Questions and bridges

How can I tell a planet from a star?

The quickest clue is twinkling: stars flicker, while planets usually glow with a steadier light. Planets also stay near the ecliptic, the path the Sun follows across the sky, and slowly shift against the stars. To be sure, check a sky map for your location and time.

Short answer

Stars twinkle; planets tend to shine steadily. Stars are so far away that they are almost perfect points of light, and Earth’s turbulent air easily bends and flickers that light. Planets are much closer and appear as tiny discs, so the flicker averages out. This is a rule of thumb, not a guarantee: low on the horizon, planets can twinkle too.

More clues

• Position. Planets travel near the ecliptic, the apparent path of the Sun. A bright light high above and far from that line is probably a star.
• Brightness. Venus and Jupiter often outshine every star. Venus is only seen in the evening or morning, never far from the Sun.
• Colour. Mars looks pale orange, Jupiter creamy white, Saturn yellowish. Some stars are reddish too, such as Betelgeuse.
• Motion. Over days and weeks planets drift against the background, while the star patterns stay the same.

The surest way

Open the Astronativa sky map and see which planets are above your horizon right now. You can read more in Which planets are visible and How to watch the sky.

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