[quote]Originally posted by Anders:
Thanks for the link j.
Went to the site mentioned on CNN and discovered that ISS is passing near me at least twice a day for the next two weeks. I just went out to see it and I would understand if people would mistake it for a UFO. Suddenly appearing in the (starless) sky, slowly moving across the sky getting brighter for a couple of minutes and then suddenly disappearing. Looking not at all like a plane (no blinking lights).
It had a magnitude of 0.9. Tomorrow it will be -0.1. Does anyone know how much more bright it will be (in relative tearms)?</strong><hr></blockquote>
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" target="_blank">heavens-above (free, no reg req)</a>
Definition of "Magnitude"
This is a measure of the brightness of a celestial object. The lower the value, the brighter the object, so magnitude -4 is brighter than magnitude 0, which is in turn brighter than magnitude +4. The scale is logarithmic, and a difference of 5 magnitudes means a brightness difference of exactly 100 times. A difference of one magnitude corresponds to a brightness difference of around 2.51 (the fifth root of 100).
The system was started by the ancient Greeks, who divided the stars into one of six magnitude groups
with stars of the first magnitude being the first ones to be visible after sunset. In modern times, the scale has been extended in both directions and more strictly defined.
** Some objects vary in magnitude **
Examples of magnitude values for well-known objects are;
Sun -26.7 (about 400 000 times brighter than full Moon!)
Full Moon -12.7
Brightest Iridium flares -8
Venus (at brightest) -4.4
International Space Station -2
Sirius (brightest star) -1.44
Limit of human eye +6 to +7
Limit of 10x50 binoculars +9
Limit of Hubble Space Telescope +30
The 15 Brightest Stars. . .
magnitude distance* \tname\t\t\t
-27\t-\tSun (aka Sol)
-0.06\t375\tArcturus (Bootes 'tail'. see below)
0.14\t815\tRigel (Yellow/White Orion 'foot')
0.80\t520\tBetelgeuse (Red giant Orion 'hand')
0.85\t68.5\tAldebaran (Red giant in Taurus)
right now, venus is magnitude -4.0 and clearly the brightest object in the evening sky (behind the moon). Jupiter is -1.7, and Mercury is -1.2, but both are too close to the sun to see without scopes now.
Antares, the red giant in Scorpio (lower sw from venus) is 1.06. Arcturus, the brightest star in Bootes (up and left from venus and straight back off the handle of the big dipper) is -.05, so the ISS will go from the apparent brightness of a non-spherical red giant 700 times the size of our sun to the apparent brightness of a star 115 times as luminous as our sun, 25 times its diameter, but only 4 times its mass. <info from Distant Suns SETI@Home edition>
according to the original <a href="http://spaceflight.nasa.gov/station/reference/index.html
" target="_blank">ISS construction plans</a> (before GWB), once completed the ISS would become the 3rd brighest object in the sky, regularly visible in daytime due to more than 400 metres of solar panels. don't expect the current lack of vision to help it become that visible.
if you're keen, check <a href="http://www.hq.nasa.gov/osf/
" target="_blank">NASA Office of Space Flight</a> for more links
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and for those who think it was the ISS the pilots were chasing, Space Radar currently tracks more than 4000 objects in orbit ranging from the ISS to wrenches that get dropped on spacewalks... they don't bother sending planes after things they already have tracking paths for... only for the unusual or unexpected traffic. while ISS is unusual, it's orbital tracks are common enough knowledge to fill updated websites with... and that pilot is gonna get razzed by the squadron after trying to catch an orbital 18000 mph 'blip'
speculation after its gone doesn't worry the air force
there'd be a lot more explaining if they'd caught