Every 14-15 years as Saturn orbits the Sun, we pass through the ring-plane of Saturn and from Earth, Saturn’s rings appear edge-on. In 2009, right now, we’re at that time. When you compare this image from early 2008, compared with this one taken almost exactly one year later (only a week ago), you can see what I mean by the rings being “edge on”.
Only during the ring-plane crossing times, do we get to witness Moon and shadow transits across the face of Saturn, as they usually pass below or above the planet from our vantage point. So on the morning of January 24th, when Saturn’s largest Moon, Titan, was due to transit, you can understand why I was hoping for clear and steady skies to capture this rare event.
Related Article: Find out when the other Titan Transits occur: Upcoming Transits of Titan at Saturn – February + March 2009
I woke at 1:30am to begin my imaging session, but before I placed the camera in the focuser, I had a look with my 5mm TMB Planetary eyepiece and saw Titan just off the disc. Within 30 minutes it would begin its crossing. The conditions weren’t great, but at that stage it was clear so I was happy to be able to capture it no matter how unsteady the skies.
Unfortunately clouds came in from the South West and my night was cut short. But I was able to capture 3 frames, and below is an animation showing Titan just on the edge of the disc, and then crossing the face.
Continue reading for more information and to see a montage of the 3 frames.
With the unsteady conditions, I wasn’t able to image Saturn at the normal resolution with the 5x powermate (approx 10 metres focal length). I stepped back to using the 2x barlow giving a focal length of approx 3.5 metres. Even at the shorter focal length, the bad seeing meant that only the red channel was sharp enough to use.
The shorter focal length did allow more light in though, changing my focal ratio from the usual f/33 to about f/11and allowing me to use 30 frames per second (fps) with a shutter of 1/30s. Gain was varied from maximum to about 90%, as clouds came and went.
I recorded for 1 minute in each channel, giving me approx 2000 frames to use, of which 500 were aligned and stacked using Registax 5 (beta). Processing included wavelets in Registax, followed by LR Deconvolution in Astra Image and final levels adjustments in Photoshop.
The three frames were made into this composite showing Titan transiting Saturn.
I’m disappointed that clouds cut my run short, but I’m happy to have captured some images of this rare event. There are a couple more Titan transits over the next few months, hopefully then I can capture a more more impressive of the rare event. More information about those transits in the next few weeks.
Chris Go, one of the world’s best planetary imagers, captured some beautiful images of the transit. Check his website to see more.
Thanks for looking.