A Star or a Planet?

Seeing a brighter point of light prompts the question, Is it a star or a planet? Stars are light sources, great nuclear engines spewing out their electromagnetic signals into space. They are a great distance from the earth, the nearest—other than the sun—being 4.3 light-years away. Light travels at about 186,000 miles [299,000 km] per second. Because the light from stars travels so far to reach us, it becomes rather feeble. It then must pass through the increasing density of earth’s atmosphere, which bends the light rays this way and that. “Twinkle, twinkle, little star, how I wonder what you are,” says the nursery rhyme, adding a touch of animation to the silent heavens. If it twinkles, it is a star.

Planets, however, only reflect light from the sun, just as the moon does. They are relatively close to us, being fellow members of the sun’s family, the solar system. So planets that can be seen with the unaided eye reflect a light that is steady and unblinking.

Knowing you are looking at a planet is evidenced by successive nights’ viewing, as a planet will take up station in a different position in relation to the apparently fixed stars.