55 terms

Astr 102 ch. 2 notes

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The Sun crosses the celestial equator going south to north at...
vernal equinox
What causes seasons on Earth?
Earth's rotation axis points in a constant direction relative to Earth's orbit, but Earth is on one side of the Sun in summer and the opposite side in winter.
The 88 _____ in the sky are patterns of stars that only appear to be close to each other.
constellations
The Zodiac consists of a set of constellations that
are seen along the ecliptic.
What is the declination of the Sun?
a number which changes significantly over a day
What is the definition of the vernal equinox?
the point on the ecliptic where the Sun crosses the celestial equator from south to north
There are many ways of defining the time of a day. Which of the following ways of defining time is most closely associated with the actual time you would read on a sun dial?
apparent solar time
The Sun rises due east in the sky when viewed from a site anywhere on
earth on the vernal and autumnal equinoxes
The _____ is the point directly overhead for any observer.
zenith
Pope Gregory XIII dropped 10 days from the calendar in 1582 because
the assumption that a tropical year is 365 ¼ days is incorrect by over 11 minutes.
The _____ is a line in the sky that always passes through the observer's zenith and the north and south celestial poles.
merdian
In New York City, the constellation Orion is high in the sky around 11 P.M. in January. Orion be high in the sky in July at _____ A.M.
11
It is hotter in North America in July than in December because the
Sun's rays strike the North American continent more directly in July.
The Sun rises due east in the sky when viewed from a site anywhere on Earth on the first day of spring and the first day of _____.
autumn
If the celestial equator passes through your zenith then you must be standing at the ____.
equator
Precession of Earth is
a slow, conical motion of Earth's spin axis, similar to that of a spinning top, with a period of about 26,000 years for one cycle.
The 88 constellations in the sky are
patterns of stars that only appear to be close to each other.
The ecliptic plane (the plane of Earth's orbit around the Sun) makes an angle of 23.5° to the celestial _____.
equator
People in which one of the following cities experience sunrise first?
new york
Where must you stand on Earth to have the celestial equator along your horizon?
either pole
You view the night sky for a period of one hour. What changes during this hour?
the declination of the star at your zenith
The mean sun is
an imaginary object that moves at a uniform rate along the celestial equator.
The Sun crosses the celestial equator going south to north at the _____ equinox.
vernal
If the horizon is considered to be split into northern and southern parts by the east-west line, can the Sun ever rise in the northern part of the sky when viewed from a mid-latitude site in the northern hemisphere?
yes, for exactly half a year
If Earth rotated on its axis in the opposite direction from its current direction but at the same rate it does now, the sidereal day would be
the same length it is now
A tropical year is the
time between successive passages of the Sun through the vernal equinox as viewed from Earth.
The path that the Sun takes as it moves through the heavens is called the _____.
ecliptic
_____ of Earth is a slow, conical motion of Earth's spin axis, similar to that of a spinning top, with a period of about 26,000 years for one cycle.
precession
The Maya followed the movement of the planet Venus in the sky very carefully because they associated Venus with
warfare
A _____ year is the time between successive passages of the Sun through the vernal equinox as viewed from Earth.
tropical
The bright star Denebola (β Leonis) rises at about midnight in early December. If you watch from this same location in early February, Denebola will rise at about
8 p.m.
You are standing at a position 45° south of the equator, and you view the stars rising above the horizon. They will move in a direction that makes a slant with the horizon. The direction of the slanted path is from the horizon to the
northwest
Suppose tonight, an hour after sunset, the bright star Regulus, in Leo the Lion, is just rising above the eastern horizon. Next week, an hour after sunset, Regulus will be
higher above the eastern horizon than it is tonight.
The difference between 1 second of sidereal time and 1 second of mean solar time is
a very small but finite and fixed interval of time.
Suppose the tilt of Earth's axis were 0° instead of 23°. Which one of the following statements best describes the consequences?
There would be no seasons as we currently experience them.

The Sun would always rise due east and set due west.

The ecliptic and the celestial equator would be the same.
To be located in the _____, a star needs to be anywhere within a band of sky 16° wide, extending 8° on either side of the ecliptic.
zodiac
Viewed from a location south of Earth's equator, the time of the year when the Sun rises as far north as possible is _____ solstice.
summer
What is the declination of the Polaris?
90 degrees
The ecliptic plane (the plane of Earth's orbit around the Sun)
remains at a fixed angle of 23.5° to the celestial equator while its axis precesses slowly in direction like a tilted, spinning top.
Ancient civilizations, using naked-eye astronomy, were able to predict three of the following phenomena but not the fourth. Which is the exception?
reappearance of Halley's Comet
A calendar year, from vernal equinox to vernal equinox, is called a ____ year.
tropical
The meridian (or celestial meridian) is a line in the sky that always passes through the
observer's zenith and the north and south celestial poles.
If the Sun's declination is 0° on March 21 of a particular year, how long will it be before it is at this declination again?
6 months
To a modern astronomer, what is the constellation Orion?
a region of the sky and all the stars within that region
The North Star, Polaris, is not always due north because of which characteristic of Earth's axis?
precession
The distorting effects of Earth's atmosphere are minimized when you observe in the direction of
the upper merdian
One hour of _____ time is defined as 1/24 of the time between when a particular star crosses the upper meridian and the next time the same star crosses the upper meridian.
sidereal
To be located in the zodiac, a star needs to be anywhere within a
band of sky 16° wide, extending 8° on either side of the ecliptic.
Right ascension and declination are used to specify the position of a star or other object in the sky. How are they measured?
Right ascension is measured eastward from the vernal equinox, and declination is measured north or south from the celestial equator.
Polaris, the North Star, is at the end of the handle of the Little Dipper. How do the stars of the Little Dipper move with respect to Polaris?
counterclockwise
In New York City, the constellation Orion is high in the sky around 11 P.M. in January. At what time of the day or night would Orion be high in the sky in July?
11 a.m.
Suppose the star Sirius rises above the eastern horizon at 2:00 A.M. on a particular night. At what time will it rise four nights later?
1:44 a.m.
You are standing in a position south of the equator but less than 45° south latitude, and you view the stars rising above the horizon. They will move in a direction that makes a slant with the horizon. The angle between this slanted line and the horizon will be
more than 45° (but less than 90°).
You are an archaeologist studying the pyramids of ancient Egypt. You find that the pyramid bases are all aligned in a particular direction. To understand the significance of this alignment, one important astronomical fact you must keep in mind is that
because of precession, true north in ancient Egypt was marked not by Polaris but instead by another star (Thuban in Draco, the Dragon).
The _____ motion of the heavens results from the spin of Earth on its axis.
diurnal
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