ASTR 130 Final

speed of light

c = 300,000,000 m/s

(3 x 10^8 m/s, in scientific notation)

"c" is an abbreviation that astronomers use for the speed of light

Heinrich Hertz

verified the existence of electromagnetic waves

unit for frequency of waves (hertz) is named after him

light

an electromagnetic wave

colors of the visible spectrum of light

"visible light"

red through orange, yellow, green, blue, and violet

(range in electromagnetic spectrum that human eye is sensitive to)

electromagnetic spectrum

(high to low)

gamma rays, x-rays, UV, visible light, infrared, radio waves

only differences between one type of electromagnetic wave and another

wavelengths and frequencies

wavelength

the physical length of one cycle of a wave

frequency

the measure of how frequently a wave repeats its cycle

ultraviolet

"above violet"

higher frequency and therefore shorter wavelength than visible light

infrared

"below red"

lower frequency and therefore longer wavelength than visible light

x-rays and gamma rays

waves with higher frequencies and shorter wavelengths than visible light and ultraviolet

microwaves and radio waves

waves with lower fre-quencies and longer wavelengths than visible light and infrared

what do all electromagnetic waves have in common?

they all travel at the speed of light in space

Our atmosphere absorbs most electromagnetic waves except for and ____

visible light and radio waves

two types of optical telescopes

refractor and reflector

refractor telescope design

two lenses, one on each end of a hollow tube

lenses are glass ground into a convex shape that will concentrate or focus the light at a certain point

refraction

a change in the direction of a light wave caused by a change of speed that occurs when light travels from one substance to another

eyepiece

smaller lens the observer looks into

objective

larger lens used to collect the light

"power" of a telescope

a measure of its magnification power

light gathering power

a measure of how much light it can gather (determined by the size of the objective)

reflecting telescope

invented by Isaac Newton

concave (curved inward) mirror and an objective to gather and focus light

in a reflecting telescope, the light travels all the way down the tube before hitting the ___ ____

primary mirror

primary mirror of a reflecting telescope then reflects the light back to a flat _ ____

secondary mirror

secondary mirror then redirects the light to an _ ____ in a reflecting telescope

eyepiece lens

newtonian focus

the focal arrangement of a reflecting telescope in which a diagonal mirror reflects light out the side of the telescope tube for easier access

cassegrain focus

An optical arrangement in a reflecting telescope in which light rays are reflected by a secondary mirror through a hole in the primary mirror

why do people place telescopes on mountain tops?

at higher altitudes, the air is less dense since there is less air above to squeeze it- thinner air will disrupt light collected by the telescopes less than thicker air

why do people prefer to place telescopes in space?

because it avoids issues related to weather, urban light pollution, and the eff ects of our turbulent atmosphere which causes star light to appear to twinkle

(it is expensive so many are placed on mountains instead)

how large can a mirror be before being distorted by its own weight

up to 4 or 5 m across

adaptive optics

a technique in which telescope mirrors flex rapidly to compensate for the bending of starlight caused by atmospheric turbulence.

spectometer

a device used to separate light into components of different wavelengths

diffraction grating

a finely etched glass surface that can split light into a spectrum

diffraction

bending of light rays caused when they encounter an obstacle

temperature

measurement of energy

Stars that give off mostly red light are cooler, while stars that give off mostly blue light are hotter. Yellow stars are in between.

3 kinds of spectra

thermal spectrum

emission spectrum

absorption spectrum

(subtracting the emission line spectrum from the continuous spectrum will leave the absorption spectrum)

thermal spectrum

"continuous spectrum"

comes from hot dense object under high pressure

emission spectrum

"bright-line spectrum"

comes from a hot gas

absorption spectrum

"dark-line spectrum"

comes from continuous spectrum light that passes through cooler gases that absorb some of the wavelengths

how do spectra tell us the composition of stars?

the emission spectrum of a particular gas is like a fingerprint or DNA pattern

no two gases have the same spectrum

when an atom absorbs energy, it will give back, or emit, the energy in the form of particles of light called

photons

blackbody radiation

the radiation emitted by a blackbody, which is a perfect radiator and absorber and emits radiation based only on its temperature

stellar spectra

7 basic types

letters, O B A F G K M are in order of decreasing temperature

magnitude

term that astronomers use for brightness

apparent magnitude

the brightness of a star as seen from Earth

objects that cannot be seen with the unaided eye have magnitude numbers greater than 6

smaller the object's magnitude number, the brighter the object

absolute magnitude

the actual brightness of a star

what its apparent magnitude would be if it were 10 parsecs away

measure their apparent magnitude and then determine their distance from Earth

stellar parallax

the apparent shift in the position of a nearby star (relative to distant objects) that occurs as we view the star from different positions in Earth's orbit of the Sun each year

the further away a star is, the less parallax there will be

parsec

"parallex-second"

about 20 trillion miles

luminosity

a measure of the actual amount of energy given off by a star

light-year

the distance light travels in a year, about 6 trillion miles

smaller than a parsec

lookback time

will always be equal to the number of light-years an object is distant

HR diagram

absolute magnitude and luminosity are plotted vertically while temperature and spectral class are plotted horizontally

brighter stars are plotted higher, higher temperatures are plotted to the left

what color are the hottest stars?

blue

what color are the coolest stars?

red

white dwarfs

hot, dim stars on the lower left of HR diagram

red giants

giants and shown in the upper right

main sequence

diagonal line that goes from the upper left, where hot and bright stars are, to the lower right, where dim and cool stars are

binary system

two stars are gravitationally bound to one another

visual binary

a binary star system in which both stars can be resolved through a telescope

eclipsing binary

a star system in which one star periodically blocks the light from another

spectroscopic binary

presence of the individual stars can only be detected by viewing the lines of their absorption spectra

optical double

not actually binaries, simply two stars lying along same line of sight

Not gravitationally bound, Not useful in determining stellar masses

mass-luminosity relationship

a relation between the mass and luminosity of main-sequence stars.

higher-mass stars have higher luminosity.

stellar evolution

life cycle of a star from formation to corpse

stars are "born" out of gigantic molecular clouds called

nebulae

what does a nebula consist of?

mostly hydrogen gas and dust

protostar

a contracting cloud of gas and dust; the earliest stage of a star's life

gravitational contraction

causes the temperature of the protostar to increase

nuclear fusion

the process by which stars create the energy that allows them to give off light and heat

once nuclear fusion begins in the core, the protostar becomes a shining star

proton-proton chain

the chain of reactions by which low-mass stars (including the Sun) fuse hydrogen into helium

neutrinos

low mass, fast moving, an ideal way for astronomers to use the Sun to test theories about energy production in stars

detected using gigantic underground pools of water

core (sun)

the region where nuclear fusion occurs and radiates energy

radiative zone (sun)

zone where the energy is transferred by radiation

convective zone (sun)

layer above radiactive zone, just under the visible surface of the Sun

photosphere (sun)

the visible surface of the sun, cool, 6000 degrees Celsius

chromosphere (sun)

the thin layer of the sun that is just above the photosphere and that glows a reddish color during eclipses

corona (sun)

the Sun's outer atmosphere, which has a high temperature and a low density, emits x-rays, layer seen during solar eclipse

sunspots

areas of gas on the sun's surface that are cooler than the gases around them

solar minimum

times when there are fewer sunspots

solar maxima

many more sunspots and the Sun is much more active

2 common types of solar activity

solar flares & prominences

solar wind

electrically charged particles that stream away from the Sun in all directions out into the solar system

aurora

an atmospheric phenomenon consisting of bands of light caused by charged solar particles following the earth's magnetic lines of force

the more massive stars burn hotter and brighter, and despite having more hydrogen fuel in their cores, use it up at a much faster rate

hydrostatic equilibrium

the balance of the inward gravitational force and the outward force of fusion within a star. this balance of forces is what keeps a main sequence star stable.

star cluster

gravitationally bound stars formed from the same gas cloud

stars less massive than our sun will be cool and dim or hot and bright?

cool and dim, living long lives

red giant

a very large star of high luminosity and low surface temperature. red giants are thought to be in a late stage of evolution when no hydrogen remains in the core to fuel nuclear fusion.

helium core will begin to fuse into carbon

planetary nebulae

shells of gas and dust that are ejected from a star during the process of its evolution from a hydrogen-burning main sequence star into a red giant and eventually into a white dwarf

white dwarf

stage in which a star has used up its helium and its outer layers escape into space, leaving behind a hot, dense core that contracts

black dwarf

a mass composed primarily of carbon formed once a white dwarf stops giving off energy

brown dwarf

a protostar that never accumulated enough mass to exert enough pressure to raise the temperature in its core high enough for hydrogen fusion to occur,

a protostar that never actually became a star

neutron star

a star that has collapsed under gravity to the point that the electrons and protons have smashed together to form neutrons

supernovae

a star that suddenly increases greatly in brightness because of a catastrophic explosion that ejects most of its mass

\shockwaves produced by a supernova explosion can stir neighboring nebulae into star formation

what is the heaviest element that can be sustainably produced by nuclear fusion?

iron

pulsars

a rapidly spinning neutron star that emits pulses of radio and optical energy at regular intervals

black holes

dense objects with gravity so strong that not even light can escape their surface

singularity

something that is mathematically or theoretically possible but not physically possible

escape velocity

the minimum velocity needed to escape a gravitational field

event horizon

a sphere surrounding the object that is the size the object was when it first disappeared from view and become a black hole

Schwarzschild radius

distance from the center to the edge of the event horizon, size of the blackhole