1. is heliocentric because it means that the sun is in the center of the solar system
2. Winter solstice- the day of the year with the shortest hours of daylight- December 21 or 22
Summer solstice- the day of the year with the longest daylight- June 21 or 22
Spring equinox- the equinox in spring- march 21 or 22
Fall equinox- the time when the sun crosses the plane of the earth's equator- September 21 or 22
Hope this helps