Optical SETI Map Conferences Map Illustrations Map Photo Galleries Map Observations Map Constructing Map
Search Engines Contents Complete Site Map Tech. Support Map Order Equip. Map OSETI Network

Search WWW Search www.coseti.org Search www.oseti.net Search www.photonstar.org Search www.opticalseti.org

colorbar.gif (4491 bytes)


Apparent Stellar Magnitude



The relationship between Apparent Stellar Magnitude (m) and the brightness of a star like the Sun, may be expressed in the form:

m = -[19 + (2.5).log(I)]

where I = received intensity (W/m2).


For instance, in the vicinity of the Earth, the solar power density I = 1.39 kW/m2. Plugging this value into the above equation, we find that the Apparent Solar Magnitude is -26.8. The 5 meter diameter Hale telescope on Mt. Palomar has a photographic sensitivity to "see" to +23 Magnitude, so that if we used a sufficiently narrow incoherent optical filter centered on 656 nm to cut out the planckian starlight, this telescope could just detect the mean power in the 1 kW ETI signal (9006-019) at a range of 10 light years (I = Ir = 2.04 x 10-17 W/m2), corresponding to the 23rd magnitude (uncorrected for wavelength).


The Planck radiation from the aliens' star has a received intensity Ir reduced by a factor of (1 A.U./10 L.Y.)2 compared to our Sun, and this makes the star appear as a +2 Magnitude object. Note that the 10 meter diameter Keck telescope and the 2.4 meter diameter Hubble Space Telescope (HST) can just "see" +28 Magnitude, while the naked eye can see to the 6th magnitude (9006-023).


The Columbus Optical SETI Observatory
Copyright (c), 1990

Home Glossary
SPIE's OSETI I Conference SPIE's OSETI II Conference
SPIE's OSETI III Conference
The Columbus Optical SETI Observatory
Copyright , 1990-2006 Personal Web Site:
Last modified:  10/28/06
Contact Info