FreeLists / az-observing / [AZ-Observing] ISS, Then HST

[Tom Polakis <tpolakis@xxxxxxx>]

Thanks for Randy Peterson for alerting us to tonight's nice passes of the two 
bright satellites.  ISS came first, passing nearly overhead.  It became 
brighter than Mars, maybe reaching magnitude -2 or so.

HST was next; it flared to nearly this same brightness when it was low in the 
west until settling to magnitude 2, and eventually nearly magnitude 0 as it 
crossed the meridian.  It flared again when it was a minute or so east of the 
meridian.  HST disappeared into the shadow very low in the southeast.

Now, it looked to me like HST was traveling much more slowly than ISS, which I 
explained as being due to orbital height.  Heavens Above shows that HST 
averages 566km above the surface, while ISS averages 347km.  It also shows that 
HST completes 15.0 revolutions per day compared to 15.7 for ISS.  I thought 
those numbers would also be much different, so the slower apparent motion of 
HST must be due mostly to its greater distance from the observer.

Tom

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