observed this while shooting a messier object.
It is definitely not an airplane, else it would have drowned out
the relatively few photons reaching Earth from M5. He thinks
it might be a satellite, but if so it is a damned slow and odd looking
one. Zoddy says is must be "glare", but the resolution is so fine,
remember we are viewing M5 that is an invisible pinpoint of
light when viewed by eye. So what is it?

Here is the website:
https://webspace.utexas.edu/gentryml/www/astro.html