I know about the magnitudes for measuring light and that my city is about a 4.5 and that irridium flares and shuttle passes can be as bright at -6 or so, but I was wondering about the scale and is there something that is considered a magnitude zero used as a point of scale and if so, what is that object? I have been doing this for several years now and I never thought or been told what a magnitude zero might be. Just wondering.
2007-11-05 14:31:41 · 4 answers · asked by B. 7 in Science & Mathematics ➔ Astronomy & Space
Alpha Centauri A, Arcturus, Capella, and Vega are all within 1/10 of a magnitude of 0.0.
2007-11-05 14:46:01 · answer #1 · answered by GeoffG 7 · 0⤊ 0⤋
Astronomy.com, space.com, or wikipedia all have some good information on apparent magnitude.
The scale originally was determined by dividing the stars visible to the naked eye into six magnitudes. The brightest stars were first magnitude, while the faintest were sixth magnitude (the limit of human visual perception without the aid of a telescope).
Each grade of magnitude was considered to be twice the brightness of the following grade (it is a logarithmic scale).
This method was popularized by Ptolemy, and is believed to have originated with Hipparchus. This original system did not measure the magnitude of the Sun.
In 1856, Pogson formalized the system by defining a typical first magnitude star as a star that is 100 times as bright as a typical sixth magnitude star. So a first magnitude star is about 2.512 times as bright as a second magnitude star.
The scale was originally fixed by assigning Polaris a magnitude of 2. Astronomers later discovered that Polaris is slightly variable, so they first switched to Vega as the standard reference star, and then switched to using tabulated zero points for the measured fluxes. The magnitude depends on the wavelength band.
The modern system is no longer limited to 6 magnitudes or only to visible light. Very bright objects have negative magnitudes. For example, Sirius (the brightest star in our night skies), has an apparent magnitude of −1.47.
The full Moon has an apparent magnitude of −12.6 and the Sun has an apparent magnitude of −26.73.
The Hubble Space Telescope has located stars with magnitudes of 30 at visible wavelengths and the Keck telescopes have located similarly faint stars in the infrared.
2007-11-05 14:54:56 · answer #2 · answered by Anonymous · 1⤊ 0⤋
The zero point by definition : VEGA.
This is the only reference I have found.
http://en.wikipedia.org/wiki/Apparent_magnitude
2007-11-05 17:25:31 · answer #3 · answered by TicToc.... 7 · 0⤊ 0⤋
vega?
2007-11-05 14:42:05 · answer #4 · answered by dong3000s 2 · 0⤊ 0⤋