Topic 5 Flashcards
(31 cards)
why are planets called planets
derived from the greek word ‘wanderers’ as they appeared to move in a retrograde motion (wandering away from stars’ rotation)
what’ the band where planets orbit called
zodiacal band (~8 degrees either side of ecliptic)
define retrograde motion
usually planets appear to move across the sky from west to east (towards the east)
when planets appear to move backwards (east to west) across the sky - ‘loop-the-loop’ or ‘zig-zag’
define inferior planet
mercury, venus
(planets nearer to the sun than earth)
define superior planets
mars, jupiter, saturn, uranus, neptune
(planets further from the sun than earth)
define superior conjunction
when planet is on other side of sun
PLANET
-
SUN
-
EARTH
define inferior conjunction
when planet is in between earth and sun
-can only be venus or mercury (for earth)
PLANET
-
EARTH
define opposition
SUPERIOR PLANETS ONLY
when earth is in between planet and sun
(OPTIMUM POSITION FOR OBSERVING)
EARTH
-
PLANET
what is the optimum position for a superior planet if we want to observe it
opposition
define transit
when one body passes infront of another body
define occulation
more ‘dramatic’ transit
when a body obscures and covers another and so blocks its light
define elongation
INFERIOR PLANETS ONLY
when planet is at 90 degrees to sun and earth
state the best position for an inferior planet to be in when we want to observe it
elongation
what are the 2 maximum angles of elongation called
greatest eatern elongation
greatest western elongation
which angle is the angle of elongation
angle planet-EARTH-sun
(the one between planet and sun)
effects of conjunctions and oppositions
effect visibility of planets
importance of transits
provide opportunities to study planetary atmospheres and to discover exoplanets
importance of occulations
can refine our knowledge of size and orbit of celesial bodies
why do we see retrograde motion
due to earth’s orbital speed being slower than inferior planets and faster than superior planets
how can scientists use retrograde motion
to understand relative motions of earth and other planets
what was added to the geocentric model to ensure it aligned with retrograde motion of planets
epicycles by ptolemy
what 2 factors do the changing positions of planets in the sky
-planet’s orbit
-earth’s orbit
define the ecliptic
the path which th sun follows across the year
what theory’s development was supported by the study of the ecliptic
gravitational preturbations (explains why planets deviate from a perfectly elliptical orbit)
