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Ephemeris: 02/12/2026 – Why do planets stop and move backward for a time? Part 1

February 12, 2026 Comments off

This is Ephemeris for Darwin Day, Thursday, February 12th. Today the Sun will be up for 10 hours and 19 minutes, setting at 6:07, and it will rise tomorrow at 7:45. The Moon, 3 days past last quarter, will rise at 5:49 tomorrow morning.

For the last month or so I’ve been talking about Jupiter in its retrograde or westward motion against the stars of Gemini. This motion isn’t due to just Jupiter itself. Jupiter orbits smoothly around the sun in one direction, in a little less than 12 years. The ancients thought that the earth was stationary, and everything in the sky orbited the earth. They thought that the planets orbited the earth in the same time that the planet orbits the sun, however every year and depending on where the planet was in the sky it would stop, reverse itself for a while and then resume its eastward motion through the sky. They thought that the planet moved on a small circle called an epicycle that rode on the larger circle called the deferent.

The astronomical event times given in this blog are for the Traverse City/Interlochen area of Michigan (Lat 44.7° N, Long 85.7° W; EST, UT – 5 hours) unless stated otherwise. Times will be different for other locations.

Addendum

A geocentric chart of the solar system.
The geocentric universe as imagined by the ancients with the Earth in the center. The outer ring is the celestial sphere of the stars. The other concentric circles around the Earth are deferents for each of the planets. Note that the line from the deferent to the planet on the epicycle is parallel to the line of the earth to the sun. One would think that screams the fact that somehow the Earth was in motion. But only the Greek astronomer Aristarchus figured it out. Then that idea was discarded until Copernicus in the 15th century of the modern era resurrected the idea.

Tomorrow, we’ll find out what’s really going on.

Categories: Concepts, Ephemeris Program, Planets Tags: ,