Observing the Sky: Observing the Planets - Introduction

Five planets can be seen in the night sky without the help of binoculars or a telescope. Planets look a lot like stars, but you can learn to tell them apart. One way is by how much they twinkle. Stars often do, planets don't. Stars are huge balls of burning gas, but because they are so far away, they appear as little points of light. This little bit of light has to pass through the Earth's thick atmosphere to reach your eyes. The atmosphere is very turbulent, meaning it moves a lot. This motion can actually shift the starlight in and out of view, making the stars seem to twinkle. Planets are much closer to Earth and so we can see them as discs of light, not points. With a bigger image coming to your eye, the atmosphere does not have as much of an effect.

Like the stars, planets appear to move across the sky from East to West each night. But over the course of days and weeks, the planets seem to wander among the stars, usually moving from West to East, just like the Sun. In fact, the word planet comes from the ancient Greek word for "wanderer." However, the planets never wander far from the ecliptic (the path the Sun takes) because they all orbit the Sun on approximately the same plane.