AST

Astronomy

Astronomy

the scientific study of planets, stars, galaxies, and the universe as a whole

• focused on measuring positions of and finding patterns among the stars

cosmic address

planet, star, galaxy group, galaxy cluster, and galaxy superstar

• eart, sun, solar system, milky way, local group, lainaka supercluster, universe

Astronomical Unit

the average distance from the sun to earth

the solar system contains...

eight planets: mercury, venus, earth, mars, jupiter, saturn, Uranus, neptune

• dwarf planets: pluto, ceres, eris

• asteroids: ida, eres

• comets: Halley

milky way galaxy

a disk containing more a hundred billion stars, along with gas and dust

• is part of a small collection of a few dozen galaxies called the local group

• the local group itself is part of a vastly larger collection of thousands of galaxies called the supercluster, which is part of the lainaka supercluster

light travel time

• how long it would take for light to travel a given distance Light travels through space at the fastest possible speed, and that speed is always the same Light travels at 30,000 kilometers per second (km/s)

light day

• the distance that light traversing 1 day - about 26 billion kilometers - the distance within the solar system

Light - Years

the distance that light travels in 1 year - about 9 trillion kilometers

• distance to the nearest star

Scientific Method:

• the formal procedure - including hypothesis, prediction, and experiment or observation - used to test, attempt to falsify) the validity of scientific hypothesis and theories

• a systematic, logical process for collecting evidence and using it to test ideas or explanations Only idea that cannot be tested is not scientific, you choose to accept of reject it on some basis other than evidence

theory

a carefully constructed proposition that takes into account every place of data as well as out entire understanding of how the world works

• a theory that has been used to make testable predictions and all those predictions have been correct

• an idea that has been examined carefully, is consistent with all existing theoretical and experimental knowledge, and makes testable predictions

hypothesis

idea that leads to a testable prediction

idea

an untested notion about how something might be

facts

an observation or measurement

law

• is a series of observations that scientists can use to make predictions, but a law has no underlying explanation of why the phenomenon occurs

falsified

proved incorrect

cosmological principle

includes the testable assumption that physical laws that apply here and now also apply everywhere and at all times

occam razor

when we are faced with completing hypothesis that explain all the observations equally well, we should use the one that requires the fewest assumptions

zenith

the point on the celestial sphere located directly overhead from an observer

• the highest point in the sky, directly above your head

horizon

the boundary that separates the sky from the ground

• half of the sky is below the horizon

scientific method order

facts obs--> hypothese-->prediction--> test

meridian

you can divide the sky into an eastern half and western half with a line that runs from the horizon at due north through the zenith as due south, divides east and west, over the course of one day, objects will rise in the eastern half of the sky, pass through the meridian, and set in the western half of the sky, pass through the merdian and set in the western half

celestial sphere

an imaginary sphere with celestial objects on its inner surface and earth at its center

day

the time for earth to rotate around its axis

sidereal day

is the time to rotate relative to the fixed stars, earths true orbital period, constellations along the ecliptic form the zodiac

solar day

the time to rotate relative to the sun

if you were transported the earths north or south pole

you would see earth rotate counter/or clockwise each day

altitude

the location of an object above the horizon, measured by the angle formed between an imaginary line from an observer to the object and a second line from the observer to the point on the horizon direction below the object

local astronomical midnight

occurs when the sun is precisely opposite from its position at local noon,

north pole/south pole rotates

counter clockwise, clockwise

latitude

the angular distance from the equator

standing at the north pole

you are standing where earths axis of rotation intersects its surface- standing at the center of the rotating wheel

• objects follow circular paths that always have some latitude

• close to the zenith, objects follow small circles

• objects near the horizon follow large circles

• northing rises or sets each day as earth turns (always see same half of the sky)

standing at south pole

same thing as north pole but start move clockwise

from the equator looking north

NCP is on the horizon, the stars arc from east to west counter clockwise

latitude 30 degrees s

SCP is 30 degrees from horizon and the stars are going clockwise

circumpolar

referring to the part of the sky, near either celestial pole that can be seen above the horizon from a specific location on the earth

• always above the horizon

NCP relation to circumpolar stars

in canadian woods, NCP would be higher in the sky so more circumpolar stars, at lower laditudes, the NCP is near the horizon so less circumpolar stas

solar year

the time for the earth to make one revolution around the sun, measured between two vernal equinoxes

zodiac

the constellations that lie along the plane of the ecliptic

summer solstice

June 21, when the sun is at its northernmost point, sun is at the greatest distance from the celestial equator

winter solstice

December 22, when the sun is at its southernmost point, the sun is also its greatest distance from the equator, dec 21 in northern hem, and june 21 in southern

autumnal equinox

September 22, one of two points where the sun crosses the celestial equator

vernal equinox

one of two points where the sun crosses the celestial equator

where does the sun set

in the west

gregorian calendar

based on the tropical year, the modern calender,

tropical year

the time between one crossing of the vernal equinox and the next

• a tropical year is slightly shorter than the time it takes for earth to orbit the sun

leap year

every 4 years, a year that contains 366 days

tropics

Northern limit. tropic of Cancer

• Southern limit, tropic of Capricorn

• the region on Earth between latitudes 23.5 degrees south and 23.5 degrees north, in which the sun appears directly overhead twice during the year

Procession of the Equinoxes:

the slow change in orientation between the ecliptic plane and the celestial quatro caused by the wobbling of Earth’s axis

days it takes the moon to orbit earth

27 days

synchronous rotation

the moon rotates once on its axis for each orbit around Earth- an effect called synchronous rotation, the moon is not perfectly round but has a bulge on the side closer to earth, earths gravity constantly tags on this bulge which causes its near side to always to fall towards earth

new moon

the phase of the moon which is between earth and the sun, and from the earth we see only the side of the moon not illuminated by the sun, up in the daytime and never visible in the nighttime sky

• appears close to the sun in the sky so it rises with the sun at sunrise, crosses the meridian near noon, and sets in the west with the sun

waxing

the changing phases of the moon as it becomes fully illuminated between new moon and full moon as seen from earth

first quarter moon

the phase of the moon in which only its western half, as viewed from earth, is illuminated by the sun

• occurs one week after a new moon

• one-quarter of the way through its orbit

• rises are noon, crosses the meridian at sunset, and sets at midnight

full moon

• occurs two weeks after a new moon, the sun and moon are opposite in the sky

• rises as the sun sets, crosses the meridian at midnight, and sets in the morning as the sun rises

when the moon is farther than earth from the sun

its in its gibbous phase, when it is closer than Earth to the sun it is in crescent phases

moon phases summary

new moon rises and sets with sun, crosses the meridian near noon, a few days later a sliver of its illumination becomes visible--> waxing crescent

first quarter moon rises at 12 pm and crosses the meridian at sunset and crosses the meridian at sunset and sets at midnight

eclipse

occurs when the shadow of an astronomical body falls on another

• the total or partial obscuration of one celestial body by another

• the total or partial obscuration of the light from one celestial body as it passes through the shadow of another celestial body

solar eclipse

occurs when the moon passes between the earth and the sun and casts a shadow on earth

• an event that occurs when the Sun is partially or entirely blocked by the moon

total solar eclipse

occurs when the moon completely blocks the disk of the sun

• at any location, a total solar eclipse never lasts longer than 7 1/2 minutes and is usually significantly shorter - an event that occurs when Earth passes through the umbra of the moons shadow, so that the moon completely blocks the disk of the sun

umbra

a region of complete shadow resulting from total obstruction of light

partial solar eclipse

an event that occurs when the earth passes through the penumbra of the moon's shadow so that the moon blocks only a portion of the sun's disk

• occurs when the moon partially covers the disk of the sun

annular solar eclipse

occurs when the moon is slightly farther away from earth in its non circular orbit, so it appears slightly smaller in the sky

• an event that occurs when the apparent diameter of the moon is less than that of the sun, leaving a visible ring of light (“annulus”) surrounding the dark disk of the moon Lunar Eclipse:

lunar eclipse

• occurs when the moon is partially or entirely in Earth’s shadow

• an event that occurs when the moon is partially of entirely in earths shadow All observers on the nighttime side of Earth will be able to see a lunar eclipse

total lunar eclipse

when the moon is entirely within earths shadow

• may last as long as 1 hour 40 minutes

• an event that occurs when the moon passes through the umbra of earths shadow

The moon often appears red during a total lunar eclipse, because it is illuminated by red light from the Sun that is bent as it travels through earths atmosphere and hits the moon

partial lunar eclipse

an event that occurs when the moon passes through the penumbra of Earths shadow

• if earths shadow incompletely covers the moon, some of the disk of the moon remains bright and some of it is

in shadow

why don't we see eclipses every month

About twice per year, the orb planes lines up at points called nodes, and eclipses can occur. These two times of year are sometimes called eclipse seasons

• The orbit of the moon is tilted with respect to the ecliptic, so we do not see eclipses every month

gravity

the force of attraction between all masses in the universe; especially the attraction of the earth's mass for bodies near its surface

• holds all planets in orbit

why is it relevant that the sun is more massive

its gravity shapes the motion of every object in the solar system from the almost circular orbits of some planets to the extremely elongated orbits of comets

geocentric

a coordinate system having the center of earth as its origin

model

a representation (often) mathematical of objects and the interaction between them

• in computing, a simulation to reproduced the behavior of a system in one, two or three dimensions

apparent retrograde motion

• movement of the planets with respect to the fixed stars in which the planets appear to move westward for a period of time before resuming their normal eastward motion

• objects in our solar system orbit the Sun at different distances and speeds.

frame of reference

a system of assumptions and standards that sanction behavior and give it meaning

• a coordinate system within which an observer measures positions and motions

Ptolemy

modified the geocentric model with a complex system of interconnected circles to try to obtain more accurate results and explain retrograde motion

• figure where each seperate planet has its own orbit around the earth including the sun, makes lots of circles a swirl

Nicholas Copernicus

Was not the first person to consider the idea that the sun was at the center of the solar system

• was the first person to develop a mathematical model that made testable predictions about the planetary orbit

• In 1543, he published a heliocentric model in a treatise called de revolutionibus orbium coelestium (“on the revolutions of the heavenly spheres”) that explained retrograde motion much more simply the Ptolemy’s

Kepler's laws

• the three rules of planetary motion inferred by Johannesburg Kepler from the data acquired by Tycho Brahe

ellipse

• a conic section produced by the intersection of a plane with a cone when the plane is passed through the cone at an angle to the axis other than 0 degrees or 90 degrees.

• this forms an oval around two points known as foci

• for any point on the ellipse, the sum of the distances to the foci is constant

major axis

the longest axis of an ellipse or ellipsoid; passes through the two foci

semi major axis

half of the longer axis of an ellipse -the semi major axis of an elliptical orbit is equal to the average distance of the orbiting body from the object at the focus

eccentricity of an ellipse

how much the ellipse deviates from a circle, found by dividing the distance between the foci by the length of the major axis

eccentricity

a measure of the departure of an ellipse from circularity; the ratio of the distance between the two foci of an ellipse to its major axis

keplers first law

a rule of planetary motion, inferred by Johannes Kepler, stating that planets move in orbits of elliptical shapes with the sun at one focus

focus

• one of two points that define an ellipse

• a point in the focal plane or a telescope

all of the planets in the solar system have eccentricities smaller than

.25

Kepler's 2nd law

also called law of equal areas

• a rule of planetary motion, inferred by Johannes Kepler, stating that a line drawn from the sun to a planet sweeps out equal times as the planet orbits the sun Kepler found that a planet moves fastest when it is closest to the sun and lowest when it is farthest from the sun

Kepler's third law

• called harmonic law

• • a rule of planetary motion inferred by johannes kepler that describes the relationship between the period of a planet’s orbit and its distance from the sun.

• the law states that the square of the period of a planet’s orbit, measured in years, is equal to the cube of the the semimajor axis of the planet’s orbit, measured in astronomical units: (Pyears)^2 = (A AU)^3

• the squares of the orbital periods of the planets are directly proportional to the cubes of the semi-major axes of their orbits

weight

• in general, relativity the force equal to the mass of an object multiplied by the acceleration of the frame of

reference in which the object is observed

newtons first law

Objects at Rest Stay at Rest; Objects in Motion Stay in Motion

• the object will remain at rest or will continue moving along a the straight line at a constant speed until an unbalanced force acts on it

force

push or pull of an object

Inertia

the tendency for objects to retain their state of motion

inertial frame of reference

a frame of reference that is not accelerating

• in general relativity, a frame of reference that is falling freely in a gravitational field Forces that cancel out have no effect on an objects motion When forces add together to produce an effect, we often use the term net force, or just force

acceleration

=f/m any change in speed or direction, the rate at which the speed and or direction is changing

• slowing down means the acceleration is opposite the direction of motion, the cup tips to the right, vs speeding up the acceleration is in the direction of motion as the cup tips to the left

• turning at a constant speed means the acceleration of the cup is perpendicular to the direction of motion

newtons second law of motion

the laws formulated by Isaac newton, stating that if an unbalanced force acts on a body, the body will have an acceleration proportional to the unbalanced force and inversely proportional to the object's mass

• A = F/m

• the acceleration will be in the direction of the unbalanced forces

intertial mass vs gravitational mass

the property of matter that resists changes in motion vs the property of matter defined by its attractive force on other objects

newton (n)

• the force required to accelerate a 1-kilogram (kg) mass at a rate of 1. enter per second p

• where 1 N = 1 kg m/s^2

forces change..

forces change an object's motion - by changing either its speed or its direction A change in speed is one way the car's motion can change A change in direction is also a change in motion

velocity

The rate and direction of change of an object's position with time

• units: meters per second (m/s) or kilometers per hour (km/h)

what causes acceleration

net force causes at acceleration since

• The acceleration depends on the strength of the net force acting on the objects to change its notion

• The acceleration occurs in the direction the net force points The acceleration that an object experiences also depends on its inertia

newtons third law

the law, formulated by Isaac Newton, stating that for every force there is an equal and opposite force

• if an astronaut pushes on a wrench, the astronaut will go backward and the wrench forward at constant velocities. while in contact with each other, the wrench and the astronauts experience accelerations proportional to the inverse of their masses

gravitational force

force due to the gravitational interaction between two or more objects

inverse square law

the rule that a quantity or effect diminishes with the square of the distance from the source