W1: Intro, Scale of the Universe, Naked Eye Phenomena, Time, Seasons, Angular Measurements, Small Angle Formula


Terms in this set (...)

hallmarks of science #1
Modern science seeks explanations for observed phenomena that rely solely on natural causes
hallmarks of science #2
science progresses through the creation and testing of models of nature that explain the observations as simply as possible
hallmarks of science #3
a scientific model must make testable predictions about natural phenomena that would force us to revise or abandon the model if the predictions do not agree with observations
scientific theory
- explains lots of observations with simple principles
- supported by lots of compelling evidence
- doesn't fail crucial tests of validity
solar system units
Astronomical Units (AU) = sun to earth = 150 mill km = 93 mill mi
speed of light
~300,000 km/sec = ~186,282 mi/sec
light year
1 ly = 9.46 x 10^12 km
1 pc = 3.26 ly = 3.09 x 10^13 km
naked eye - Day
E to W rotation of heavens
sun and stars rise in East, sets in West
naked eye - Month
W to E motion and phases of the moon
moon's positions shift to east
naked eye - Year
N-S altitude change of Sun due to season
sun high in summer, low in winter
naked eye - long term changes
procession of equinoxes
path of sun in the sky, where one finds planets
earth's tilt
23.5 deg relative to sun (relative to ecliptic)
summer solstice
sun highest in celestial sphere
winter solstice
sun lowest in celestial sphere
autumnal equinox
ecliptic intersects celestial equator on sun's way down
vernal equinox
ecliptic intersects celestial equator on sun's way up
right ascension
longitude on celestial sphere, measured in hours w respect to spring equinox
latitude on celestial sphere, measure in degrees above celestial equator
point on celestial sphere directly overhead (different for everyone)
line on celestial sphere from dead N to S through zenith (changes as ppl move)
ante meridian (further east)
post meridian (further west)
sun's placement at noon
on meridian
sidereal vs solar time
sidereal days are 23h56m but earths rotation adds an extra 4 min bc of how it rotates for the sun to appear in the same place in the sky, hence solar days are 24h
star path at north pole
stars stay at same altitude as the Earth rotates
star's altitude above horizon = declination bc horizon = celestial equator
star paths at equator
stars remain above horizon for 12 hours each day
celestial equator passes overhead
star paths in northern hemisphere
stars w dec > (90 - [your latitude]) are circumpolar
stars that never go below horizon (visible all night)
celestial equator seen in southern part of sky
star paths in southern hemisphere
stars w dec < (-90 + [your latitude]) are circumpolar
celestial equator seen in northern part of sky
sun location on summer solstice
sun is 23.5 deg above celestial equator on summer sol
hanover's lat is 43.7 deg: celestial pole lies 43.7 deg aboce nothern horizon, so celestial equator is 90-43.7 = 46.3 deg above southern horizon. so sun is 46.3 + 23.5 = 69.8 deg high in the sky at Noon
current north star
earth's wobble as it rotates
what causes seasons
23.6 deg tilt of Earth's axis and directness of rays
summer - more vertical rays
winter - fewer vertical rays
earth sun distance only changes 3% during year, we're closest to sun in january
angular measurements
1 deg = 60 arc min= 60'
1 arcminute = 60 arc sec = 60"
therefore 1 deg = 3600"
night sky angle rule of thumb
one finger width = 2 deg
one fist width = 10 deg
to have an angular size of
small angle formula
D = (a x d) / 206265 arcsec
D = linear size of obj
a = angular size of obj (in arcsec)
d = distance to the obj
206265 = number of arcsec in 1 rad