Chapter 2: Discovering the Universe for Yourself Flashcards
a region of stars with well-defined borders
constellation
the imaginary sphere on which objects in the sky appear to reside when observed from Earth
celestial sphere
the point on the celestial sphere directly above Earth’s North Pole
north celestial pole
the point on the celestial sphere directly above Earth’s South Pole
south celestial pole
the extension of Earth’s equator onto the celestial plane
celestial equator
the Sun’s apparent annual path among the constellations
ecliptic
the sky as seen from wherever you happen to be standing
local sky
a boundary that divides what we can see from what we cannot see
horizon
the point directly overhead, which has an altitude of 90 degrees
zenith
a half-circle extending from your horizon due south, through your zenith, to your horizon due north
meridian
one of the two coordinates needed to pinpoint an object in the local sky; the direction, such as north, south, east, or west, in which you must face to see the object
direction
the angular distance between the horizon and an object in the sky
altitude
a measure of the angle formed by extending imaginary lines outward from our eyes to span an object
angular size
a measure of the angle formed by extending imaginary lines outward from our eyes to span the space between two objects
angular distance
1/60 of 1 degree
arcminutes
1/60 of an arcminute
arcseconds
a star that always remains above the horizon for a particular latitude
circumpolar star
the angular north-south distance between Earth’s equator and a location on Earth’s surface
latitude
the angular east-west distance between the prime meridian and a location on Earth’s surface
longitude
the meridian of longitude that passes through Greenwich, England; defined to be longitude 0 degrees
prime meridian
the constellations on the celestial sphere through with the ecliptic plane passes
zodiac
the moment when the Northern Hemisphere is tipped most directly toward the Sun and receives the most direct sunlight
summer solstice
the moment when the Northern Hemisphere receives the least direct sunlight
winter solstice
the moment when the Northern Hemisphere goes from being tipped slightly away from the Sun to being tipped slightly toward the Sun
spring equinox
the moment when the Northern Hemisphere first starts to be tipped away from the Sun
fall equinox
