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The WHAC Meeting was held on May 8, 2007 in the Canada-France-Hawaii Telescope Headquarters in Waimea.

Craig Combes facilitated the club meeting. He opened the meeting with a welcome to all members both new and old. Those new to WHAC were asked to introduce themselves to the club. There were about 38 members in attendance, with about a half-dozen new faces. This might be a new high-water mark for attendance! We had visitors from as far away as American Samoa and Germany!

Cliff Livermore presented our regular feature The Sky This Month. Cliff had a bit of help from Pizza Dan's son, Paul. Cliff indicated there is a conjunction of M35 and Venus soon. The Leo/Virgo supercluster of galaxies is nearly overhead at sunset. Cliff spent time sharing some of the far southern objects that barely clear our southern horizon here in Hawaii; many of these objects are not visible from the mainland states. He highlighted the Jewel Box, which he described as a "very cool open cluster!" Cool in the sense of "Awesome!" The name Jewel Box is derived from having five bright stars of differing colors, reminiscent of the different colors of gems in a well-stocked jewel box. Eta Carina (both the star and the nebula) were prominent in the discussion as this object was observed frequently in the recent WHAC observing sessions. The Eta Carina star is the brightest star in the Milky Way, and a leading supernova candidate. When it goes supernova, it will be visible in the daytime and persons will be able to read a newspaper at night by the light it will produce. Next, Omega Centauri is the biggest, brightest globular cluster in the night sky. Omega Centauri is so large, far exceeding the size of "typical" globular clusters, that it is hypothesized that it is the core of a dwarf galaxy that was stripped of stars by the Milky Way in the past. Centaurus A (NGC 5128) is a spectacular galaxy with a large, prominent dust lane. This peculiar, large galaxy has a black hole in its core, and it one of the brightest radio sources in the sky. Moving north to "mainland friendly objects", Cliff mentioned the Sombrero Galaxy (M104). As the name implies, it resembles a sombrero. This is a nearly edge-on galaxy having a prominent dust lane. There is an interesting asterism of arrow-shaped stars that points the way to the Sombrero. Cliff mentioned a handful of nice globulars moving towards the north. M5 is a beautiful globular in Serpens. M13, the great globular in Hercules is fantastic. Don't forget about another globular close to M13 called M92. It is often ignored due to the proximity of the great M13. Cliff mentioned the locations of the planets including Mercury and Jupiter, as well as the Moon's phases over the coming month.

Carlton Lane shared some recent news about the "brightest supernova ever seen". This supernova occurred in the 240 million light-year away distant galaxy NGC-1260. The supernova has the attractive name SN2006gy. Web searches will unearth a plethora of information about this event, first detected last September. Some scientists consider this distant supernova to forecast the future explosion mechanism of the Eta Carnia star, being even more energetic that previously thought. There was much open discussion about this in the meeting.

Continuing the discussion with Eta Carina, Carton shared images of the Homonucleus Nebula, the material immediately surrounding the star. He showed images taken by Hubble of the large nebulosity which is the Eta Carina Nebula. The "Keyhole" is the broad, dark dust lanes that cross the nebula.

We then took a break for a bit of socializing, enjoying the tea and snacks.

The main program of the evening was by Marc Baril, an amateur astronomer/telescope & CCD camera builder who is CFHT's detectors engineer. He presented an overview of the basics of astrophotography.

Marc started with the simplest form of astrophotography, astrophotography without tracking. All that is needed is a sturdy tripod, a suitable camera, and a shutter release mechanism. One can take pictures of aurora, planetary/Moon conjunctions, large comets, meteors, star trails, and the like. He shared several examples of this type of photography. Star trails are exceptionally interesting and are well suited for digital SLR (DSLR) cameras. If a DSLR has a "burst mode" then the camera can be set to take a continual sequence of images. These images can be stacked to create the final image. This is in contrast with the old film techniques of opening the shutter for an extended period of time.

Next, it was discussed what makes for a good digital camera. Marc considers the following to be highest priority features, moderately useful features, and desirable features:

Highest Priority:
• Low readout and thermal noise. Read web reviews of various cameras to determine this. Using a DSLR camera up on Mauna Kea in cold conditions will yield better performance.
• Ability to trigger the shutter remotely.
• Exposures of 15 seconds minimum; ideally 30 seconds.
• Ability to generate and subtract dark frames on the fly. This is a feature available in many newer DSLR's.
• For deep sky photos, either no IR filter in the camera, or a removable IR filter. IR filters also partially block the hydrogen-alpha spectral line which contains a significant portion of the light emitted by a deep sky object. Presently you can attempt to remove the filter yourself (if you are brave -- done improperly this may damage/destroy your camera). Or, a firm called Hutech (www.hutech.com) sells warranted cameras that have the IR filter removed. Or, there are firms that you can ship your DSLR to and they will remove the IR filter and replace with a non-IR blocking optic.

Moderately Useful:
• Ability to control and/or capture images to a computer directly. Especially useful for lunar and planetary photography.
• Cable shutter release preferred to an IR remote.

Desirable:
• Ability to dim the LCD screen. Or, just tape some red filter material over it.

The next astrophotography step-up from non-tracked photography is tracked wide-field astrophotography. The keys to success are to have a sturdy tracking mount, a suitable camera (see above) and windless, clear, dark skies. The mount needs to be well-aligned to the north celestial pole to minimize field rotation of the images. For lenses with a focal length of >100mm, the tracking must be good to excellent. Use the camera to take many images and stack them. The photographer must take care to obtain "perfect" focusing. It is highly recommended that a new astrophotographer start with a lens of <150mm focal length. This will yield a nice, wide field of view, deferring the challenge of narrower field imaging until the photographer becomes more experienced.

A nice platform for the camera is a so-called "barn door drive". A web search will reveal lots of practical information to build one of these devices. Or, any equatorial driven telescope, such as a classical C8, makes a nice platform for wide field astrophotography.

Once you have images, inevitably, they must be processed. It helps to understand the sources of noise in the images. Noise is the random occurrence of artifacts, including an apparent glow of light over the image, and so forth. There are three primary sources of noise.

1. Photon noise - is the random arrival of photons which brighten the background of the image. This noise is defeated by taking a long exposure, or stacking multiple short exposures.
2. Dark Current - is a thermal effect of the detector. This can be mitigated by cooling the detector. Since DSLR's are not cooled, this is the major limiting factor in the performance of DSLR cameras.
3. Readout Noise - is noise on the image generated by the electronics that remove the image from the chip. In theory, stacked images cumulate readout noise as each readout adds noise; as compared to a single long exposure where the detector is read-out only once. Typically readout noise is insignificant as compared to photon noise and dark current.

Noise is mitigated by image stacking. The random nature of the noise becomes reduced since the signal (i.e., image details) is persistent throughout all the images. And, this technique removes other unwanted non-noise artifacts such as satellite trails, cosmic rays, and meteor trails.

Stacking is accomplished through any of a large and growing number of software packages:

• Registax - free and widely used in the astrophotography community. /
• Maxim DL - not free, but a full-featured image processing package.
• Photoshop - Not specifically made for astrophotography, but highly useful
• PixInsight - free, relatively new and promising. /
• Pixmantec Rawshooter - inexpensive application for manipulating raw files
• Pyxis Cam - Marc's software which is available on his site, below.

The Scribe later found that Marc has an awesome astrophotography website.

Back to the meeting minutes: Marc compared digital SLR cameras (i.e., "DSLR") to the classic astronomy-oriented CCD systems. This would be like comparing a high-end Cannon DSLR with a CCD system from SBIG.

• DSLR's inevitably use CMOS detectors. These have a lower "fill factor" which is the percentage of the surface of the detector which is sensitive to light.
• Readout noise is comparable. No difference, really.
• Dark Current is the major difference. CCD's are cooled, while DSLR's are not. This is the biggest performance knock on DSLR's. This can be mitigated somewhat by using the camera in cold conditions, such as a sub-freezing night on Mauna Kea.
• CCD's are about 4X the cost. This is due to the hardware to cool the detector, the inevitable (desirable) inclusion of a filter bank mechanism, a mechanical shutter, and the tiny market for these products. (i.e., product development costs shared among a tiny pool of consumers). High end CCD systems are "big bucks!"

Marc mentioned a phenomenal niche of astro-imaging - the use of inexpensive web cameras to image the planets. The theory is that in good seeing conditions the predominant wavefront error is tip/tilt. This results in a slight shift of the image on the detector, but otherwise yields a diffraction limited image. The web cam is used to take a large burst of images (say, 1,000). The Registax software analyses the images and selects out those images that appear to only have errors of tip/tilt (10% of all images, thereabouts). These are then de-shifted and stacked to yield phenomenal Voyager-like images of the planets. Best of all, the web cameras are cheap, about $100. Registax is even better…free! With any electronic imaging it is important to match the detector to the telescope/lens/imager. The Airy disk of the imager should be larger than two pixels of diameter on the detector. There are several rules of thumb that all point to this fact. Marc demonstrated his custom made CCD imaging system. This is thoroughly detailed on his web site. Marc closed with an impressive gallery of images that he has taken: Eta Carina, Omega Centauri, Horsehead Nebula, Goldfish Nebula, Trifid and Lagoon nebulas, Veil Nebula, Rosette Nebula, and the North America Nebula. These images and more are also on Marc's website.

The WHAC Business was short as always. Check with the WHAC Yahoo group page for email announcements and planning for the upcoming weekend observing. There will be an observing session for schoolkids at QLCC on Wednesday evening May 16. Craig Combes has the particulars. Laura Kinoshita is looking for volunteers to help with a scouting observing session at the Kilohana Girl Scout camp (located on Saddle Road) on Saturday June 2. Yes, it is a Full Moon night, but Jupiter and Saturn will be prominent and not too bothered by the Moon. As with all WHAC events, members are asked to monitor the WHAC Yahoo group site for specific information about upcoming events.

The next WHAC meeting is Tuesday June 12, 2007 in the Keck Headquarters Hualalai conference room at 7pm. The meeting agenda is on the WHAC web site. The traditional pre-meeting dinner is at 6pm at the Parker Ranch Food Court.