ASTR 250 MIDTERM TEST WITH VERIFIED ANSWERS #15
Horizon Coordinate System - correct answer A Celestial Coordinate System, uses the
observer's local horizon as the fundamental plane, measures the altitude of a celestial
body above the horizon and the compass direction. Altitude is the angular distance of a
celestial body above the horizon, measured along a vertical circle. Azimuth is angle of
the object around the horizon, usually measured from the north point towards the east.
Celestial Coordinate System - correct answer a coordinate system for mapping
positions on the celestial sphere. Not relative to position of observer.
Right Ascension (RA) - correct answer Analogous to longitude, but on the celestial
sphere; the angular east-west distance between the spring equinox and a location on
the celestial sphere.
Declination (DEC) - correct answer Analogous to latitude, but on the celestial sphere; it
is the angular north-south distance between the celestial equator and a location on the
celestial sphere.
North and South Celestial Poles - correct answer the points in the sky directly above the
Earth's North and South poles
Ecliptic - correct answer Plane that contains Earth's orbit around the Sun.
Vernal Equinox - correct answer the day of the year that marks the beginning of spring
in the northern hemisphere. March 21st
Solar day - correct answer the time between successive meridian transits of the sun at a
particular place.
Sidereal day - correct answer the time for one complete rotation of the earth relative to a
particular star, about 4 minutes shorter than a mean solar day
Astronomical Unit (AU) - correct answer the average distance between the earth and
the sun. 1.5 x 10⁸ km
Heliocentric - correct answer sun-centered
Inferior conjunction - correct answer A conjunction of an inferior planet that occurs when
the planet is lined up directly between the Earth and the Sun.
Superior conjunction - correct answer A conjunction that occurs when an inferior planet
passes behind the Sun and is on the opposite side of the Sun from the Earth.
Opposition - correct answer when a superior planet is directly behind the earth with
respect to the sun.
, Elongation - correct answer the angle between the sun and a planet as viewed from
earth
Kepler's First Law - correct answer The orbit of each planet around the Sun is an ellipse
with the Sun at one focus.
Kepler's Second Law - correct answer As a planet moves around its orbit, it sweeps out
equal areas in equal times
Kepler's Third Law - correct answer The square of the orbital period of a planet is
directly proportional to the cube of the semi-major axis of its orbit.
Eccentricity - correct answer ratio of the distance between the foci to the length of the
major axis; defines the shape of a planet's elliptical orbit.
Perihelion and Aphelion - correct answer The closest/farthest point from the Sun on a
planet's orbit.
Semimajor axis - correct answer half of the longest diameter across an ellipse
Escape velocity - correct answer The velocity an object must reach to fly beyond a
planet's or moon's gravitational pull.
Local Sidereal Time (LST) - correct answer time since vernal equinox last passed the
local longitude
Exoplanet - correct answer A planet outside of our Solar System.
Exoplanet detection methods - correct answer Transit, Direct Imaging, Radial Velocity
Transit exoplanet detection - correct answer observing change in amount of light as
exoplanet passes in front of star
Direct Imaging Exoplanet Detection - correct answer Seeing an exoplanet directly
through a telescope
Radial velocity exoplanet detection - correct answer a technique used to detect
extrasolar planets by observing Doppler shifts in the spectrum of the planet's star
Light curve - correct answer graph of light intensity vs time as a planet or other star
moves in front of a star
Hot jupiter - correct answer a class of planet that is Jupiter-like in size but orbits very
close to its star, causing it to have a very high surface temperature
Horizon Coordinate System - correct answer A Celestial Coordinate System, uses the
observer's local horizon as the fundamental plane, measures the altitude of a celestial
body above the horizon and the compass direction. Altitude is the angular distance of a
celestial body above the horizon, measured along a vertical circle. Azimuth is angle of
the object around the horizon, usually measured from the north point towards the east.
Celestial Coordinate System - correct answer a coordinate system for mapping
positions on the celestial sphere. Not relative to position of observer.
Right Ascension (RA) - correct answer Analogous to longitude, but on the celestial
sphere; the angular east-west distance between the spring equinox and a location on
the celestial sphere.
Declination (DEC) - correct answer Analogous to latitude, but on the celestial sphere; it
is the angular north-south distance between the celestial equator and a location on the
celestial sphere.
North and South Celestial Poles - correct answer the points in the sky directly above the
Earth's North and South poles
Ecliptic - correct answer Plane that contains Earth's orbit around the Sun.
Vernal Equinox - correct answer the day of the year that marks the beginning of spring
in the northern hemisphere. March 21st
Solar day - correct answer the time between successive meridian transits of the sun at a
particular place.
Sidereal day - correct answer the time for one complete rotation of the earth relative to a
particular star, about 4 minutes shorter than a mean solar day
Astronomical Unit (AU) - correct answer the average distance between the earth and
the sun. 1.5 x 10⁸ km
Heliocentric - correct answer sun-centered
Inferior conjunction - correct answer A conjunction of an inferior planet that occurs when
the planet is lined up directly between the Earth and the Sun.
Superior conjunction - correct answer A conjunction that occurs when an inferior planet
passes behind the Sun and is on the opposite side of the Sun from the Earth.
Opposition - correct answer when a superior planet is directly behind the earth with
respect to the sun.
, Elongation - correct answer the angle between the sun and a planet as viewed from
earth
Kepler's First Law - correct answer The orbit of each planet around the Sun is an ellipse
with the Sun at one focus.
Kepler's Second Law - correct answer As a planet moves around its orbit, it sweeps out
equal areas in equal times
Kepler's Third Law - correct answer The square of the orbital period of a planet is
directly proportional to the cube of the semi-major axis of its orbit.
Eccentricity - correct answer ratio of the distance between the foci to the length of the
major axis; defines the shape of a planet's elliptical orbit.
Perihelion and Aphelion - correct answer The closest/farthest point from the Sun on a
planet's orbit.
Semimajor axis - correct answer half of the longest diameter across an ellipse
Escape velocity - correct answer The velocity an object must reach to fly beyond a
planet's or moon's gravitational pull.
Local Sidereal Time (LST) - correct answer time since vernal equinox last passed the
local longitude
Exoplanet - correct answer A planet outside of our Solar System.
Exoplanet detection methods - correct answer Transit, Direct Imaging, Radial Velocity
Transit exoplanet detection - correct answer observing change in amount of light as
exoplanet passes in front of star
Direct Imaging Exoplanet Detection - correct answer Seeing an exoplanet directly
through a telescope
Radial velocity exoplanet detection - correct answer a technique used to detect
extrasolar planets by observing Doppler shifts in the spectrum of the planet's star
Light curve - correct answer graph of light intensity vs time as a planet or other star
moves in front of a star
Hot jupiter - correct answer a class of planet that is Jupiter-like in size but orbits very
close to its star, causing it to have a very high surface temperature
