Two important sky paths intersect on the eastern and western horizons as night falls now: the ecliptic and the celestial equator.
The ecliptic is much easier to trace. It marks the Sun’s path across the sky. That path held great significance for many cultures, so they gave extra weight to the constellations it crossed – the constellations of the zodiac.
As night falls, the ecliptic arcs near a couple of the zodiac’s more prominent star patterns. It passes close above the “teapot” outlined by the stars of Sagittarius. And it nicks the “head” of Scorpius, with most of the scorpion’s body below it.
The Moon and planets all stay close to the ecliptic as well. As twilight fades this evening, for example, brilliant Venus is quite low in the west, with fainter Saturn about the same height in the east.
The equator is harder to see. It’s the projection of Earth’s equator on the sky, so it divides the sky into northern and southern hemispheres. Its closest bright star in early evening is Altair, which is high in the southeast. It’s in the northern half of the sky.
The equator maintains the same angle across the sky every hour of every day. But the ecliptic changes position as the night rolls on. It also shifts position from day to day. The two paths intersect along the horizon at some time during every day of the year. But they come together at nightfall only a couple of times a year – near the fall and spring equinoxes.
Script by Damond Benningfield