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49 Cards in this Set

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Why did all attempts to detect stellar parallax fail until the 1830s?
All scientists were trying to detect parallax on stars that were bright because they thought that meant they were the closest. This was false because some stars were brighter than others and they were too far to detect parallax.
What did Halley announce about stars in the early 1700s? How did this discovery aid the detection of stellar parallax?
Halley compared ancient star catalogues with current star positions and found moving stars, not moving within constellations but independently, thus it couldn’t be due to earth’s precession or due to parallax (all stars would be effected), suggested that stars have unique motion across the sky. He suggested using old star charts to determine which stars moved the most as this would help display parallax
What is our nearest star, and how far away is it (approximately) in light years?
Alpha Centauri is the nearest star, it is appx. 4.4 light years away
What is the definition of a light year? What is the definition of a parsec? (NOTE: the specific values in km aren't necessary here). Which unit is bigger, and by approximately how much?
A light year is the distance light travels in a year and a parsec is the inverse of parallax measured in arcseconds. The parsec is larger; one parsec is equal to about 3 light years.
According to the wave theory of light, what are all light waves composed of?
All light waves are composed of a magnetic wave and an electric wave that propagate perpendicular to each other.
Describe how a wave from a bright blue light source is different from a wave from a faint red light source.
A bright blue source wave will have a large amplitude, low wavelength (and so high frequency). A dim red light will have a low amplitude, long wavelength (and so a low frequency).
What colour of visible light is shortest in wavelength? What colour of visible light is longest in wavelength? What colour of visible light has the lowest frequency? What colour of visible light has the most energy?
Blue is the shortest wavelength and highest frequency (highest energy) and red is the longest wavelength with the lowest frequency (lowest energy
In the full spectrum of light, what kind of light is shortest in wavelength? What kind of light is longest in wavelength? What kind of light has the most energy?
Radio waves are the longest and lowest-energy waves, while gamma waves are the shortest and highest energy waves
What is a spectroscope?
A spectroscope an apparatus that produces a light spectrum that can be observed through a telescope
What is Fraunhofer’s Spectrum a spectrum of? What does it contain (ie., continuum emission, absorption lines, and/or emission lines)?
He found black lines on his sun spectrum every time and the lines always appeared at the same colors on the spectrum. He mapped the lines and labeled them with a letter. He never explored what those lines meant but they were absorption lines
Describe (briefly) how the chemical composition of a star can be determined
Through spectroscopy the chemical composition can be measured through a spectra of light where different elements emit different amounts of light of different colors on the spectra. Each element emits light at certain wavelengths and thus would have its own unique identifiable “fingerprint”
What did Bunsen and Kirchhoff observe in the spectrum of sunlight combined with a gas flame? What was their correct explanation for this, and what did it cause them to predict about the Sun? How was their prediction proven in the 1860s?
They noticed that the absorption lines got thicker when combined with the gas flame. They hypothesized that the element was absorbing its unique wavelength of light so the white light from the sun was seen in every wavelength except those that were absorbed by the element in the flame. This was used to hypothesize that the sun had an atmosphere of elements that would absorb certain wavelengths of light. In the 1860s the sun was observed during a solar eclipse so that only the outer atmosphere of the sun would be observed and emission lines were observed at the wavelengths where the absorption lines were previously observed proving that there was an atmosphere emitting those wavelengths of light.
How did the element Helium get its name?
It was discovered as a new emission line in the sun’s atmosphere and was named after Helios, the Greek God of the sun
In a graphical spectrum, what do emission lines appear as? What do absorption lines appear as?
On a graphical spectrum peaks are emission lines and dips are absorption lines
What does the spectrum of a star contain (ie., continuum emission, absorption lines, and/or emission lines)? How about the spectra of a gas cloud, a star cluster, and a gas/star system?
Stars contain continuum spectra with absorption lines, gas clouds are just emission lines, star clusters are continuum and absorption spectra and gas/star systems are continuum, absorption and emission spectra.
Why was the element Oxygen originally named "Nebulium"?
The emission lines of a spectrum of a planetary nebula were originally unidentified until matched with Oxygen.
What does the spectrum of a planetary nebula contain (ie., continuum emission, absorption lines, and/or emission lines)? When Huggins discovered this, what did it prove about planetary nebulae (ie., what are they made of)?
He saw that it contained only emission spectra so the nebula had to be made of gas.
What is radial motion? How does it effect light waves? What is the name of this effect?
the approaching or receding motion; only detectable from star’s light spectrum via the “Doppler effect” (the stretching or compressing of a wave due to the approaching or receding motion of the source of the wave)
How does a light source's spectral lines reveal that the spectrum is redshifted? How aboutblueshifted? If a spectrum is redshifted, what does this tell us about the motion of the light source? How about if the spectrum is blueshifted?
Stretched waves are redshifted, compressed waves are blueshifted. If a spectrum is blueshifted then the source is approaching, if it is redshifted then it is receding
What is astrophotography? Why does it allow us to see deeper into space than with the eye and telescope alone? Who was one of the pioneers of this? What sort of survey did he conduct?
Henry Draper was a Pioneer of astrophotography (the production of long-exposure sky photos using a camera attached to a telescope) Cameras can use long exposure to capture more light than our eye would be able to. Sky photos allow us to see deeper into space and can be stored on film for later analysis. He photographed the 1st stellar spectrum and began a photographic spectroscopic survey of all visible stars so they could be classified through chemical composition
What were the members of "Pickering's Harem" hired to do?
They were hired to classify the stars according to their chemical compositions revealed by their spectrums.
What property of stars was used to place the spectral types in their original alphabetical order? What property of stars was used to re-arrange their order into their current order (O-B-A-F-G-K-M)?
They were initially instructed to classify stellar spectra into alphabetical spectral types by the strength of their Hydrogen lines. Strong hydrogen lines would be an A star and weak ones, a Q star. The property used to re-arrange them into their current order was their color, (hottest to coldest)
What do we know about the chemical composition of the reddest stars, due to their numerous spectral lines?
The reddest stars have more metals than other types
If a star has a spectral type of B8, which type of star is it more similar to, O or A?
It would be more similar to A
What is a photon?
A photon is a particle of light
According to the Bohr model of the atom, what are the 3 components of an atom? What determines an atom's chemical element?
It consists of a central nucleus of protons and neutrons surrounded by a shell of orbiting electrons. The # of protons determines the chemical element of an atom
Explain (briefly) what causes atoms to produce absorption lines. What about emission lines?
When an electron absorbs a photon with the exact energy it needs to get excited, the electron jumps to a higher shell causing an absorption line. An emission line is formed when an excited electron drops down a shell, it emits a photon with the exact energy to return to ground state.
What unusual discovery did Cecilia Payne make about the chemical composition of stars?
She discovered that all stars are predominately composed of H (and He)
Describe how Eddington proved one of the predictions of Einstein's General Relativity theory.
During a total solar eclipse, he proved general relativity by observing that when light rays pass near the sun, their path is bent by the curved space around the sun.
What was Eddington and Bethe's correct explanation for the energy source of stars? Why does this process release energy? How does it explain why stars produce so much energy? How does it explain the existence of Helium in stars? How does it explain the full spectrum of light that we receive from stars? How does it explain the long lifetimes of stars?
He proposed that the energy from stars is produced from the fusion of Hydrogen nuclei into Helium at high temperatures. Nuclear fusion explains why stars produce enormous energy (Hydrogen atoms are plentiful in stars). Helium is a product of hydrogen fusion and thus is found in large quantities in stars. Stars emit a full spectrum of light (the gamma-rays downgrade to other wavelengths as they interact with atoms in the star). Stars last for billions of years, the initial fusion reaction of Hydrogen takes a billion years
At what rate does light dim with distance?
Light dims with distance according to the inverse square law (the amount of light we receive from a source is 1/d^2 of its actual light production)
What is the difference between the apparent brightness and the intrinsic brightness of a light source?
Apparent brightness is the brightness of a light source as it appears from earth, intrinsic brightness is the total amount of light that a source produces.
Which appears brighter, a star with an apparent magnitude of 2 or a star with an apparent magnitude of -2?
A star with a magnitude of - 2 would be brighter
For a group of stars in the same star cluster (i.e. at the same distance from Earth), how can we tell which stars are the most luminous?
We have to take into account which star has the lowest absolute magnitude, not their apparent magnitude. The brightest one would be most luminous.
What relationship among Main Sequence stars was found by Hertzsprung & Russell in the 1910s? What two kinds of stars were found to not follow this relationship?
Hertzsprung and Russel found that sprectral type and luminosity. Red giants do not follow this trend. White dwarfs also do not follow this relationship.
What is the spectral type of the Sun?
The sun is a yellow dwarf
Using the HR diagram, compare the luminosity, temperature, colour, and size of Red Giants to the Sun.
Red giants are more luminous than the sun, colder than the sun, more red than the sun and much larger than the sun (1000x bigger)
Describe the mass and size of a White Dwarf. Using the HR diagram, compare their luminosity, temperature, and colour to the Sun.
White dwarfs are smaller, hotter and bluer than the sun
What relationship among Main Sequence stars was found by Eddington in the 1920s? What 2 things did this discovery tell us about the Sun?
He found that there was a link between mass and luminosity; the more massive a star was at birth, the brighter it was. This told us that our sun is a low mass star that is not very bright which is the most common type of star on the main sequence.
Compare the luminosity, temperature, colour, size and mass of a Main Sequence O star to a Main Sequence M star.
A main sequence O star is brighter, bluer and larger than a main sequence M star
What determines a star's spectral type on the Main Sequence? How do we know that a star's Main Sequence spectral type can't change?
It is determined by luminosity and mass, this can’t change because it would violate conservation of mass and energy
What was Hoyle's correct explanation for the existence of elements heavier than Helium in stars? How do these elements get on to planets like ours?
Hoyle’s explanation used nucleosynthesis (the creation of heavier elements from existing atoms) to explain the existence of elements heavier than helium in stars. When stars die, they eject their heavy elements into the interstellar medium. Gas clouds in the chemically enriched medium eventually collapse into new stars and planets
How do we know that our solar system must have come from the ejecta of other stars?
Our solar system must have come from the eject a of other stars since it contains Carbon since when the universe was first born, the only available elements were Hydrogen and Helium
When a star is on the Main Sequence, what allows its properties to remain stable?
A stable star remains stable when its forces are equal (gravitational pressure = radiation pressure)
What causes stars to leave the Main Sequence?
When a star’s gravitational pressure is not equal to its radiation pressure. When hydrogen fusion runs out it leaves the main sequence
Why do we find more low-mass Main Sequence stars than high-mass ones?
The H-fusion phase is shorter in high mass stars, as fusion is faster at high temperatures. This leaves more low-mass stars on the main sequence
Describe what will happen to our Sun from the time it leaves the Main Sequence to its ultimate corpse. Include how its luminosity, temperature, colour and size will change as it evolves, and how these changes are due to the shifting in the balance between gravity and radiation pressure.
The sun will run out of Hydrogen and fuse He which will cause it to swell into a red giant. It is now much larger, much redder, brighter and cooler than it was. This is because the energy output is so large from fusing heavier atoms and so the radiation pressure will be much larger than the gravity pressure. After this the star will not be hot enough to fuse He products so it will run out of He to fuse and the gravitational pressure will be much larger than the radiation pressure and the star will shrink down to a white dwarf. This is smaller, blue-white, hotter and dim. The outer layers of the star are ejected as a planetary nebula.
What kinds of stars are able to fuse elements heavier than Helium, and why?
High mass stars because they have the mass and thus the temperatures to fuse the heavier products.
Describe what will happen to an O-star from the time it leaves the Main Sequence to its ultimate corpse. Include how its luminosity, temperature, colour and size will change as it evolves, and how these changes are due to the shifting in the balance between gravity and radiation pressure.
It will start consuming He and become a red giant (more red, larger, brighter, cooler due to larger radiation pressure than gravitational pull). Once He is all used up it will start consuming the products of the He fusion and become a red supergiant (radiation pressure is larger than gravitational pull) and becomes larger, cooler, redder and brighter. When all the products are used up and heavy materials remain, the gravitational pull will become much larger than the radiation pressure and collapse into itself (super nova). The core of the star will fuse together and if the mass is larger than 2 sun masses it will become a blac hole, if not it will become a neutron star.