Titan and Iapetus

The planet Saturn with moons Titan and Iapetus on display. Canon 600d DSLR with Samyang 135 F2 ED lens on a Star Adventurer EQ mount. 12x60sec lights at ISO800 stacked using AffinityPhoto software. Overlay of star field data courtesy of Astrometry net. Credit: Karl Sequine and UNWISE

Annotated star field Credit: Stellarium

 " Whilst we were calibrating our set up for imaging NGC7000 we tested by imaging the planet Saturn which was low on our southern horizon. We believed that we had captured two of Saturn's moons, Titan and Iapetus but we were unable to identify them within the star-field. We decided to upload the our image to the Astrometry net plate solver which identified the main stars in the constellation Capricornus but unfortunately did not annotate Saturn's moons. The plate solving software did however provide an overlay from the  unWISE survey data which Kurt realised would not include Saturn or its moons because the position of planets against the unchanging starry back-drop varies with time. Pip Stakkert took this forward by using software to 'blink' between the two images. Saturn and it's two moons then just 'popped' into view.

Our home-made 'Blink Comparator'

Titan is the largest moon of Saturn and the second-largest natural satellite in the Solar System. It is the only moon known to have a dense atmosphere, and is the only known object in space other than Earth on which clear evidence of stable bodies of surface liquid has been found.

Titan (false colour) Credit: ESA- Cassini

Iapetus s the third largest moon of Saturn. It has an orbit much further out than Titan and has an inclined orbit when compared with Saturn's other large moons. We were extremely lucky to have captured Iapetus with our simple camera lens set up. Iapetus can only be captured when it is at maximum western elongation in its orbit when viewed from Earth. We can only see the planets and their moons by means of reflective sunlight. Their brightness is determined by their size, distance and albedo (how much incident light is reflected). Venus is very bright because it is roughly the same size as Earth, is a near solar system neighbour close to the Sun and has a atmosphere full of clouds that are highly reflective of sunlight. Iapetus has a bright hemisphere and a dark hemisphere and is tidally locked to Saturn. We can see its bright reflective hemisphere at 'western elongation' and we see (or actually cannot see) its dark hemisphere at 'eastern elongation. We were lucky to capture our images at approximately maximum western elongation. Iapetus also looks like the 'Death Star' and how cool is that?" - Karl Sequine Out-reach Coordinator at the Jodrell Plank Observatory

Iapetus Credit ESA- Cassini