NOVA NOTES, the newsletter of the Halifax Centre of the Royal Astronomical Society of Canada, is published bi-monthly in February, April, June, August, October, and December. The opinions expressed herein are not necessarily those of the Halifax Centre. Material for the next issue should reach the editor by May 31th, 1996. Articles on any aspect of astronomy will be considered for publication. "Letters to the Editor" or to our resident expert: GAZER are also most welcome. Contact the editor at:
This photo was taken by David Lane using
a Tele Vue Genesis (500mm f/5 refractor). It was taken on the
night of March 25/26 (at the time of the comet's closest approach
to the Earth) from the Centre's St. Croix Observing Site. The
exposure was 19 minutes on Fuji HG400 Colour film.
INSIDE THIS ISSUE...
Star's of Fancy by David Turner
How to Clean Mirrors and Lenses by Lenny Abbey
Meeting Report: February 96 by Pat Kelly
Meeting Report: March 96 by Pat Kelly
Comet Hyakutake Enlargements Available for Sale (not including in the web version of Nova Notes)
Notice of Meetings and other Stuff
BY DAVID CHAPMAN
If someone had told me it would be this exciting to be President of the RASC Halifax Centre, I might have volunteered sooner! It has been a busy time since our last newsletter: preparations for the Lunar Eclipse (which hasn't happened yet, but will be over by the time you read this), two interesting outside speakers (see the meeting reports elsewhere), and of course: C/1996 B2, otherwise known as Comet Hyakutake, but commonly referred to at dark observing sites as Holy $%#@%!
The comet has been the big news. I hope everyone has had a chance to observe it. (You know it is bright when the "armchair" astronomers are looking at it in their pajamas from their living rooms through the window!) Personally, the night of March 24/25 at our St. Croix observatory site will endure in my memory as one of the most satisfying experiences in my life. The comet was bright and large, the brightest comet ever for me (and for a lot of others). Having viewed it earlier the same night from within the murk at Saint Mary's University, I feel sorry for those who did not make the effort to leave the city to view this comet. For me, the wide-angle photo taken that night by Dave Lane preserves the memory well: it is rare that one's naked-eye image of a comet matches so closely the photographic image. (I heard someone say: Finally! A comet that actually looks like the pictures!) Having said that, there was a certain texture to the comet's coma and the nearby portion of the tail that photographs just cannot reproduce. Perhaps film does not have enough dynamic range, so the brighter portions of the image may saturate during the long exposures required to capture the faintest wisps of the tail.
In honour of the comet and the Lunar Eclipse, we are having a special Members' Night at the May meeting (that is, no main speaker). By then, the comet will have rounded the Sun and people will have had a chance to gather their thoughts and images to share with others. (We will have a very brief "teaser" in April, but we don't want comet chat to interfere with the presentation on meteorites by Bob Hawkes from Mount Allison University.) If you want to give a micro-talk during the May Member's Night, please contact me.
We are still looking for suggestions for an "alternate social activity" to replace the Annual Banquet traditionally held in May. A large majority of the executive have become fed up with organizing this event, to have the same small turnout every year. Accordingly, we have not planned a banquet this year, but we are considering some sort of get-together. It will have to be in June, I suppose, as we don't want to get too close to Nova East in August. Ideas anyone?
Finally, I take great pleasure to announce
that Immediate Past President (also Supernova Hunter Extraordinaire,
man-who-works-30-hours-a-day, Nova Notes Editor, etc.) Dave Lane
has been awarded the prestigious Chant Medal by the RASC
by the National Council at the recommendation of the Halifax
Centre. The formal citation and presentation are yet to come,
but I could not resist telling everyone, so they may congratulate
him personally in April. It was the design and coding of his software
package ECU (Earth Centered Universe) that earned him the medal.
Well done, Dave!
STARS OF FANCY:
BY DAVID TURNER
"Away high in the East swung Remmirath, the Netted Stars, and slowly above the mists red Borgil rose, glowing like a Jewel of fire. Then by some shift of airs all of the mist was drawn away like a veil, and there leaned up, as he climbed over the rim of the world, the Swordsman of the Sky, Menelvager with his shining belt."
"Peering out, Frodo saw that the night was still clear. The Sickle was swinging bright above the shoulders of BreeñHill."
"The Hunter's Moon waxed round in the night sky, and put to flight all the lesser stars. But low in the south one star shone red. Every night, as the Moon waned again, it shone brighter and brighter."
All of the lines quoted above are from J. R. R. Tolkien's famous fantasy epic The Lord of the Rings (Ballantine Books). This trilogy is set in the mid-northern latitudes of Middle-Earth at some unspecified distant epoch in the Earth's past. Although the constellation and star names seem strange, the descriptions should strike a familiar chord with all experienced star-gazers. The first passage is from a scene set late at night towards the end of September, and clearly refers to the Pleiades star cluster in Taurus, with red Aldeberan lying just below. As the mists close to the eastern horizon clear away, the bright stars of Orion come into view, skewed of course at Orion's rising. The "Sickle" referred to in the second passage, from a scene several nights later, is the Big Dipper, as Tolkien explains in a footnote. Frodo must have been looking towards the northern horizon at the time.
The last passage is from a scene that takes place at mid-evening a month or two later. The bright red star sounds intriguing, but cannot be a planet (say, Mars) since the zodiac crosses close to the zenith during winter evenings. A better candidate is the bright star Sirius, which lies to the southeast of Orion. Although Sirius, the brightest star in the sky, appears distinctly white or blue-white in our twentieth century sky, it is accepted from stellar evolutionary theory that this would not have been true some millions of years ago. At that time the faint white dwarf that orbits the much more luminous A-type main-sequence star in the system would have been a luminous red giant with a brightness greater than that of its companion. The combined light of the system would have been both redder and brighter (by a few magnitudes) than it appears today, making Sirius comparable in brightness to the planets Venus or Jupiter. Astronomers have been aware of this possibility for many years, and it seems clear that Tolkien was also aware of the idea when he wrote The Lord of the Rings.
By all accounts Tolkien must have had more than a passing interest in astronomy, although that was not his area of academic expertise. Appendix D of The Lord of the Rings is devoted to a discussion of the various calendar systems in use at the time of the epic, and demonstrates Tolkien's thorough understanding of the topic. The Shire Calendar, for example, stands as an excellent example of a potential replacement for the current calendar system, which has been handed down to us from the time of the ancient Romans with only minor modifications. Like many proposed schemes for calendar revision, the Shire Calendar contains 12 months, each 30 days long. Two extra days (Yule 1 and Yule 2) separate December from January, and three extra days (Lithe 1, Midyear's Day, and Lithe 2) separate June from July. An extra day (Overlithe) is added after Midyear's Day every leap year, and Midyear's Day and Overlithe are celebrated outside of normal week days so that there are exactly 52 weeks every year. The result is a calendar system in which the first day of the month falls on the same day of the week every year ó and never on a Friday! ó so that each day of the year is tied to a specific weekday. In such a system diaries do not differ from year to year, and the specification of a day by both its calendar date and weekday becomes redundant. That is in keeping with the Hobbit characteristic of simplicity.
Tolkien also describes two other calendar
systems used in MiddleñEarth, with full details on each.
His fanatical attention to details of this type undoubtedly accounts
for some of the tremendous popularity of his MiddleñEarth
stories. Every reader finds scenes from their personal experiences
intermixed with scenes of pure fantasy, thereby making the latter
all the more acceptable. This characteristic of Tolkien's writing
has been noted by many commentators previously in various published
reviews. If it seems that astronomy, of all the sciences, is given
special prominence, then perhaps that reflects Tolkien's own fascination
with the subject.
HOW TO CLEAN MIRRORS AND LENSES:
BY LENNY ABBEY (OBTAINED FROM THE INTERNET
BY SHAWN MITCHELL)
The cleaning of optical surfaces, especially those of first-surface mirrors, is the most delicate and exacting task which the astronomer is called upon to perform. At the time of cleaning, a lens is most vulnerable to damage; damage which cannot be repaired. Yet if a telescope is to perform at its greatest potential, cleaning must be done from time to time.
I have used the following method for over twenty-five years without adding a single scratch to the surface of my mirrors and lenses. It has the advantage of requiring only materials which are readily available at the neighborhood pharmacy or grocery store. The cost is less than twenty-five cents per cleaning.
First you must realize that usually
the best advice on cleaning mirrors and lenses is.........DON'T
DO IT. Dirt and grease which are adhering to the surface of mirrors
and lenses may degrade image quality, but they will not damage
the delicate optical surface until they are moved against it.
Removing dirt without allowing it to rub against the underlying
optical surface is what makes cleaning such a tricky task. If
your mirrors and lenses are so dirty that they must be cleaned,
then this is the way to do it:
DO NOT UNDER ANY CIRCUMSTANCES REMOVE
A LENS FROM ITS CELL, OR THE CELL FROM THE TELESCOPE.
This restriction means that the above
procedure must be modified. Only the front surface can be cleaned.
If you remove the cell from the telescope, you will be in big
trouble. There are probably not more than 25 people in the United
States who can effectively collimate a refractor!
Follow the procedure given for objective
lenses, but use Q-Tips (cotton on plastic sticks) instead of cotton
balls. You may, of course, clean both surfaces. The eyebrow juice
on the eye lens of eyepieces may require repeated applications.
I think that this is OK in this case.
MEETING REPORT: FEBRUARY 1996
BY: PAT KELLY
The February meeting began on a bit of a different note as Comrade Chapman had called for an abbreviated meeting of the Politburo. This was to allow for taking our main speaker to dinner without having to rush back to the museum. During the brief interlude between the end of the Politburo meeting and the start of the regular meeting an interesting piece of information came to light. According to rumors, Dave Lane's typing skills are no match for his programming skills. Apparently 25% of his keystrokes are on the Backspace key! (Editor's Note: the number of backspaces isn't important when the forward rate is sufficiently high!) Also, Debbie Storey was discovered in the audience. Those who are frequent attendees at Nova East will remember Debbie as "the crazy woman from Saint John". She is now living and working in Halifax and we hope that she will be at future meetings. As part of the introduction, mention was made of the upcoming eclipse, including the information brochures that had been produced to help publicize the event. There were two versions, a general one and an "adult" one, which featured a cartoon. (The cartoon will be appearing in the next issue of the BULLETIN, which appears to be guaranteed to come out after the event.)
Paul Gray was next with "What's Up!" After twenty years of "no good comets" and eight months of "there is a good one coming", we actually have a new, good comet. At the meeting, it was predicted that Comet Hyakutake would get as bright as first magnitude. As we know now, those predictions were remarkably accurate. Finder charts of the comet were also shown and printed copies were made available to all who wanted them.
The evening's main speaker was Derek Richardson. He is one of the few people that I have met from Vancouver who were actually born there! He was awarded a Commonwealth Scholarship and attended Cambridge to get his Ph.D., which he received in 1993. It was while he was in England, when he was looking to find something to emphasize his Canadian identity that he discovered the Vancouver Canucks and he has been an avid hockey fan ever since. (He even wore his Canucks hat to dinner!) For the last three years he has been a research associate at the Canadian Institute for Theoretical Studies in Toronto. He is about to leave for a position in Seattle, where, it was pointed out, the weather would definitely keep him in the theoretical rather than the observational side of astronomy. Members who want to know more about him can check out his home page, which is part of the CITA web site.
His talk was on the research that he had done looking at comets that come to close to Jupiter. In the case of Comet D/Shoemaker-Levy 9 (the "D" is for "disappeared"), it was found that the comet was initially captured by Jupiter in 1929. On its final orbit it spent about four hours inside the Roche limit, the theoretical boundary, inside of which Jupiter's tidal effects would disrupt a natural object. He showed an image of Callisto which displayed a chain of eleven large craters, all forming a line. It is thought that an even similar to the SL9 incident happened in the past, but this time the string of fragments hit a moon, rather than the planet itself.
He had modeled the nucleus of the comet using the "flying junk pile" model, a collection of spheres packed together. He showed some movies that were generated by the computer software that was used to analyze the tidal effects. As the spheres were disrupted by their close approach to Jupiter, they formed a large number of smaller particles which then clumped back together to form the now-famous "string of pearls". In fact, in their model, this process is completed before the comet gets out to the orbit of Ganymede, which is consistent with the craters on Callisto being made by a small number of larger objects. They even found that their model produced "binary clumps" similar to the one found in SL9. In fact, one of their models produced twenty-one clumps, the same as the number that SL9 had. From the theoretical side, the three parameters that they looked at were density, initial rotation and volume. They found that in comets that had prograde rotation, the rotation aided the breakup of the nucleus. In comets with retrograde rotation, the rotation worked to prevent breakup. Another interesting result was that the length of the string that was formed depended only on the initial size of the nucleus.
Another of Richardson's interests is the search for planets around other stars. He was involved in one study that looked at twenty-one stars, but they did not find any extra-solar planets. While they had been looking for planets and had found none, the astronomers who discovered the object orbiting 51 Pegasi were not even looking for planets! They were looking for pulsation in the atmospheres of sub-giant stars. 51 Peg is a normal main sequence dwarf, but was mislabeled as a sub-giant in the catalog that they were using!
Shortly after this discovery was announced, objects were also found orbiting 47 Ursae Majoris and 70 Virginis, although in that case it seems awfully hard to explain how a planet with six times the mass of Jupiter could end up in an orbit with an eccentricity of 0.4. At this point, he gave a brief tutorial on how the Doppler effect is used to find planets. The biggest problem, familiar to anyone who has studies binary star systems, is that if the inclination of the orbit to our line of sight is unknown, the mass of the planet ends up containing a term involving the sine of the inclination angle. As a result, all of the mass estimates that are derived are lower limits.
Changes in the radial velocities of stars can now be measured quite precisely. Using an instrument that contains hydrogen fluoride gas (a sapphire window is required to let the light in) an accuracy of 13 metres per second can be obtained. For comparison, the effect that Jupiter has on the Sun is 12 m/s. Another group that has started using iodine gas has done even better, getting an accuracy of 3 m/s.
The discovery at 51 Peg also raised some interesting questions because the star has a planet that has half the mass of Jupiter, orbiting it a distance of only 0.05 astronomical units with an orbital period of just 4.2 days! Models of solar system formation do not allow for the formation of such a massive planet that close to its star.
He and others have worked on a hypothesis that the planet was actually formed elsewhere in the star system and then moved to its current location. This "orbital migration" is accomplished by a transfer of orbital momentum. [It can also be accomplished with a very large warp field generator and a level 7 tractor beam, but that is another story!]
What occurs is a reverse of the process that is currently causing the Moon to move away from the Earth. After the planet is formed, a tidal bulge occurs in the outer part of the accretion disk. This slows the planet causing it to move inwards. Eventually the planet will get so close to the star that the planet will raise a tidal bulge on the star which speeds the planet up balancing the effect, and then, after the disk dissipates, slowly moving the planet back out.
The question then arises as to why
Jupiter is so far from the Sun. It may be that it is the last
of a series of precursors which was formed after the accretion
disk no longer had enough mass left to cause it to migrate. After
the main speaker, we had the handbook talk, which was done by
Eric Poisson. The section that he had chosen to explain was the
moonrise and moonset tables. He used overheads of the tables and
the corrections chart to show just how "easy" it was!
Dave Chapman noted that angle that the "correction"
line makes on the chart gets steeper (and the amount of the correction
gets smaller) the closer that you get to the prime meridian. He
was in Greenwich for a few years and while he was there he did
not have to apply any correction to the times given in the handbook!
MEETING REPORT: MARCH 1996
BY: PAT KELLY
Isn't this great! By doing two reports in a row and knowing that they will be the only ones in the next issue of Nova Notes, I don't have to worry about having to follow up after one of David Turner's columns. (Brains, eh!)
As Comrade Chapman had known well in advance that he would not be able to be at this meeting, there was no executive meeting this time either! Instead, we held a meeting the week before at the residence of Doug Pitcairn, and had a great time. This reporter can also attest that Doug's home brew skills are improving and he may soon be promoted to Brewmeister, Junior Grade. For those who were not on the executive, we may hold more meetings at Doug's as a recruitment incentive when nominations come up in the fall!
Blair MacDonald hosted this evening's event, and he did an excellent job if I do say so myself. He made a few pre-meeting announcements. One concerned the upcoming lunar eclipse and the plans that had been made to host observing sessions in both Halifax (Point Pleasant Park) and Dartmouth (Shubie Park). Also of note was the science exhibit that was being held at the Halifax Shopping Centre which would feature a display of telescopes and the new Starlab inflatable planetarium which had just been purchased by the Atlantic Space Sciences Foundation. During the course of the day, 270 children enjoyed planetarium shows; an excellent start to a very worthwhile project.
Our observing chair, Paul Gray has joined the ranks of the gainfully employed, but he to work evenings every second month. As a result, Dave Lane filled in for "What's Up". He surprised everyone by starting off with Venus! He also gave some details on the eclipse and on Comet Hyakutake, which was becoming brighter every evening. He even found a web page from which you could download a file giving the comet's correct pronunciation. Dave also showed some animations showing the path that the comet would follow, as well as some pictures that he had taken a few nights before at Roy's place. He finished up with an animation that showed a rotating Pluto, complete with the light and dark features that had been resolved by the Hubble Telescope. What a machine!
The main speaker was Dr. Gretchen Harris, of the University of Waterloo. Her talk was entitled "Is Our Galaxy Older Than the Universe? What's the Problem?" At present, astronomers have determined that the age of the oldest stars in our galaxy appears to be at least 15 billion years old. At the same time, the age of the universe appears to be less than 10 billion years old. This appears to create a paradox which cannot be resolved, since the universe cannot be younger than objects contained within it.
Dr. Harris noted that the methods used to determine these two numbers are not the same. The age of the galaxy is based on models of stellar evolution and nuclear physics (which are theoretical) and the ages of star clusters based on main sequence fitting (which is observational). The age of the universe is based on observing the current expansion and projecting it backwards to its starting point. This also requires getting the distances to the galaxies being studies and may involve theoretical consideration such as whether the universe is expanding more slowly than in the past. The age of a star can be essentially thought of as the amount of fuel that it has available, divided by the rate at which it is using its fuel. The amount of fuel available depends on the reactions that are taking place at the core, how much hydrogen the star has and how much of that fuel it can actually process. The rate of fuel consumption depends on the temperature, pressure, density, etc. at the core of the star and also on our ability to determine what is going on at the core from what we can observe at the surface.
When one looks at an H-R diagram, one finds that a star's luminosity is approximately proportional to its mass, raised to the power of 3.5. Thus a star that is twice as massive will give off over eleven times as much light. In a star cluster, where all of the stars have essentially the same composition and age, it is the difference in their initial masses that causes the massive stars to leave the main sequence first. By comparing a theoretical models of the H-R diagrams of clusters of different ages with the H-R diagrams actually observed, the age of the cluster can be determined. Telescopes are now available which can, for the first time, detect the faint low mass stars that form the lower part of the H-R diagram for globular clusters. This method yields an age of twelve to fourteen billion years for 47 Tucanae and an age of fourteen billion years for M15.
Studies of all of the globular clusters indicates that they formed over a period of several billion years, with the oldest ones being about seventeen billion years old. If one allows for all possible errors (at least the ones the we can anticipate) being cumulative in the "old" direction, the best that we can do is to make the clusters about a billion years younger.
The age of the universe is determined by observing galaxies and measuring the rate at which they are moving away from us. The expansion that this implies, was first detected by Edwin Hubble. It is quickly seen that the expansion is not stronger than the gravity that binds galaxies together, so the galaxies stay the same size, but simply keep moving further apart. The rate of expansion can be used to determine the amount of time since the expansion began. Since velocity is distance divided by time, if we measure the velocity (based on the red shift of the galaxy's light) and the distance (done by various methods) then we can calculate the time. If we take v = d/t and replace the 1/t with the Hubble Constant, H, we get v = H * t, with 1/H giving the age of the universe. The value for H (the Hubble Constant right now) appears to be around 80 kilometers per second per Megaparsec. This yields a "Hubble time" for the universe of 11.5 billion years.
This age assumes that the universe has been expanding at a constant rate since its beginning. If gravity is slowing the expansion down, so that it will expand more slowly in the future, then it must have been expanding more quickly in the past. This means that the universe actually would be younger than if it had expanded at a constant rate. If the universe is flat, that is if it is at the critical density at which it will eventually stop, then its current age is 2/3 of the Hubble time, or about eight billion years old. Unfortunately, there is no discernible change in velocity that is measurable as we look out to further galaxies; it appears that there is no deceleration that we can measure. If the universe was not at the critical density, we should be able to see this deceleration effect, so that implies that eight billion years is the correct age. Are there any escape routes out of this dilemma? It appears that one possible solution is to accept that the universe is not at the critical density, but even so, the age could only be pushed to eleven billion years. Another way out is to add a cosmological constant, or expansion factor that would have caused the universe of the past to have accelerated at a much higher (and not necessarily constant) rate. The inflationary theory in which there was a phase during which the early universe rapidly expanded, is such a model. Another possibility is that we are measuring only a "local" value of H and not a "global" value. We may not be allowing for motion within clusters, and attractions of one galactic cluster for another, etc. This is related to another problem, that of knowing the distances to the galaxies. The distances over which we can get data to compute the value of H is only 2% of the distance to the most distant galaxies. In effect, we are only sampling 0.0008 % of the universe. Our current cosmological models are still quite simple, mostly due to this lack of data beyond the tiny part of the universe that we are in.
Dr. Harris concluded by saying that there is important information in this contradiction and when we do resolve it, we will know, not only more, but maybe some things that we cannot even imagine at the present. She expects this area of astronomy to be both exciting and challenging.
After her talk, there were more questions
from the audience than at any other meeting that I can recall.
Date: Regular Meeting - Friday, April
19 at 8pm; 7pm for the council meeting.
Place: Lower Theatre, Nova Scotia Museum
of Natural History, Summer Street, Halifax. Access is from the
Topic: Main Speaker: Dr. Bob Hawkes
of Mount Allision University (Sackville, NB) will be talking to
us about meteorites.
Date: Regular Meeting - Friday, May
17 at 8pm; 7pm for the council meeting
Place: Lower Theatre, Nova Scotia Museum
of Natural History, Summer Street, Halifax. Access is from the
Topic: Main Topic: Members Night.
The focus of this evening will be the recent passage of Comet
Hyakutake and the Lunar Eclipse. If you have some slides to show
or experiences to relate please call the president prior to the
meeting. There will also be a preview of the next (?) great comet:
The Halifax Center has several telescopes
for loan to members. These include a Celestron C8 equipped for
photography, a Questar 3.5", a 4" rich-field telescope,
a 4" Maksutov-Cassegrain, and a 10" Dobsonian. Contact
the Observing Chairman, Paul Gray, for further information.
The Halifax Planetarium, located in
the Dunn Building at Dalhousie University, provides shows each
week on Thursday evenings at 7pm. Contact the Nova Scotia Museum
of Natural History at 424-7353 for show information.
The Burke-Gaffney Observatory at Saint
Mary's University provides scheduled Saturday evening "star
nights." Call the recorded information line at 496-8257 for
Honorary President Dr. Murray Cunningham
President David Chapman 463-9103
1st vice-president Blair MacDonald 445-5672
2nd vice-president Shawn Mitchell 865-7026
Secretary Tom Harp 465-4928
Treasurer Ian Anderson 678-8009
Nova Notes Editor David Lane 443-5989
National Representative Pat Kelly 798-3329
Librarian Clint Shannon 889-2426
Observing Chairman Paul Gray 864-2145
Councilors Darren Talbot 443-9373
Dr. David Turner 435-2733
Mary Lou Whitehorne 865-0235