Ready? Set? Let’s try to imagine the ecliptic, or sun’s yearly path across our sky. Three bright stars and two planets in the June evening sky can help you find the ecliptic crossing your sky tonight.
The video below does a good job at showing the ecliptic for what it really is. It’s really a function of Earth’s orbit around the sun, but appeared to the early stargazers as simply the sun’s yearly path in front of the backdrop stars. They thought the Earth was stationary, while the sun revolved around it. But of course Earth goes around the sun, and the sun’s apparent motion through the heavens is a reflection of our planet’s orbit.
So astronomers use the word ecliptic to mean both the imaginary great circle etched onto the surface of an imaginary celestial sphere, and the plane of Earth’s orbit around the sun. The ecliptic is a projection of Earth’s orbital plane onto the stars. We call those special stars and constellations along the sun’s annual path the zodiac.
Because the solar system planets orbit the sun on nearly the same plane that the Earth circles the sun, practiced sky gazers know to look for the planets on or near the ecliptic.
In June 2017, let two brilliant planets and three bright stars of the zodiac (Regulus, Spica and Antares) introduce you to the ecliptic in the evening sky. The moon passes all these bright celestial streetlights of the zodiac once every month. For instance, you’ll see tonight’s waxing crescent moon (on June 1, 2017) between between dazzling Jupiter, the brightest starlike object in the evening sky and Regulus, brightest star in Leo the Lion. Watch for the moon to pair up with Jupiter on June 3 and then sparkling blue-white Spica on June 4. Yes, that star to the immediate east of Jupiter is Spica, the brightest star in the constellation Virgo the Maiden.
Look in the southeast at nightfall or early evening to see the planet Saturn and the star Antares quite close to horizon. Practiced sky gazers might even want to try finding Zubenelgenubi, the modestly-bright star in the constellation Libra the Scales, in between Spica and Antares.
Now … draw an imaginary arc across the great vault of the heavens, using these bright lampposts. That imaginary semicircle crossing the sky’s dome marks the ecliptic, or sun’s annual path in front of the constellations of the zodiac, as shown in green on our charts.
Bottom line: Spot two brilliant planets and three bright stars. Then use your mind’s eye to imagine the ecliptic, or sun’s path, crossing your night sky.