CoK 2 Flashcards
Most of the bright stars are NOT among the stars that are very close to us. Why then do they look so bright to us?
these stars are intrinsically so luminous that they can easily can be seen across great distances
most of the stars we can see with the unaided eye from earth are
more luminous than the sun
the most common kinds of stars in the galaxy have
low luminosity compared to the sun
two stars that are gravitationally associated and orbit each other are called
binary stars
if the most common type of star in our galaxy are M-type “red drawf” stars why don’t we see very many of them in the sky
red drawfs have intrinsically low luminosity so they’re faint and hard to detect
how can we tell that what appears like a single star in out telescopes is actually a binary star system
their spectra will contain the absorption line of two stars
when one of the stars is moving towards earth in its orbit, we observe
that the lines in its spectrum show a blueshift
the HR diagram plots the luminosity of stars against their
surface temperature
if a of the stars we can possibly detect could be independently plotted on an HR diagram, 90% of them would fall into the region called
the main sequence
white drawfs are very hot but are also very small compared to the main sequence stars. as a result they are located in the _________ region of the HR diagram
lower left
on the HR diagram, where would you find the most massive main sequence star
toward the upper left of the main sequence
what would be a reasonable classification for a red giant star
M2III
in order for a cold atom of hydrogen to emit a 21-cm wave, it must first be in a slightly higher energy state. what event usually kicks the hydrogen atom up to this higher state
gas atoms within the cloud collide
an HII region is
a region around a hot star where hydrogen atoms are ionized
the red color we see on a lot of phtotgraphs of nubulae comes from
hydrogen
Given the presence of dust throughout the disk of the Milky Way Galaxy, what is the best technique for learning about more distant regions of our galaxy’s disk?
Look for radiation at long wavelengths, for example in the infrared region of the spectrum.
Interstellar extinction refers to the phenomenon that foreground dust has on the appearance of background stars. In particular, dust can make stars appear ______ and ______ than they would if the foreground dust wasn’t present.
fainter; more red
the dust in the dust clouds in interstellar space consists of
pieces of ice ranging from several meters to a kilometer in diameter
a Herbig-Haro (HH) object is
where a jet from a star in the process of being born collides with and lights up a nearby cloud of interstellar matter.
Astronomers identify the “birth” of a real star (as opposed to the activities of a protostar) with what activity in the star?
When nuclear fusion reactions begin inside its core.
when does a protostar “arrive” on the main sequence and “switch on” to become a star?
when it begins fuding hydrogen into helium in its core
why do all stars spend most of their lives on the main sequence
stars fuse hydrogen on the main sequence and every star is mostly made of hydrogen
As a star’s core contracts, it gets hotter. What happens to the star’s outer layers?
they expand and cool
When does a star “leave” the main sequence and begin its post-main sequence evolution?
when the core fuses the last of its hydrogen into helium
