I think you have that backwards. Smile

Rolando



-----Original Message-----
From: Mike Dodd <mike@...>
To: main@ap-gto.groups.io
Sent: Wed, Sep 9, 2020 7:26 pm
Subject: Re: [ap-gto] Hydrogen clouds of the Bubble Nebula

On 9/9/2020 2:59 PM, Richard Hennig wrote:
> Mike, I agree that satellite’s or planes are more likely to show up
> in long sub-exposures. However, shouldn’t these trails go away when
> you stack your image using the median of each pixel or
> sigma-clipping? Those methods require that you have at least a few
> sub-exposures to stack.

Possibly, but the real issue is, you need more than a few exposures to
get a good signal-to-noise ratio. Signal increases directly with the
number of exposures, while noise, being random, increases as the SQUARE
ROOT of the number of exposures.

The more exposures, the better. and hour-long exposures limit how many
you can acquire.

--- Mike