Estimating Betelgeuse

Clyde Tombaugh, who discovered Pluto in 1930, began his career with astronomy on a Kansas farm. To brighten up one long day of farming he asked himself, “How many cubic inches are there in Betelgeuse?” His answer, with what we know today, would have been 10 to the 41st power! On the next clear night he looked skyward, with a twinkle in his eye, to the reddish chief of Orion. One of its secrets given away, Betelgeuse twinkled back.

Orion is master of the winter sky. From city sky or country, from almost any part of the world, the majestic figure of the Hunter dominates the sky with belt, sword, and club. Look to the southeast early in a January or February evening, or to the south in a March evening, and discover Orion. The keys to this constellation are the three stars that line up in a neat row. The westernmost one is called Mintaka, a delightful Arabic name meaning belt. Using the belt as a beacon, Betelgeuse is one of the easiest stars in the sky to find. The three stars in a row are surrounded by a four-sided figure of four bright stars. The star in the northeast corner of the figure is Betelgeuse. The best time to see Betelgeuse is at the end of January, when it is in the sky most of the night.

The sole poster in Part VI is entitled Introducing astronomy through solar and lunar calenders and comes from Moedji Raharto.

In Indonesia, the lack of competence of many teachers in basic science, astronomy, and space science implies that knowledge of astronomy and space science will be transmitted to the young generation improperly.

Priority in a curriculum of basic science includes only a small amount of general astronomy. The public perception is that astronomy is less important than basic science. Both of these points create a disadvantage for the developing astronomical community in Indonesia, a country with more than 230 million people.

The Muslim community in Indonesia has a tradition of using the lunar calendar to determine the first day of the important months Ramadhan, Syawal and Dzulhijjah. Recent disputes over determining the first day of these months is partly due to a lack of understanding of how the exact time of the first visibility of the lunar crescent is calculated by astronomers.

The challenges of introducing astronomy to a wider community with little background concerning astronomical education was discussed in this paper.

What is the first thing you notice about the stars? Quite likely, it is their differing brightnesses. Although this appears obvious, it is the single most important concept with which you should become familiar before you can be a variable-star observer.

Magnitude

Why do stars differ in brightness? Is it because they are at different distances from us, so that the farther stars appear fainter, like the glow from lamps at the far end of the street? Or are the stars themselves of different brightnesses? As you have likely guessed, both are correct. Sirius, a blue star off the southeast corner of Orion the Hunter, is normally the brightest star in the night sky, not so much because it is actually large and bright, but because it is close. At a mere 8 light years away, Sirius is one of our nearest neighbors. However, there exists a star only a little farther away; Wolf 359 is a “red dwarf” star whose intrinsic brightness is so low that it cannot be seen with the unaided eye. Famed in Star Trek legend as the site of a Borg battle, Wolf 359 is a red dwarf star. Meanwhile, the brightest star in Cygnus the Swan, Deneb, is well over 1000 light years away from us, and is one of the intrinsically brightest stars in the sky. S Doradus is even brighter, but it appears to us as a faint star because it is so far away, actually in a neighboring galaxy.

The quantity and quality of the astronomy that is taught in our schools has a critical impact on the health of astronomy. It affects the recruitment and training of future astronomers. It affects the awareness, understanding, and appreciation of astronomy by the citizens who, as taxpayers and decision-makers, support our work. They form the society and culture within which we operate. In many countries, astronomy does not appear in the school curriculum at all; in other countries, it has a place in the curriculum, but the curriculum may be flawed, or teachers may have neither the training nor the resources to present it effectively. Much is known about effective teaching and learning of astronomy. Very little of this knowledge is implemented in schools and universities. Rather, teaching may be ineffective; it may sometimes intensify misconceptions, and may create an incorrect or negative impression of our subject.

Yet we live in a golden age of astronomy. In the last half-century, astronomers have explored dozens of planets and moons in our solar system, and astronauts have set foot on one moon - ours. Astronomers have discovered over a hundred planets around other stars. They have learned much about the life cycle of stars, including their bizarre end products - white dwarfs, neutron stars, and black holes. On a wider scale, they have mapped the universe of galaxies and, in the twenty-first century, they have determined the age, shape, and composition of the universe with unprecedented accuracy. We have begun to understand our cosmic roots: the origin of our universe, our galaxy, our star, and our planet, and of the atoms and molecules of life.

The best way to get a good start on observing is to discover the stars for yourself. Becoming familiar with the sky – on your own terms – is an important first step toward useful observation.

We do need a place and time to start, so let's try your backyard, under an evening sky of late spring or early summer. High in the west will shine the seven bright stars of the Big Dipper, possibly the best known asterism, or group of stars, in the entire sky. Since Roman times they have been part of Ursa Major (UMa), the Great Bear. The Dipper's handle represents the tail of the Bear, while the feet and nose are shown by fainter stars to the south and west of the bowl (Fig. 1.1).

The Dipper as a road sign

Much as I have tried, I have never seen a bear in the region of Ursa Major, or a plough. The seven stars of the Big Dipper, however, are easy to spot. At any time of night and in any season of the year, the two stars at the end of the Dipper's bowl point towards Polaris, the North Star. All the stars in our sky, the Sun included, circle the celestial poles, and for our lifetimes Polaris will stay within a degree of the true North Celestial Pole. Polaris is the brightest star of another constellation, Ursa Minor or the Little Bear.

Someone may have once told you that astronomy calls for large, expensive equipment. You may even have flipped through the pages of an astronomy magazine in amazement at all the fantastic technology on display there. At some point in your development as an astronomer, you may feel that a telescope will build your interest and extend the power of your observations. But for now, you are probably much better off with a simple pair of binoculars, and this is true for viewing some of the most interesting variable stars, the large, bright “semiregular” stars. Because binoculars are mass-produced and sold almost everywhere, they are far less expensive than are telescopes, even those of the same size. By taking advantage of both your eyes, binoculars present the sky in an efficient, almost three-dimensional way.

Choosing binoculars

The only problem with binoculars is that the two small telescopes that form their optical system must be precisely aligned. So many binoculars lose their adjustment with the bumps and insults of regular use. Before you buy, test the binoculars by pointing them to a distant building or mountain. Holding them securely, make certain that the image in one side is precisely the same as that in the other; landmarks should fall in the same place in both circular fields of view. If the distant object, like mountain or telephone pole, is in the center of one field but near the edge in the other, then the binoculars are out of alignment.

Z Ursae Majoris and the AAVSO method

A huge red giant, Z Ursae Majoris displays some unusual behavior in this late stage of its life. Although it usually ranges from magnitude 6.5 to 8.3, it occasionally surprises us. Once I watched it drop to 9.5, more than a full magnitude below its normal minimum.

With the earlier starter stars we used a simple method where “1” represents the brightest and “5” the faintest. Now that we have some understanding of what the process means, we need not use it; now we are going to play the variable star game by the rules as outlined by the American Association of Variable Star Observers.

Look closely at the two charts (Figs. 8.1 and 8.2) for Z Ursae Majoris. Figure 8.1 is designed for binoculars and has north up. Figure 8.2 is meant for Newtonian viewing where the image is usually inverted. South is up, north down, and east and west are exchanged.

In Fig. 8.1 you recognize the Big Dipper, and near the top of the bowl is the circle-and-dot symbol for the variable star. Near other selected stars are numbers like 66, 54, and 64. These numbers represent magnitudes and tenths, but the decimal point is left out to avoid confusion with the other points that represent stars. Therefore, read “66” as “6.6” and so on.

A thousand years ago

There is something magical about a star that, in its final phase of life, announces its end to the entire Universe. On July 4, 1054, Chinese skywatchers were stunned by something new in the sky. The “guest star” they reported was the outburst of a supernova, triggered by a major instability and collapse within the star. Since then at least three other supernovae have been easily visible from Earth, in 1572 and 1604, a time when European civilization was just about ready to accept new thoughts on the stability and arrangement of stars in space, and in 1987, when our understanding of the process of a supernova was finally good enough to be tested.

The Chinese were not the only ones who might have recorded the guest star of 1054. In 1054, native American records consisting of a rock carving in what is now Chaco Canyon, New Mexico, welcomed a bright new star in Taurus with a waning crescent Moon right next to it. More accurate Chinese records have given us information so that we can pinpoint the date of the event as July 4, 1054. Much brighter than nearby Aldebaran, the exploding star would have been visible in daylight.

For a few days around January 4, 2003, the sky put on a repeat performance, as the planet Saturn happened to be precisely at the spot of the supernova of 1054.

S Persei

In the field of the Double Cluster in Perseus, one of the most spectacular objects in the whole sky, is a special type of red supergiant. It is a representative of a family whose periods of variation are far less certain than those of the Miras. S Persei is a semiregular variable star. The 5000 semiregular variables are a highly independent group of stars, too independent to predict accurately.

Compared to other variables we've looked at, S Per can be glacially slow. If it happens to be quiescent, you may not see much change over several months. While it does have a stated period and range, these figures are somewhat decorative in that they are based on many years of observations, and do not necessarily show the star's current behavior. From one month to another, it may not change at all, or it may surprise you. Observe this star at least once each 30 days.

To find S Persei, use the chart in Figure 17.1, by going north from the cluster NGC 869 (No. 869 in Dreyer's 1888 New General Catalog), until you pass the 6.2 magnitude star 7 Persei, then continuing north to 8 Persei, of 6.1 magnitude. Take care with the next step, which is a jump to the northeast by about one degree.

What happens to observations once an observer has submitted them to a variable-star organization like the AAVSO? It is possible to see how a particular observation compares to other data, and how it fits into measuring how a star is behaving.

According to Elizabeth Waagen, long-time assistant to the director of the AAVSO, here are the steps involved in processing an observation.

Reporting observations

(1) After making an observation, you can send it to AAVSO through its website www.aavso.org, using a program called “WebObs.” (That's how I do it.) Alternatively, you can send in observations via email. Emailed observations are automatically checked by the AAVSO for errors or omissions. A third method is the classic paper report form which, when received at AAVSO headquarters, is entered into the AAVSO database.

(2) All observations sent electronically can be viewed on the website www.aavso.org. Click on “Access Data” and “Light Curve Generator” or go directly to http://www.aavso.org/data/lcg/. Soon you will see a plot of recent observations that will show a star's light curve, the actual story of the star's behavior.

The light curve that you examine of recent data on the AAVSO website is a “quick look” representation of the data. It might come with a notice that the data have not been “validated,” meaning that the data points have not yet passed the AAVSO's strict quality control. Each one is plotted against others and added to the star's light curve.

The International Astronomical Union (IAU) was founded in 1922 to “promote and safeguard astronomy … and to develop it through international co-operation.” There are currently (2005) 9,014 individual members in 87 countries. The IAU is funded through the adhering countries, and is administratively “lean.” The total staff consists of a secretary and an assistant. The officers serve voluntarily, usually with support from their academic institutions. Almost all of the funds supplied from the dues are used for the development of astronomy.

One of the 40 IAU “commissions,” or interest groups, is Commission 46, formerly called “The Teaching of Astronomy,” and more recently, at the 2000 General Assembly, renamed “Astronomy Education and Development.” It is the only commission that deals exclusively with astronomy education; a previous Commission 38 (“Exchange of Astronomers”), which allocated travel grants to astronomers who need them, and a “Working Group on the Worldwide Development of Astronomy,” have been absorbed by Commission 46. The 40 commissions, and the many working groups, were recently organized into 11 scientific divisions. Commission 46 is part of a 12th division, “Union-wide Activities,” which deals with issues of concern to all IAU members.

The commission's mandate is “to further the development and improvement of astronomy education at all levels, throughout the world.” In general, the commission works with other scientific and educational organizations to promote astronomy education and development; through the national liaisons to the commission, it promotes astronomy education in the countries that adhere to the IAU; and it encourages all programs and projects that can help to fulfil its mandate.

Premise

Astronomy plays an essential role in human culture: there is nothing quite like the study of astronomy to capture the imaginations of our students, to make them understand phenomena and introduce them to the fundamental ideas and methods of science and mathematics.

The discovery of TV Corvi

On April 11, 1963, a group of visitors stood in the small gallery facing the largest telescope at Kitt Peak National Observatory at the time, the 84-inch reflector. After the tour guide explained the operation of the great telescope, he asked if there were any questions. One 14-year-old certainly had one. “How does an astronomer get permission to use this telescope?” he asked. “This telescope at the National Observatory,” the guide hissed, “is available only to qualified personnel.”

I was that 14-year-old. Two years later, on December 17, 1965, I began my project to search the sky. On that night, my goal was to begin a search of the sky that might yield a comet, or possibly a nova. A quarter century later, I found a nova, but it did not involve my use of a telescope.

On February 9, 1986 – coincidentally the perihelion date of Halley's Comet – I was in the basement archives at Lowell Observatory poring through hundreds of paper envelopes that Clyde Tombaugh used to store his photographic plates. It was a part of a biography I was writing about the man who had discovered Pluto. These plate envelopes had been replaced with modern archival envelopes, but the originals, complete with Clyde's detailed notes of observation, were still stored in a filing cabinet.

There is an interesting cartoon that shows two small boys and a dog. In the first panel, one boy says to the other “I taught Stripe (the dog) how to whistle!” In the second panel, the other boy replies “I don't hear him whistling!” In the third and final panel, the first boy says “I said I taught him; I didn't say he learned it”.

This cartoon emphasizes the difference between teaching and learning. Research shows that, in the most traditional methods of teaching, the amount of learning may be zero. Of course, there is more to teaching than the learning of facts. In fact, there is an old saying that “education is that which remains after the facts have been forgotten.” So it can include the intangible effects of an inspirational teacher.

There are many important challenges in the effective teaching and learning of astronomy, and most of them are amenable to research. One challenge is students' deeply rooted misconceptions about astronomical topics; non-expert teachers often share the same misconceptions. Some of these misconceptions are caused by the influence of religion or of popular culture. Others result from the three-dimensional nature of many astronomical concepts, or from the problems of moving from an observer-centered frame of reference to an external one, or from the enormous astronomical scales of size, distance, and time. Many of these concepts are intrinsically difficult, and the work of Piaget and others seemed to show that these concepts require students to have reached the appropriate stage of intellectual development - secondary school, for instance.