Science

These stars are visible in broad daylight

This article is taken from Les Indispensables de Sciences et Avenir #209 April/June 2022.

A sun with an apparent magnitude (its brightness from Earth) of -26.7 doesn’t make daytime astronomical observations any easier! We can still see Venus, the Evening Star, which reaches magnitude -4.9. Then, as the Sun drops below 10° above the horizon, the human eye begins to detect less bright objects down to magnitude -2.5. A careful observer will notice Jupiter and Mars, as well as Sirius at magnitude -1.47, the second brightest star in the sky. But the stars, visible in broad daylight and to the naked eye, appeared at several points in history.

New shadows on earth

Since the thousandth year there have been five. This extraordinary spectacle is the result of supernova explosions, explosions that mark the end of the lives of massive stars, sometimes producing more light than the host galaxy’s billions of stars. The most powerful supernova in historical times, with a magnitude of -7.5 and a quarter-moon brightness, appeared around May 1, 1006 and lasted two years in the constellation of the Wolf. It was the only star other than the Sun to cast a shadow on the Earth. Shortly thereafter, in July 1054, the star Taurus began to shine down to magnitude -6. Here are some of the adventures of the Galaxy!

François Folier

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