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Notes 1.12-1.22
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Mercator Projection of Earth:
~ a cylindrical map projection
~ the standard map projection for nautical purposes because of its ability to represent
lines of constant course
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Mercator Projection of the sky
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beginning of winter has the least sun, but mid-winter are the coldest parsecs
light second ~ the distance light travels in an absolute vacuum in one second
about 10.5 minutes to communicate from Earth to Mars
1 parsec = 206 264.806 AU
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Parallax:
~ S = rθ
θ must be in radians
2AU = rθ
S & r are in AU’s
R = (1AU)/(θ in rad)
[θ is usually measured in arcsecs, not rad]
1 arcsec = 1/3600(π/180) = .000004848 rad
1 rad = 206265 arcsec
~
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S = rθ
r = S/θ
[S is always 1 AU]
suppose the paralaz is 0.25 arcsec
r = (1 AU)/(0.25 arcsec)(1 rad/206265 arcsec)
r = 206265(4 AU) = 4 parsecs
10 miliarcsec = 1/100 arcsec = 100 parsecs
if s = 1 AU & θ in arcsec
[replace s with r = 1/θ in arcsec]
Andronmeda:
~ about 2.5 million light years away from earth
~ 2-3x the size of the moon
luminosity ~ the amount of energy a body radiates per unit time
apparent magnitude (m):
~ a measure of its brightness as seen by an observer on Earth, normalized to the
value it would have in the absence of the atmosphere
~ 5 lower magnitude: 100x brighter
absolute magnitude (M):
~ the apparent magnitude of an ob ject would have if it were 10 parsecs away
~ log10^(2/5)(d/10 pscs)2 = m - M
2[log (d/10 pscs)/ log10^(2/5)] = m - M
2[log (d/10 pscs)/(2/5) = m - M
5 log (d/10 pscs) = m - M
5 (log d - 1) = m - M
the sun is 6-8 parsecs away
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astrometry ~ the branch of astronomy that relates to precise measurements and
explanations of the positions and movements of stars and other celestial bodies
brown dwarfs are the most in the universe
stars in sky are mostly giant stars
space is not empty so light gets blocked at times
Hubble’s Law ~ the statement in physical cosmology that the redshift in light coming from
distant galaxies is proportional to their distance
Hubble deep field ~ an image of a small region in the constellation Ursa Major,
constructed from a series of observations by the Hubble Space Telescope
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center of galaxies are the brightest
far sounds sound lower than closer sounds (higher)
wave lengths move the same as it reaches the eyes/ears
things look bluer when you walk closer
things look reder when you walk farther away
hydrogen & helium make up most of the air
billions of galaxies are moving farther away from Earth
Andronmeda & our galaxy are slowly moving closer
if a light gives off 1000 light years away, you see the object 1000 years ago
isotropy ~ property of a system that is direction independent; uniformity in all directions
red-shifts are isotropic
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density of earth ~ 5.52-6 g/cm3
1 supernova = bright as a galaxy (lasts for days or weeks)
white dwarf:
~ a small star composed mostly of electron-degenerate matter
~ density - 1 x 109 kg/m3
~ it no longer undergoes fusion reactions, so the star has no source of energy
~ it is Earth-sized
Type 1A supernova:
~ a sub-category of cataclysmic variable stars that results from the violent explosion of
a white dwarf star
~ used as a standard candle in the galaxy
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Chandrasekhar limit:
~ limits the mass of bodies made from electron-degenerate matter, a dense form of
matter which consists of nuclei immersed in a gas of electrons
~ no non-rotating white dwarf can be heavier than M = 1.4 Msun
supernova explosions last a few seconds
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stars are usually just points
Andronmeda is the closet and biggest galaxy to us
7 milimeters is usually the size range in an adult’s pupil
charged couple device (CCD) are more sensitive than film
Messier 13 (M13):
~ great globular cluster
~ 25, 100 light years away
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Messier 14 (M14):
~ distance of about 30,000 light-years
Messier 42 (M42) // Orion Nebula:
~ Orion’s sword is a nebula
~ Orion is a big open cluster (almost, it’s changing)
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globular cluster stars usually are formed around the same time together
open clusters:
~ dissipate
~ represents where stars used to be formed
~ a group of up to a few thousand stars that were formed from the same giant
molecular cloud, and are still loosely gravitationally bound to each other
red nebula:
~ a nebula that had drifted away from the main body of the galaxy
planetary nebula:
~ an emission nebula consisting of a glowing shell of gas and plasma formed by
certain types of stars when they die
~ similar to the appearance to giant planets when viewed through small optical
telescopes
~ unrelated to the planets of the solar system
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terminator ~ defined as the line which separates day and night on the moon
the moon can be seen during daylight
daytime seeing of the moon is a problem when the ground is warm
narrow band filter ~ type of filter which transmits light over only a very restricted range of
wavelengths or over narrow spectral bands
cat’s eye nebula:
~ a planetary nebula in the constellation of Draco
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ring nebula:
~ located in the northern constellation of Lyra
~ one of the most prominent examples of the deep-sky objects called planetary nebula
nebulas grow older & dimmer (planetary nebulas)
horse head nebula ~ a dark nebula in the Orion constellation
nebulas are categorized by light into:
~ absorb nebula
~ reflection nebula
~ emission nebula
~ refraction nebula
planets are not a problem in light pollution, but are too small to see detail
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EM radiation:
~ gamma rays not really possible through air
~ x-rays
~ ultraviolet
marginally possible through air
~ visible
~ infrared
tough through air; warm stuff gives off IR: space telescopes better
~ microwave
~ radio
visible light is blocked best with something equal to a wave length
almost nothing blocks radio waves
barred spiral galaxy:
~ a spiral galaxy with a central bar-shaped structure composed of stars
~ bars are found in approximately half of all spiral galaxies
everything gives off infrared waves at all times