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Chapter 2: Patterns in the Sky-Motions of Earth
Terms in this set (55)
The moon undergoes synchronous rotation, and as a consequence the:
rotational period of the moon equals the orbital period of the moon around the earth
If the Sun is located at one focus of Earth's elliptical orbit, what is at the other focus?
A circle has an eccentricity of _____ and a line has an eccentricity of _____.
The shortest day of the year for a person living in the southern hemisphere is the:
On average, how far away is the earth from the sun?
150 million kilometers
If you go outside at exactly 9 pm each evening over the course of one month, the position of any given star will appear to move westward. What causes this apparent motion?
the revolution of the earth around the sun
Leap years occur because:
the earth's orbital period is 365.24 days
If tonight the Moon is in the waxing gibbous phase, in three days the Moon will most likely be in the
What statements are true about the moon?
the phases of the moon cycle with a period of approximately one month, everyone on earth observes the same phase of the moon on a given night, in some phases the moon earth can be observed during the day
Solar and lunar eclipses are rare because:
the moon's orbital plane is tipped by 5.2 degrees relative to the earth's orbital plane
When the Earth catches up to an outer planet moving more slowly than it, and passes it in orbit, the planet ____ .
exhibits retrograde motion
Kepler's third law is a relationship between an orbit object's ____ and ____ .
period; semimajor axis
Suppose an asteroid had an orbit with a semimajor axis of 4 AU. How long would it take for it to orbit the Sun once?
If you traveled 20 miles from home to school in 30 min, what is your average velocity?
The direction directly overhead of an observer defines their:
If the star Polaris has an altitude of 35 degrees, we then know that:
our latitude is +35 degrees
The meridian is defined as a great circle on the sky on which the ____ and the ____ lie.
zenith; north and south celestial poles
The ecliptic plane is defined by the motion of what in the sky?
The earth's rotational axis precesses in space and competes one revolution every:
You went outside tonight at midnight and looked at the sky. 6 months from now, at what time of day would you have to do the same thing in order to see the exact same stars in the same position? Assume that the stars are visible at any time of day.
Ideally, which planet would astronomers prefer to build their telescopes?
Is the earth's moon larger than pluto?
Ceres has a thin atmosphere of water vapor, what does this finding tell us?
asteroids may have delivered some of the water on earth, Ceres may have accreted materials from outer regions of solar system, active icy volcanoes
Why is it so hard to directly see an earth-like planet around another star?
the stars are far away, the planets are much fainter than the stars, the planets are too close to the stars in the angular seperation
1 parsec=3.26 light yr
1Au=earh-sun distance, 8.3 light min
1 parsec=206,265 Au
1 degree=60 arcmin
1 radian=206,265 arcsec
projection of earth's axes and equator into space
-celestial poles=north and south, directly above earths poles
-celestial equator=projection of earth's equator into space
-ecliptic=sun's annual path around the celestial sphere
What is a constellation?
a region of the sky with an arbitrary pattern. 88 regions within celestial sphere
as earth rotates, the sky appears to us to rotate in the opposite direction
counterclockwise on axis, each rotation takes 23 hrs 56 min
-at north pole, you would see half of the celestial sphere
-can never see south hemisphere
-stars rotate counterclockwise in a day
-no star rises or sets, their circumpolar
-at earth's equator, all stars rise and set
-the angle between the north celestial pole and the horizon equals the latitude
If you are standing on the north pole where in the sky is Polaris?
directly above you
If you're on the equator, which stars are circumpolar?
none of them
Iowa city has a latitude of 41 degrees, at what altitude is the north celestial pole?
In iowa city which stars are circumpolar?
those within 41 degrees of the north celestial pole
Earth's orbit around the sun
nearly circular, sun's motion on the celestial sphere reflects the earth's orbit around the sun
the path of the sun on the celestial sphere
-tilted 23.5 degrees because that is the earth's spin axis axis from the plane of its orbit around the sun
Earth's slightly elliptical orbit
earth's orbit is only slightly eccentric
-due to 23.5 degree tilt
-causes angle of sunlight is more direct in summer and the sun is in the sky longer in the summer
-southern hemisphere experiences opposite effect
-Autumn Equinox=sept 23
----sun at celestial equator
-Summer Solstice=june 21
----sun is north of celestial equator
-Vernal Equinox=march 21
----sun is on the celestial equator
-Winter Solstice=dec 22
----sun is south of celestial equator
If the ecliptic were aligned with the celestial equator, what would happen to the
we would not have seasons at all
You observe that a bright star rises at 10pm tonight, a month later when will it rise?
Changing Celestial poles
1. the north/south poles change directions on the celestial sphere
2. the zodiac constellation of each month changes
Precision of the earth
-location of the poles shift slowly
-earths axis changes over 26,000 yrs
-zodiac constellation changes over time
-EX. sun is no longer in the constellation Cancer on summer solstice
When would there be no precision?
the earth is a perfect sphere, the earth's spin axis is aligned with the ecliptic pole
Phases of the moon
When does the full moon rise?
When would the third quarter moon rise?
Types of Solar Eclipses
Total=the moon completely blocks the sun's light
Partial=only part is blocked
Annular=the sun appears as a bright ring surrounding the moon
-always happens at new moon
-moon passes between earth and sun
-only small part of earth can see total eclipse (inside the umbra), but a large part can see the partial eclipse (inside the penumbra)
Penumbra, Umbra, Antumbra
-happens at full moon
-earth is between sun and moon
-visible over wider area of earth
-lasts a lot longer than solar eclipse
Why don't eclipses occur each month?
because the moon's orbit is tilted about 5 degrees with respect to the ecliptic plane (sun's path to earth)
-without the tilt, there would be a solar eclipse every new moon
the point at which an orbit crosses the ecliptic plane going south
the point at which an orbit crosses the ecliptic plane going north
*Eclipses only occur at lunar nodes
If the moon is relatively far from the earth, so that its umbra does not reach the earth, someone in the middle of the eclipse path will see what?
Synchronous Rotation of the moon
the moon rotates once on its axis for each orbit around earth, so it keeps the same face toward earth at all times
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Chapter 4: Light and Telescopes
Chapter 14: Measuring Galaxies
Intro to Astronomy 1
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