(The two little crescents in the above picture are the planets Jupiter and Venus. Their shape is an artifact of my camera and blowing up the picture beyond what it can manage.)

There are two definitions of the ecliptic that are easy to find. One says that the ecliptic is the plane of the earth’s orbit around the sun. Imagine a flat disk with a hole in the center where the sun is. The edge of this disk would be where the earth orbits. This is not, of course, the same as a disk stretching out from the earth’s equator. That imaginary disk is tilted.

The second definition says that the ecliptic is the apparent path of the sun across the heavens. … that road of the sun where Phaethon couldn’t control his chariot … We know that the earth is turning on its axis and that this causes the sun to appear in the east every morning and disappear in the west every evening. But to our normal senses the sun moves and we stand still. And the sun stays within a very small band in the sky. The other planets also stay very close to that same band, as does the moon.

“Very close” is not the same as identical, by the way. Only when the the path of the moon actually crosses the ecliptic plane can there be an eclipse. And yes, that is where the name came from.

Dante had no trouble with this idea but we do not pay as much attention to the sky as the medievals did. But over the past month as Jupiter and Venus have appeared in the western sky after sunset it has been easy to follow the wide band in the sky where the sun and planets make their appearance. As you can see in these pictures the planets are nearly in a straight line. They are nearly in line with the moon. They are very close to the path of the sun.

As Jupiter and Venus reached their closest approach the sideways distance between them became apparent. But afterwards they went back to looking quite linear. And after I had watched these planets for a couple of weeks I could SEE the ecliptic in a way I had never done before. Diagrams drawn to show the ecliptic are often done as though the observer is looking down on the solar system from above the North Pole. This really complicates the geometry of what is actually seen.

So here are some extra APOD pictures to look up for more entertainment.

This lovely picture of the planets, Jupiter and Venus, and the moon features the occultation of Jupiter, briefly hidden, as it passes behind the moon. See the line the three celestial objects are making. https://apod.nasa.gov/apod/ap230225.html

This picture includes the zodiacal light along with an explanation of it as Jupiter’s satellites producing dust that spirals in towards the sun. https://apod.nasa.gov/apod/ap230227.html

The closest approach of Jupiter and Venus is shown over a lovely landscape in Sicily. https://apod.nasa.gov/apod/ap230305.html (The crescent in the upper right is a trademark NOT the real moon.)

https://apod.nasa.gov/apod/ap230304.html   This picture consists of ten panels showing the position of Jupiter and Venus for ten days. Strip #2 includes the crescent moon which looks as if it is next to the planets. But if you were looking up into the whole sky you would see how close together all these celestial objects are. Jupiter began high in the sky above Venus. The two planets were ‘next’ to each other on March 1 and now Jupiter is below Venus, while Venus has risen high in the sky and is very bright after sunset.

Dante describes several different heavenly arcs. This arc is the line of light and dark that runs around the earth, pole to pole.

To that horizon had the sun now come,

an arc that circles both the hemispheres,

whose zenith stands above Jerusalem …

And Night below, in circling the same way,

rose from the Ganges …

Purgatorio, Canto 2, Esolen

Here Virgil is discussing why Dante sees the sun on his left as he looks at the dawn. He is in the Southern Hemisphere. Virgil includes the idea that the sun’s shifts north or south with changing seasons.

… [Virgil] remarked, “now if the Gemini

were in the company of the flashing mirror (the sun)

which lights from dawn to dusk across the sky,

You’d see that firestar of the zodiac (the sun again)

wheel even tighter … “

Purgatorio, Canto 4, Esolen

And one more quote from Paradise, Canto 29, Longfellow. The children of Latona are the sun and the moon, which with various constellations, are forming a zone or band around the horizon. The moon in this case is full and therefore opposite the sun. When the sun sets and the moon rises they “change their hemisphere” and Beatrice has been silent for these few moments.

At what time both the children of Latona,

    Surmounted by the Ram and by the Scales,

    Together make a zone of the horizon,

As long as from the time the zenith holds them

    In equipoise, till from that girdle both

    Changing their hemisphere disturb the balance,

So long … did Beatrice keep silence …