When Sirius Was Red
The brightest star in the night sky shines white and blue. But ancient writers, including the astronomer Ptolemy, seem to describe it as red.
What was reported
Sirius, the Dog Star, is the brightest star in the night sky, and it shines with a clear white-blue light. Yet in the 2nd century AD, the astronomer Ptolemy, working in Alexandria, listed it alongside other stars he described as reddish. The Roman writer Seneca said it was redder than Mars.
This puzzled later astronomers. Could the star have changed colour in less than 2,000 years?
Explanations offered
Stars don't normally change colour so quickly, and Sirius's companion, a white dwarf, became a white dwarf far too long ago to explain it. Most scholars think the descriptions refer to the star's appearance near the horizon, where it flashes red and other colours as its light passes through thick air, or come from mistranslation. Not everyone is convinced.
- When
- Described about 150 AD
- Where
- Alexandria, Egypt
- Witnesses
- Ptolemy and other ancient writers
- Status
- Debated
Famous cases are real, widely reported events. Each file sets out what witnesses said and the explanations that have been offered, without taking a side.
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