Question: How can you tell a planet from a star? Stars twinkle but planets don't, right? Not quite. Twinkling is caused by turbulence in our atmosphere. It tends to affect stars more than planets because stars are further away and have narrower beams of light. But planets can twinkle too especially if they are lower in the sky. So what's a better way to tell a planet from a star?
The first step is to use location: planets are always found along the ecliptic, an imaginary line in our southern sky that stretches E to W (see above). It marks the plane of the solar system upon which the planets orbit our sun.
Tap the toggle button to see that the ecliptic is high in winter and low in summer. This is due to earth's tilt as it orbits the sun. Notice that the ecliptic goes through a special set of constellations known as the zodiac, or the circle of animals, since many of these constellations are named for animals.
The second step is to look for movement. The word 'planet' means 'to wander'. Stars appear fixed in constellations but planets move eastward through the zodiac. But don't expect to see planets move in realtime. Instead, it may take days or even weeks to detect a change of location within a constellation.
The next time you are stargazing, look south, imagine the ecliptic and look for possible planets. The Starry Hill Stargazing Calendar gives month-by-month info on when and where to view planets. Be sure to check out the other topics below.
