Capitol Skies - Dec 97 /Jan 1998


Newsletter of the Madison Astronomical Society

 

In this issue


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Members hear Jane Bruen discuss Atmospheric phenomena at the January meeting of the Madison Astronomical Society

Jane Bruen, the society’s program chairman, gave the speakers presentation at the regular January 12 meeting of the MAS. The talk was about atmospheric phenomena. As sky watchers, this turned out to be a most interesting, even fascinating, discussion of the effects of water vapor and ice crystals on the light of the sun, moon and other bright objects in the sky.

Because of the strong refractive effects of water droplets and of the multiple reflecting facets of ice crystals literally dozens of imaging effects can take place. We have all seen rainbows of various types and "sun dogs" as well. There are a host of well defined but not so often seen phenomena due to these crystals and droplets. These phenomena are dependent on a variety of factors such as temperature, humidity, and especially the size and orientation of the ice crystals with respect to the incoming light rays.

Jane obtained and showed several dozen wonderful slides of these phenomena. Sun dogs, rainbows, multiple rainbows, various arcs, tangents, pillars, halos and glories were presented. Jane provided a description of the causes of these phenomena in her commentary on the images. A lively discussion of the personal experiences of members who have seen even some of the more rare effects followed.

We thank Jane for her excellent research into and fine presentation of this topic to our group.


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Observing the Planets

Physical Aspects - Terminology — Bob Manske

There are two basic coordinate systems which are used when observing planets. One is centered on the observer, the other on the planet. From the observer’s point of view, the north point of the planet is that part of the planet’s disk closest to the observer’s celestial north. East is located in the direction of the observer’s east. From the planet’s point of view, east and west for reversed. For this reason, east and west are not preferred terms. If you observe the planet without a clock drive, the planet, along with the stars, will seem to drift across the field of view. The direction of the drift is called "Preceding", the opposite direction is called "Following". These terms are preferred to "east" and "west". Years ago only the observer’s point of view was used. Therefore, on the Moon, Mars, Jupiter, Saturn, and indeed most of the large bodies in the solar system, the Sun rose in the west and set in the east, despite the fact that these objects rotated in the same direction as the Earth. With the dawn of the space age and the landings of machines and humans on other worlds, this strange situation was reversed by the International Astronomical Union (IAU). Since that time, planetary observers have had to qualify their use of these terms by defining whether they meant "east" or "IAU east" and similarly for "west". The use of "following" and "preceding" is always unambiguous and correct. On observing charts, they are designated with their initials: "P" and "F".

planetdiagram.bmp (815114 bytes)

Diagram. This planet is depicted as seen in a typical inverting telescope so that North is down and East is to the right. Adapted from Oliver Montenbruck: Practical Ephemeris Calculations. Springer-Verlag, 1989. Angles are measured from the observer’s north toward the observer’s east, i.e "following" direction.

Rotation

Regardless of the direction of the planet’s rotation, its north pole is defined by the IAU as being the one most closely aligned with the Earth’s north pole. The Position Angle of the North Pole is the angle between the observer’s north pole and the planet’s north pole. The IAU also defines the location of zero degrees longitude for all planets. This point, called the null meridian, is arbitrarily selected. Longitudes are measured in degrees from 0 around to 360. A line drawn from the planet’s north pole through the center of the disk and then through the south pole is called the central meridian. As the planet rotates, various longitudes pass beneath the central meridian. Rotations are defined so that the longitude beneath the central meridian is always increasing.

Terms: Observer’s North, Planet’s North Pole, Position Angle of the North Pole, Null Meridian, Central Meridian

Illumination

The sub-Earth point is located in the center of the disk. An observer on the planet at this location would see the Earth directly overhead. An observer located at the sub-Sun (or sub-Solar) point would see the Sun directly overhead. For planets located further from the Sun than Earth, the sub-Solar point is always located somewhere on the visible disk, but for Mercury, Venus, and the Moon this point may be located on the "back" side. A line drawn from the center of the disk through the sub-polar point points directly at the Sun. The angle between the observer’s north and the line on the disk which points at the Sun is called the position angle of the Sun. It is important to remember that this angle by itself does not tell you whether the planet’s phase is crescent or gibbous. The position angle of the Sun is called the bright limb. The greatest defect of illumination is exactly 180o away from this point.

Phase is defined as the ratio of the illuminated portion of the disk to the total area of the disk. Do not confuse the total area of the disk with the spherical surface area of the planet. Therefore, phase is a number between 0.0 (the planet is exactly between the Earth and the Sun and presents a completely unilluminated disk) and 1.00 (the sub-Solar point is coincident with the sub-Earth point). The phrase defect of illumination returns, this time it means the greatest width of the unilluminated portion of the disk measured in arcseconds, i.e. as measured from the Earth. If you see it listed simply as "defect", resolve the ambiguity by noting whether the unit of measure is in degrees or arcseconds.

Terms: Position Angle of the Sun, Greatest Defect of Illumination, Phase

Miscellaneous

Phase angle is the angle measured from the Sun to the Earth as seen from the planet.

Apparent Diameter is the angular diameter of the whole disk as seen from the Earth. For planets this is always measured in arcseconds. For the Moon it is measured in minutes of arc.

There are several ways of measuring the planet’s elongation from the Sun. It can be measured in terms of right ascension - the difference between their positions measured east-west along the equator; in terms of ecliptic longitude - the difference between their positions measured east-west along the ecliptic; or measured directly along the line from the Sun to the planet. The latter is a true measure of distance from the Sun. Elongation is always measured from 0o to 180o with and "E" or "W" identifying east or west of the Sun.

Terms: Phase Angle, Apparent Diameter, Elongation From the Sun.


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Got The World On A String?
by Wynn Wacker

For most of the 20th century, the Holy Grail of physicists has been to create a grand unified Theory of Everything (TOE) which could explain all the basic forces of nature in one conceptual framework. That such a theory may be possible is suggested by the history of physics. James Clerk Maxwell unified electricity and magnetism in 1873. In 1968 Steve Weinburg and Abdus Salam unified electromagnetism and the weak nuclear force (responsible for beta decay) in the electroweak theory. In the 60's and 70's, attempts were made to construct a Grand Unified

Theory (GUT) which would also tie in the strong nuclear force. Quantum chromodynamics with its quarks and gluons was a step in this direction. A TOE would then tie gravitation into these quantum forces to give a complete description of the basic laws shaping the universe. And that, as it turns out, is the big problem.

Gravity is unlike the other forces in that it is comparatively very weak at a small scale but combines to become the major force shaping the universe on a large scale. This has some serious consequences for attempts to develop a theory of gravity with the same structure as the quantum theories of the other forces. When using the laws of quantum mechanics to solve equations describing the behavior of matter, terms with values of infinity invariably arise. Physicists are able to work around this difficulty by using a mathematical technique called renormalization, in which infinite terms are canceled out on opposite sides of the equation. Unfortunately, the nature of the gravitational force is such that this technique cannot be applied and infinite terms remain, making predictions from the theory impossible. Einstein's relativity theory gives a perfectly good description of the effects of gravity on a large scale, so why should astronomers worry about the failure to come up with a quantum theory of gravity? Because such a theory is needed for understanding what happens at the very largest scales and under the most intense conditions, such as during the creation of the universe in the Big Bang and in Black Hole singularities of collapsed stars and in galactic cores.

It may even be crucial in identifying the dark matter which is important in sculpting galaxies. Because it is so critical to a fundamental understanding of the universe, physicists such as Steven Hawking have been awarded Nobel prizes for work which even partially elucidates the connection beween quantum and relativistic physics.

The main thrust of attempts to come up with a TOE have revolved around supersymmetry. This is the idea that every quantum particle having an integer "spin" has a counterpart with the same mass but half-integer spin. This isn't true currently, so the symmetry is broken and the super partners must have higher mass, but such a condition might have held in the very early universe and making the assumption allows a TOE to be developed. The first such attempt was called supergravity, which postulated the existence of both a graviton and gravitino. It also set an upper limit of 11 dimensions, 10 of space and one of time, on the structure of space-time, and it was quickly determined that the most elegant form of the theory required all 11. Those of us still trying to get a grip on our 4-dimensional world-lines wondered where these extra dimensions came in, but the theorists had an answer for that too - they were closed (as a sphere is a closed two-dimensional surface) and so tightly curved that they were hidden below the quantum "froth" of the Plank length (1E-33 cm). Interesting as it was, supergravity could not explain the handedness of the weak nuclear force (e.g. neutrinos always have a left-handed spin).

Enter the superstring. Many of the necessary properties of matter seemed to be explained as vibrational modes of 1-dimensional quantum strings in 10-dimensional space. Unfortunately, string theory proved an embarrassment of riches in that five different versions of it were developed and advocated by various groups. Equally unfortunate was the fact that, as was the case with gravity, important equations in the theory could not be solved by known mathematical techniques. Despite these problems, superstrings remained the theory of choice for most theoreticians until a few years ago, when a seminal talk by Edward Witten tied together a number of lines of work under the umbrella of M-theory in 11 dimensions.

The "M" in M-theory stands for membrane, and the basic entities in the theory are not strings but p-dimensional membranes, called p-branes, where p is a number less than 10. The history of the development of M-theory and some of its recent developments are described by British physicist Michael J. Duff in the February issue of Scientific American [1]. What's tweaking the heartstrings of the theoretical physicists is that it appears that all of the popular string theories can be derived as just special subsets of M-theory. What's more, some of the dualities implied by the theory allow some calculations to be carried out that were not possible before.

Three of the predictions of M-theory are of special interest to cosmologists. The extra dimension of M-theory can be shrunk into a line segment, resulting in two 10-dimensional universes connected at the ends of a line in 11-dimensional space-time. The particles in each universe can communicate with the other only by gravity. It's one really cool way to explain the "dark matter" found by galactic rotation studies. Also, choosing the size of the 11th dimension correctly means that all four forces (electomagnetic, weak and strong nuclear, and gravitational) become equal at the same particle energy, where previous theory said gravity would be weaker. What's more, the energy is a mere 1E+16 giga electron volts, far less than the Plank energy of 1E+19 giga electron volts which were predicted before. This means that quantum gravitational effects are more likely to have a role in cosmic evolution.

Finally, some recent developments indicate some p-branes have the properties of black holes. In 1974 Steven Hawking showed that black holes are not entirely black, but that they can radiate some energy and may evaporate if small enough. That meant that black holes have entropy, but the origin of that entropy was unexplained. Calculation of the quantum states of the "black-branes" gives exactly the same values as Hawking's predictions. Is M-theory the answer to life, the universe, and everything? The theorists have a GUT feeling that they're on the right track. We mere mathematical mortals can only stand back and hope they aren't stubbing their TOE on a p-braned idea.

[1] "The Theory Formerly Known as Strings". Michael J. Duff. Scientific American 278(2): 64-69. February 1998.


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Observatory Notebook  by Mark Bauernfeind

Good News! The C-11 is back in service in the new AKO and everything is working well. A few small details need finishing on the building but they should be taken care of in a couple of weeks. A hearty thank you to all who helped on this project.

As announced in the Fall edition of Capitol Skies there was a cleanup and picnic held on October 11th. A very nice crowd of diligent (and hungry) workers were on hand to turn YRS into a well groomed and tidy observatory site. We managed to nearly fill a 30 yard container with construction debris and assorted odds and ends accumulated over the years. The shrubs were pruned, weeds cleared and brush was piled at the North boundary of the site. We hope there will be a Winter bonfire party to take care of the brush pile, or more accurately the brush mountain. Details will be discussed at an upcoming monthly meeting.

After several hours of hard labor the cleanup crew was rewarded with a picnic featuring tasty brats boiled in beer and grilled to perfection. Chef Mary Ellestad did a fine job preparing them. There were plenty of additional culinary delights to satisfy the appetite. This was a very productive and enjoyable afternoon. I hope that it will be possible to make this an annual event.

As the year comes to a close it is customary to reflect upon what has come to pass in the previous twelve months. From my perspective, I see a long line of worthwhile accomplishments by the MAS members. This year we have added climate control in the main building. There are now four permanent mounted and three portable telescopes available for observing at YRS. The opportunity to enjoy some quality time under very dark skies has never been greater. With a little help from the weather this coming year should be a great time to utilize the facilities at YRS. Thanks again to all who have shared in making YRS a special place. Please have a safe and happy holiday season.


It seems as though it was just yesterday that I was reflecting on all of the things we accomplished during 1997 and suddenly its New Years Resolution time! Perhaps instead of resolutions a list of important "things to do" will be more appropriate for the observatory in 1998. One of four new committees formed at the January meeting will study the present condition of the KMO (Koster Memorial Observatory) and the future of the building and telescope. Since some of the same difficulties that occurred with the old AKO (Art Koster Observatory) are now appearing in the KMO, this is an important issue to resolve in the next few months so that a recommendation can be presented to the society at the annual picnic in June. If you have an interest in being a member of this committee please let me know soon.

As the MAS begins to study the possibility of bringing more people to the YRS it will become imperative to upgrade the present restroom "facilities". This is really not such a difficult problem to resolve, and I think it would be an easy project to begin the new year with. Last fall I did some research on the cost and availability of used portable toilets and found that they are available and reasonably inexpensive. The February business meeting would be a good time to discuss whether this is an issue the society feels is necessary to deal with at this time. In the last issue of Capitol Skies I mentioned the need for a brush-burning party at YRS. Since it would be safer for the property around us to do this with snow on the ground, now that we actually have some it is time to get this taken care of. If any of you have pyromaniac tendencies, or just enjoy a good bonfire every now and then, let me know and we will schedule a time for this event.

Several maintenance chores, mentioned earlier, need to be dealt with on the main building. Deferred for a couple of years, these really ought to be taken care of during the coming months. When the weather breaks in the spring we should paint the soffit and fascia, install a new threshold for and paint the front door, do something about the Saturn symbol and inspect the condition of the roof shingles. These are relatively simple tasks to complete and will be much easier to accomplish in a group setting. Setting aside a Saturday or two would put these things in order. With the completion of the construction projects at the north boundary of the site it may be time to improve the landscaping. Ruts remain from the heavy equipment that was needed to finish our new buildings. These have made walking around in the dark a bit adventurous. This is certainly not a priority, but if any members have expertise in this area it would be helpful to know what we can do to make the site easier and safer to negotiate at night.


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