The November meeting of the Auburn Astronomical Society will be on Friday, November 5, in room 215 of the Aerospace Engineering building on the campus of Auburn University. Montgomery area car-poolers should meet at my house (518 Seminole Drive). We'll head for Auburn at 7:00 PM.

The regular November Star Party will be the following Saturday, November 6 at the Snipes' Farm. On Monday, November 15 you'll have a chance to observe the Transit of Mercury, low in the west, just before sundown. Then, on the following Wednesday, a possible Leonid Storm. Reminders and locations will be sent out a day or two before these two special events. As with any solar observation, use safe solar  filters only!

Sky & Telescope magazine and Astronomymagazine club subscriptions will be due this month.

Sky& Telescope magazine will cost $ 29.95 (regular $ 39.95). We will need at least 5 subscriptions to qualify. SKY Publishing gives 10% discount on books and products to those in Club Plan.

Astronomy magazine will cost $ 29.00 (regular $ 39.95). Kalmbach Publishing Company gives discount on their list of Kalmbach books:
1-4 books 33 1/3% off
5-9 books 35% off
10+ books 40% off
We will need at least 5 subscriptions to qualify.

You can bring your checks to the November meeting or mail them to:
John Zachry
Treasurer, Auburn Astronomical Society
501 Summerfield Road
West Point GA 31833

If you have any questions, e-mail John at: jbzachry@mindspring.com

Q. What do the constellations of the Fall sky: Pisces, the fishes; Capricorus, the sea-goat ; Delphinus, the Dolphin; Picis Austrinus, the Southern Fish; Eridanus, the river ; Cetus, the whale; Aquarius, the water carrier ; the ancient constellation Argo, the ship (which today is subdivided into its component parts, Carina, the keel; Puppis, the stern; Vela, the sails; and Pyxis, the compass) have in common with the 1999 Deep South Regional Star Gaze?

A. The constellations are collectively known as the "Wet Region" of the sky while Deep South Regional Star Gaze '99 was the wet region on Earth.

Statistically, October offers the greatest number of clear nights for us here in the southeast U.S., and Wednesday, October 6, was great. The drive over was under clear skies that lasted until after midnight, followed by partly clear skies until just before dawn. Representing AAS this year were: Phillip Hosey, Tom McGowan, Robert Rock, and your editor, Russell Whigham. Tom had stayed up all night the Tuesday night before putting the finishing touches on his just completed 16-inch Dob and arrived to set-up with the rest of us just before dark. Tom was searching out faint planetary nebula as first light for his latest creation; Phillip was in full CCD imaging mode with his 8-inch, Celestar Deluxe; Robert was putting his Meade 4.5-inch SCT through its paces; and I stayed busy Messier hopping, and hunting down Comet Lee, C/1999 H1, with the C-11. The mag 9 comet made itself especially difficult to find by hiding right over a mag 7 star at the time I was trying to track it down. Once revealed, it moved at a respectable clip as we followed it for most of the evening.

This was to be the only evening of observing for the long weekend at DSRSG. Thursday's clouds and sprinkles gave way to Friday's deluges. Not even heavy applications of "cloud filter- in- a- can" in a heroic cooperative effort on the part of the Auburn and Mobile club members would deter the Mississippi Monsoon. Forecasts for Saturday night promised more of the same, so I headed back home midday Saturday.

On the brighter side of the weekend, the Friday afternoon programs, included a presentation by Ken Dauzat demonstrating his "Rings & Things" http://users.kricket.net/ken telescope accessories that he sells via the Internet ; Tom Klekamp with a progress report of his on-going struggle to battle light pollution on Lake Pontchartrain's North Shore, followed by a panel discussion that included myself, Marv Uphaus, of the Mobile Astronomical Society, and Astronomy Magazine editor, Dave Eicher on "The influence of the Internet on Amateur Astronomy".

The weekend was also redeemed by the social aspects of the event -- the virtually compulsory annual trips to the Fernwood Truck Stop for Wednesday supper, "Mr. Whiskers" catfish on Thursday evening, and long awaited reunions with our special friends from Mobile and Pensacola clubs, as well as the regulars from the Jackson, Baton Rouge, and "Nawlins" clubs. Special thanks to Barry Simon for the endless hours of work in preparation for the event.

Next year's DSRSG will be from October 25 - 29.

Clear skies,

Russell
 
 

No mirror in an optical system (or an _even_ number of mirrors, as in a Newtonian) means that the image is inverted, but mirror correct right to left.

An odd number of mirrors--an SCT with a diagonal or a refractor with a diagonal--means an right side up by mirror reversed image.

Emily Carter carter@usfs.auburn.edu wrote:

Cactus Point Society member Harmon Windsor, has been experimenting in amateur construction of wide field eyepieces. Harmon demonstrated his prototype 25mm eyepiece at a recent observing session. The eyepiece was made at a total cost of 75 cents, plus labor, and gives an impressive 105-degree apparent field of view.

His method involves careful grinding and polishing of the bases of eleven jars, which formally contained pickles and onions. Years of experimentation demonstrated that if the right combination of brand names was arranged in the correct sequence, minimum figuring and polishing was required.

Rough grinding was accomplished using a Ryobi Angle Grinder, while fine grinding was done using a small concrete mixer full of carefully screened Lonesome River sand.

The lenses were then polished using a domestic floor polisher and iron oxide fine ground using a coffee grinder. They were then inexpensively araldited in proper sequence using an empty beer can, so that Harmon’s focuser had to be fitted with a special adapter.

Field tests were encouraging. The eyepiece brilliantly displays all the colors of the moon, and many hitherto unsuspected planetary nebulae. Harmon hopes to use the new eyepiece with his Ultra Rich field 18" Newtonian with a stainless steel main mirror fabricated from a quality Chinese restaurant wok.

Filippo J

Please join me in welcoming our newest members: Nichole Long nlong@hotmail.com of Montgomery and Jack C. Lewis, of Alexander City. Also, new to the mail list this month is Bob Willingham Bob.Willingham@ibfsrp.com of Mathews, in south Montgomery County, who owns a new Celestron Ultima-8. Bob writes:

Phillip Hosey has posted his first attempts at prime-focus astrophotography with his Celestar Deluxe 8" f/10 SCT on his web site http://www.mindspring.com/~jphosey/film.html.

The AAS roving ambassador of dark-sky observing, Tom McGowan, is taking his big Dobs to Ft. Davis Texas this week for a dream holiday of deep-sky observing with friends he made on his trip to Australia last spring. We will expect a full report on his for the December Astrofiles.

Total completed hits for October: 10,444
Average completed hits per day:       348

As if to reinforce the WORLD part of the WWW, we received the following "Who R U" biographical profile questionnaire submission:

Victor Smagin, from Moscow Russia vr_astro@mail.ru Victor ask that we not disclose all of his submission, but I'm sure he would like to hear from anyone to share observing reports.  Victor enjoys observing deep-sky objects, planets, variable stars with his 150mm, Dobsonian.

Most experts agree that 1999 is a likely year for a Leonids meteor storm.

Imagine tuning in to the local TV weather report and hearing this from the weatherman:

"Good evening space weather lovers! Last night Earth was hit by a high-pressure solar wind stream. It’s expected to persist for 3 or 4 more days producing a 50% chance of mid-latitude aurora. But the big news today is the 1999 Leonid meteor shower. Experts are predicting a big storm on November 18^th with up to 100,000 shooting stars per hour. Of course, we could be off by a couple of years. The storm might hit in 2001 instead. Or maybe not at all! Hey, if predicting these things were easy we wouldn’t need experts!"

One day, space weather forecasts like this could be commonplace. As our society comes to rely on satellites, cell phones, and other space-age gadgets, forecasting solar storms and meteor showers can be just as important as knowing the chances of rain tomorrow. Three weeks from now we may be treated to a very visible reminder of space weather when the Leonid meteor shower strikes on November 18, 1999.

What’s the probability of significant meteoroid precipitation? That’s what stargazers and satellite operators everywhere would love to know.

Most experts would agree that predicting the Leonids can be tricky. To understand why it’s helpful to know the difference between a "meteor shower" and a "meteor storm." Simply put, meteor showers are small and meteor storms are big. Meteor showers produce a few to a few hundred shooting stars per hour. Meteor storms produce a few thousand to a few hundred thousand meteors per hour. A meteor storm, like a total solar eclipse, ranks as one of Nature’s rarest and most beautiful wonders.

A Leonid meteor shower happens every year around November 17 when Earth passes close to the orbit of comet Tempel-Tuttle. Usually not much happens. The Earth plows through a diffuse cloud of old comet dust that shares Tempel-Tuttle’s orbit, and the debris burns up harmlessly in Earth’s atmosphere. A typical Leonid meteor shower consists of a meager 10 to 20 shooting stars per hour.

Every 33 years something special happens. Comet Tempel-Tuttle swings through the inner solar system and brings a dense cloud of debris with it. For 3 or 4 years after its passage the Leonids can be very active. In 1966 for instance, over 100,000 meteors per hour were seen from parts of North America. Curiously, there isn’t a full-fledged storm every time Tempel-Tuttle passes by. Sometimes there’s simply a stronger-than-average shower. Sometimes nothing happens at all!

Will there be a storm in 1999? (Probably, yes.)

Tempel-Tuttle visited the inner solar system most recently in late 1997 and early 1998. The subsequent Leonids display, in Nov. 1998, was marvelous as observers all over the world were treated to a dazzling display of fireballs (shooting stars with magnitudes brighter than -3). Nevertheless, the 1998 Leonids were a shower, not a storm. The maximum rate of meteors last year was about 250 per hour. Scientists have learned that if Earth crosses the orbit of Tempel-Tuttle too soon after the comets passage, then there is no storm, just a strong shower. Apparently that’s what happened in 1998. In recent history no Leonid storm has ever occurred less than 300 days after Tempel-Tuttle passed by Earth’s orbit. In 1998, Earth followed the comet to the orbit-crossing point by only 257 days.

The period of maximum activity during the 1998 Leonid shower took place about 12 hours before the earth crossed Tempel-Tuttle’s orbital plane. The early activity caught many observers by surprise, but it was business as usual for the unpredictable Leonids. Rainer Arlt of the International Meteor Organization noted that while the maximum activity came early, there was a secondary maximum when the Earth passed the comet’s orbit. This pattern is similar to that observed in 1965, the year that preceded the great Leonids storm of 1966. In his report, Bulletin 13 of the International Leonid Watch: The 1998 Leonid Meteor Shower, Arlt wrote:

Instead, there was an stunning display of shooting stars over western North America. This recollection by James Young at JPL’s Table Mountain Observatory in California gives a sense of what the storm was like:

Joe Rao, a Leonids expert who lectures at New York’s Hayden Planetarium, also advocates 1999 as possibly the best year for a storm during this 33 year cycle. Writing for Sky &Telescope he says:

Rao is also a meteorologist for News 12 Westchester, which seems a suitable occupation for predicting meteor showers.

In 1999, the Earth will pass nearly three times as far from the comet’s orbital path as it did in 1966 and more than six times farther than it did during the great storm of 1833. If the peak of the Leonids arrives exactly when the Earth passes through the comet’s orbital plane, Donald Yeomans of JPL gives 01:48 UT on November 18, 1999 as the most likely time for the 1999 maximum. That would make Europe and West Africa the best places to watch the show. However, Leonid meteor showers frequently arrive much earlier or later than predicted, so any place on the globe could be favored.

If the peak of the Leonids occurs over Europe or the Atlantic Ocean, then observers in the USA could be in for an unusual treat. The Leonid radiant would just be rising over North America at the time. In the eastern US sky watchers would see a large number of earth-grazing meteors skimming horizontally through the upper atmosphere. "Earth grazers" are typically long and dramatic, streaking far across the sky.

To look or not to look, that is the question

If 1999 is the year, when should you look? Most experts predict that the Leonids peak will occur between 0100 and 0400 Universal Time on November 18^th. However, it is important to remember that such predictions are always uncertain. The 1998 Leonid fireball display occurred nearly 16 hours before the predicted maximum! No matter where on Earth you live, the morning of November 18 will probably be the best time to look for Leonids in 1999. This is true even if morning where you live occurs much earlier or later than 0100-0400 UT.

Conventional wisdom says that meteor observing is always best between midnight and dawn local time on the date of the shower (November 18 in this case). For a shower or storm like the Leonids that might be relatively brief, it is best to start watching no later than midnight. In fact, when the author of this story went outside last year at midnight to view the 1998 Leonids, the shower was already well underway! With this in mind you may decide it’s a good idea to begin observing even earlier, say, 10 p.m. on November 17.

In the coming weeks Science@NASA will post more stories about the Leonids with observing tips for meteor watching with the naked eye, video cameras and other types of recording devices. One thing seems sure, no matter where you live: The Leonids are coming and, on Nov 18, 1999 the place to be is outside, looking up!

Promising New Comet

A faint comet discovered on September 27th by MIT Lincoln Laboratory’s LINEAR robotic telescope in Socorro, New Mexico, may become a naked-eye object next summer. The location of Comet LINEAR (C/1999 S4) then is still uncertain by a couple of degrees. Although extremely faint right now, this comet is expected to reach perihelion next July 24th after dipping inside the Earth’s orbit to about 0.75 astronomical unit from the Sun (that is, at roughly the same distance as Venus from the Sun). Around the time of the total lunar eclipse on July 16th, C/1999 S4 could be as bright as magnitude 3 or 4, low in the northwest evening sky.

COMET LINEAR MOVES SOUTH

The OTHER Comet LINEAR is slipping quickly south, making it easier to spot in the Southern Hemisphere. This coming week, the comet moves from Canis Minor, through Monoceros, and into Puppis. It rises after 1 a.m. By dawn in the Northern Hemisphere, LINEAR will drop from about 50 degrees up in the east-southeast to only 20 to 30 deg. In the Southern Hemisphere, the comet rockets upward moving from 40 to 60 degrees high before sunrise in the northeast in a week’s time. Here are positions for Comet LINEAR at 0 hours Universal Time for the coming week in 2000.0 coordinates:

Date R.A. Dec.
Oct 9 7h 54m + 6.1 deg.
Oct 11 7h 49m + 0.4 deg.
Oct 13 7h 45m - 5.8 deg.
Oct 14 7h 39m -12.4 deg.

COMET LEE IN THE NORTH

Comet Lee remains well placed for Northern Hemisphere observers. It is about 45 deg. above the northeast horizon at the end of twilight, climbs nearly overhead by 11:30 p.m., and is 25 to 30 deg. up in the northwest at dawn. This week Lee moves out of Andromeda and into Pegasus. Here are its positions for the coming week:

Date R.A. Dec.
Oct 9 23h 51m +42.4 deg.
Oct 11 23h 38m +39.5 deg.
Oct 13 23h 27m +36.6 deg.
Oct 15 23h 17m +33.9 deg.

http://www.spaceviews.com/1999/10/13b.html

New Comet May Put on a Show Next Year
SpaceViews
October 13, 1999

A comet discovered last month may become bright enough to be visible to the naked eye come the middle of next year, although it is unlikely to be as brilliant as two other comets visible this decade.

Comet C/1999 S4 LINEAR was discovered last month by the LINEAR automated telescope in New Mexico as part of an asteroid and comet search program. First classified as an asteroid when discovered, follow-up observations by other astronomers revealed a distinct fuzzy coma around the body, evidence that the object is a comet.

Based on 18 observations in late September, astronomers at the Minor Planet Center of the Smithsonian Astrophysical Observatory calculated a parabolic, highly-inclined trajectory for the comet, passing about 0.75 AU (112 million km, 70 million mi.) from the Sun at its closest approach in late July.

While the comet is very dim at the moment—about magnitude 16, requiring moderate to large telescopes to see it—it will brighten considerably as it approaches the Sun. Taking into account both the comet’s distance from the Earth and the Sun, it may brighten to as much as magnitude 3 or 4 and thus be visible to the naked eye by July.

Predicting the brightness of comets is difficult, as it is hard to estimate in advance not only the size of the comet but how much gas and dust it will produce as it approaches the Sun and warms up. However, current indications are that the comet will not be anywhere as bright as comet Hyakutake in March 1996 or Hale-Bopp one year later.

The best time to observe the comet will likely be in mid-July, when the comet is near its peak brightness. It will be seen in the northwest sky after sunset in the northern hemisphere.

From: Skywayinc@AOL.COM
Date: Tue, 19 Oct 1999 18:44:08 EDT
Subject: [ASTRO] Potential "Surprise" Meteor Shower on November 11?

To: BAALKE@KELVIN.JPL.NASA.GOV, astro@lists.mindspring.com
Reply-To: Skywayinc@AOL.COM

The recently discovered Comet LINEAR (C/1999J3) may serve to give rise to a new meteor shower on November 11.

The circumstances concerning a prospective "Linearid" display on the evening of November 11th is most intriguing. The moment when Earth passes closest to the descending node of C/1999J3 at 2:41 p.m. EST/11:41 a.m. PST. Unfortunately—daylight for North America, although well into evening darkness over Europe.

The radiant for this prospective display very near to the star Phecda, the lower left star in the bowl of the Big Dipper. From my own calculations, I come up with an RA of 11h 40m, Dec. +53 deg. So even for Europeans, the radiant stands only about a mere 5-degrees above the northern horizon (at latitude 40N) at the time that the shower may reach its peak!

Nonetheless . . . the separation between the Earth’s orbit and that of the parent comet is just over 0.011 a.u. As to what type of activity might be expected, it should be noted that the 1985 Giacobinids briefly produced an outburst of ZHR’s of 600 to 800 from Japan, with the Earth following 21P/Giacobini-Zinner to its node by just 26.5 days. The separation between the orbit of the comet and Earth was 0.033 -- or three times the separation between the upcoming case of Earth and C/1999J3.

In 1933, when a major Giacobinid storm (ZHR = 3000 - 29000) occurred, these values were 80 days and 0.005 a.u. Earth is following LINEAR to its ascending node by ~39.9 days. Hence, the situation regarding the prospective LINEARIDS is roughly midway between the two above cases.

Among the chief differences between Giacobini-Zinner and LINEAR is that Earth intersected comet debris on the inside of Comet G-Z’s orbit, whereas we would intersect debris on the outside of comet LINEAR. In addition, the dust-distribution surrounding LINEAR is completely unknown. Also, Giacobini-Zinner is a well-known short-period comet of 6.5 years and has been observed to circle the Sun on many other occasions, whereas LINEAR is a newly discovered long-period object of ~63,000 years.

Nonetheless . . . I would strongly urge all observers to carefully monitor the skies for possible meteors from this shower, especially during the pre-dawn hours of November 11 (when the radiant is high up in the northeast sky), as well as later that evening. It appears that should any significant outburst occur, those in western and central Asia would have the best chance of viewing it (for them, in the after-midnight/pre-dawn hours of November 12 local time).

Although we know that the Earth will be closest to the comet’s ascending node at ~19.6 UT on November 11, this doesn’t mean that the actual peak of a prospective LINEAR display could not occur many hours earlier or later. An example of this occurred one year ago with the 1998 Giacobinids: the time when Earth was predicted to cross the node of 21P/Giaconini-Zinner was 20:53 UT on October 8; but the shower actually reached its peak at 13:15 UT—more than 7.5 hours earlier.

Thus, I would strongly suggest that all interested observers should be on high-alert for a 24-hour interval on either side of the predicted nodal crossing time of 19.6 UT/November 11.

Who knows? It might prove to be an interesting warm-up for the Leonids, which are due to peak just a week later!

• joe rao

More details concerning the (prospective) LINEARID meteor display:

1) On November 11, we will be arriving at the comet’s DESCENDING node, not ascending (as originally stated).

2) The comet in question (LINEAR or C/1999J3) is a long-period comet. It’s orbital eccentricity is estimated at 0.999366 giving it an estimated period of 60,475 years. As such it is not a "new" or "virgin" comet in the Oort sense and may very well have been here before in the far-distant past.
 
 

There unfortunately has never been a recorded case of any truly historic meteor showers emanating from a comet of such a long period as this. Most of the comets that have given rise to spectacular meteor outbursts are of the short-period variety (Tempel-Tuttle, Giacobini-Zinner, Biela, Pons-Winnecke). The Perseids are related to Comet Swift-Tuttle, whose period is roughly 130 years. Perhaps the most extreme case for a long-period comet are the Lyrids, which have produced occasional, unpredictable outbursts of activity (such as 1982 and 1803, the latter case producing many hundreds of meteors per hour). The Lyrids are associated with Thatcher’s Comet of 1861 whose period is approximately 415 years.

3) The prospective LINEARID radiant position was originally given as R.A .11h40m Dec +53 degrees. Which would place it within a few degrees of the star Phecda (Delta Ursae Majoris). This position was recently called into question by meteorobs member Chrystian Steyaert, who independently obtained a position of R.A. = 7h20m, Dec = -40 deg. However, once it was realized that the nodal crossing point was descending and not ascending (see #1 above), he later wrote: "After correction, my results agree fully with yours!" Steyaert also added that: "( I ) don’t recall if you gave a velocity, but the 57 km/s is certainly a bonus for the radio observations."

4) While I commented that prospective observers should be on high alert within 24 hours either side of the predicted nodal crossing, I have since done some research into other comets that have produced brief meteoric outbursts.
 
 

The "Bootids" or Pons Winnecke Meteors provided a very sharp and unexpected outburst on June 28, 1916, observed by the British Observer William F. Denning.

Interestingly, the parent comet passed through its nodal crossing point on September 8 of the previous year. The comet’s orbit at the node was 0.043 a.u. sunward from that of the Earth. More interestingly, the outburst observed by Denning came nearly three days before the Earth reached the node!

Similarly, another Bootid/Pons Winnecke outburst occurred on June 27.21 (UT), 1927 and was observed by both Russian and Japanese observers. On this occasion, at the nodal crossing point, the parent comet was 0.028 a.u. outside of Earth’s orbit. Earth would arrive at the node only 2 days behind the comet—yet maximum activity again came about three days before the Earth reached the node.

Biela’s Comet (which of course, no longer exists), apparently was the cause of large numbers of meteors and occasional bright fireballs from Andromeda which were observed on December 7, 1830 (from France) and on December 7, 1838 (Connecticut). What makes these observations interesting is that although the orbits of Earth and Biela very nearly coincided at the nodal crossing point, the 1830 observation came nearly two years before Biela’s arrival at the node and the 1838 observation occurred about seven months before Biela reached the node. In addition, the 1830 and 1838 "Bielid" nodal crossing points corresponded to the November 30 point in our orbit—yet, as noted above, the two above displays were noted a full week later!

Which, put simply, means that we should not have tunnel-vision and concentrate solely on the aforementioned nodal crossing time for the supposed LINEARIDS of November 11.82 UT, but be on the lookout for any unusual prospective activity perhaps a week before to a week after this time (~November 4-18). This, of course, means a potential cross-over with both the northern and southern Taurid shower branches which peak in the first week of November, as well as the long-awaited arrival of the Leonids on November 17-18. In a recent exchange of e-mails on this subject, Dr. Brian G. Marsden of the Central Bureau for Astronomical Telegrams noted that: "I’m skeptical about meteors like this from a long-period comet, but I suppose one never knows."

Indeed, as noted above, a significant or noteworthy meteor display from a long-period object such as C/1999J3 is quite unprecedented. Absolutely nothing may come of it. But, on the other hand . . . you never can tell!

• joe rao

In 1981, with a newly purchased full aperture solar filter, I turned my C8 telescope to the Sun for the first time. I was absolutely amazed that one could actually view the fiery surface of our daytime star. I was also amazed at how quickly it changed. It only took a year to add a hydrogen-alpha solar filter to my observing arsenal. I was hooked forever on solar observing. snip My first test of the material I received from Baader came on an evening shortly before sunset. I mounted a piece of the AstroSolar in a cardboard cell and went outside. I first checked the material by holding it up to the Sun. The Sun could be seen through the film. I judged it to be about neutral density 5. The image was white in color with little scatter and no pinholes apparent. I then mounted it securely to my 5.1" f/8 Astro-Physics refractor and pointed the scope towards the Sun. I next viewed the Sun through the telescope with a star diagonal, but no eyepiece. I again examined the filter for scatter and pinholes. Again, there appeared to be little scatter and what appeared to be one small pinhole in one side of the coating. This small imperfection was faint and not needing to be darkened with a felt tip pen because of the two-sided coating process. I then placed a 19 mm Panoptic eyepiece in the star diagonal and brought the Sun into focus. At 53x the Sun's image was an off white color with a slight blue-grey tint simulating what you would see through a Herschel Wedge Prism with neutral density filters. The image was sharp with black sky adjacent to the solar limb. Although seeing was particularly good this late in the day, granulation was easily seeing as were sharp boundaries between the sunspot's umbra and penumbra. Faculae were easily seen well into the disk. The image was bright, however, at low magnification the image should be fairly bright so that when higher magnifications are used the image is not too dim.

And a reply from Nick Martin

I have also used the film and it does give nice solar images but I have not observed the sky around the solar limb to be as black as Gordon Garcia describes.

I would suspect that a 5" aperture is best for using the filter. I have used a 4" aperture ( on a 20" f4.4 stopped to 4" f22) and the image is a bit dim for daylight viewing at higher magnifications around 150-200X. The best solar images I ever saw were with a 4.5" f30( I think) with an unsilvered mirror and the solar light dimmed by 2 Brewster angle (53 degrees) reflections from glass flats. The image brightness could be adjusted by rotating one of the flats to alter the degree of crossed polarization of the reflected sunlight. The sun was perfectly neutral white in color and the limb darkening was visible as a change in the color of the solar surface.

Nick

Nick Martin, Bonnyton House, By Ayr, Ayrshire KA6 7EW ,Scotland, UK.
Latitude 55 24'56" Longitude 4 26' 00".
 

Hope to see everyone at the meeting,

Russell