Category Archives: 1991

PeGASus Newsletter Issue #25 – Nov. 23, 1991

Hello, everyone!! Well, not a lot has been happening (astronomically speaking); the weather has been poor (this is the ‘blah’ season!). Work is proceeding on the design of the new observatory and plans are afoot to start a mirror-grinding group. Indoor activities seem best for now.


LAST MEETING:

Your new executive was elected. The members are:

  • President: Bob Nelson
  • Vice Pres: Al Pretty
  • Secretary: Brian Potts
  • Treasurer: Jim Livingstone
  • Mem. at Large: Rod Marynovich

Many, many thanks to David Sundberg for serving as treasurer for a number of years. While the duties were not extensive, David was there when he was needed in spite of a busy workload. Thanks, Dave.


SPECIAL FEATURE – MIRROR MAKING:

Three people at the last meeting expressed an interest in mirror making. This is not an arduous task (it’s really quite a lot of fun) and provides a means of obtaining a decent-sized telescope (8″ or 10″) for a very modest cost ($100 – $200 or so). I’ve sent for information and we hope to get our orders off soon. Since one or two other people might be interested in participating, let’s have a look at the basics. (Ref: Jean Texereau, How To Make A Telescope.)

The basic requirements are a mirror blank (usually made of pyrex, but other materials can be used), a tool (made of pyrex, ceramic material or whatever) of the same diameter, various abrasives (grinding powders) ranging from 60 grit (coarse) to 500 (fine), rouge (powder) for polishing, polishing pitch, a squeeze bottle (for water) plus a working stand (oil drums work well). Various testing equipment is also needed.

One starts by mounting the tool so that is is firmly supported on the work surface. Holes may be (previously) punched in the oil drum so that grinding powders may be flushed safely into the drum, out of harm’s way. (Cleanliness must be followed scrupulously to prevent contamination of the finer powders by the coarser ones.) With a little of the coarse powder plus some water to make a ‘slurry’ of just the right consistency, one is ready to start.

The basic motion is one of sliding the blank back and forth over the tool. Long strokes, where the blank overhangs almost 50% at the end of each stroke, should be used. Every once in a while, one rotates the blank 10 or 15ø or so and rotates oneself the other way. It will be necessary to add a few drops of water when the slurry dries out; also, (less frequently) one should replace the slurry altogether. Because of the overlap at the ends of each stroke, the motion is such that material is gouged from the edges of the tool and

PeGASus Newsletter Issue #24 – Oct. 20, 1991

Hello, everyone!! As winter approaches, we have to readjust our plans. Except for the occasional clear night, we’ll be devoting our energies to indoor activities.


OBSERVATORY NEWS:

Well, I had hoped to be able to report the start of construction on our new observatory on Tedford Road, but things have been quite slow. Whenever one is dealing with government agencies, there are delays. The folks at the Ministry of Crown Lands have been quite helpful but they have their requirements. In order to get our License of Occupation (on the 1-hectare plot) we had to buy $1,000,000 liability insurance and post a $2000 bond to ensure that the old observatory is properly dealt with. I had hoped to avoid the latter by getting a group such as the snowmobile club (clubhouse) or the Naturalists (wildlife viewing) interested, but to no avail.

The requirements for a license have been satisfied and the document awaits only a signature and may even be in the mail now.

Another delay was in the plans for the building. The engineer-architect who designed our building on Tabor Mountain was asked if he could again help us out and design our new building. Dave Dennis has been quite busy and only came out with the plans a week or so ago.

I had hoped that we could have the excavations done, and install the footings, pier and foundations before winter. In the spring, the bricklaying would be done, the floor and roof installed, the telescope and dome moved and the electrical hookup completed.

Winter is now imminent and it looks as if we should postpone the start of construction to spring. I really didn’t want to do this, but we have to be practical. You CAN work in the weather we have been having of late, but who wants to? With any delay in laying the foundations, we could be in trouble.

In the meantime, we should get our act together: form a working group, decide on the exact design we want, and do all the necessary planning over the winter in order that we may have a good start in April or so. We will have the advantage of having another casino event next summer (that I shall apply for) plus the nearly unlimited time I shall be able to put into the project in May and June (it’s my professional development time). The good news is that the College carpentry class will be working all summer and may be able to assist us in building the floor and roof.

This winter, we could get going on inside projects such as making the club telescope, instrument building and testing, and possible mirror grinding. What about it?


LAST MEETING:

A small but loyal group was brought up to date on recent occurrences. After some discussions, we looked at “The Astronomers”, episode 1. Quite interesting.


WHAT’S GOING ON IN THE SKY:

The only planet reasonably visible is Saturn, low near the meridian at sunset. Venus and Jupiter are morning objects, arising a few hors before the sun. In case you haven’t looked at the sky recently (I haven’t, being busy with other things), the summer triangle with Deneb (à Lyrae), Deneb (à Cygni) and Altair (à Aquarii) plus part of the rich norther Milky Way are still visible in the evening sky.


NEXT MEETING:

On Wednesday Oct 23 at 7:30 in the Physics Lab (Rm 2-223) at the College. We need to decide on our new executive, plus set up a working group to plan our new observatory. I hope to set up a test for resolution of telescopes using artificial double stars as described in Sky and Telescope recently. Plus, we can look at the second episode of “The Astronomers”. I hope to see you there!!

Bob Nelson, President

PeGASus Newsletter Issue #23 – Sept. 23, 1991

Hello, everyone!! Welcome back from the summer as we look ahead to another year.


CASINO EVENT:

We had our scheduled casino event June 4, 5, 6. Overall it was quite successful – we earned a net amount of $4434.41. This is practically identical with the earnings from our last event (1989 July 30, 31, Aug 1) where we earned $4464.50. I am particularly happy how the last night turned out – we were losing at one point and managed to turn it around. With the total we now have in the bank ($9500) plus the 1/3 we will get with the B.C. Lotteries grant, we should have enough to erect the first phase of the new observatory on the Blackwater Road.

Many, many thanks to all the volunteers who helped out! They are: Diane Bailey, Gerhard Bierman (2 nights), Gordon England, Fred Garneau, Rod Marynovich, Steve Marynovich (2 nights), David Mercer, Valerie Mosser, Bob Nelson (2 nights), Alan Pretty, Mike Pretty, and Brian Stauffer. The hours were long but not unpleasant – it’s certainly an easy way to earn substantial money!


OBSERVATORY NEWS:

I would love to be able to tell you that everything is progressing at a great pace, but alas, things take time, as always. At this instant, we have a site, the licence of occupation is imminent, the B.C. Lotteries grant is still valid, and the clearing of land, etc is not a problem. We still need a set of plans (imminent) and once we have our licence, we can dig for the foundations. That is when we will have work parties: we have to prepare for the footings (then pour redi-mix) and install the forms and sono-tube (then pour redi-mix). At that point, we can hire a bricklayer and have the walls erected.

We will try to get the above completed before winter (but we’ll have to close up to keep the snow out); with luck, the College carpentry class will install the floor and roof; we’d then be ready to move the telescope and dome by May or June (hope, hope).

We should have enough money, although we may have to float a loan (using the mirror as collateral) on the strength of a casino licence for next summer. That is the game plan.


WHAT’S GOING ON IN THE SKY:

Well, yours truly was fortunate to travel to Mazatlan for the eclipse of 1991 July 11. The following is a brief account:

My wife, Lois and I were part of a tour that the Royal Astronomical Society of Canada, Calgary Section (otherwise known as the RASCals) had organized. At 5:30 on the great day, we boarded buses (in the humid heat) for the anticipated 3 hour trip to the observing site. (We had a military escort!) As we travelled inland, the clouds seemed to get thicker and yours truly did not have a lot of hope. However, member Alan Whitman (a professional meteorologist) was aboard the bus and exercised his judgement (on visual and other data). He suggested that we turn back and head to the coast along a road that we had passed some 40 or 50 km back. The site turned out to be ideal – on the beach with lots of room to set up (plus a thatched roof to get out of the sun!). There were a total of 10 or 15 buses there with people from other groups.

There was some uncertainty as to whether we might have to move (and I had a Celestron to set up!), but as the first partial phase progressed, it got clearer and clearer. I set up and got some photos, both with a piggy-back camera with a 400 mm lens, and through the telescope with 2000 mm f.l.

At totality, it was totally clear. Great excitement with people applauding and crying out with glee! I took photos until Lois reminded me that I hadn’t looked through the telescope yet. I was rewarded with fine views of the inner corona plus two large solar prominences, one on the east side and the other on the west. Without the telescope, one could easily see two planets to the east of the sun: Jupiter and Venus (with Venus being further away). Two others, Mercury and Mars were also present to the east of the sun but were some 3 magnitudes fainter than Jupiter and harder to see. There was so much to see, and in spite of the fact that this was the longest eclipse for the next 100 years or so, the time just flew by.

Other observers noted phenomena I hadn’t: shadow bands were seen, the fainter planets and stars were seen, plus a pig tethered nearby flopped on its side when it got dark! Some birds overhead, however, continued to fly.

I don’t have my slides at the present; I sent them by Loomis to the RASCals where copies of my best ones will be combined with selected ones from the others. A full set of slides, as well as a videotape will be made available by all. Therefore, we shall have to wait until probably the January meeting until we will see a presentation on the eclipse.


NEXT MEETING:

On Wednesday, Sept 25 at CNC in room 2-223 (Physics Lab). We can discuss the observatory situation, set up the observers’ list, look at some recently acquired slides or look at the first episode of “The Astronomers”. See you there!!

Bob Nelson, President

PeGASus Newsletter Issue #22 – May. 23, 1991

Hello, everyone!!

Well, a lot has happened since our last meeting and newsletter. I have talked with many of you personally, but for those of you who haven’t heard, we are actively attempting to relocate our observatory.

As you will recall, last month we were planning to put in a power line and security system to our building up there on Tabor Mountain. This would have allowed us to install a security system and reopen the observatory. The bombshell landed when I was talking to the airport manager and she informed me that the M.O.T., to save money, will not be plowing the road to their site next winter. Needless to say, this will affect us deeply. Not only will we be unable to get up there 5 months of the year, but this poses a security threat as well. What is the use of having a fine security system, monitored 24 hours a day when we can’t get up there? What is more, the vandals will know it too. Carried possibly by snowmobiles, they would have all the time in the world to break in.

Sure, we could make the door as strong as possible, install a second set perhaps and maybe hook up a cattle fence power supply to the door and dome. Probably nothing would happen the first year, but sooner or later we would have another break-in, especially when we really begin to load the place with valuables. I am afraid we could never again regard the place as secure.

The thought occurred to me while I was up there: why not use the approximately $12,000 – $14,000 we will have after the next set of casino nights and relocate the telescope and dome somewhere else? A call to a company that rents cranes revealed that they could move the telescope and dome within the Prince George area for about $450. This is peanuts.

Well, what about a wood or concrete block building about 20′ by 50′ or so? A square room at one end would be for the telescope with the rest left for a heated control room and classroom. With better security, one storey would suffice (the dome would have to be modified so that the lower shutter swings out rather than down); it would be cheaper and more convenient. The classroom area would be great for school and other groups – we could have a slide projector permanently loaded with predesigned programme(s) set up for easy use. Other equipment such as a computer, CCD camera, videotape machine, other electronics etc, etc would enhance the observatory. A site closer to town using better roads would not only be more pleasant but would encourage the use of school buses to this destination.

I’ve talked to members of the executive and a number of other people; everyone agrees that we are on the right track. The trick will be to find the right site and to bring it off. The architect of the original building, Dave Dennis, says that the amount we have is “a little light” for a building of this size. There are a few bright spots – the College could build – over time – a wood building perhaps not that large for around $6000 – 8000. Would wood be secure enough? Prince George Lock and Key plus the RCMP told me that thieves are getting in buildings by cutting through walls with chain saws, also that police protection in the district is confined to one (!!) officer patrolling around. The finest security systems are worthless without immediate backup. The best plan, I’m told, is to have nearby neighbours. All depends on the site.

We have looked at a number of potential sites. The criteria are that we want to be at least 15 km out of town (preferably in a southerly direction), close to power, close to neighbours (but not too close), have an absence of bright lights around, have easy access in winter, and have a good horizon in all directions (but we may have to compromise on this point). Red Rock school, 20 km south of here would have been ideal except for the fact that people living there tell me that they get a lot of ground fog in the fall. Thumbs down. In fact, I believe anything off highway 97 south is subject to fog (because it’s downwind of the Fraser and all its moisture). Former member, Alan Whitman offered his property off the Chief Lake Road, but it is in the wrong direction, has lots of trees around and is somewhat bothered by car lights. We were offered room at the old Baldy Hughes site but it is rather far away and has a poor horizon. We may have a site only 6 km down the Blackwater (Baldy Hughes) Road on a farm also used by the model flying club. Security remains a concern as we would not be in site of any nearby houses. Maybe, but let’s keep looking.

I’ve included sketches of the proposed building – these should give you an idea of the potential this observatory would have. Wood or concrete? Wood is cheaper and can be moved; it also burns and is less secure. The advantages and disadvantages are reversed for concrete. My feeling is that we would be more secure in a wood building in sight of neighbours than in a concrete building further away. It all depends on the site.

Once a site is decided upon, we have to cost it all out and make firm plans. We may still be light in terms of cash. I have applied for funding in a variety of places but don’t get your hopes too high. Stay tuned. Sometime we’ll get this built.


CASINO NIGHTS:

Planning is continuing for our casino nights June 4, 5, and 6. Four of us, Steve and Rod Marynovuch, Gerhart Bierman, and myself attended a casino volunteer training session Wednesday evening – two of the above have to be on duty every night. The other three positions each night will have to be filled by others. I’ve phoned most people and will be assigning slots soon. If I haven’t phoned you please give me a call at 563-6928. The hours are long (5:30 PM or so to probably 3:00 AM next morning) but this is the easiest way to earn probably $4000 – $6000 in three nights’ work (about $35-40 per hour for each person).


CLUB TELESCOPE:

The secondary mirror has been ordered and construction should begin soon.


NEXT MEETING:

Thursday, May 30 at 7:30 at CNC in room 2-223 (Physics lab). I’ll have the latest news regarding the new observatory and would like to have a full discussion of everything. Please attend if you possibly can. Afterwards, if there’s time, we could look at the first part of The Astronomers which I taped from PBS (I have all 6 segments). See you there!

Bob Nelson, President

PeGASus Newsletter Issue #21 – Apr. 24, 1991

Hello, everyone!!

Hey, great news – WE HAVE OUR CASINO LICENSE. This is really a relief to me as there are so many things that could have happened (delays of up to a year, an outright “no”, problems with our society status, etc) that did not happen. We’re in!! We now have to make sure that we have a full team of volunteers (plus spares) and that everything will run smoothly.

At the same time, we can start planning intensively for the construction of the power line. As long as we do not actually go into debt (we will not do this), we can start work as soon as possible. At the present time, we have a lot to do: engaging a contractor, surveying the right-of-way and drawing up the plans, hiring a cat operator and make arrangements for the loan/rental of the machine (its transportation up there, etc.), obtaining the poles and getting them “planted”, getting the wire strung, and the building wired up. Next, we will need the telephone line and the security line. A second set of doors should be built and the building “toughened up” as much as possible. Lastly, certain modifications will have to be made to the telescope to accept the new secondary mirror. Eventually, it should get digital setting circles, but that may have to wait.

Without wanting to count on too much, I would think that it ought to be possible to get the power line installed this summer and the observatory re-opened in the fall. It should then be vastly better than it ever was before. We should also concentrate on making the observatory as comfortable, as convenient and as well-equipped as possible. Astrophotography and general viewing should be better than ever. Let’s all do our very best to ensure that the observatory becomes all that it can be!


SPECIAL PROJECT:

Let us not forget the club telescope. This is a lot less work than the observatory and we should be able to build it this spring.


RECENT EVENTS AT TMO:

Nothing really, except that the road will soon be dried out and passable to any vehicle. Your editor was up there recently – two mice were trapped. I hope eventually to seal the building so that the traps will no longer be necessary.


LAST MEETING:

We did some “indoor astronomy”: general discussion, followed by looking at several constellation slides, identifying features on star charts, and looking them up in Burnham’s Celestial Handbook. A very enjoyable evening.


WHAT’S GOING ON IN THE SKY:

Hey, with the mild weather returning, let’s get out to the observatory site and look at galaxies!

While looking up events in the sky for this summer (at the request of Citizen reporter and member Diane Bailey), I noticed that there will be a triple (quadruple?) conjunction of planets late this spring: for about a week centred around June 18, Venus, Mars and Jupiter will be within about a degree of each other in the western sky. In addition, Mercury will be making another appearance around the end of July and will be close to the other three planets. This is a splendid opportunity for some nice photographs (which anyone with a decent camera and fast film can take). Let’s get going on this – why not have a club competition?


LAST MEETING:

(for those not at the meeting this is being mailed out)

Thursday, April 25th at 7:30 in room 2-223 at the College. I plan to repeat the talk that I gave to the Science I group at the College. It is entitled “Observational Astronomy with a Small Telescope” and it outlines the scientific projects that one can undertake with a small telescope along with a summary of my activities. Be there!

Bob Nelson, President

PeGASus Newsletter Issue #20 – Mar. 25, 1991

Hello, everyone!! (Brian speaking)

With the warmer weather approaching, it is a bit more liveable for those of us who are fair weather astronomers.

On the 10th of March I was able to watch Callisto eclipse Europa (these are the 4th and 2nd Galilean satellites of Jupiter, resp.). I was surprised to actually see a difference in brightness in Europa as Callisto passed between it and the sun. The eclipse lasted for 12 minutes.

I hunted unsuccessfully for Comet Levy, which is now between the head of Hydra and the star Alphard (= à Hya 9h 27m, -8ø 37′) and a little bit to the west. I would like to know if anyone else has seen it yet.

For those amongst us who are armchair astronomers, PBS is featuring a six-part series “The Astronomers” starting April 15th. Maybe it is just what some of us need to spark interests once again.

Planets: Mercury will be visible about 30-45 minutes after sunset starting the 15th of March reaching greatest elongation on March 27 only to disappear 2 weeks later. To know where to look, draw an imaginary line between the two brightest objects in the sky (Jupiter and Venus) and a spot on the horizon where the sun has just set. Mercury will be less than 12ø above the horizon (which is the width of your hand held at arm’s length). Mars is still visible; March is your last chance to see it before it returns to a pinpoint of light. (Next opposition is 2 years away!) Mars is just below Auriga and shines at magnitude +0.8. Let’s see if we can observe all 8 planets this year!

The club is in the planning stages of making a 10″ Dobsonian that will be made available to everyone in the club to use – feel free to participate in the planning and construction of this club project. [Editor’s note: the spider and secondary mirror holder arrived Mar 15. I may order a secondary mirror from Sky Instruments in Vancouver presently.]

If anyone is wanting star charts, I believe Bob may still have some left from previous meetings [we do – Editor] – they’re free! (It helps to know what you’re looking at.)

Armed with rusty woodworking skills, progress on my mount and tripod is slowly happening – I hope to have it finished by April. It will host a 3″ f/15 refractor (perfect for lunar and planetary viewing).

– Brian Potts


LAST MEETING: (Bob again)

This went well with 3-D charts of comet orbits and a slide show on Kitt Peak Observatory based on my visit in 1980. Yuh shudda been there!

[By the way, note the renumbering of the newsletter, based on a review of previous editions: 15 becomes 18, 16 becomes 19.]


RECENT EVENTS AT TMO:

Well, I managed at long last to get up there on Sunday last. (Any vehicle with snow tires could make it that day.) All is well, no unauthorized person has been in there and there is no more evident damage from rodents. I set 6 mouse traps to make sure that it stays that way.


OBSERVATORY NEWS:

Well, I phoned the Gaming Branch in Victoria and was told that our application for a casino licence is being reviewed by the appropriate official and, if approved, will be typed up and submitted to the commission for final approval. It will be “another month at most”. My informant tells me that the time span for Prince George is 4-5 months from initial submission to casino dates. We submitted early December, so that would be “late spring or early summer” if all goes well. That would be OK with me, because once we have the license and the dates firmly committed, we could start on the planning and work for the power line and security system. Yours truly can also start on the necessary modifications to the telescope to accept the new secondary mirror (the overall focal length has changed slightly).

I shan’t go on about what else will transpire, but I can tell you that there would be work “bees” and lots of activity up there, transforming the largely empty building up there to a functioning observatory again. It promises to be quite exciting. Let’s hope that all goes well.


PROJECTS:

Well, the spider and secondary mirror holder have arrived from Kenneth Novak & co. With a secondary, we will have all we need to mount the Coulter 10″ mirror for a club telescope. (We can make the mirror cell ourselves.) I’ll set up something with Al Pretty soon so that we can get working in his workshop on this. Other possible projects are camera platforms and Poncet mounts for Dobsonian telescopes (which mimic equatorial motion). Stay tuned.


SOFTWARE NEWS:

My program ASTROTIME (for the IBM pc) which, upon input of location, date, time, and astronomical coordinates of an object, calculates the precessed coordinates, local sidereal time, julian date, location in the sky (horizon coordinates) and air mass, now also calculates the constellation the object is in and gives the galactic coordinates. If you’re interested, bring a disk and snag yourself a copy of this useful program. (NO CHARGE!!)


WHAT’S GOING ON IN THE SKY:

See above. On March 7/8, Rod Marynovich were able to find Comet Levy in Hydra. It was a moderately faint smudge with no tail visible, good to find at last. Unfortunately the moon is working around to gibbous again and will probably wash out the comet in future nights.


NEXT MEETING:

1991 March 28 at 7:30 PM in room 2-223 at CNC. I plan to give a condensed version of the talk I have to give to the Science I class the following week. It will be comprised of the following: A thumbnail sketch of the major problems of astronomy over the ages, a summary of what amateurs (or anyone with a small telescope) can contribute, and details of what I have been able to accomplish plus future possibilities. Incidentally, I’ll have news of the newly-formed Association of Binary Star Observers (ABSO).

See you there!

Bob Nelson, President

PeGASus Newsletter Issue #19 – Feb. 20, 1991

LAST MEETING:

Hey, all you people who stayed home missed a good presentation! Brian Potts talked about comets, where to find some of the current ones, etc. He also talked about his trip to Hope in an attempt to time an occultation (unsuccessful, unfortunately). Star charts were passed out and a good time was had by all (I believe).


WHAT’S GOING ON IN THE SKY:

Well, there’ve been a few clear nights lately. Forests for the World is a reasonable viewing site and I and a few others have been up there. Jupiter is prominent and when the air is steady, one can see many features on the planet.

Since we have the ephemerides for several comets, now would be the time to look for them! Comet Levy, although past its maximum, should still be visible high in the southern skies around 10:00. Comet P/Wild 2 is a more difficult object low in the southeast in the wee hours. Comets Machholz, Hartley 2, Wirtanen and Faye will be upcoming in late spring, summer and fall. See Sky and Telescope for 1991 Jan or come to the meeting for details.

The giant Coma and Virgo clusters of galaxies will be visible in dark skies to the southeast these nights and are a fascinating sight.


SHORT ARTICLE – COMETS:

Comets have been observed since the earliest times. Until comparatively recently, they were not recognized as celestial objects; moreover they were thought to be indicators of coming evil. The first “modern” observer to investigate comets was Tycho Brahe in 1577. He determined (by a lack of diurnal parallax) that comets were at least several times away as the moon and were therefore celestial. Kepler observed what was later called Comet Halley in 1607. Newton, applying his law of gravitation to comets, recognized that comet orbits should be conic sections (circles, ellipses, parabolas or hyperbolas). Only the first two are bound orbits, that is periodic (ie returning). Edmund Halley published calculations of the orbital constants 24 comets, noting that the comets of 1531, 1607, and 1682 could well be the same comet, returning to perihelion (closest approach to the sun) every 76 years. If this were true, Comet Halley (as it came to be called) would return about 1758. True to prediction, the comet was discovered Christmas night in 1758 and has been named in Halley’s honour. Subsequent investigations revealed that Comet Halley has been observed off and on since 239 BC. The 1986 apparition was the 30th observed perihelion passage of the comet.

Today, much is known about comets. Most of them travel highly elongated orbits, close to parabolic (eccentricity = 1), but all are believed to be members of the solar system. There are the short period (periodic) comets having periods as short as 3.3 years (Comet P/Enke) – these only go out as far at aphelion as the orbit of Jupiter or so (Comet Halley goes out to Uranus’ orbital distance). Also seen are the non-periodic orbits, so-called because their periods are too long to have been seen more than once (these periods can range up to millions of years). If they are bound objects they could go out to 50,000 AU from the sun (over 1000 times Pluto’s orbital radius).

There are two complications to comet orbits: one is that the major planets (esp Jupiter) can perturb the orbits, changing an elongated orbit to one more nearly circular, and changing a long-period orbit into a periodic one. Another complication is that of non-gravitational forces.

Comets are known to be mostly ice with impregnated dust (the “dirty snowball” theory). Therefore when they approach the sun, the intense rays vapourize some of the ice making a jet and creating a tail. The tail can actually consist of two parts: and ion (gas) tail and a dust tail. These are accelerated outwards by the solar wind and radiation pressure resp. The action of the jet(s) then can give non-gravitational forces.

Come to the meeting for more comet tales (pun).


NEXT MEETING:

This Thursday, Feb 28 at 7:30 in room 2-223 (Physics lab) at CNC. I hope to talk further about comets and show 3-D images of comet orbits using high quality stereo viewers. We have on the Physics computer a recently acquired piece of software “Deep Space 3D” which, among other things, generates these 3D diagrams of comet orbits. It’s shareware, so if you have access to an IBM-compatible, bring along a 3«” high density floppy diskette.

If there’s time and interest, I’ll show slides of my 1980 trip to Kitt Peak. Tea and coffee will, as usual, be served.

See you there!

Bob Nelson, President