Astro 1

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local group

Back 1

cluster of galaxies the milky way belongs to; part of local supercluster

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great attractor

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a very large supercluster; 100,00x the mass of milky way; pulls M.W. and other galaxies to it

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electromagnetic force

Back 3

force betwn charged particles

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strong force

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force that holds nuclei together

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weak force

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responsible for radioactive decay

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astronomical unit

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defined as distance between earth and the sun

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light year

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defined to be the distance light travels in one year

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horizon

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line where sky meets ground; below it view of celestial sphere is blocked

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celestial poles

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2 points, 1 N, 1 S, on the celestial sphere that dont move on a daily basis; above north and south poles

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celestial equator

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circle on celestial sphere traced out by earth equators

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ecliptic

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the line the sun traces along the celestial sphere- not same as celestial equator

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equinox

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days when sun crosses celestial equator;equal day and night at about march 21 and sept 23- when sun rises directly east

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solstice

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days when sun is furthest away from celestial equator; june 21 dec 21, sun rises at most extreme north and south points

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zodiac

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band in a narrow zone around the ecliptic in which the planets move

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declination

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like latitude

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right ascension

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like longitude

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altitude

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objects angle above the horizon

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azimuth

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angle measured from north, eastward towards the point on the horizon directly below the object

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diurnal motion

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daily motion- sun moon planets stars rise in east set in west- due to earths rotation about its axis

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annual motion

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yearly motion- due to earths revolution about the sun- as earth orbits sun, sun is in a diff position against the backdrop of stars- a star will rise 3 min 56 sec earlier then night before every night

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periods of zodiac

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when sun appears in front of corresponding constellation

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tilt of earths axis

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23.5 degrees tipped in respect to sun; tilt of of rotation axis causes ecliptic not to be aligned with celestial equator; explains seasonal altitude of sun at noon, highest in summer, lowest in winter

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what causes seasons

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the rotation of the earths axis maintains nearly the same tilt and direction all year; northern and southern hemispheres alternate receiving the majority of direct sunlight from the sun

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when does waxing crescent moon rise?

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morning- after sunrise

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when does 1st qtr moon rise?

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abt noon

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when does waxing gibbous moon rise?

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midafternoon

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when does full moon rise?

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sunset

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when does waning gibbous rise

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midevening

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when does 3rd qtr moon rise?

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abt midnight

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when does waning crescent moon rise?

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early morning-predawn

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when does new moon rise?

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sunrise

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eclipse

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occurs when sun, earth and moon are in line with each other

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solar eclipse

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occurs when moon passes between earth and sun w/ moon casting shadow on earth causing it to look like night for a few min

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lunar eclipse

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earth passes between sun and moon casting its shadow on moon giving it a dull red color

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Classical period of astronomy

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1st to use systematic manner to explain workings of the heavens; logic and math;ancient greeks knew earth was round

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geocentric model

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earth center of universe

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retrograde motion

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occasionally planet will move from E to W relative to the stars

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Ptolemy of Alexandria

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small circles called EPICYCLES were used to explain retrograde motion

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heliocentric model

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sun center of universe- explains retrograde motion as a natural consequence of two planets passing each other- greeks didnt observe parallax

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Kepler's first law

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planets move in elliptical orbits w/ the sun at one focus of the ellipse

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Kepler's second law

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orbital speed of a planet varies so that a line joining the sun and the planet will sweep out equal areas in equal time intervals- the closer a planet is to the sun the faster it moves

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Keplers 3rd law

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The square of the orbital period of a planet is directly proportional to the cube of the semi-major axis of its orbit; p^2=a^3

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Newtons 1st

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law of inertia- body at rest stays at rest body in motion stays in motion unless acted on by a net force

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newtons 2nd

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force is proportional to acceleration- F=ma

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newtons 3rd

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when two bodies interact they exert equal and opposite forces on each other

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acceleration-

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any change in velocity

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uniform motion

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if an objects speed and direction remain unchanged

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constant velocity

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object in uniform motion has this

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surface gravity

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acceleration a mass undergoes at surface of celestial object; determines weight of an object; influences shape of celestial objects and whether they have atmospheres

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law of special relativity

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light doesnt depend on motion of observer

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bose einstein condensate

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found that speed of light depends upon color when in a material

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wave particle duality

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all particles of nature behave as both a wave and a particle

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photoelectric effect

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(einstein)- if you shine a light on some metals, metal will eject electrons

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amplitude

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height above wave; related to brightness or intensity; taller- brighter

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wavelengths

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distance between peaks of any 2 similar points on wave; measured in nm; long - red, short- blue

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frequency

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number of crests that pass a given point in one second; measured in Hz

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visible spectrum

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color human eye is sensitive to

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infrared radiation

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radiation related to visible light- off the red end of the solar spectrum; longer wavelengths than visible light

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ultraviolet light

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mostly absorbed by atmosphere; responsible for sunburns

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microwaves

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longer wavelengths than infrared

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radio waves

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used to study a wide range of astro bodies

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x rays

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used to detect black holes and tenuous gas in distant galaxies

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gamma ray

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atmosphere absorbs- sometimes see from deep space- still relatively unexplored

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spectrum

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a measure of intensity of light as a function of wavelength

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continuous spectrum

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produced by objects that are solid and dense gases- blackbody objects, radiators

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emission line

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produced by hot tenuous gases- fluorescent tubes, aurora and many interstellar clouds

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dark line or absorption line

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light from black body passes thru the cooler gas leaving dark absortion lines

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blackbody

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an object that absorbs all the radiation falling on it; doesnt reflect light- black when cold- as it is heated it radiates more efficiently then any other kind of object

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nucleus

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composed of neutrons and positively charged protons

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element

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substance composed only of atoms that have the same number of protons in their nucleus

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electron orbits

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quantized- can only have discrete values- energy of atom goes up if electron moves out (excited) atoms energy decreased if an electron moves to an inner orbit

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conservation of energy

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energy change of an atom must be compensated elsewhere

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angular size

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how big an object looks

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moon illusion

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if u measure the moons angular diameter u will find it to be smaller when it is near the horizon than when it is overhead

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parallax

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positions of stars change during course of year, resulting from earths motion

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electromagnetic wave/radiation

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bc light is a mix of electric and magnetic energy it is often called this

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photons

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packets of energy which produce sensation of light

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wiens law

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states that the wavelength (color) at which an object radiates most strongly is inversely proportional to the objects temperature

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quantized

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the restriction on the allowable sizes of orbits

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emission

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energy released when an electron drops from a higher to a lower orbital becomes an electromagnetic wave

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spectroscopy

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the technique used to capture and analyze a spectrum from an astronomical body

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doppler shift

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if a source is moving toward us, the wavelengths of its light will be shorter; away- longer

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refractors

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telescopes in which light is gathered and focused by a lens

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reflectors

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telescopes use mirrors rather then lenses to gather and focus light

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redshift

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an observed increase in wavelength (due to doppler shift)

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blueshift

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an observed decrease in wavelength (due to doppler shift)