Elementary Astronomy

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in the northern hemisphere, stars near the _______________ will never be above the horizon
south celestial pole
you can see 1/2 of the sky when you’re at
the north or south pole
number of degrees north or south of the equator your position is located
imaginary plane defining what we can
or cannot see in the sky
celestial poles
the extension of the Earth’s
rotation axis to the sky
celestial equator
the extension of the Earth’s
rotation axis to the sky
point straight overhead
solar day
the amount of time it takes the Sun to
reappear on the local meridian
local meridian
the line connecting the North and South celestial poles through the zenith
because of the Earth’s tilt, the solar day is not the same amount of time each day
the apparent motion of the Sun on the sky at the same time over 1 year
to simplify the keeping of time, the mean solar day was defined as exactly
24 hours (clock time)
24 hours
railroads contributed to
sidereal time
amount of time it takes the Earth to rotate exactly 360° on its axis
sidereal time is approximately the time it takes
a star to reappear at the same point on the sky
slowly accumulating over the year, the difference between the solar day and the sidereal day is
about 4 minutes
the line connecting the sun-earth moves on the sky by only 1 degree (2x the size of the moon) every 24 hour period
so over the course of a single day the Sun and stars appear to move essentially as one with the celestial sphere as the Earth rotates, but over the course of several days one can easily see
the change in position of the stars with time of day (SEASONAL CHANGES)
as the earth moves around the sun, the sun appears to drift among the zodiac constellations along the path called the
the projection of the earth’s orbit on the sky
the ecliptic
the sun appears to move through a set of constellations known as the
not all constellations are the same size
takes 1 month
to go through each constellation in the zodiac
each day a constellation will rise and set
earlier in the day
how many hours does it take for the Earth to rotate through 360 degrees
slightly less than 244 hours
if the Earths motion around the Sun was reversed how many degrees would the Earth rotate through in a sidereal day?
exactly 360 degrees
If the Earths motion around the Sun was exactly reversed, which day is now longer?
a sidereal day, because the sun will have again reached its highest point in the sky before the Earth has rotated 360 degrees.
the difference between the Earth’s axis of rotation and the Earth’s orbital motion around the sun
about 23 degrees
the sun’s path through the sky varies throughout the year
because of the tilt of the Earth’s axis
the tilt of the Earth
which of the following describes one reason that the Northern and Southern Hemispheres have different seasons at the same time?
during a day of the year when the sun is high in the sky in the northern hemisphere it will be ow in the sky in the southern hemisphere, and vice-versa
the moon is the one body in the solar system which actually does
move around the Earth
the MOON is approximately _____ the diameter of the Earth, and orbits at an average distance of ___________.
1/4, 60 Earth radii (384,000 km)
the moons orbital period is
about 27.3 days
the moon’s orbit is inclined slightly by about 5 degrees to the
ecliptic (the orbital plane of the Earth around the sun)
the moon always points the same face toward earth because about 27.3 days is the moon’s rotational period and
it’s orbital period
the far side of the moon cannot be seen from earth
true, because of the moon’s synchronous rotations
approximately every 29.5 days the _______ of the Moon repeat
29.5 days; the phases of the moon
synodic period of the moon
when the Moon lies on the opposite side of the Earth from the Sun, so the sunlight reflected from its surface can be seen from Earth
the Moon shines by
reflected sunlight
the moon rises and sets with the sun
new moon
the moon is high in the sky near sunset
first quarter
the moon is high in the sky at midnight
full moon
the moon is high in the sky near dawn
third (or last) quarter
“quarter moon”
1/2 the visible side of the moon is illuminated
“new moon”
the moon appears un-illuminated
“full moon”
the entire visible side of the moon is illuminated
the length of time between a repeat of a moon phase (new moon to new moon)
synodic period
how much of the moon’s total surface is illuminated by the sun at “new” moon
the synodic period of the moon (29.5 days) is the time required for the moon to
return to the same phase once
the synodic period of the moon is longer than the moon’s orbital period because
the earth orbits the sun counter-clockwise AND the moon orbits the earth counter-clockwise
you are on the moon when it is new moon on earth. you are on the side of the moon facing toward the earth, if you look at the earth the phase you see:
full earth
if the moon is in last quarter (AKA third quarter) it rises and sets
midnight and noon
the moon’s orbit is inclined to the earth’s orbit
most times, during a new or full moon the moon is ________________the Earth
above or below
the moon is between the earth and sun, so the Earth is in the moon’s shadow
solar eclipse
the Earth is between the Moon and the Sun, so the moon is in the earth’s shadow
lunar eclipse
Mercury and Venus are always seen in the sky near the sun, because
they lie closer to the sun than the earth
mercury and venus can never be seen in the part of the sky
opposite the sun
mercury and venus can easily be seen
just before sunrise or after sunset
copernicus developed the
heliocentric solar system model
400 years ago, galileo first saw that the inner planets (mercury and venus) also have phases, somewhat like the moon
outer planets
lie farther from the Sun than the Earth, and can be found anywhere along the ecliptic
the word _____ comes from the greek word for “wanderer”
planets appear to drift slowly eastward (over the months) relative to the stars
because the planets are also orbiting the sun and in the same direction ast he earth
the tendency for the planets to drift eastward relative to the stars as observed from earth is called
prograde (or “normal” motion)
the Earth moves faster in its orbit than the outer panets, so the Earth “passes” the outer planets in their orbits, causing the planets to appear to change their direction of motion relative to the stars to “drift westward”
drifting westward (slowly move westward relative to the stars) is called
retrograde motion
since the inner planets (mercury and venus) “oscillate” from appearing on one side of the sun to the other, their motion will be
split approximately equally between both prograde and retrograde motion
where would you look to see a planet rise when it is in retrograde motion?
near the eastern horizon, because the rising and setting of objects is due to the rotation of the Earth and not the motions of the objects themselves
a planet will, over the course of one night, appear to
move east to west
a planet is moving in “normal” (prograde) motion. over the course of several nights, how will the planet appear to move relative to the background stars?
west to east
a planet is moving in retrograde motion. over the course of several nights, how will the planet appear to move relative to the background stars?
Since Earth completes its orbit in a shorter period of time than the planets outside its orbit, it periodically overtakes them. When this occurs, the planet we are passing will first appear to stop its eastward drift, and then drift back toward the west – ie. move retrograde.
Categories: Astronomy