AstroNotes 1983 June Vol: 22 issue 05

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ASTRONOTES ISSN 0048-8682
The Newsletter Magazine of the Ottawa Centre of the RASC
Vol. 22, No. 5 $5.00 a year June 1983

Editor.......Rolf Meier.....4-A Arnold Dr......820-5784
Addresses....Art Fraser.....11-860 Cahill Dr___737-4110
Circulation...Robin Molson..2029 Garfield Ave...225-3082

 

OBSERVER'S GROUP MEETING - MAY 6

Chairman Rolf Meier opened the meeting at 8:15 pm with about 30 people in attendance. He made several announcements as follows.

Several meteor observing sessions have been held at Quiet Site so far this spring with more planned. A public "regional" star night is planned for the night of May 13 at D. Aubrey Moodie Intermediate School. The General Assembly will be held on May 20-23 in Quebec City. The June meeting of the Observer's Group will be instrument night, and will also be the main Centre meeting.

Rolf had some exciting news about a new comet. Then at 4th magnitude, it was expected to brighten in a few days, but be gone within a week. Clear weather is hoped for.

Gary Susick, our Vice-Chairman, then presided over the observational portion of the meeting. He first gave a talk concerning eyepiece design, covering the most popular types and their advantages and disadvantages. Two of the new Nagler eyepieces were put on display.

Next up was Brian Burke. He described the preferred methods for observing variable stars. He also pointed out the observing circumstances for the planets in the coming month.

Linda Warren showed some of the slides she had taken over the past few months. Included were views of the moon, sunsets, and some constellations. Also shown was a slide of Venus near the Pleiades.

Rolf Meier ended the meeting with some aurora slides, which Was followed by a lively discussion.
 

MAY 13 PUBLIC STAR NIGHT Rob McCallum
 
At the April 14 Ottawa Centre council meeting it was recommended that the Publicity Committee, in conjunction with the Observer's Group, hold several public "regional star nights" this summer. Hopefully, these would attract new members.

The first of these star nights was held on Friday, May 13, behind D. Aubrey Moodie Intermediate School in Bells Corners. Conditions were ideal - clear skies, few lights, and no mosquitos - for the 40 to 50 people who showed up. They were treated to good views of Venus, Saturn, Jupiter, Uranus and some brighter deep sky objects. We even had an aurora flare up for about half an hour. For some people, it was the first time they had seen a satellite, as several were seen to pass over during the course of the evening. Members brought out a number of telescopes, including a 60-mm refractor, 4 Celestron-8's, a 6-inch Newtonian, a 10-inch Newtonian, and a 17.5-inch Newtonian - a total of 8 telescopes. Several also brought binoculars.

Thanks go to the members who showed up to help Rolf Meier, Brian Burke, and myself out. They include Fred Lossing, Robin Molson, Art Fraser, Bill Dey, Linda Warren, Gary Susick, Frank Roy, and Sandy Thuesen. Your assistance (and telescopes) were appreciated.

We plan to hold the next star night on Friday, June 17 at Vincent Massey Park on Heron Road. As it will not get dark until quite late on that night, making deep sky observing difficult, we have selected a night when the moon will be visible. Anyone who could bring along a telescope is more than welcome. Phone either Rolf (820-5784) or myself (729-9977) at least a few days before the star night or speak to us at the June Observer's Group meeting. We also welcome suggested locations for future star nights.

COUNCIL MEETINGS - JAN 26 AND APRIL 14 Ken Tapping

At the beginning of each new session, the operating methods and organization of the Centre are reviewed and new committees set up. Since we are a voluntary organization, we are forced to use whatever resources are available, and these are constantly changing.

In the first Council meeting, held on January 26, the new committees were formed and the health of the Centre discussed. This work was continued at the April 14 meeting. Over the last year the financial position of the Centre has improved markedly and a major element in the discussion was how to use our resources to increase the quality of service available to the membership and to encourage people to become members. The first move in this was to ask the committees to prepare proposals for activities and facilities and to submit budgets to Council. Among ideas that were discussed were speaker exchange programs, to hold regional star nights, and to make it easier for the general public to reach members of the Centre administration. In an attempt to get more potential members to hear about the RASC, information sheets have been produced for circulation around Ottawa high schools.

One of our major interfaces is Astronotes, the Centre's newsletter, which is for many members the only contact they have with the Centre. The declining number of articles being submitted for publication has led to it not being possible to produce Astronotes on at least two occasions in the last year. This problem has been discussed several times at previous Council meetings and again on April 14. The possibility of making Astronotes a bi-monthly, rather than a monthly, publication is felt by Council to be avoided if possible, and encouragement should be given to getting more articles submitted. This would entail more activity on the part of coordinators and more articles from those in the Centre who observe and develop projects without passing the word. As a further incentive, Council has approved the inauguration of a prize for the best Astronotes Article of the Year. The choice would be made by the Editorial Board and the award would be made at the annual meeting.

Some of the coordinators of the Observer's Group recently held a meeting to discuss getting more activity within the group. They then made a detailed report at the Council Meeting. It was stated that the full potential of the group was not being realized and that action had to be taken. They suggested that a good start would be to set up some guidelines for the roles of the coordinators. They tabled a draft set of recommendations. These were discussed with much enthusiasm and held over for consideration. It was generally agreed that this was a matter of great importance.

For some time the condition of the club house at IRO has been a matter of some concern. The frequent paintings over old paint cannot be continued and either the building should be stripped down to bare wood and then repainted or some other external finish should be applied. It was decided that to attach masonite siding would be the best idea; besides being very durable it would improve the insulation of the building. Money was approved for this and the Observatory Committee instructed to go ahead.

It was reported to Council that the Kitchener-Waterloo Centre has written to us for advice concerning their new radio telescope project. There was general agreement that we would help in any way possible and that opportunities for inter-Centre cooperative activity are always very welcome.

THE 1983 GENERAL ASSEMBLY Rolf Meier

The 1983 General Assembly of the RASC was held in Quebec City this year on May 20-23 at Laval University. About 10 Ottawa Centre members were able to attend.

This was not just an RASC affair. This was a joint meeting with two other organizations, namely the AAVSO and the AGAA, the latter being a union of Quebec's astronomy clubs which are separated from the RASC.

The fun started at 7pm on Friday night, with a wine-and-cheese party. This provided an opportunity for all attendees to meet each other and to renew old friendships.

After that, a series of informal slide shows and movies were presented. Of particular interest was a 3-D spectacular presented by one of the Quebecers. It was concluded with an impressive view of Comet IRAS-Araki-Alcock, which clearly showed the comet in front of the stellar background.

Next came the song contest. The winner in the English category was Peter Jedicke of the London Centre, with a child's black hole song.

The festivities broke up into a series of informal gatherings after this, lasting into the early morning.

Next day, the first of three paper sessions was held. Attendees were thoughtfully provided with simultaneous translation receivers, so that they could understand the talks not in their native tongue. The translation voices were provided by two human beings. Papers were on a wide range of topics, with speakers from all three societies.

On Saturday afternoon, a tour of Old Quebec was provided. Some members took the guided bus tour, but I and a few others chose a driving/walking tour of the old back streets. And what a beautiful, historic city it is. The old section is small enough to be explored by walking, and it was a nice, warm day for it. Our walk was preceded by a lunch in an outdoor restaurant.

On Saturday night, the banquet was held. Awards were presented for various achievements, including a service award to Ottawa member Lloyd Higgs, and the Ken Chilton Prize to Chris Spratt of Victoria for his variable star work.

The banquet was followed by a talk (in French) given by Dr. Hubert Reeves of France. His theme was "The Arrow of Time in Astronomy", dealing with the ultimate fate of the universe, namely through entropy. In this way the direction of time can always be ascertained, since entropy is always increasing with time.

Sunday morning began bright and early with the second paper session.

After lunch, the General Assembly of the RASC was held, followed by a National Council meeting. Two important items arose. First, the Society has purchased a new headquarters building in downtown Toronto, and will no longer be renting on Merton Street. Second, the location of the 1984 General Assembly will be Hamilton, and in 1985 it will be in Edmonton.

The third and final paper session was held on Sunday night. This was followed by the presentation of the display awards.

Frank Roy and Jim Hayes of Ottawa won first prize in the Radio Astronomy category with their display of work using the IRO interferometer. Other awards went to other entrants. But there was no entry in the Variable Star category! Nevertheless, Janet Mattei received an award for being there.

Well, that was it, right? Not quite. Some informal gatherings followed, lasting into the morning. This was hard on some who had to get up early for a day-long tour to the Mont Megantic Observatory. However, we did not go and thus saved $20 each person, plus a lot of sleep.

Now is the time to start planning for Hamilton! The Quebec GA was a lot of fun. Members should try to get some good displays together by next year, by doing a lot of observing, and stuff. Let's put the Ottawa Centre back on the map.

HOW FEW PHOTONS PER SECOND CAN YOU SEE? Fred Lossing

Burnham's Celestial Handbook mentions that in experiments with faint artificial stars on a really black background, an experienced observer could see a "star" of magnitude 8.5. This is about one magnitude fainter than is usually stated for real stars, probably because the sky is never really black, and the eye therefore never fully dark-adapted. From the primary light standard, and the unit of light intensity, the lumen, an equation can be derived which gives the intensity of light (in lumens) falling on an area (for instance the pupil of the eye, or the aperture of a telescope) from a star of a given magnitude. This equation is:
log Q = -(22.4 + m - 5 log A)/2.5
where Q is the number of lumens arriving, m is the stellar magnitude, and A is the aperture of the eye pupil or telescope in indies. From this equation we can calculate the minimum number of photons which correspond to the artificial star of 8.5 magnitude. This will then be the smallest number of photons per second which can be seen by the eye.
So, put a new battery in your calculator, and let's go! We will need some other units: 1 lumen = 1.5 x 10-3 watt, 1 watt = 107 erg-sec-1. Thus 1 lumen = 1.5 x 104 erg-sec-1. Take the diameter of the pupil of the eye as 0.28 inch (7 mm) and take m = 8.5, and solve for Q.
log Q = -13.4657 or 14.5343
and Q = 3.42 x 10-14 lumen
This is 3.42 x 10-14 x 1.5 x 104 = 5.13 x 10-10 erg-sec-1.

Now, let us work out what this amount of light corresponds to in the number of photons per second, using photons of the wavelength the eye is most sensitive to: 560 nanometers (5600 Angstroms). From this we calculate the energy per photon, using the famous Einstein equation, energy E = hV. The quantity h is Planck's constant,6.63 x 10-27 erg-sec. We can get the frequency V from the relationship: velocity of light (in cm-sec-1/wavelength):
frequency V = 3 x 1010 cm-sec-1/560 x 10-9cm = 5.36 x 1014 sec-1
 
The energy of the photon is then
E = hV = 6.63 x 10-27 erg-sec x 5.36 x 1014 sec-1 = 3.55 x 10-12

So now we have the amount of light we can just see, and the amount of light energy per photon. To get the number of photons we can just divide:
No. of photons per second = 5.13 x 10-10 erg-sec-1
3.55 x 10-12 erg = 145 per second

This shows how amazingly sensitive the eye is. Just imagine: if the eye were only 10 times more sensitive, we would see a flutter effect at low light levels as individual photons arrived!

It is also interesting to compare the sensitivity of the unaided eye with the sensitivity of a photomultiplier tube (as used in the photocurrent mode). According to the specification sheet, the sensitivity of the 1P21 photomultiplier is 1.2 x 105 amperes per watt. This decreases to 3.6 x 104 amperes per watt at 560 nanometers, where the eye is most sensitive. What will the current be for a flux of 145 photons per second? At a sensitivity of 3.6 amperes per watt, the amplified photocurrent will be 1.9 x 10-12 amp. This will have to measured in the presence of a "dark current" of 1 x 10-9 amp. This dark current is the current output of the 1P21 in the complete absence of light. It is not always constant, and it is dependant on the temperature. So, for a flux of 145 photons per second the problem would be to measure a signal current of 1.9 x 10-12 amp in the presence of a somewhat variable dark current 500 times larger. Evidently the 1P21 will not be very useful for measuring photon arrival rates of a few hundred photons per second if it is operated in the "photocurrent" mode. In my 8-inch telescope my photometer could just cope with stars of magnitude 10 - 11.

However, the 1P21 can be used in a "photon counting" mode, in which the dark current does not interfere, and which can probably measure one photon per second with some accuracy. The difficulty in this mode will be for bright stars. Going back to our log Q equation and substituting magnitude m = 0 and aperture A = 16 inches, there will be arriving at the focus 7.6 x 109 photons pier second, each photon giving a pulse of electrons at the anode of the 1P21. To count these pulses this rapidly one will need a really fast counting circuit. Alternatively, one can use filters of known transmission to reduce the counting rate to a more reasonable rate.

* * *

COMET SEARCHING Linda Warren

Well, actually the search was complete since the comet (IRAS-Araki-Alcock) had been discovered. What we were searching for were clear skies.

It was Thursday night when Leo Enright telephoned Rolf to let him know that a very fast-moving comet had been discovered and which was to pass very close to the earth, probably closer that any other comet except for P/Lexell in 1770. A position was also difficult to obtain as it was moving so fast.

A meteor storm had been predicted for Monday, May 9 as a result of this comet. As usual, Ottawa skies were cloudy. Not wanting to miss this rare event, we decided that, after establishing where possible clear skies might be, we would simply drive in that direction until we found them.

We had been driving for about an hour or so when just about 20 miles west of Kingston Venus appeared as a beacon, in and out of the clouds, beckoning us on. There were highs and lows as it appeared clear and then... not. Further and further we went and finally, just outside Peterborough we saw the stars and the front. We knew we had finally reached our destination.

It was great! Rolf stepped out of the car, looked up, and said "Oh, there it is". And so it was, not too far from Polaris was a fuzzy patch, amazingly bright and large. Through the binoculars you could see the fan shape of the comet. Also it was easy to see the movement of the comet in such a short period of time. Naturally we took photos which will be shown at the June meeting. As for the meteor storm - I saw one very fast, dim meteor, possibly resulting from the comet.

But what was very interesting to learn (and in retrospect, appropriate) was that co-discoverer George D. Alcock is from Peterborough, where he made his discovery, only he's from the Peterborough in England.
This whole journey was exciting to me, particularly because this was my first naked-eye comet.
 

TWO COMET SURPRISES Rolf Meier

During the month of May we were treated to a rather bright comet, which reached naked-eye visibility for several days. Unfortunately, due to its rather rapid and unannounced apparition, Comet IRAS-Araki-Alcock, 1983d was probably only seen by those fortunate enough to have good weather and be well-informed of its coming a few days in advance. The rapid motion and appearance was caused by the rather close approach of this comet, to with .03 AU of the earth. It is now gone, being a rather small comet and only visible because of its rare close approach.

Imagine the surprise, then, when on May 8.77 UT, while Comet IRAS-Araki-Alcock was approaching its greatest brilliance, another new comet was discovered, which will be approaching to within .06 AU of the earth on June 12! To have two comets approach this close in such a short period of time is truly rare. Comet Sugano-Saigusa-Fujikawa, 1983e will become as bright as 4th magnitude. The following ephemeris is from BAA circular 635:

1983 ET    R.A. (1950.0) Dec.    ?    r    Mag.
h m    '
May 16    01 14.1    + 40 47    o.8o8    o.593    7.0
21    01 01.4    41 07    0.667    0.670    7.1
26    00 48.2    41 06    0.523    0.754    7.1
31    00 31.0    40 41    0.379    0.841    6.8
June 5    23 59.3    39 16    0.236    0.930    6-3
6    23 48.5    38 38    0.208    0.947    6.1
7    23 34.7    37 43    0.18o    0.965    5.8
8    23 16.5    36 18    0.152    0.983    5.5
9    22 51.9    34 02    0.126    1.001    5.2
10    22 17.4    30 03    0.101    1.018    4*8
11    21 28.4    22 46    0080    1.036    4.4
12    20 21.6    +09 52    0066    1 054    4*0
13    19 02.0    -07 44    0063    1.071    4.0
14    17 46.1    22 38    0.074    1.089    4*4
15    16 46 6    31 16    0.093    0.107    5.0
16    16 04.2    35 41    0.116    1.124    5*5
17    15 34.4    38 02    0.142    1.142    6.1
18    15 13.0    39 20    0.170    1.159    6.5
19    14 57.3    40 07    0.198    1.176    6.9
20    14 45.3    40 37    0.226    1.194    7.5
25    14 13.8    41 33    0.373    1.280    8.9
30    14 01.6    -41 47    0.521    1.365    9*9
Mag.1    - 9.7+5 log    ? + 10 log    r

 

IMPORTANT NOTICE CONCERNING SUMMER MEETINGS

Due to the timing of Dominion Day, which occurs on the first Friday in July, and Stellafane, which occurs on the day following the first Friday in August, the July and August Observer's Group meetings have been re-scheduled. They will be held as follows:

July meeting - will be held on Friday, June 24
August meeting - will be held on Friday, July 29
The place, as usual, will be room 3001, 100 Sussex Drive, and the time will be 8 pm.

* * *
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