scientific notation
the style of writing large and small numbers using powers of ten
asteroid
(minor planet) any of the rocky objects larger than a few hundred meters in diameter (and not classified as a planet or moon) that orbits the sun
meteoroid
a small rock in interplanetary space
comet
a small body of ice and dust in orbit about the sun. while passing near the sun, a comet's vaporized ice gives rise to a coma, tails, and a hydrogen envelope.
blackhole
an object whose gravity is so strong that the escape velocity from it exceeds the speed of light
celestial sphere
a hypothetical sphere of very large radius centered on the observer; the apparent sphere of the night sky.
constellation
any of the 88 contiguous regions that cover the entire celestial sphere, including all the objects in each region; also, a configuration of stars named after an object, a person, or an animal.
celestial equator
a great circle on the celestial sphere 90 degrees from the celestial poles
celestial poles
points about which the celestial sphere appears to rotate
north celestial pole
the location on the celestial sphere directly above the Earth's northern rotation pole.
south celestial pole
the location on the celestial sphere directly above the Earth's south rotation pole.
declination (dec)
the coordinate on the celestial sphere analogous to latitude on Earth; measured north and south of the celestial equator.
right ascension (r.a.)
the celestial coordinate analogous to longitude on Earth and measured around the celestial equator from the vernal equinox
vernal equinox
the point on the ecliptic where the sun crosses the celestial equator from south to north; the beginning of spring, around March 21.
rotation
the spinning of a body about an axis passing through it
diurnal motion
cyclic motion with a 1-day period
revolution
the orbit of one body about another.
arc angle
the measurement of the angle between 2 objects or 2 parts of the same object
angle
the opening between 2 straight lines that meet at a point
degree
a unit of angular measure of a temperature measure
angular diameter (angular size)
the arc angle across an object
sidereal period
the orbital period of one object about another measured with respect to the stars
zenith
the point on the celestial sphere directly overhead
circumpolar stars
all the stars that never at a given latitude; all the stars between Polaris and the northern horizon
ecliptic
the annual path of the sun on the celestial sphere; the plane of the earth's orbit around the sun
equinox
either of the 2 days of the year when the sun crosses the celestial equator and is therefore directly over the earth's equator
winter solstice
the point on the ecliptic where the sun is farthest south of the celestial equator; fewest hours of daylight in the northern hemisphere, around December 22
summer solstice
the point on the ecliptic where the sun is farthest north of the celestial equator; the day with the largest number of daylight hours in the northern hemisphere, around june 21
autumnal equinox
the intersection of the ecliptic and the celestial equator where the sun crosses the equator moving from north to south. the beginning of autumn.
zodiac
a band of 13 constellations around the sky through which the sun appears to move throughout the year
solar day
from noontime to the next noontime; it is 24 hours
time zone
one of 24 divisions of the earth's surface separated by 15 degrees along lines of constant longitude (with allowances for some political boundaries)
gravitation (gravity)
the tendency of all matter to attract all other matter
precession
(of the Earth) a slow, conical motion of the earth's axis of rotation caused by the gravitational pull of the moon and sun on the earth's equatorial bulge
precession of the equinoxes
the slow westward motion of the equinoxes along the ecliptic because of the earth's precession
lunar phases
the names given to the apparent shapes of the moon as seen from earth
terminator
the line dividing day and night on the surface of any body orbiting the sun; the line of sunset or sunrise
sidereal month
the period of the moon's revolution about the earth measured with respect to the moon's location among the stars; 27 1/3 earth days
synodic month (lunar month)
the period of revolution of the moon with respect to the sun; the length of one cycle of lunar phases; 29 1/2 earth days
lunar eclipse
an eclipse during which the earth blocks light that would have struck the moon
solar eclipse
an eclipse during which the moon blocks the sun
line of nodes
the line along which the plane of the moon's orbit intersects the plane of the ecliptic
umbra
the central, completely dark portion of a shadow
penumbra
the portion of a shadow in which only part of the light source is covered by the shadow-making body
penumbral eclipse
a lunar eclipse in which the moon passes only through the earth's penumbra
partial eclipse
a lunar or solar eclipse in which the eclipsed object does not appear completely covered
total eclipse
a solar eclipse during which the sun is completely hidden by the moon, or a lunar eclipse during which the moon is completely immersed in the earth's umbra
solar corona
the sun's outer atmosphere
eclipse path
the track of the tip of the moon's shadow along the earth's surface during a total or annular solar eclipse
annular eclipse
an eclipse of the sun in which the moon is too distant to cover the sun completely so that a ing of sunlight is seen around the moon at mid-eclipse
transit
when a star is in transit, it is passing over your celestial meridian (not all stars rise and set - circumpolar)