With a long slit orientated

Forums Venus Ashen Light and Spectroscopy With a long slit orientated

Robin Leadbeater

With a long slit orientated appropriatelyand a suitable image scale you might be able to get all you need in one shot (Well 2, one exposed for the bright side)  You would need a  flat field illumination source which is nice and even in the slit direction so  the subtractions work accurately. 

Funnily I was just reading Paul Abel’s beginners article on Earthshine and musing about  measuring that spectroscopically, perhaps mounting the spectrograph behind a camera  lens to get a sensible image scale to match the slit. Much easier than Ashen Light though !