Seeing Conditions
A naked-eye test to determine the sky's transparency
(from Bob Berman's Desperately Seeking Dark, Astronomy Aug 2000)
Superb . . . . . . . You can see M33 and/or 11 or more Pleiades
Excellent . . . . . . M13, M16, M17, M35, Uranus, Orion's Belt
starfield
Very Good . . . .. M31 is obvious, M13 fades in and out, M44 is easy
Fairly good . . . . Four Little Dipper stars, M31 is so-so, M44
is so-so
Fair . . . . . . . . . . 3 Little Dipper stars, Orion's head so-so,
Only 6 Pleiades
Fair to Poor . . . 2 Little Dipper stars, No Orion's head stars
visible
Poor . . . . . . . . Only Polaris is visible
X-ray Solar Flare Classification
(from NASA Space Weather - 07/08/00)
The classification of a solar flare is based on its x-ray
energy output. Flares are classified by the Space Environment Services
Center according to the order of magnitude of the peak burst intensity
(I) measured by Earth-orbiting satellites in the 0.1 to 0.8 nanometer spectral
band as follows:
Class Peak, 0.1 to 0.8 nm band
(W/square m)
B
I < 10.0E-06
C 10.0E-06 < = I < 10.0E-05
M 10.0E-05 < = I < 10.0E-04
X
I > = 10.0E-04
[Note: 10.0E-4 means 0.0001]
C-type flares are common. M-class flares are larger and more rare.
X-class flares are even less common and are considered to be major events.
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