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Jul 10, 2012 · The brightest star in the sky is about as bright as a 100-Watt incandescent bulb viewed from a distance of more than 5 miles!** Even the brightest star in the sky is not very bright.
- Luminosity
- Apparent Brightness
- The Magnitude Scale
- Other Units of Brightness
Perhaps the most important characteristic of a star is its luminosity—the total amount of energy at all wavelengths that it emits per second. Earlier, we saw that the Sun puts out a tremendous amount of energy every second. (And there are stars far more luminous than the Sun out there.) To make the comparison among stars easy, astronomers express t...
Astronomers are careful to distinguish between the luminosity of the star (the total energy output) and the amount of energy that happens to reach our eyes or a telescope on Earth. Stars are democratic in how they produce radiation; they emit the same amount of energy in every direction in space. Consequently, only a minuscule fraction of the energ...
The process of measuring the apparent brightness of stars is called photometry (from the Greek photo meaning “light” and –metry meaning “to measure”). As we saw Observing the Sky: The Birth of Astronomy, astronomical photometry began with Hipparchus. Around 150 B.C.E., he erected an observatory on the island of Rhodes in the Mediterranean. There he...
Although the magnitude scale is still used for visual astronomy, it is not used at all in newer branches of the field. In radio astronomy, for example, no equivalent of the magnitude system has been defined. Rather, radio astronomers measure the amount of energy being collected each second by each square meter of a radio telescope and express the b...
But this means that if a star looks dim in the sky, we cannot tell whether it appears dim because it has a low luminosity but is relatively nearby, or because it has a high luminosity but is very far away.
Why are some stars bright and others dim? The stars are not all at the same distance from us. Some stars are closer and some are farther away. The closer a star is to us, the brighter it will appear. Also, stars come in a variety of sizes and brightnesses. Larger stars usually shine more brightly than smaller stars do.
Stars with a magnitude of 8 or more are too dim to see with the naked eye. Stars are identified by their color, which indicates their temperature. They are divided into what are known as spectral classes. These classes are O, B, A, F, G, K, and M. Class O stars are the hottest and are blue in color.
Jun 20, 2021 · In the fall of 2019, Betelgeuse — one of the brightest and best-known stars in the sky — began dimming dramatically. By February 2020, it had lost about two-thirds of its normal luminosity.
Feb 5, 2020 · The star, which forms the eastern “shoulder” of Orion, was first observed in December to be dimming. Astronomers are now closely watching the star to see if it’s about to return to its normal...
