Sky lines

In March our calendars and clocks Record the vernal equinox. The sun, our astral arbitrator, Slides over an immense equator And briefly, from that dizzy height, Grants equal time to day and night. The sun rides neatly, it appears, A highway in those starry spheres - A path someone has named ecliptic. The explanation's mighty cryptic. The whole thing has a sweeter ring Wrapped up in one glad shout: It's spring!