate at which a star or other object emits electromagnetic energy into space; the total energy emitted by an object per second at all wavelengths

apparent brightness/magnitude

measure of the amount of light received by Earth from a star or other object; how bright an object appears in the sky

absolute magnitude

Measures a star’s true luminosity (energy output) 

mass-luminosity relation

the observed relation between the masses and luminosities of many (90% of all) stars.

star color and temperature

Hottest stars appear blue or blue-white (>10,000 K), cooler stars appear yellow (5,000-6,000K), orange, or red (<3,500K).

UBV filters

standard photometric system used to classify stars by measuring their brightness across Ultraviolet, Blue, and Visible light

Oh Be A Fine Girl, Kiss Me, Less Tongue, Yo

List the spectral classes from hottest to coolest.

brown dwarf

object intermediate in size between a planet and a star; capable of deuterium fusion, but not hydrogen fusion

giant

a star of exaggerated size with a large, extended photosphere

How are star masses measured

using Newton’s form of Kepler’s third law in visual, eclipsing or spectroscopic binaries

How are eclipsing binaries useful

determining mass, radius, luminosity, and temperature

H-R diagram (Hertzsprung–Russell diagram)

Graph of temperature vs. luminosity for a group of stars

main sequence

a sequence of stars on the Hertzsprung–Russell diagram, containing the majority of stars, that runs diagonally from the upper left to the lower right

white dwarfs

low-mass star that has exhausted most or all of its nuclear fuel and has collapsed to a very small size; near its final state of life

parallax

an apparent displacement of a nearby star that results from the motion of Earth around the Sun

light curve

a graph that displays the time variation of the light from a variable/eclipsing binary star or any other object whose radiation output changes with time

cepheid characteristics

vary periodically in brightness, larger period → greater luminosity. period-luminosity relation allows distance measurement

RR Lyrae

a class of giant pulsating stars with periods shorter than 1 day, useful for finding distances

H II region

region of ionized hydrogen in interstellar space

21-cm radiation

the spectral line emitted by neutral hydrogen atoms as they change energy states, producing a wavelength of 21 cm

molecular cloud

a large, dense, cold interstellar cloud; because of size and density, can keep ultraviolet radiation from reaching its interior, where molecules can form

giant molecular clouds

large, cold interstellar clouds with diameters of dozens of light-years and typical masses of 10⁵ solar masses; found in the spiral arms of galaxies

Dust grains affecting starlight

through interstellar extinction, where they absorb and scatter visible/infrared/UV light, making stars appear dimmer and redder (reddening)

cosmic rays

atomic nuclei (mostly protons) and electrons that are observed to strike Earth’s atmosphere with exceedingly high energies.

when cosmic rays hit Earth’s atmosphere

collide with gas atoms (mostly nitrogen and oxygen) at 10-20 km altitude. triggers a chain reaction creating showers of secondary particles (muons, neutrinos, electrons).

baryon cycle

cycling of mass in and out of the ISM, including collecting of gas from intergalactic space, loss of gas back into intergalactic space, and conversion of interstellar gas into stars

Where do stars form

in giant molecular clouds

protostar

a very young star still in the process of formation, before nuclear fusion begins

How do protostars evolve?

Collapse, spin, flatten (contraction). Heating of core → hydrogen fusion → main sequence

T Tauri star

Protostars that have gathered nearly all available mass

Herbig-Haro (HH) object

luminous knots of gas in an area of star formation that are set to glow by jets of material from a protostar

How do planets form

Dust and gas gathering in disks around young stars (protostars); dust grains collide and grow

transit method for exoplanets

Planet crosses star → dims light → measures size and orbit

mini-Neptunes

planet that is intermediate between terrestrial planet Earth and the smallest jovian planet __; sizes between 2.8 and 4 times Earth’s size

More massive protostar

results in faster formation

selection effect

picking sample data in a nonrandom way, causing the sample data to be unrepresentative of the entire data set

active region

area on the Sun where magnetic fields are concentrated; sunspots, prominences, flares, and CMEs all tend to occur in these areas

aurora

regions where light radiated by atoms and ions in the ionosphere are excited by charged particles from the Sun

chromosphere

the part of the solar atmosphere that lies immediately above the photospheric layers

corona

outer atmosphere of the Sun

coronal hole

a region in the Sun’s outer atmosphere that appears darker because there is less hot gas there

coronal mass ejection (CME)

a solar flare in which immense quantities of coronal material—mainly protons and electrons—is ejected at high speeds (500–1000 kilometers per second) into interplanetary space

differential rotation

the phenomenon that occurs when different parts of a rotating object rotate at different rates at different latitudes

granulation

the rice-grain-like structure of the solar photosphere

how is granulation produced

by upwelling currents of gas that are slightly hotter, and therefore brighter than the surrounding regions, which are flowing downward into the Sun

Maunder Minimum

a period during the seventeenth century when the number of sunspots seen throughout the solar cycle was unusually low

photosphere

the region of the solar (or stellar) atmosphere from which continuous radiation escapes into space

plage

a bright region of the solar surface observed in the light of some spectral line

plasma

a hot ionized gas

prominence

a large, bright, gaseous feature that appears above the surface of the Sun and extends into the corona

solar flare

a sudden and temporary outburst of electromagnetic radiation from an extended region of the Sun’s surface

solar wind

a flow of hot, charged particles leaving the Sun

sunspot

large, dark features seen on the surface of the Sun caused by increased magnetic activity

sunspot cycle

the semiregular 11-year period with which the frequency of sunspots fluctuates

transition region

region in the Sun’s atmosphere where the temperature rises very rapidly from the relatively low temperatures that characterize the chromosphere to the high temperatures of the corona

conduction

process by which heat is directly transmitted through a substance when there is a difference of temperature between adjoining regions caused by atomic or molecular collisions

convection

movement caused within a gas or liquid by the tendency of hotter, and therefore less dense material to rise, and colder denser material to sink under the influence of gravity, which consequently results in transfer of heat

fission

breaking up of heavier atomic nuclei into lighter ones

fusion

building up of heavier atomic nuclei from lighter ones

hydrostatic equilibrium

balance between the weights of various layers, as in a star or Earth’s atmosphere, and the pressures that support them

neutrino

fundamental particle that has no charge and a mass that is tiny relative to an electron; it rarely interacts with ordinary matter and comes in three different types

positron

particle with the same mass as an electron, but positively charged

proton-proton chain (p-p chain)

series of thermonuclear reactions by which nuclei of hydrogen are built up into nuclei of helium

radiation

emission of energy as electromagnetic waves or photons also transmit the energy itself

brown dwarf mass

approximate mass range is from about 1/100 of the mass of the Sun up to the lower mass limit for self-sustaining nuclear reactions, 0.075 the mass of the Sun 

color index

difference between the magnitudes of an object measured in light of two different spectral regions

magnitude

an older system of measuring the amount of light we receive from a star or other luminous object

larger the magnitude

the less radiation we receive from the object

proper motion

the angular change per year in the direction of a star as seen from the Sun

radial velocity

motion toward or away from the observer

space velocity

the total speed and direction with which an object is moving through space relative to the Sun

spectral class/type

classification of stars according to their temperatures using the characteristics of their spectra

binary stars

two stars that revolve about each other

eclipsing binary

a binary star where the plane of revolution of the two stars is nearly edge-on to our line of sight, so the light of one star is periodically diminished by the other passing in front of it

L~M^3.9

Mass-luminosity relation equation

spectroscopic binary

a binary star where the components are not resolved but whose binary nature is indicated by periodic variations in radial velocity, indicating orbital motion

visual binary

a binary star in which the two components are telescopically resolved

cepheid

star that belongs to a class of yellow supergiant pulsating stars

luminosity class

classification of a star according to its luminosity within a given spectral class

D = 1/p

Parallax equation

period-luminosity relation

an empirical relation between the periods and luminosities of certain variable stars.

longer period

higher luminosity

parsec

unit of distance in astronomy, equal to 3.26 light-years; at distance of 1 _, a star has a parallax of 1 arcsecond

pulsating variable star

a variable star that pulsates in size and luminosity

G2V

Spectral and luminosity class for the Sun

interstellar dust

tiny solid grains in interstellar space thought to consist of a core of rocklike material (silicates) or graphite surrounded by a mantle of ices; water, methane, and ammonia

interstellar extinction

the depletion or absorption of light by dust in the interstellar medium

interstellar medium/matter (ISM)

the gas and dust between the stars in a galaxy

Local (Hot) Bubble

region of low-density, million degree gas in which the Sun and solar system are currently located

Local Fluff

a slightly denser cloud inside the Local Bubble, inside which the Sun also lies

nebula

a cloud of interstellar gas or dust; most often used for clouds that are seen to glow with visible light or infrared

reddening

__ of starlight passing through interstellar dust because dust scatters blue light more effectively than red

exoplanet

a planet orbiting a star other than our Sun