logoalt Hacker News

erutoday at 3:10 AM1 replyview on HN

Well, the brightness of celestial objects is also sometimes negative:

> The apparent magnitude of known objects can range from −26.832 for our Sun to about +31.5 for objects in deep space imaged by the Hubble Space Telescope.[3]

See https://en.wikipedia.org/wiki/Apparent_magnitude


Replies

Sharlintoday at 10:51 AM

And this is because Ptolemy’s catalog in which he ranked stars by their apparent brightness on a scale of one to six, one being the brightest. Ptolemy’s scale was (much later) retrofitted to a log scale (base 100^(1/5) or about 2.512), allowing extrapolation to both brighter and dimmer objects. The brightest of Ptolemy’s first-magnitude stars actually have negative magnitudes by the modern definition.