Astronomy test 1

-big bang created space and time, not just energy and matter, roughly 14 billion years ago.
-denser regions of Big Bang collapsed under gravity, formed galaxies. Smaller clumps probs coalesced to form larger clumps.
-conservation of angular momentum: as the system gets smaller, it has to rotate faster to conserve angular momentum. Reason galaxies spin faster as they get smaller.

plays according to rules (Eienstein's General Theory of Relativity) that are very different from our everyday experience
-space is "warped" by the presence of matter

-flat swirling disk of material divided up, apparently, into spiral arms
-bright central nucleus
-halo of globular clusters
-nature of rotation suggests black hole at center

L=mvr
-angular momentum L for localized mass m moving with a velocity v in a circular orbit of radius r
-remains constant in the absence of external torques

-gas, dust, dark matter
-stars: fusion from weight of overlying material compresses center of the star-->center material (mostly Hydrogen) is ionized (electrons separated from protons), then protons can combine to make heavier nuclei. large energy release

star formation

pre-stellar cloud collapsed, flattened out as it spun faster due to angular momentum

"after the sun lit up a strong "wind" of particles swept light elements out of the inner solar system, leaving small planets composed of relatively heavy elements."

Historically: figures associated with star patterns
Today: sky divided into sections roughly associated with the historical figures

Bright stars usually have many

-Brightest stars (roughly)--1st magnitude
-Faintest naked eye stars (roughly)-- 6th magnitude
-difference in 5 magnitudes corresponds to a factor of 100 in intensity, so each magnitude corresponds to a factor of about 2.5.

the rotation of the earth causes this illusion.

"the points on the CELESTIAL SPHERE directly above the N and S poles of the earth"

a circle around THE CELESTIAL SPHERE above the earth's equator, 90 degrees from the NCP and SCP. Just like the Earth's equator

-point on THE SKY directly overhead

the semicircle in THE SKY extending from N. Horizon, through the zenith, to the S horizon

Point on THE SKY which divides the earth and the sky

stars that never set as seen from a particular location

directly overhead

on the N horizon

Altitude of the NCP above the N horizon is equal to the observer's latitude. (CE is 90 degrees from NCP)

the N/S coordinate measured in degrees (+ and -) from the celestial equator. Like latitude on the earth

The E/W coordinate in the CELESTIAL SPHERE measured in hours (0-24). Like longitude on the earth.

meridian

its altitude (a)

-"the direction of the earth's axis of rotation wobbles slightly over time (one revolution in 26,000 years). This is called precession of the equinoxes, or just precession"
-means declination, right ascension of stars changes slightly over time
-that polaris is the "pole star" is only a temporary coincidence

path of the sun on the celestial sphere

23.5 degrees, same as tilt of earth's axis relative to its orbit

sine wave-esque

sun on CE going N, first day of spring, about March 21

sun at maximum declination (+23.5), first day of summer, about June 21

sun on CE going S, first day of fall, about September 21

sun at minimum declination (-23.5), first day of winter, about December 21

sun is up longer, gets higher in the sky

-time for the sun to return to the meridian.
-about 4 minutes longer than sidereal day

-time for a star to return to the meridian
-about 4 minutes shorter than solar day
-for this reason stars rise about 4 minutes earlier each night

because the solar system is on the same plane, more or less.

loops planets make in their motion along the ecliptic

ecliptic more or less passes through

individual planet, time

-approximately follows ecliptic because moon's orbit is only slightly inclined to the earth's orbit
-takes about one month to go around the earth, so takes about one month to go around the ecliptic

E-->W

-E-->W
-the earth rotates faster than the moon orbits

near sun in sky, invisible

90 degrees east of sun in sky, half visible

opposite sun in sky, fully visible

90 degrees west of sun in sky, half visible

-moon passes between sun and earth, casting shadow on earth.
-full solar eclipses rare: moon's shadow on earth is small

-moon passes directly behind the earth relative to the sun, so earth's shadow falls on the moon.
-everyone who can see the moon at that time can see the eclipse

-earth at the center (geocentric), other objects rotate around
-sun, moon, planets revolve on epicycles (small orbits) that are attached to the main orbit (deferent)

-stellar parallax unaccounted for

-earth, other planets orbit the sun (heliocentric)
-retrograde loop, other phenomena understood as apparent rather than real
-religious consequences

-planets move in elliptical orbits with the sun at one focus of the ellipse
-for the planets in our solar system, these ellipses are almost circles

-the sun-planet line sweeps out equal areas in equal times.
-means that a specific planet moves faster when it is closer to the sun
-*reflects conservation of angular momentum!

-P[squared] is proportional to r[cubed]
-but actually an equality if P is measured in years
where p is the period and r is the radius of the orbit
-means planets with smaller orbits move more rapidly

-retrograde loops are explained
-kepler's laws of planetary motion work
-correct phases of the inner planets are observed
-observations of jupiter's (and other planets') moons-->earth not the unique center of revolution
-stellar parallax is observed
-aberration of starlight is observed (shift in star positions resulting from the finite speed of light)
-space probes get where they are supposed to go