Heavens-above indicates that this evening, it will fly almost over my head (79°) with a sizzling magnitude of -3.9. What is the maximum brightness it can have?
Is there a formula to calculate its lowest magnitude, theoretically?
Heavens-above indicates that this evening, it will fly almost over my head (79°) with a sizzling magnitude of -3.9. What is the maximum brightness it can have?
Is there a formula to calculate its lowest magnitude, theoretically?
The ISS maximum brightness is reported at about -5.9, sometimes -6. I guess you could technically estimate it analytically by considering how much light it receives, but I imagine that would be messy to get accurate.
Here you can see an archived version of the original fact sheet by heavens-above, where the maximum is given as -5.7: https://web.archive.org/web/20090705134152/http://heavens-above.com/satinfo.aspx?SatID=25544
I believe whoever came up with the -5.9 value simply observed the ISS when it's best lit by the sun and the Earth is in perihelion (closest to the sun in its orbit).
Personally, I've only seen the ISS once, the night of 29/04/22 when it shined at -2.4.