Despite the bright Moon dominating the evening sky, I needed to take advantage of another clear sky. So what better object to image than the Moon itself. Now, look at the black sky around it. There are no stars visible – but we know there definitely are several background stars within the field of view!
The brightest one is called HD 108978 and you can’t see it.
Why? Because to properly expose the bright reflected sunlight from the lunar surface, the shutter timer needs to be set very short, in this case around 1/12th of a second – and that is not nearly long enough exposure time to record the stars.
So that is why all those images taken on the Moon, taken five decades ago by the Apollo astronauts, did not feature any stars!
😲 Strange Coincidence
The area of the whole sky covers a huge 41,253 square degrees but coincidentally my lunar image, which is less than 2/3rds of one square degree, also contains the exact location of Quasar 3C273, which I imaged only last month.
If it were bright enough to be seen in this exposure, it would appear just below the Moon’s lower left quadrant.
|Exposure:||60 x 0.085 sec stacked (best 20% of video frames from 300)|
|Lunar Diameter (Apparent)||32.8 arc-sec|
Telescope & Imaging Details
|SkyWatcher Esprit 120 mm apochromatic 3-element refractor; 840 mm f/l @ f/7.|
|Field flattener; ZWO Duo-band Hα (656nm) and [OIII] (500nm) filter.|
|SkyWatcher EQ6-R Pro mount; ZWO ASI120 guide camera.|
|Imaging camera: ZWO ASI 071 MC Pro (CMOS 28.4mm 16 Mpx).|
|Software: Telescope control: Cartes du Ciel, EQMOD, PHD2, Imaging: SharpCap, AutoStakkert, Gimp.|
|Observatory location: 34° South.|
Thanks for reading! 🙃
Images © Roger Powell
I’m one of the founder members of Macarthur Astronomical Society and current webmaster.