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Astro. Test 1
Chap 2
43
Astronomy
Undergraduate 1
02/17/2009

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Term
Where was the July 11, 1991 solar eclipse seen from? Why was this a big deal?
Definition
Mauna Kea in Hawaii, it was the largest telescopes every to be able to point directly at the sun
Term
What is positional astronomy?
Definition
study of positions of objects in sky and how they change
Term
What is remarkable about Stonehenge, the Incan stone temple, and the Anasazi stone petroglyphs?
Definition
They were built to predict where the sun would rise and set during key times in the year, Incas had a window that the sunlight would go through on the summer solstice, anasazi had carvings that have a single band of light strike the center of a spiral on the first day of winter
Term
What is about the great pyramids of egypt?
Definition
they are oriented north-south and east-west with an accuracy of far less than 1 degree
Term
Mayan astronomers studied which planet most?
Definition
Venus, the believed it to be associated with war and chose the dates to attack based on its phases
Term
What is the daily motion of the stars called?
Definition
diurnal motion
Term
Constellations rise in ____ and set in ____, but do so approx. _____ (time) earlier each night.
Definition
east, west, 4 min
Term
Earth rotates which direction?
Definition
west to east (which is why stars seem to move from east to west)
Term
Time = ?
Definition
distance/velocity
Term
What is the point in the sky directly overhead an observer anywhere on Earth called? The distance from the horizon to this point is thus ______.
Definition
zenith, 90 degrees
Term
Why is Polaris able to be seen at any time of night on any night of the year in N. America or Europe?
Definition
it is a circumpolar star
Term
how does where you are standing on the earth relative to the celestial poles/sphere change the stars you see and their motion?
Definition
if you are standing at the poles then you always see the same stars and they never rise or set, they just go around, if you are standing at the equator you see all the stars and they always rise and set, for most people stars move at an angle (rise in east & set in west)
Term
what causes the seasons?
Definition
the earth's tilt, when the northern hemisphere is tilted towards the sun it is summer there and winter in the southern hemisphere tilted away
Term
what is the plane of the earth's orbit around the sun called?
Definition
the ecliptic plane
Term
how many days does it take the earth to go around the sun? what fixes (and who fixed) this time difference?
Definition
365.2442, leap year (as established by Caesar) fixed this to 365.24 but it was still off 11 min and 14 sec which over time added up, pope Gregory instituted a Gregorian calendar which fixed this by dropping 10 days that year and then modifying caesar's leap year system by saying that only centuries evenly divisible by 400 should be leap years instead of all calendar years divisible by 4
Term
how long does it take the earth to rotate around its axis once? what fixes this time difference from 24 hours?
Definition
23 hours and 56 minutes, the earth's rotations around the sun
Term
what is an equinox?
Definition
the 2 times a year when the ecliptic and the celestial equator intersect, at this time day and night are equal
Term
what is march 21 and sept 22?
Definition
vernal equinox and autumnal equinox
Term
what is the point on the ecliptic farthest north of the celestial equator? what day is that? farthest south? what day is that? [all according to n. hemisphere]
Definition
summer solstice, june 21
winter solstice, december 21
Term
what is the circular path the sun appears to trace out against the background of the stars?
Definition
ecliptic
Term
what is 23.5 degrees south & north latitude called?
Definition
tropic of capricorn
tropic of cancer
Term
who was the first person to use a telescope? what year?
Definition
Galileo (although a man in holland invented it), 1709
Term
what planets can we see without a telescope?
Definition
mercury, venus, mars, jupiter, and saturn
Term
when was Haley's comet first seen to have appeared in the sky?
Definition
1066 AD, we know this because we found a tapestry with the comet on it (it was thought to be a portent of good or evil at the time)
Term
when is the sun never directly overhead?
Definition
north or south of 23.5 degrees latitude
Term
what does the north pole look like june 21? december 21?

the south pole?
Definition
light all the time/always day/sun never goes below horizon
dark all day/always night/sun never rises above horizon

opposite
Term
baton rouge is at what latitude?
what is it like june 21? december 21?

australia?
Definition
+30 degrees
longer day than night/hot/sun higher up in sky
opposite

-30 degrees, opposite
Term
what is the equator like on june 21? sept 21? march 21?
Definition
sun is at 23.5 degrees. sun directly overhead moving south. sun directly overhead moving north.
Term
the moon moves about how many degrees in the sky each day?
Definition
12
Term
the moon moves along a band called what?
Definition
its own ecliptic, the zodiac
Term
does the moon cause a change in Earth's rotation? if so, how?
Definition
yes, it has a gravitational pull on the Earth
because the earth is bigger around then from pole to pole, it has a "equatorial bulge" which the gravitational pulls of the moon and sun affect

precession (slow, conical motion of Earth's axis of rotation caused by the gravitational pulls)
Term
the gravitational pull of the moon and sun try to twist the Earth's axis of rotation to be perpendicular to the plane of the ecliptic but the Earth only has a 23.5 degree tilt. what motion fights against this gravitational pull?
Definition
the earth's rotation
Term
how long does it take for the earth to make one precessional circle?
Definition
26,000 years
Term
because the Earth's axis of rotation precesses, so does the ___________?
Definition
celestial equator and thus the intersection of the celestial equator with the ecliptic and thus the equinoxes

thus the precession of earth is aka precession of equinoxes
Term
who was the first person to detect precession of equinoxes?
Definition
Hipparchus
Term
what is a meridian?
Definition
line between celestial poles (hits zenith), used to measure time
Term
what is an apparent solar day?
why is it different at different times of the year?
Definition
the interval between 2 successive upper meridian transits of the sun
b/c Earth's orbit is an ellipse and Earth moves on its orbit faster when farther away thus the solar day is longer in january when the Earth is moving slower along its orbit
Term
what is sidereal time?
Definition
system of time based on the apparent motion of stars
Term
what is a sidereal year?
Definition
the time required for the sun to return to the same position with respect to the stars
Term
what type of solar year do we use?
Definition
the tropical year, the time needed for the sun to return to the vernal equinox
Term
what is parallax and what does it measure?
Definition
angular shift (the apparent displacement of an object due to the motin of the observer), distance
Term
what is a parsec?
Definition
a star with a distance of 1 parsec is one with a parallax angle of 1 second of arc

(yet all stars are father away than that)
Term
what is the closest star? how far away is it?
Definition
proxima/alpha centauri, 4.2 ly so just over 1 parsec
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