Question

Where is the eastern horizon, solstices and equinoxes in relation to one another?

Answer 1

Revolving-about-Sun Earth (E)-to-Sun (S) direction ES is the eastern horizon. Equinoxes are the instants when the Earth's poles are in the ecliptic. At solstices, poles are farthest from the ecliptic.

Explanation:

For the same observer, the morning East is seen as evening west, due to the Earth's day-night spin about its axis.
An equinox is the instant ( by about 21st March and 23rd September ) at which Sun is right overhead, at the location where the equator transits the ecliptic.
When this transit is farthest away from the ecliptic, it is a solstice ( by about 21st June and 21st December).