Term
| The sun is mostly composed of |
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Definition
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Term
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Definition
| 15 million Kelvin hot dense plasma |
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Term
| The solar flares represent a process of |
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Definition
| magnetic energy release in the solar atmosphere |
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Term
| The sun's outermost layers can be viewed directly during |
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Definition
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| The Solar Dynamic Observatory has recently provided high resolution images of |
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Definition
-the solar corona
-the solar photosphere
-the chromosphere
-the solar core |
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Term
| In proton-proton fusion chain four hydrogen nuclei fuse together to form |
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Definition
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| The solar activity cycle is characterized by |
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Definition
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| The solar corona appears to be so hot because of the heating provided by |
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Definition
| the magnetic field energy driven from the below |
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Term
| The energy flows from the solar core to the solar photosphere due to |
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Definition
| thermal convection and radiation |
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Term
| Loop-like arched shapes of plasma in the solar atmosphere are |
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Definition
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Term
| Hot (multi-million kelvin) and rarefied solar plasma is |
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Definition
| concentrated in the solar coronal active regions |
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Term
| The solar chromosphere produces mostly |
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Definition
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Term
| The solar cycle occurs every |
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Definition
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Term
| The continuous spectrum of the Sun is created in |
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Definition
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Term
| Sunspots are characterized by |
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Definition
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Term
| Interaction of the solar wind with the Earth's magnetosphere causes |
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Definition
| Geomagnetic storms and Aurora Borealis and Aurora Australis events |
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Term
| The sun generates its energy due to |
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Definition
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Definition
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Term
| To explain cycle variations in the number and location of sunspots at the photosphere, astronomers developed |
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Definition
| the magnetic dynamo theory |
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Term
| Magnetic reconnection is presumably one of the most efficient ways to convert |
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Definition
| magnetic energy into kinetic energy and the heat |
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Term
| The star with twice the Sun's radius and the same surface temp |
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Definition
| is four times more luminous than the Sun |
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Term
| The star with the surface temp of 20,000K emits most of its power in |
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Definition
| a blue part of the spectrum |
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Term
| The star with twice the Sun's surface temp is |
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Definition
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Term
| The luminosity class of a star determines its |
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Definition
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Term
| The star of O5 spectral class ________ the star of F5 spectral class |
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Definition
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Term
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Definition
| luminosity class V (the Main sequence) |
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Definition
more abundant than hotter stars
and
less massive than hotter stars |
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Term
| Spectral classification is based on the star's |
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Definition
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Definition
more massive
and
younger than less luminous stars |
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Term
| A star's spectral class defines |
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Definition
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Term
| To discriminate between a giant and a dwarf star of the same spectral class astronomers use |
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Definition
| the widths of absorption lines in their spectra |
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Term
| The Hertzsprung-Russell diagram uniquely describes |
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Definition
| the star's mass, temp, color and radius |
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Term
| The star's luminosity depends on |
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Definition
| its mass, temp, radius and color |
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Term
| From the measurements of the apparent and absolute stellar magnitudes astronomers can directly measure |
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Definition
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Term
| Trigonometric parallax defines |
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Definition
| the star's distance to Earth |
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Term
| Absolute stellar magnitude does NOT depend on the stars |
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Definition
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Term
| A star of the apparent magnitude of m=5 is ___ than the star of the 6th apparent magnitude |
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Definition
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Term
| The hotter the star, the greater its |
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Definition
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Term
| The Main Sequence stars in the H-R diagram contribute |
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Definition
| over 90% of the total population in our Galaxy |
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Term
| A star’s color is uniquely characterized by its |
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Definition
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Term
| When starlight passes through interstellar dust |
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Definition
it gets fainter
and
the blue light tends to be scattered more efficiently than red light |
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Term
| What process stops the contraction of a protostar? |
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Definition
| initiation of thermonuclear reactions in its core |
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Term
| If a protostar's mass is less than 0.08 Msun, it becomes a: |
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Definition
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Term
| Why can't a cloud with less than 0.08 solar masses become a star |
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Definition
| its temp will never rise to 10 million K required for initiation of thermonuclear fusion |
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Term
| Structures that are usually associated with formation of a young star include |
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Definition
| bipolar outflows, collimated jets, stellar winds, and circumstellar disks |
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Term
| What is the range of timescales for a star to reach the main sequence |
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Definition
| from 10,000 years for the most massive stars (100 solar masses) up to 100 million years for the least massive stars (0.1 solar masses) |
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Term
| CNO chain of thermonuclear reactions is efficient if |
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Definition
| a star's core temp is greater than 15,000,000K |
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Term
| When does a star arrive at the main sequence? |
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Definition
| the instant when hydrogen fusion gets ignited in the star's core |
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Term
| The interstellar medium contains |
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Definition
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Term
| A molecular cloud is unstable to gravitational collapse if its |
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Definition
mass is greater than about a few hundred solar masses
and
its gravitational force is greater than the thermal pressure force, thermal pressure force is greater than its gravity force |
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Term
| why do protostars are surrounded by rotating disks of gas and dust |
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Definition
if an initial cloud spins at a slow rate, its spin increases as the clouds contracts
and
conservation of angular momentum |
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Term
| what is the energy source that heats a contracting protostar? |
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Definition
| gravitational potential energy released as the matter is pulled inward |
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Term
| why do astronomers think that stars are formed from clouds of gas and dust |
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Definition
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Term
| The initial process in the formation of a protostar is represented be |
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Definition
| gravitational collapse of gas and dust |
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Term
| Coronal gas in the interstellar medium is mostly formed due to |
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Definition
| shock waves produced by stellar winds and supernova explosions |
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Term
| regions of ionized hydrogen heated to 10,000K are visible in the optical bands due to |
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Definition
| photoexcitation, photoionization and recombination processes |
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Term
| cold and warm neutral atomic hydrogen is observed via |
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Definition
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Term
| dust grains heated by stellar radiation are good emitters in |
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Definition
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Term
| Molecular clouds represent |
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Definition
| cold and dense complexes of molecular hydrogen |
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Term
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Definition
| 99% of the total mass of the interstellar medium |
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Term
| A low-mass (sun-like) star evolves in the following sequence |
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Definition
| photostar, main-sequence, red giant, white dwarf |
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Term
| Low mass stars (sun-like) do not form iron cores during their evolution because |
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Definition
| their cores never become hot enough to create iron by nucleosynthesis |
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Term
| in the late phase of evolution a star's core |
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Definition
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Term
| triple-alpha fusion chain converts |
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Definition
| helium into carbon and oxygen |
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Term
| As a sun-like star exhausts its hydrogen fuel it takes _____ years to expand into red giant stars |
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Definition
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Term
| A planetary nebula is a result of |
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Definition
ejection of stellar material from a star via stellar winds
and
excitation and ionized of atoms via UV radiation with subsequent recombination of elections forming emission lines |
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Term
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Definition
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Definition
| the result of accretion of matter from a main-sequence starts of an evolved red giant star into a white dwarf |
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Term
| in the final phase of evolution of a higher-mass star |
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Definition
| further collapse of its core ignites carbon buring |
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Term
| ___ is the heaviest element produced in a series of fusion reactions inside of a high-mass star (greater then 8 solar masses) |
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Definition
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Term
| the latest phase of evolution of a high-mass star (greater than 8 solar masses) results in formation of |
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Definition
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Term
| sun and other young stars have high abundance of heavy elements contributing about |
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Definition
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Term
| the cooler the star of the main-sequence, the |
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Definition
| larger (wider) its convection region |
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Term
| onion-like structure of the latest phase of a massive star is caused by the fact that |
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Definition
| hot plasma in central region burns heavier elements, while cooler plasma in outer regions of the star burns lighter elements |
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Term
| Supernova explosion occurs at the latest phase of evolution of |
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Definition
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Term
| Supernova explosion may create |
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Definition
| a super-dense degenerate core and a supernova remnant |
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Term
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Definition
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Term
| a millisecond pulsar star is observed when |
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Definition
a neutron star spins at the rate of 1000 rotation periods every second
and
beams of radiation formed along the magnetic pole sweep past the line of sight |
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Term
| event horizon of a 10-solar-mass black hole is |
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Definition
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Term
| Every atom of a heavy element is a human body was formed |
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Definition
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