Equinoxes & Solstices

Question 1

what’s the plane of the ecliptic

Answer 1

the orbital plane of the sun. It’s inclined 23° from the equator

Question 2

what are the vernal and autumnal equinoxes

Answer 2

the two points in the year when the sun crosses the equatorial plane.
vernal (spring) and autumnal (autumn)

Question 3

what are the summer and winter solstices

Answer 3

the points of closest (winter) and furthest (summer) approach to the sun.

Question 4

what’s sidereal time

Answer 4

time measured according to the motion of the distant stars. its day is 4 minutes shorter (1 day per year)

Question 5

why does the vernal equinox move westward against the stars

Answer 5

the spin axis of the earth precesses due to the gravitational pull of the sun and moon acting on the equatorial bulge of the earth

Question 6

what’s a sidereal and synodic period

Answer 6

sidereal period: period with respect to the distant stars

synodic period: period with respect to the earth

Question 7

what causes the suns position to lag behind the clock time

Answer 7

1. The axial tilt of the earth causes the sun to have a north-south and east-west component of motion across the sky. clock time is based only on the east component. At the equinoxes the sun has a greater east component so leads the clock time
2. earth’s orbit is elliptical. so when it orbits faster at the perihelion the sun appears to move across the sky faster,