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astronomy-discovering the universe

unit 1 1st six weeks
by

angela barnes

on 1 October 2016

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Transcript of astronomy-discovering the universe

Chapter 1
Discovering the Universe
sizes range from the diameter of the observable universe (10^26), down to diameters smaller than sub atomic particles (10^-24)
the size of the universe and the range of sizes of the objects in it are truly staggering
scaleofuniverse.com
scientic notation- powers of ten
asteroid/meteoroid- made up of rock and metal
comet- made up of rock and ice
black hole- matter so dense that light cannot escape its gravitational field
the big dipper helps us find the north star, polaris, and the leo constellation
the winter triangle connects orion, canis major, and canis minor
the summer triangle connects the stars vega, deneb, and altair
easily recognized constellations
(asterisms)
can allow us to orient ourselves on earth and help us locate specific stars
constellations- word reserved by astronomers to describe an entire area of the sky and all the objects in it
asterisms- recognizable patterns of bright stars
celestial sphere- sky map
celestilal equator- divides the sky into northern and southern hemispheres
north celestial pole- along earth's axis of rotation in the northern hemisphere
south celestial pole- along earth's axis of rotation in the southern hemisphere
declination- 0-90 degrees north and south of the celestial equator
right ascension- 0-24 hours around the celestial equator
vernal equinox- the point where the sun crosses the celestial equator from south to north
the stars, year after year, seem to be stuck in place (relative to one another), and throughout the night, this entire pattern of stars seems to rigidly orbit earth like an enormous hollow shell
astronomers have created a star map that allows them to use latitudinal
(declination)
and longitudinal
(right ascension)
coordinates to locate celestial bodies quickly and easily
julian calendar- based on 365.25 days
gregorian calendar- based on 365.2425 days
how could you use the sun's motion across the sky as a yearly calendar?
rotation- spinning on an internal axis
diurnal motion- daily motion; caused by earth's rotation
revolution- spinning around an external axis
sidereal period- the length of any period of motion in relation to the stars
some constellations are only visible certain times of the year due to earth's revolution around the sun
earth rotates on its axis which causes the apparent rising of the sun, moon, and planets in the eastern sky, their apparent movement across the sky, and their apparent setting on the western horizon
the seasons result from the tilt of earth's axis of rotation combined with earth's revolution around the sun
ecliptic- the path on the celestial sphere traced by the path of the sun
equinox- means "equal night"; the sun is directly over earth's equator so there are exactly 12 h of day and 12 h of night everywhere on earth
vernal equinox- spring in the northern hemisphere, autumn in the southern hemisphere
autumnal equinox- autumn in the northern hemisphere, spring in the southern hemisphere
summer solstice- the day in the northern hemisphere each year with the most amount daylight
winter solstice- the day in the northern hemisphere each year with the least amount of daylight
earth's axis of rotation is tilted 23.5 degrees
therefore, on the celestial sphere, the celestial equator and the ecliptic are different circles tilted 23.5 degrees with respect to each other
these two circles intersect at only two points, exactly opposite from each other on the celestial sphere, the
equinoxes
the northernmost point on the ecliptic is called the
summer solstice
the southernmost point on the ecliptic is called the
winter solstice
what causes earth's seasonal changes?
solar day- the length of time between when the sun is highest in the sky one day to when it's highest in the sky the next
mean solar day- the average time interval between consecutive noontimes throughout the year; 24 h
time zones- based on the time at 0 degrees longitude, the prime meridian, in greenwich, england
sideral day- the length of time from when a star is in one place in the sky until it is next in the same place; 23 h 56 m
is using the sun's location in the sky a good way to create a daily clock?
why or why not?
what kind of problems may arise from this type of calendar?
like a wobbling top in slow motion, the earth's axis of rotation changes slightly over time with respect to the celestial sphere
precession- the motion in which earth's axis of rotation changes over a 26,000 year period
gravitation- universal force of attraction between all matter
the combined actions of gravity from the sun and the moon plus the earth's rotation causes earth's axis to trace a circle in the sky while remaining tilted about 23.5 degrees
lunar phases- the apparent shapes of the moon as seen from earth
new moon- the sunlit hemisphere of the moon faces away from earth
first quarter moon- half of the moon's sunlit hemisphere and half of its dark hemisphere is seen with the sunlit half on the right
full moon- the sunlit hemisphere faces earth
third quarter moon- half of its sunlit hemisphere and half of its dark hemisphere is seen with the sunlit half on the left
waxing- sunlit hemisphere is seen on the right; crescent and gibbous
waning- sunlit hemisphere is seen on the left; crescent and gibbous
terminator- the boundary between the bright and the dark regions of the moon
sideral month- the period of time it takes for the moon to make one revolution around earth; 27.3 days
synodic month- the period of time it takes for the moon to complete one full cycle of phases; 29.5 days
the sun illuminates one-half of the moon at all times
the moon's phase that we see depends on how much of its sunlit hemisphere is facing us
only one half of the moon can ever be seen from earth; the moon has a far side that never faces earth
model the difference between a lunar eclipse and a solar eclipse
lunar eclipse- occurs when the moon passes through earth's shadow from the sun
solar eclipse- the moon's shadow moves across earth's surface; the sun as seen from earth is blocked out by the moon
line of nodes- where the moon crosses the plane of the ecliptic during its new or full phase; only time eclipses occur
eclipses occur when the sun, the earth, and the moon are all in perfect alignment
three different types of lunar eclipses can occur depending on which part of earth's shadow the moon is in
a
penumbral lunar eclipse
occurs when the moon passes only through earth's penumbra; the moon looks full, slightly dimmer and reddish; easy to miss
umbra- part of earth's shadow where all direct sunlight is blocked
penumbra- part of earth's shadow where only some of the sunlight is blocked

when the moon completely covers the sun, the result is a
total solar eclipse
and only the
solar corona
can be seen
because of their different distances away, the sun and the moon have approximately the same diameter in the sky as seen from earth
three types of solar eclipses can occur
a
partial eclipse
of the sun occurs when the moon only partly blocks the sun and it is seen as a crescent
when the moon is farthest from earth during a solar eclipse, an
annular eclipse
occurs
the moon is too small to cover the sun completely and the sun appears as a ring
solar corona- hot gases escaping from the sun
when the moon, during a penumbral eclipse, passes slightly through earth's umbra, a
partial lunar eclipse
occurs; the full, reddish moon seems to have a bite taken out of it where direct sunlight is blocked
when the moon travels completely into the umbra of earth's shadow, a
total lunar eclipse
occurs; lasting for up to 1 hour and 47 minutes, the full moon glows red and orange
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