Comet C/2006 P1 McNaught

Fig. 4 Comet C/2006 P1 McNaught imaged by Chris Brown (Shetland) from Scord over Scalloway Castle and the Blackness Pier with Green Holm in the distance. January 10 2007, 16h 30m UT. Olympus F400 digital camera. Click for an enlargement.

Fig. 5 Comet C/2006 P1 McNaught imaged by Chris Brown (Shetland): early evening of January 10 2007. Olympus F400 digital camera.

Fig. 1 The Moon imaged January 30 2007 at 16h 28m UT. 100mm f/9.5 apochromatic refractor 1/500 sec ISO 500.

Fig. 2  Proclus and surrounding area imaged  January 30 2007 at 16h 22m UT. 100mm f/9.5 apochromatic refractor 1/250 sec ISO 500.

Fig. 3   Plinus and surrounding area imaged  January 30 2007 at 16h 23m UT. 100mm f/9.5 apochromatic refractor 1/250 sec ISO 500.

Chris Brown in Shetland took good advantage of a short break in cloud cover to secure some images of the comet on January 10. (Figs 4 & 5)

The comet would have been at magnitude -4 or thereabouts well over one hundred times the ephemeris value for that date.

From Orkney that evening thicker cloud had built up preventing any observation in twilight from Rousay. My thanks to Chris for supplying me these images.

Imaging the Moon Digitally (II)

Since writing the short feature on this topic (Archives December 2003) quite a lot has happened in the digital camera world.

The purpose of the feature was to indicate how reasonably good and interesting images of the Moon might be obtained using modest equipment. It is assumed that the observer has a good telescope firmly mounted. It is further assumed that the modern breed of Plössl eyepieces will be used.

Apochromatic refractors of small aperture (80mm) having excellent optics are now available at reasonable prices – around £300. With small “f” ratios they are easily mounted on video camera tripods or similar. A drive is not necessary in order to photograph the Moon at low powers.

As I explained, the simplest way to image the Moon is through the eyepiece using a digital camera having a small barrel diameter of around 28mm (lens 15mm). The other requirement is to have some control over aperture and shutter speed.

Unfortunately few small digital cameras now offer shutter or aperture priority. The Cannon Power Shot A620 and D700 are current exceptions but neither are as effective as the now discontinued Minolta Dimage F series. Anyone interested in this work should grab the opportunity of getting their hands on a F200 secondhand.

Single-lens reflex digital cameras are vulnerable when used at the prime focus of a telescope due to the entry of small particles which show up easily on a lunar photograph. The same applies when the camera is used as a piggyback for wide field work, although it is not as noticeable against a dark sky background.

Some manufacturers have introduced a means of partially overcoming this particle accretion. In any case, it is as well to avoid changing lenses with the camera pointing upward.

Incidentally, the problem was one I had noted from the start when using the Nikon D series of single-lens reflex digital cameras for terrestrial work. It is to be hoped Nikon will introduce a system similar to that used by its rivals.

Bright features on the Moon

Even to the unaided eye the Moon appears far from uniform in brightness across it surface. Indeed, without optical aid and a knowledge of its physical nature the Moon appears superficially not unlike the Earth. And so it is not surprising that the large dark areas were described as mare (Latin sea).

Bright features generally show up best when the Moon is close to full phase. One may also use much faster shutter speeds at this time.

Three very noticeable small bright spots are associated with the craters Aristarchus, Plinus and Proclus (Fig. 1). In the photograph Aristarchus appears close to the terminator. Plinus, on the other hand, is lit from the Sun high in the lunar sky.

The brightness emanating from Prolcus (Fig. 2) is particularly phase sensitive. Even with the space of fifteen minutes or so its appearance may change noticeably.

Both Proclus and Plinus are associated with extensive ray systems. Rays generally show best when the Moon is close to full.

There are any number of other interesting craters which show well close to full Moon, many appearing as bright ringlets.

JV
05/02/07