Term
| What is the relation between a star's apparent magnitude and absolute magnitude? |
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Definition
m - M = 5 log(d/10)
or m - M = 5 log(d) - 5
Where m = apparent magnitude
M = Absolute magnitude
d = distance to star in parsecs |
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Term
| What is the order of spectral classes in order of decreasing temperature? |
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Definition
OBAFGKM
("Oh, be a fine girl, kiss me") |
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Term
| A star with surface temperature of 5800 K and a luminosity of greater than 100 times that of the sun is a member of which luminosity class? |
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Definition
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Term
| A star with surface temperature of 5800 K and a luminosity of greater than 1000 times that of the sun is a member of which luminosity class? |
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Definition
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Term
| A star with surface temperature between about 6000-20000 K and a luminosity less than 100 times that of the sun is a.... |
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Definition
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Term
| What is the relation between distance and parallax? |
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Definition
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Term
| A magnitude difference of 1 corresponds to a factor of ____ in brightness |
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Definition
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Term
| The color index of a star (the difference between the apparent magnitudes B and V at two different colors, blue and visual) is a direct measure of what property of the star? |
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Definition
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Term
| Compared to a star in the middle of the HR diagram, a star in the lower left part is... |
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Definition
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Term
| Compared to a star in the middle of the HR diagram, a star in the upper right part is... |
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Definition
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Term
| Giants and supergiants make up about what percentage of stars in the sky? |
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Definition
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Term
| About how big are white dwarfs? |
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Definition
| Approximately the same size as Earth |
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Term
| What proportion of visible stars in the nighttime sky are binary or multiple-star systems? |
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Definition
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Term
| What is Kepler's third law? |
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Definition
M1 + M2 = a^3 / P^2
Where M1, M2 are masses of two stars in a binary system, in solar masses
a = semimajor axis of one star's orbit around the other, in AU
P = Orbital period, in years |
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Term
| What is the density of a white dwarf? |
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Definition
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Term
| One spoonful of a white dwarf weighs how much? |
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Definition
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Term
| Where do we find the most massive stars on the Main Sequence in the HR diagram? |
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Definition
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Term
| What is the luminosity of the most luminous main sequence star? The least luminous? |
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Definition
L = 50,000 solar
L = 0.005 solar |
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Term
| What is the radius of the most luminous stars in the main sequence? The radius of the least luminous? |
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Definition
R = 400 solar
R = 0.1 solar |
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Term
| What is the surface temperature of the most luminous star in the main sequence? The least luminous? |
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Definition
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Term
| What is the stellar type of the most luminous star in the main sequence? Of the least luminous? |
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Definition
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Term
| The most important datum about the nearby stars is that they are ______________ |
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Definition
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Term
| How many of the nearest 50 stars are visible to the unaided eye? |
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Definition
| 10 of the 50 nearest stars are visible to the unaided eye. |
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Term
| How many of the nearest 50 stars are as intrinsically luminous as the Sun? |
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Definition
| 3 of the 50 nearest stars are as intrinsically luminous as the Sun |
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Term
| 43 of the nearest 50 stars have luminosities less than _____ solar |
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Definition
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Term
| If the stars in our immediate stellar neighborhood are representative of the stellar population in general, we must conclude that the most numerous stars are those of _________________ (what characteristic) |
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Definition
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Term
| In the sample of the nearby stellar neighborhood, how many of the stars are as luminous as the sun? |
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Definition
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Term
| In the sample of the nearby stellar neighborhood, what % of the stars are main sequence and what % are white dwarfs? |
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Definition
90 % are main sequence
10 % are white dwarfs |
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Term
| How many stars are within 5 pc of Earth? |
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Definition
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Term
| Only __ of the 43 nearest stars are among the 20 brightest stars. What are they? |
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Definition
3:
Sirius
Alpha Centauri
Procyon |
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Term
| Nearby stars tend to have what kind of proper motion? |
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Definition
| Large, fast proper motion |
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Term
| How many of the 20 brightest stars are within 10 pc of the Sun? |
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Definition
| Only 6 of the 20 brightest stars are less than 10 pc away |
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Term
| The HR diagram is a statistical plot of what two stellar parameters? |
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Definition
| Luminosity and Surface Temperature |
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Term
| What is the most significant feature of the HR diagram? |
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Definition
| That the stars are not distributed at random, but rather they cluster together into certain parts of the diagram |
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Term
| What are the 4 regions of the HR diagram? |
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Definition
| Main sequence, red giants, supergiants, white dwarfs |
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Term
| Luminosity is proportional to what values? |
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Definition
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Term
| What is the relationship between mass and luminosity? |
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Definition
L <>< M^4.0
if 0.1 solar < M < 60 solar |
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Term
| What is the equation relating Luminosity to Radius and Temperature? |
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Definition
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Term
| How many AU are in a parsec? |
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Definition
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Term
| What is the relationship between parsecs and light years? |
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Definition
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Term
| About ____ of all stars are binary or multiple star systems |
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Definition
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Term
| What are the 3 major types of binary stars? |
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Definition
Visual binaries
Spectroscopic binaries
Eclipsing binaries |
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Term
| What is the skinny triangle approximation? |
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Definition
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Term
| What is the equation for the resolution of a telescope? |
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Definition
alpha = 2.1 x 10^5 (lamdba) / D
lambda in meters, D in meters, alpha in arcseconds |
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Term
| The atmosphere limits all telescopes to a resolution of.... |
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Definition
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Term
| Ellipses are described by what two factors? |
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Definition
The semi-major axis and their eccentricity
e = delta(foci) / major axis |
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Term
| What does an ellipse with eccentricity = 0 resemble? |
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Definition
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Term
| As the eccentricity of an ellipse increases, what happens to the ellipse? |
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Definition
| It starts to look almost like a line (a very thin ellipse) |
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Term
| What were Kepler's 3 laws? |
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Definition
1. All orbiting bodies have a conic-section orbit, with the massive body (i.e. the Sun) at a focus.
2. Law of equal areas - Equal areas are swept out in equal time intervals.
3. (M + m) P^2 = k a^3 where k = 1 if P is in Earth years, a is in AUs, and (M+m) is in solar masses. For objects orbiting the Sun, (M+m) = 1 |
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Term
| If two stars with the mass of the sun had a circular orbit (radius = 5 AU), the orbital period would be about... |
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Definition
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Term
| What 2 resolution improvements allow resolutions of .02'' and .001'', respectively? |
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Definition
Speckle Techniques (alpha = .02'')
Interferometric techniques (alpha = .001''). |
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Term
| What is the equation for the conservation of angular momentum? |
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Definition
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Term
| If orbits of binaries are circular, then r1 and r2 are constant and the equation for conservation of angular momentum becomes... |
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Definition
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Term
| What is the equation for Doppler shift? |
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Definition
| Delta(lambda)/lambda = v / c |
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Term
| If the orbital velocity of Star A is 5 times that of star B, then star A is how many times as massive as star B? |
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Definition
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Term
| What's up with the orbital planes of eclipsing binaries? |
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Definition
| The orbital planes lie close to our line-of-sight |
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Term
| Are eclipsing binaries resolved? |
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Definition
| No, they are unresolved, which means they appear as a single star |
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Term
| Two stars in a binary system have the same temperature but the diameter of star A is twice that of star B. How many times brighter is Star A than star B? |
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Definition
Since L <>< R^2 T^4,
star A has a luminosity 4X that of star B and since they are the same distance, 4X the brightness |
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Term
| What spectral type has the coolest stars? |
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Definition
OBAFGKM (T ---> t)
M are the coolest stars |
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Term
| What is the technique that allows astronomers to decode the messages contained in starlight? |
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Definition
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Term
| What can stellar spectra tell us? |
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Definition
| Intrinsic luminosity, temperature, how fast it rotates, and its composition |
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Term
| 5 magnitudes exactly corresponds to what ratio? |
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Definition
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Term
| Numerically __________(smaller/larger) magnitudes correspond to brighter stars |
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Definition
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Term
| If star A has a magnitude of 10, and star B is 10,000X brighter, then the magnitude of B is... |
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Definition
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Term
| What is the equation relating the apparent magnitudes of two stars? |
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Definition
| m1-m2 = delta m = 2.5 log (F2/F1) |
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Term
| What is the distance to a star if its m = +20 and its M = -5 |
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Definition
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Term
| How many kilometers are in 1 AU? |
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Definition
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Term
| The speed that a star approaches or recedes from the Sun is what? |
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Definition
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Term
| The rate at which a star's apparent position on the sky changes is called... |
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Definition
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Term
| What is the proper motion of Barnard's star? |
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Definition
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Term
| The star's actual speed is called its....and the equation for it is.... |
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Definition
Tangential velocity,
T = 4.74 u*d km/s
where u is the proper motion |
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Term
| If a star has a proper motion of 10 arcsec per year and is at a distance of 2 pc, what is its tangential velocity? |
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Definition
T = 4.74 ud =approximately=
T = 5 u d = 5 * 10 * 2 = 100 km/s |
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Term
| The Total Space Velocity is... |
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Definition
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Term
| What stellar characteristics are dependent on the Earth? |
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Definition
Position (RA, decl. and distance)
Motion (Proper motion and tangential velocity, Radial motion and space velocity)
Brightness |
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Term
| What stellar characteristics are independent of the Earth? |
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Definition
| Size, Variability, Surface Temp and Color, Mass, chemical composition, magnetic fields, luminosity, number of components |
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