STUDY FOR QUIZ ON MONDAY Asterism is a group of very bright stars in a constellation ex. Big dipper in ursa major Astronomical Unit A.U. – Avg. distance of the earth from the sun about 93 million miles Light year – distance light travels in one year – 6 trillion miles Apparent Magnitude- the brightness of a star as seen from earth 1st magnitude being the

brightest observable w/ the naked eye Celestial poles - North celestial pole is the direction above the earths north pole Polaris is 1

degree away from the north celestial pole. South celestial pole is the direction above the earth’s south pole, there is no south star. Precession- slow wobbly motion of the earth’s rotation axis caused by the gravitational pull of

the moon / sun on the earth. Precessison causes our north star to change. Ecliptic-Apparent path the sun takes through the sky over a year’s time. Zodiac-twelve constellations that lie on the ecliptic, come from greek meaning circle of animals Meridian-passes throught southern/northern points of horizon/zenith. Bisects the sky. When the sun is east or to the left of the meridian we have AM. When its to the west or to the

right of the meridian we have PM. Fall (9/22)/Spring Equinox (3/21)- name means equal night. Day/night have exactly 12 hours/ ea. Summer solstice-this is the point on the ecliptic when the sun is farthest north of the celestial

equator. Marks 1st day of summer/ occurs Jun 21. Winter Solstice- this is the point when sun is farthest south of celestial equator. Marks 1st day of

winter/occurs dec. 21. Perihelion- planets closest distance to the sun/ planets move fastest/ summer Aphelion-planets farthest distance from the sun, we have winter. Asteroid-rocky object that orbits a star Comet – icy object that orbits a star Small solar system body – an asteroid, comet, or other object that orbits a star but is too small

to qualify as a planet or a dwarf planet. Solar system-usually only pertains to our sun and what orbits it, but it can be applied to other

star systems Star System-a star ( sometimes more than one) & any planets & other materials that orbit it. Galaxy- great island of stars in space all held together by gravity and orbiting a common center. Cluster or group of galaxies - collection of galaxies bound together by gravity. Small

collections up to a few dozen, are generally called groups, larger collections are called clusters. Supercluster- gigantic region of space where many individual galaxies / many groups/clusters of

galaxies are packed more closely together than elsewhere in the universe. Expansion of the universe – increase in avg. distance between galaxies as time progresses. Chapter 2.1 Constellations: a region of the sky w/ well defined borders; the familiar patterns of stars merely

help us locate constellations.

The celestial sphere: 4 parts: North Celestial pole, South Celestial pole, Celestial equator (projection of earth’s equator into space), ecliptic (sun’s apparent path as it circles the celestial sphere. Crosses the celestial equator at 23.5 degrees b/c thats the tilt of the earth’s axis.)

Moon Phases: 1. New moon. Rise/set at 6a/pm 2. Waxing crescent rise/set at 9a/9pm 3. 1st quarter Rise/set at 12p/am 4. Waxing gibbous Rise/set at 3p/am 5. Full moon Rise/set at 6pm/am 6. Waning gibbous Rise/set at 9p/am 7. 3rd quarter Rise/set at 12a/pm 8. Waning crescent Rise/set at 3a/pm Eclipses Lunar eclipses occur when earth is in the middle of the sun/moon and its shadow falls on the

moon. SUN – Earth- Full MOON Solar eclipses occur when the moon is btwn the sun and the earth and the moons shadow falls on

the earth ppl will see the sun blocked or partially blocked from view. SUN – New Moon – EARTH

For an eclipse to occur the moon’s orbit must cross the ecliptic plane (this crossing is called a node.) The moon must be full for a lunar eclipse and new for a solar eclipse at the time when the moon crosses the sun’s ecliptic plane..

Sunlight is fully blocked in the umbra and partially in the penumbra. Shadow of the moon or earth causes pen/umbra.

3 types of lunar eclipses-total (moon passes entirely through earth’s shadow umbra), partial (PART of moon passes through earth’s shadow umbra), & penumbral (Moon passes through earth’s shadow’s penumbra) p44.

3 types of solar eclipses: Total (Moon’s shadow umbra touches small area of earths surface), Partial (occurs in penumbral part of moon’s shadow seen on earth), Annular (occurs b/c moon’s umbral shadow does not reach earth). During an annular eclipse in the penumbral part of the moons shadow on earth you would witness a partial eclipse.

Saros cycle 18 years and 11 and 1/3 days between when eclipses occur innacruate b/c cant figure out where will occur and what kind will be

Planets sometimes experience retrograde motion because they move slower than the earth does making them appear to move backwards/eastward instead of westward

Stellar parallxx – “The apparent shift in the position of a nearby star (relative to distant objects) that occurs as we view the star from different positions in Earth’s orbit of the Sun each year. “ - determines that the sun is the center of the universe b/c stars change position as seen from earth according to where the earth is in its orbit. However, the Greeks thought the earth was the center of the universe b/c stellar parallax is unobservable to the naked eye.

Ptolemy’s geocentric model- held that each planet moves around earth on a small circle which turns with a larger circle. Accounts for retrograde motion.

Copernicus- proposed a sun-centered model but was just as accurate as ptolemys

Tycho Brahe- took most accurate naked eye observations ever made of mars; said earth is center but other planets revolve around sun;

Kepler-discovered planets orbits are ellipses. Kepler’s laws of planetary motion: The orbit of each planet around the Sun is an ellipse with the Sun at one focus. As a planet moves around its orbit, it sweeps out equal areas in equal times More distant planets orbit the Sun at slower average speeds, obeying the relationship p2 = a3

p = orbital period in years a = avg. distance from Sun in AU

Galileo-demonstrated that a object move until a force stops them. Newton’s 1st law. Galileo observed sun spots, craters on moon = flawed, observed star composition of milky way

proving stars were more distant/numerous than tycho observed, discovered juipiter’s moons, observed phases of venus-proved sun centered system. Overcame nature of motion doubts/heavenly perfection ones. Proved that not all objects orbit earth.

S1 Sidereal day-23 hours 56minutes –earth’s precise rotation period (time it takes for stars to reach

highest point from one day to next) Solar day-time it takes for sun to make trip around local sky (time takes for sun to get to highest

point one day to next day.) Synodic month- 29.5 days req. for ea. Cycle of moon phases. Sidereal month- the moon’s true orbital period 27 and 1/3 days (time it takes for moon to

complete orbit relative to position of stars.) Sidereal year-time it takes for earth to complete one orbit relative to the stars. Tropical year- time from one spring equinox to the next (20 min. shorter than sidereal year) Planet’s Sidereal period- time it takes a planet to orbit the sun Planet’s synodic period - time between when a planet is lined up with the sun in our sky from

that one time to the next similar alignment. Conjunction- when planet’s line up with the sun Opposition- when a planet rises and sets with the moon, closest to the earth (brightest), opposite

the sun. Inferior /superior conjuction- venus and mercury very close to the sun and may cause eclipses Apparent solar time- when we base time on the sun’s actual position in the sky according to a

sundial. Mean solar time- (local measure of time/differs from place to place) average differences btwn

the time a clock would read & the time a sundial would read. More convenient than apparent solar time b/c can always tell you the mean solar time unlike sundial which can’t be used at night or on rainy days.

Leap years- A calendar year with 366 rather than 365 days. Our current calendar (the Gregorian calendar) incorporates a leap year every 4 years (by adding February 29) except in century years that are not divisible by 400.

Analemma- The figure-8 path traced by the Sun over the course of a year when viewed at the same place and the same time each day; it represents the discrepancies between apparent and mean solar time.

Declination- like latitude, parallel to celestial equator, labeled pos/negitive south celectial pole= -90degrees instead of 90 degrees S.

Right Ascension- lines extend from n. to south poles, RA 0 runs through the spring equinox, measured in hours/minutes east of spring equinox. Ea. Of hoor of RA=15 degrees

Tropic of cancer- northernmost latitude at which the sun ever reaches the zenith. (summer solstice)

Tropic of Capricorn- southernmost latitude at which the sun ever reaches the zenith. The precise dates at which the sun can reach the zenith varies with latitude. The Arctic circle and the Antarctic circle are places where the sun can remin continuously above

the horizon for a full day each year. 66.5N/S. Can reach extreme of 6 months of daylight at north/south poles.

Your latitude is = to the altitude of the celestial pole in your sky. Measure the altitude of Polaris in n. hemisphere. You are in the n. hemisphere b/c the celestial equator crosses the meridian in the south.

The celestial equator crosses the meridian at an altitude of 90degrees minus the latitude. The elevation of Polaris always equals the latitude of the observer. Great square of Pegasus The summer triangle consists of Deneb, Altair, and bluish Vega Take notes on assignments online