石澳觀星 (27-3-2016)

Observing (Deep Sky) - 星雲、星團、星系攝影及觀測

石澳觀星 (27-3-2016)

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David » 2016-03-28, 21:06

The sky was completely clear yesterday and about 10 students attended our stargazing activity, and almost none had any stargazing experience before. We used the 18 inch Obsession Ultra Compact as usual. The main focus tonight was Jupiter.

When we began observing shortly after 7pm, Io started crossing the Jupiter disk. At the same time, we had to pay attention to Europa approaching Jupiter from the other side, about the hide behind Jupiter shortly. As students observed one by one, Europa was noticeably closer every time the same student observed Jupiter. Seeing the Galilean satellites moving definitely reminded us of what Galileo saw and felt when he pointed his tiny scope to Jupiter for the first time. Gradually, the gap between Europa and the Jovian disk closed, and Ganymede was about the repeat the same half an hour later.

While we were waiting for this to happen, a tiny black dot started transiting the Jovian disk. It was the shadow of Io. We imagined the view of total solar eclipse from Jupiter in the region of the black dot, and wondered what we would see if Io's volcanoes were erupting at the same time.

Then we turned our attention to the major constellations and objects in the winter sky: the winter triangle, Orion the hunter, the potential supernova explosion of Betelgeuse at any time, Sirius the brightest star in the sky, the belt and the sword of Orion, etc.

We first pointed the scope at M42 the Great Nebula of Orion. At low magnification, the central bright quadruple stars (Trapezium cluster) were already easily resolvable with vibrant colour contrast. These central four stars already provided most of the energy given out by this 24-light-year-wide nebula. Wow! The view was the best with the 13mm ethos eyepiece. At about 150x, the 3D filamentary structure of the gas and dusts was mesmerizing. Half of the students found the view with UHC filter better, which suppressed some of the background light pollution.

Then we moved the scope towards my favourite winter star cluster. No, it was not M45 the Pleiades as this was better viewed with a binocular or even with naked eye rather than a scope. My choice was the Tau Canis Majoris open cluster. The cluster came to life at about 150x, with hundreds of stars buzzing around a very bright central star, like ‘flies around honey’.

Next, we moved to M46 where we could find an open cluster but with a star which had already evolved to a planetary nebula. A planetary nebula is formed from the ejected gas from the central dying star. This beautiful stage lasts about 10,000 years only, which is extremely short compared with the lifetime of a typical star which is about 10,000,000,000 years.

We couldn’t spend too much time with the ‘faint-fuzzies’ as we needed to watch Io (the fastest moving Galilean satellite as it is closest to Jupiter) moving out of Jupiter’s disk. A few minutes before exiting, Io easily stood out from the Jupiter background as the edge of Jupiter is dimmer. Io appeared three dimensional like a pimple on the face. As Io began to move out of Jupiter, the ‘pimple’ gradually bulged out and even ‘came out of the face’. Interesting.

As we were still trying to catch up with our breath, the longest lasting storm in the solar system, the Great Red Spot, began to rotate to the front side of Jupiter and allowed us to view it in all its glory. With the size of three Earths, it was still not easy to spot for beginners especially when it was near to the edge of Jupiter at the beginning. Thanks to the fast rotation of Jupiter, the storm quickly moved towards the centre and all students could spot it easily. Yes, it is not as big as the pictures one can find on the web. But it is real and brilliant.

While Jupiter continued to deliver one fantastic sight after another, a big red object rose from the sea. It was, of course, our moon. While it rose high enough, we observed with the 18 inch scope. The three dimensional view of craters turned out to be some of the most satisfying views of the night.

What an end to an exhilarating night of observation.
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APM 80/480, SW 120mm Equinox, C8, Obsession 18"UC with Argo Navis & StellarCat
Lunt LS60T/CaK, LS152T with DSII
DMK31AF03, DMK21AF04, DBK21AF04
Mark V Binoviewer, Ethos (3.7mm, 6mm, 13mm), 19mm Panoptic, 5mm TMB mono
http://www.imsc.edu.hk/pages/astronomy
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David
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