Why do Stars Twinkle?

Stars are, in general terms, millions of miles away from Earth. Yet we can stand outside on a night when the air is clear and see hundreds of stars. Many of these seem to “twinkle,” a term that implies slight changes in the amount of light. But is are the stars getting brighter then dimmer then brighter again as we look at them.

Stars shine with a steady light in most cases. As the gases and other elements in these celestial bodies burns and produces heat, the visible light travels across the miles until it reaches our sensitive eyes. But this light doesn’t really vary as much as it might seem when we are stargazing.

The change in brightness that we think we see is actually caused by moving air. Any slight disturbance in the atmosphere can cause these apparent changes in the level of light, producing a twinkle. The light waves that usually move in a straight line can be turned or “bent” slightly. Other light waves from the same source might move in a straighter line. The difference in the speed at which the light reaches our eyes is generally responsible for the twinkling.

Careful observation will also reveal that stars higher in the sky don’t twinkle as much as those near the horizon. This is due to the existence of more “air” closer to the horizon. The atmosphere is heavier, thicker, and denser – whatever our choice of words, there is more to move and bend the light between the star and us.

We don’t see a “twinkling” in our Sun because it is so massive and so close to the Earth. Stars we see in the night sky may be as big or nearly as big but they are much farther away. This is why we see them only as small dots of light, even with a telescope. (To give the stars some perspective in our solar system, the planets are smaller and closer.)

Sometimes we may even think that the light of a star “goes out” for a short time. This is only true in that the light doesn’t reach our eyes for a split second. Because of the turbulence in the atmosphere or pollution that can hide the light for a short time, it does appear that the star disappears.

It’s important for astronomers and other research scientists to get past this apparent twinkling. To them stars have to be considered steady sources of light, at least as they study them from earth. These scientists also see very bright moments during which the stars seem to have an unusual, momentary “spark.” Sometimes stars may even appear to have colored light.

To get a true picture of what the stars are and what they are made of, astronomers try to view and measure a star’s light as relatively steady, changing only in larger amounts over longer periods of time. Twinkling stars are just one interesting and amazing illusions that occur in our solar system.