Posts tagged 'Opposition'

Observing Report 3rd-4th April 2011 (Saturn in opposition)

Posted by on April 6th 2011 in Astrostuff, Observing Reports, Pics

Once a year the Earth passes almost exactly between the Sun and Saturn, at this time Saturn is said to be in opposition (Saturn and the Sun are directly opposite each other relative to an Earth-bound observer). With the Earth being "piggy in the middle", it stands to reason that at that time Saturn will be illuminated almost exactly face-on from behind the Earth, and this causes an interesting phenomenon, The Seeliger Effect. This is an apparent relative brightening of Saturn's rings due to the fact that we don't see so many shadows between the rings and between the ring particles.

This year's opposition occurred at 01:00 BST (00:00 UTC) on the 4th of April. I managed to get several imaging runs of it during the period one hour either side of the actual opposition, typically at the exact time there were clouds in the way so time-wise the closest I could manage was at about 00:10 BST:


Saturn in opposition
8" Newtonian, SPC900NC webcam, eyepiece-projection.
300/5400 frames stacked with RegiStax6, post-processing with PSCS3

Observing Report 29th-30th January 2010 (Mars just after Opposition)

Posted by on January 31st 2010 in Astrostuff, Observing Reports

The original plan was to observe Mars on the 27th, the night of its closest approach to Earth (the closest approach distance was 0.664 AU (99.33 million km), giving Mars an apparent diameter of 14.105") but the skies were cloudy so the deal was off. Instead, I had to be content with observing just after opposition on the 29th when the skies were nice and clear, the reflected light-pollution was minimal and the seeing was good. The only downside was that the Moon was almost full and visually quite close to Mars, so the sky wasn't as dark as usual. It was damned cold here, but I wasn't about to let the falling temperatures get in the way of seeing Mars at such close quarters.

Before opening the obsy roof I had to put the fan-heater on for a few minutes to warm up the mount as it had been iced-up for a couple of days and it doesn't like starting in the cold (ice in the gears isn't a good thing). After that it was a doddle, except for the frost that formed on everything unheated. The scope was soon pointing at Mars and I cranked-up the new camera.

This time I was trying something different - using RGB filters and a mono camera. This meant grabbing filtered avi data-runs for each of the three colour-channels and another for the luminance-channel... all within a four(ish)-minute period so as to minimise any image-blurring due to Mars' rotation. After a few failed attempts I managed to get the suss on it, and after that the data-sets were quite easy to get, if a tad rushed.

Soon it was time to move on. I had a good look at the Moon but didn't think it merited any camera-work, as the surface-contrast was low due to the face-on illumination. Still, it was fun trying to find the Apollo landing areas. Next time out I might try for some images of them, just for the hell of it.

After an hour indoors to warm up, I went back out and slewed the scope around to Saturn. This time the rings were more open so I grabbed some filtered avi data, but yet again it didn't turn out well due to the planet being so low above the horizon. I'll probably process the data anyway, but if they're crap I'll just bin 'em.

After another hour or so of watching Saturn the temperature had fallen to -7C. The mount was struggling, no doubt due to the cold thickening the grease inside, so I ended the session, closed the obsy roof and put the fan-heater back on to get rid of the ice.

Anyway, this is the result:

Not bad for my first attempt at this method, eh?

Again, you'll have to wait for me to find time to process the Saturn data.

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