Ready? Set? Let’s try to imagine the ecliptic, or sun’s yearly path across our sky. Then I’ll point out some planets in the evening sky that can help you find the ecliptic, in your night sky.
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 also to mean 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 summer, 2016 – or winter, 2016 if you’re in the Southern Hemisphere – three brilliant planets (Jupiter, Mars Saturn) and three bright stars of the Zodiac (Regulus, Antares, Spica) can introduce you to the ecliptic in your night sky.
First, look westward for dazzling Jupiter, the brightest starlike object in the evening sky. Below Jupiter, fairly low in the sky, you’ll find Regulus, brightest star in Leo the Lion. Regulus sinks below the horizon as evening deepens, so catch this star at nightfall, if you can.
Next, look for Mars. It’s the second-brightest “star” to grace the nighttime, after Jupiter. From the Northern Hemisphere, Mars shines relatively low in the southern sky at nightfall and early evening. From the Southern Hemisphere, it appears high in the north, nearly overhead by mid-evening.
Finally, star hop from Mars to the nearby planet Saturn and the ruddy star Antares. They are located to Mars’ east. Then, in between Mars and Jupiter, look for sparkling blue-white Spica, the only bright star to shine in between these two brilliant worlds.
Practiced sky gazers might even want to try finding Zubenelgenubi, the modestly-bright star to the west of Mars.
Now … draw a line between all of these objects. That imaginary line on your sky’s dome will mark the ecliptic or sun’s path, shown in green on our charts.
Bottom line: Spot three brilliant planets and three bright stars. Then use your mind’s eye to imagine the ecliptic, or sun’s path, crossing your night sky.