02/11/2024
In the Sky: November
For those with a telescope, this November will present an opportunity to see a very rare phenomenon; the shadow of Saturn's largest moon, Titan, passing across the planet's disc. Regular observers of Saturn will have noticed that over the years, the tilt of Saturn's rings varies a lot. Sometimes they appear wide open, then slowly over the following years they narrow eventually reaching a point where they're aligned edge on to the Earth and all but disappear. This is due to Saturn's tilt relative to its orbital plane and the changing angle of view from the Earth as Saturn slowly progresses through its 29.4 year orbital cycle.
The rings have to be aligned at a very particular angle for the shadow of Titan to cross the planet's disc and we're now approaching that point. Between November and February there will be a number of transits visible. The first of these will occur on November 4th between 9 and 11pm. The shadow will only just clip Saturn's southern limb, so around 10pm it will look like a tiny bite out of the edge of the planet! On November 20th between 8pm and 11pm, there will be a better transit, with Titan's shadow passing deeper into the disc.
These Titan shadow transits should be fairly easily visible in most amateur telescopes of 75mm aperture and above if you use higher magnification. You can find Saturn very easily, it's the bright, slightly yellow object, fairly low down in the sky due south at around 10pm. It's well worth having a look as once this series of transits are done, it will be almost 15 years before the opportunity arises again!
Fortunately for transit observers, similar shadow transit events are far more common on Jupiter. One or more of its four large Galilean moons cast a shadow on Jupiter's disc every few days.