Jovian Moon - Himalia


Aside from the well known Galeliian moons, Io, Europa, Ganymeade and Callisto, Jupiter boasts many minor moons. I've decided to see which of these can be tracked down using my F5 200mm Inch newtonian and modified Toucam.

The first one to go for is the easiest. Himalia is an 85km wide lump of rock in a large orbit around jupiter which takes it around the gas giant once every 250 earth days. This means it moves much much further from the main planet. This is a Good Thing. Himalia is about magnitude 15.10 currently, and if it was close to the planet, it would be very difficult to pick out of the background planet glow.

Finally on March 16th between 22:15UT and 23:15UT I had some very rare clear skies, and was able to attempt to capture this faint moon. I had recently taken delivery of a focal reducer... and this produced a decision. Using the FR I would have a much greater chance of recognising the starfield and checking I was in the right area. Also, dim targets would show up better. However, it would mean that any movement of the moon would be harder to detect, and the glow from jupiter would be increased. I decided to start with the FR, mainly because it would make it easier to find the starfield.

How was I going to know if I was in the right place and looking at the right object?

1. Get hold of a decent ephemeris from the internet. For this datetime, I found the following information:
2004-Mar-16 21:00 10 57 43.4500,+08 42 07.379, 10 57 57.2548,+08 40 44.782
2004-Mar-16 22:30 10 57 42.0192,+08 42 15.528, 10 57 55.8267,+08 40 52.945
2004-Mar-16 23:00 10 57 41.5415,+08 42 18.236, 10 57 55.3495,+08 40 55.658
The first coords are true astrometric coords, and the second bunch are, I quote, Airless apparent right ascension and declination of the target with respect to the Earth true-equator and meridian containing the Earth true equinox of date. Corrected for light-time, the gravitational deflection of light, stellar aberration, precession and nutation
That should cover everything I guess!
2. Using this info I could then figure out the starfield to aim for in skymap. 3. Finally I would compare to the Digital Sky Survey images of the area.

There is resulting image. About 100 stacked 20 second exposures.

The slighly elongated object marked in red is, I feel, not a star.
Why? First of all, its obviously elongated. Secondly, compare with the digital sky survey image below:

Page last updated 2004-02-18