Table Talk: Naked Eye Observations

Historically, the zenith of naked-eye astronomy was the work of Tycho Brahe (1546–1601), who built an extensive observatory to make precise measurements of the heavens without any instruments for magnification.

Under typical dark sky conditions with a minimum of light pollution, the naked eye can see stars with an apparent magnitude of up to 6 on the apparent magnitude scale.

The scale now used to indicate magnitude originates in the Hellenistic practice of dividing stars visible to the naked eye into six magnitudes. The brightest stars were said to be of first magnitude (m = 1), while the faintest were of sixth magnitude (m = 6), the limit of human visual perception, the naked eye (without the aid of a telescope). Each grade of magnitude was considered twice the brightness of the following grade (a logarithmic scale). This somewhat crude method of indicating the brightness of stars was popularized by Ptolemy in his Almagest, and is generally believed to originate with Hipparchus. This original system did not measure the magnitude of the Sun. The scale works in retrospect, rather the brighter the star, the smaller the grade of magnitude, where the sun would be an apparent magnitude of -26, and as we know, the naked eye would be damaged by direct observation of the sun's brilliance.

Some of the faint light of distant stars and planets which would be perceived with color are not perceived by the naked eye with color due to the detection of weak optical signals by the neurons within the human visual system which are detected by optic nerve rods rather than cones.

There is also a consideration of dark stars, how they are detected and how to determine which is the darkest star. I'll write about that another time. But so far, since the observation cannot be made with the naked eye, and a dark star is a dark matter, here is one candidate for The Darkest Star: