Monday, May 14, 2018

Seven Jovian Moons in Under and Hour

On the night of May 8-9, 2018, Jupiter moved into opposition. Now officially and “evening object”, there is no better time to attempt imaging its smaller moons. Although, I was unable to successfully image the tiny satellite that was my primary objective, I did succeed in imaging seven Jovian Satellites … all within an hour’s time.

When a planet or asteroid is in “opposition,” it can be found directly opposite the sun. For the superior planets, this generally means the planet is closest to the earth as well. The combined effect of the “opposition surge,” a brightening of rough surfaces when opposite the sun, and closeness makes the days around opposition the best time to search for faint moons orbiting the planets.

I really want to image Thebe. Orbiting close to Jupiter, Thebe was discovered by the Voyager spacecraft in 1979. I can find no example of amateur imaging of Thebe. However, the satellite orbits outside the orbit of Jupiter’s closest observable satellite, Amalthea. Although it is one magnitude fainter than Amalthea, the relative ease in which I imaged Amalthea makes me hopeful that imaging Thebe is a possibility.

Unfortunately, Thebe passed through its greatest elongation only one hour after Jupiter-rise. Our planet’s thick and turbulent atmosphere thwarted my imaging attempt.

Later that evening, Amalthea passed through its greatest elongation. I had never attempted to image Amalthea with the new ZWO1600 camera or color filters. I took a number of exposures through several different filters. The most successful image was created from a stack of 50 three-second captures imaged through the luminance filter.

Jupiter and Five Satellites

Amalthea can easily be seen taking her place among her larger brothers and sisters.
Even more exciting to me is this faint star just off Jupiter’s southern limb.

Detail of Last Image showing 14th Magnitude Amalthea and a 16th Magnitude Star

Its name is GSC 06168-0775, and it is a nondescript 16th magnitude star in Libra. It made me happy because at magnitude 15.85, it is the same brightness as Thebe. Moreover, it appears closer to Jupiter than Thebe at greatest elongation. I have proven I can image Thebe. All that is left to accomplish is to actually image Thebe. Keep watching the blog to follow this ongoing sage.

Because Jupiter’s blinding light is much dimmed by the CH4 filter, I attempted to image the inner system with the CH4 filter. I didn’t get any convincing evidence of capturing Amalthea even with a 90-second exposure. In the future, I plan to attempt longer exposures.

Jovian System imaged with a CH4 Filter.

On this night, I could actually see 4th magnitude stars in my suburban sky. I decided to attempt to image Jupiter’s faint outer satellites.

Jupiter has 69 confirmed moons. Many of them may be photographed with amateur equipment. Using, JPL’s Horizon Website, I obtained the position of Jupiter’s sixth and seventh discovered satellites, Himalia and Elara. Because these tiny moons are faintly traveling through highly-populated star fields, I imaged each predicted star field 30 minutes apart. While the stars would remain static, the tiny moons would move between the exposures.

I had already successfully imaged Himalia two years ago, so I was not surprised to have captured it.

Elara, had eluded all attempts at imaging. It took me a long time to find star-like Elara moving among the stars. I was looking for faint stars, Elara surprised me with her brightness. I have now imaged 24 planetary satellites.

Although my main objective, Thebe, could not be images, enjoyed a highly successful evening. Not only did I add another elusive moon to my list of accomplishments, I now am more confident that I am able to image Thebe in the near future.

Keep Looking Up to Clear Skies.


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