Astronomy Exam 2
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Energy associated with electromagnetic radiation is emitted or absorbed in discrete amounts which are proportional to the frequency of radiation.
Objects of different temperature emit spectra that peak at different wavelengths. Hotter objects emit most of their radiation at shorter wavelengths; hence they will appear to be bluer, Cooler objects emit most of their radiation at longer wavelengths; hence they will appear to be redder.
- Relates the temperature of a star to its wavelength of maximum intensity.
The total radiation given off by 1 square meter of the surface of the object in joules per second equals a constant number, represented by sigma times the temperature raised to the fourth power.
- You can see that a small difference in temperature can produce a very large difference in the amount of energy a star's surface emits.
Inverse Square Law
The strength of an effect (such as gravity) decreases in proportion as the distance squared increases.
- The equation relates the relative distances of two objects as compared to a third.
Apparent change in the wavelength of radiation caused by the motion of the source.
- Measures the wavelengths of the lines in a star's spectrum and can be used to find the velocity of a star.
Determining the location of a point by measuring angles to it from known points at either end of a fixed baseline, rather than measuringdistances to the point directly.
The distance to an imaginary star with a parallax of 1 arc second.
Units of Angular Measurement
Usually expressed in degrees, arc minutes, or arc seconds. 60 arc minutes in 1 degree, 60 arc seconds in 1 arc minute.
Magnitude Scale (Apparent and Absolute)
- Apparent - How the stars look to human eyes from Earth.
- Absolute - Intrinsic brightness of a star; the apparent visual magnitude the star would have if it were 10 PC away.
The difference between the apparent and absolute magnitude of a star; a measure of how far away the star is.
Stars whose brightness changes periodically.
Determination of Stellar Masses
Direct determination of masses observationally using binaries, or inference of stellar masses using models.
Stellar Spectral Sequence
A plot of the intrinsic brightness versus the surface temperature of stars; it separates the effects of temperature and surface area on stellar luminosity; commonly absolute magnitude versus spectral type but also luminosity versus surface temperature or color.
Birth of Stars
Astronomers believe that molecular clouds, dense clouds of gas located primarily in the spiral arms of galaxies are the birthplace of stars. Dense regions in the clouds collapse and form "protostars". Initially, the gravitational energy of the collapsing star is the source of its energy. Once the star contracts enough that its central core can burn hydrogen to helium, it becomes a "main sequence" star.
Planets outside the solar system.
American astronomer famous for discovering more extrasolar planets than anyone else, 70 out of the first 100 to be discovered.
- Electrons - negatively charged
- Protons - positively charged
- Neutrons - no charge
Forces in Nature
- 1. Gravity - This force acts between all mass in the universe and it has infinite range
- 2. Electromagnetic - This acts between electrically charged particles. Electricity, magnetism, and light are all produced by this force and it also has infinite range.
- 3. The Strong Force - This force binds neutrons and protons together in the cores of atoms and is a short range force.
- 4. Weak Force - This causes Beta decay (the conversion of a neutron to a proton, an electronand an antineutrino) and various particles (the "strange" ones) are formed by strong interactions but decay via weak interactions (that's what's strange about "strangeness"). Like the strong force, the weak force is also short range.
The nucleusof an atom splits into smaller parts (lighter nuclei), often producing free neutrons and photons (in the form of gamma rays), as well.
Hydrogen fuses into Helium + gamma rays
- At approximately 10million degrees F, hydrogen fusing begins, and a protostar is then a star.
Life Cycle of a 1 Solar Mass Star
There is a high density nebula, becomes protostar and the temperature rises enough to create hydrogen fusing, stops contracting then becomes main sequence star, remains in main sequence for about 10 billion years until all hydrogen has fused to helium, helium now starts to contract, temp rises for helium to form carbon and is now a red giant, helium core runs out and forms a planetary nebula, then becomes a white dwarf and eventually a black dwarf.
Life Cycle of a Massive Star
Evolve similarly to small stars until reaching main sequence, hydrogen fusing takes place and eventually becomes a red supergiant, multiple nuclear reactions occur over millions of years, the core eventually collapses in less than a second called a supernova, after explosion if the core is small it will become a neutron star, if the core is big it will become a black hole
An elementary particle in matter
A neutral, massless atomic particle that travels at or nearly at the speed of light
Expanding shell of gas at the end of a stars birth
The explosion of a star
The maximum mass of a white dwarf, about 1.4 M
Extremely high density matter in which pressure no longer depends on temp, due to quantum mechanical effects
The remains of a dying star that has collapsed to the size of Earth and is slowly cooling off; lower left of HR diagram
A small, highly dense star composed almost entirely of tightly packed neutrons; radius about 10km
A mass that has collapsed to such a small volume that its gravity prevents the escape of all radiation
Gamma Ray Bursters
Sudden bursts of gamma rays thought to be associated with neutron stars and black holes
Used to see gamma ray bursters
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