Chapter 2 Flashcards
Nodes
the two points in the Moon’s orbit where it crosses the ecliptic plane
Totality
the portion of a total lunar eclipse during which the Moon is fully within Earth’s full shadow or a total solar eclipse during which the Sun’s disk is fully blocked by the Moon
Prime meridian
the meridian of longitude that passes through Greenwich, England; defined to be longitude 0 degree
Celestial equator
the extension of Earth’s equator onto the celestial sphere
Local sky
the sky as viewed from a particular location on earth
Angular distance
a measure of the angle formed by extending imaginary lines outward from our eyes to span an object
Circumpolar
a star that always remains above the horizon for a particular latitude
Stellar parallax
the apparent shift in the position of a nearby star (relative to distant objects) that occurs as we view the star from different positions in Earth’s orbit of the Sun each year
June Solstice
both the point on the celestial sphere where the ecliptic is farthest north of the celestial equator and the moment in time when the Sun appears at that point each year
Horizon
a boundary that divides what we can see from what we cannot see
March equinox
both the point in Pisces on the celestial sphere where the ecliptic crosses the celestial equator and the moment in time where the Sun appears at that point each year
Full shadow
the dark central region of a shadow
Synchronous rotation
the rotation of an object that always shows the same face to an object that it is orbiting because its rotation period and orbital period are equal
Sidereal day
the time of 23 hours 56 minutes 4.09 seconds between successive appearances of any particular star on the meridian; essentially, the true rotation period of Earth
Eclipse seasons
periods during which lunar and solar eclipses can occur because the nodes of the Moon’s orbit are aligned with Earth and the Sun
Solar eclipse
an event that occurs when the Moon’s shadow falls on Earth, which can happen only at new moon
Direction
one of the two coordinates needed to pinpoint an object in the local sky
Latitude
the angular north-south distance between Earth’s equator and a location on Earth’s surface
Partial shadow
the lighter, outlying regions of a shadow
Total solar eclipse
a solar eclipse during which the Sun becomes fully blocked by the disk of the Moon
Constellation
a region of the sky covering the celestial sphere
Angular size
a measure of the angle formed by extending imaginary lines outward from our eyes to span an object
Total lunar eclipse
the Moon becomes fully covered by Earth’s full shadow
Zenith
the point directly overhead, which has an altitude of 90 degrees
Apparent retrograde motion
the apparent motion of a planet, as viewed from Earth, during the period of a few weeks or months when it moves westward relative to the stars in our sky
Solar day
24 hours, which is the average time between appearances of the Sun on the meridian
Ecliptic
the Sun’s apparent annual path among the constellation
Lunar eclipse
an event that occurs when the Moon passes through Earth’s shadow, which can happen only at a full moon
Partial lunar eclipse
a lunar eclipse during which the Moon becomes only partially covered by Earth’s full shaodw
Meridian
a half-circle extending from your horizon due South, through your zenith, to your horizon due north
Celestial sphere
the imaginary sphere on which objects in the sky appear to reside when observed from Earth
North celestial pole
the point on the celestial sphere directly above Earth’s North Pole
Penumbral lunar eclipse
a lunar eclipse during which the Moon passes only within Earth’s partial shadow and does not fall within the full shadow
Longitude
the angular east-west distance between the prime meridian and a location on Earth’s surface
Zodiac
the constellations on the celestial sphere through which the ecliptic passes
Saros cycle
the period over which the basic pattern of eclipses repeats, which is about 18 years 11 1/3 days
Partial solar eclipse
a solar eclipse during which the Sun becomes only partially blocked by the disk of the Moon
December Solstice
both the point on the celestial sphere where the ecliptic is farthest south of the celestial equator and the moment in time when the Sun appears at that point each year
Arcminutes
1/60 or 1 degree
Altitude
the angular distance between the horizon and an object in the sky
Precession
the gradual wobble of the axis of a rotating object around a vertical line
September equinox
both the point in Virgo on the celestial sphere where the ecliptic crosses the celestial equator and the moment in time when the Sun appears at that point each year
South celestial pole
the point on the celestial sphere directly above Earth’s South Pole
