James B. Kaler

Department of Astronomy, University of Illinois

First published in the Proceedings of the 36th Annual GLPA Conference, Chicago, IL, October 11-14, 2000. Reprinted by permission.


The year ranged from wonderful views of the sky -- a lunar eclipse, a planetary gathering, a nova -- to the discovery that the Universe may be flat after all. In between, we saw new discoveries about how the Sun heats its corona, looked close-up at an asteroid, admired new planets orbiting other stars, delved further into gamma ray bursts, and sometimes seemed to know less rather than more.

From Earth

How fine to be at Adler Planetarium, one of the great icons of astronomy. The first actual article I saw on astronomy when I was eight years old was illustrated by nothing less than the sight of Adler's great dome from down the street.

And casual stargazing from the planetarium or anywhere else on Earth was, in theory at least, no better than the wonderful gathering of planets we had in May of this year, when Jupiter, Saturn, Mars, Venus, and Mercury were all in a tight bunch. Unfortunately, they had to include the Sun in their midst, making the whole thing quite impossible to see. Unless you used the SOHO spacecraft, which showed it all against the daytime sky. Shortly afterward, on May 31, Jupiter and Saturn passed each other for their "grand conjunction," which takes place every 20 years. It is my third grand conjunction since I have been in this business. And in spite of some predictions, no buildings fell down under the planetary influences; probably because of the power of planetarium astronomers!

Not only was planetary disaster averted, but so was "OH radio" disaster, as the Iridium satellite system, which was to have interfered with radio astronomy, went bankrupt, and we don't have to listen to the "noise" anymore. Danger was also averted in Kansas, where the Big Bang first went bust and was then rescued by the election of a new school board.

The telescopic picture -- of the instruments needed to learn the wonders of the Universe -- is mixed. Europe's Very Large Telescope, while not finished, is partially up and running and producing spectacular results. On the other hand, the highly successful Compton Gamma Ray Satellite was brought down as a result of gyro failure and the worry that another failure would render the machine out of control, a sad and contentious day for the high-energy people, as there was considerable argument about it. And of course we weep for the demise of the Mars Climate Orbiter and the Polar Lander, which never even had their chance, thanks to NASA failures (let's see, if the speed is 50 furlongs per fortnight...). But on the positive side, the HST was again upgraded and 2MASS, the 2 Micron All Sky Survey, is not only pouring out the data, but all the data are on the Web for all of us to use. Even better, the Next Generation Space Telescope, an 8-meter to be optimized for the infrared, is on track for 2009 even though the design has not yet been set.

Back to the long-wave folks, the Green Bank 100-meter radio telescope, with microwave capability, is done, and the Square Kilometer Array is underway, 30 interferometric stations with a total collecting area of (guess what) a square kilometer (how many acres is that?), is now planned for 2010.

The Moon

It's nice, though, to have something that we can see with the naked eye too. How about that wonderful eclipse of the Moon last January! Apparently some Leonids were seen to strike the dark side last November.

And the Sun

Without the Sun (segue here), we could not see the Moon at all. We passed the solar maximum sometime between last January and April, and are now on the downside of the solar cycle. What a sight SOHO and other spacecraft have provided for us. The increased ultraviolet radiation seems to affect the ozone layer, and for reasons that are still mysterious affects climate and the Earth's global temperature as well. Another spacecraft, the remarkably successful TRACE, has been able to disentangle the solar loop structures into narrow threads, and is leading the way in showing how the corona is heated, apparently from below. Most remarkably, solar astronomers have been able to use the myriad solar oscillations to "image" what is on the BACKSIDE of the Sun, allowing us to know of active areas that will soon be visible on the front side. Since these active areas can strongly affect the Earth through coronal mass ejections and flares, such observations give us warning and more time to prepare. This technique cannot help but improve with time.

And its Planets

The Sun was of course the background for the transit of Mercury last November, which I missed because of clouds, OF COURSE. (I did however, get to see the lunar eclipse, and one out of two in the midwest "ain't bad.") The near-grazing transit was also nicely visible against the chromosphere and the corona as well.

Features on Mercury were actually seen for the first time this year reasonably well from the ground, using multiple imaging techniques, in which the best of a great number of individual pictures were combined. The result was the discovery of features on a portion of Mercury not yet seen by spacecraft.

And then there is Mars. In spite of spacecraft failures, new Martian data continue to pour in. The Mars Global Surveyor finds evidence for "recent" (at least geologically) water flows, from now-dry watercourses inside and over craters. If we ever arrive, the water does seem to be there for us to use. There is also some evidence for "recent" volcanism (both in landforms and from uncratered areas), suggesting that the planetary god of war still has some life in him. Though of little research value, it was also intriguing, and certainly instructive, to see a picture of the shadow of Phobos against the Martian terrain, knowing that a solar eclipse was taking place below.

The outer planetary system is no less intriguing. Stability has been on many minds. Orbital simulations continue to suggest that Neptune formed much closer to the Sun than its present distance, and then moved outward under the action of Jupiter and Saturn (or by gravitationally scattering comets), which makes sense in terms of formation, as it seems that there was not enough raw material where Neptune is now ever to have formed a planet. To some degree the same is true for Uranus.

Formation problems still exist for Jupiter and Saturn too. One side contends that the two giant planets formed (4.5 billion years ago) by accumulating dense cores and then gravitationally attracting hydrogen and helium from the surrounding solar nebula; the other side suggests that the planets formed whole out of instabilities in the circulating protosolar disk. We are far from knowing all the details of planetary formation.

Jupiter, the big boss of it all (excepting the obvious Sun), is now seen to produce massive lightning bolts over a thousand kilometers long, perhaps one way in which the giant planet removes its internal heat. Jupiter's Io is, in its own way, just as violent. Its volcanic energy swamps what we have on Earth, the volcano called Loki, at 1800 Celsius generating more volcanic energy than what we see on Earth. Activity is monumental, with even non-volcanic mountains over 15 kilometers high. The Galileo craft shows red to yellow color changes in lava flows that represent the transition of molecular sulfur from one form to another. Europa is hardly left behind. We see fractured tidal bumps 30 meters high that apparently move across the satellite's surface, demonstrating the existence of a warm ocean below. (Imagine such a thing coming at you across a cornfield!)

These satellites have more company than we thought. I recall a time when Jupiter had but 12 satellites (or so we thought), then the count went up to 16, and now number 17 (1999UX18 = S/1999 J1) enters the ranks, a little bitty thing about 2 km across that takes two years to orbit the planet retrograde (and is probably a captured asteroid). Uranus seems to have hit 20 satellites!

Vastly farther out lies Pluto, which is eerily akin to Neptune's Triton, both of them captured by Jupiter (Triton directly, Pluto in a resonant orbit in which it circuits twice for Neptune's thrice, a word you don't get to use much.) From the estimated impact rates from the bodies of the outlying Kuiper belt of comets (to which Pluto sort-of belongs, though it is distinctly NOT a comet), Triton's surface appears relatively young, perhaps only 100 or so million years old, suggesting a lot of internal heat and activity, and a capture only 1-2 billion years ago (tides from the capture heating the satellite).

Pluto itself has ethane in its snow-cover, mixed in with the nitrogen, methane, and carbon monoxide. Nice place. Of course no argument ever seems settled. Some think that the whole gang, Pluto, Charon (Pluto's satellite), and the "plutinos" that share Pluto's 2:3 orbit might all be collision relics. Some 300 of these Kuiper Belt Objects are now known and the number will surely increase rapidly.

Asteroids and Stuff

The great collection of collision relics of course is the set of asteroids. A big new carbonaceous chondrite fall (500 pieces) in Canada (Tagish Lake) will tell us more about asteroids' parents. Chondritic meteorites (the ones with small round chondrules in them, inclusions that have been flash-heated and cooled), have been found to contain such things as amino acids and diamonds, and now of all things both liquid water and halite, which suggest the existence of larger water inclusions or perhaps a collision with a comet.

The "big guy," the Willamette meteorite, is now secure at the Hayden planetarium after the planetarium and the Clackamas tribe in Oregon have agreed on the meteorite's sacred use.

NEAR is also safely orbiting, and is observing Eros, revealing craters and an old surface. A complete map is even available. Someone calculated that, given the odd shape of the asteroid, you could actually fall up a hill.

The real water supply in the little stuff is in the comets, The fragile things eventually disintegrate under sunlight, Comet LINEAR simply falling apart, the destruction well-viewed by Hubble. Sublimation of the ice leads to immensely long comet tails. Until recently no one knew exactly how long. The Ulysses spacecraft (which is observing the solar poles) went through the tail of Comet Hyakutake at a distance of 3.8 astronomical units!

Interstellar Medium and Star Formation

Ethyl alcohol, water: these and a hundred other molecules are found in the dark clouds of interstellar space. And now, Sweetheart, SUGAR, a form called glycolaldehyde. Now if someone will discover interstellar lemon juice...

The intense cold of the dark clouds, which makes these molecules possible, also breeds stars. Dense blobs of interstellar matter collapse under their own weight, and as the stars form in the middle, they spin out to produce dusty disks, from which assemble the planets. And they are there -- planetary systems -- in abundance. At this moment we know of 46 stars with planets, plus 13 others above the 13 Jupiter-mass brown-dwarf limit (at which point the interior temperature is high enough to fuse the natural deuterium that was given to the body at birth).

The radial velocity technique used to find these planets (we observe the star moving back and forth along the line of sight as a result of a planet's gravity) gives only lower limits to the planetary masses, as we do not necessarily know the orbital tilts. Remnant disks have been seen around 55 Cancri and Rho Coronae Borealis, and their clearly defined inclinations give actual respective masses of 1.9 and 1.5 Jupiters. Better yet, the planet of HD 209458 was observed to cross directly in front of its star, right on schedule, beautifully nailing down the tilt and giving a mass of 0.69 Jupiters. Lower yet in mass, 79 Ceti was found to have a planet with a lower mass limit of only 0.35 Jupiters, in the neighborhood of Saturn. We also established a new nearness record to the Earth (11 light years, maybe close enough to see our TV programs), when good old Epsilon Eridani (the subject of many earlier studies) was found to have a planet in the neighborhood of 0.8 to 1.6 Jupiters orbiting at 3.4 astronomical units from the parent star. The Astronomy Picture of the Day actually used my photo of Eridanus. Everybody else photographs Orion, the Big Dipper. I do Eridanus. (It was the only one they could find).

On the negative side, TMR-1C does not have a visible planet. The faint body, which seemed to be "attached" to the star by some kind of filament, is just a background (or foreground) object. Planets did not show up in the core of 47 Tucanae either. With all those stars, we should have seen some transits, and none were observed, suggesting that these stars do not have planets. Maybe the stellar density is too great, or maybe the stars need higher metal contents, implied by the finding that many of the stars with planets have above-average metal abundances.


Speaking of stars (the good segues never stop, do they), the faint ones keep making news. There may be twice as many L and T dwarfs as M dwarfs. L dwarfs are "later," cooler, than M dwarfs, and have hydrides in their spectra; they are a mixture of low-end stars and brown dwarfs. T dwarfs have methane! and are all brown dwarfs down near 1000 Kelvin or below; the new cool record is only 750 Kelvin, for a brown dwarf 19 light years distant. There are not enough of these faint bodies to account for much "dark matter," however. There are some suggestions that brown dwarfs might be created below the upper mass limit for bodies we call "planets," stars so light that they cannot even fuse deuterium. Do planets (formed presumably from the "ground up" by accumulation of dust and gas), and "stars" (formed whole and in place by condensation) overlap?

The physics of these cool stars is not well understood. The coolest of M dwarfs should be fully convective, leaving no radiative core on which to anchor magnetic fields (so goes theory). They should therefore not produce solar-like flares (which result from local magnetic field collapse), but they do. So here is the brown dwarf LP 944-20 Fornacis popping a big flare. Nobody knows how or why.

Stars, stars, stars everywhere. A quick look at the Orion Nebula reveals the Trapezium and a few fainter stars. The infrared view by 2MASS reveals hosts of stars, cascades of them, this region a densely packed cluster in which the Trapezium stands at the top.

Even normal stars can do funny things. Delta Scorpii just brightened by half a magnitude as it apparently turned itself into a Be (class B emission-line) star, necessarily ejecting some matter as it did so. The "funniest" thing to see might be a collision between stars, at least as long as we are not part of it. Students commonly ask about it, and are told that in our part of the Galaxy it just does not happen, as stars are too far apart compared with their diameters. Not so in the centers of globular clusters. Here the stars collide and merge to produce the "blue stragglers," stars that lag behind their cousins in evolution and appear above the turnoff point in the HR diagram where the giant branch joins the main sequence. At least again so goes the latest theory.

Lower Mass Star Death

All these stars, whatever they are, are doomed, as their initial fuel supplies are sure to run out. Those like the Sun will eject their outer layers as planetary nebulae. We thought we understood them pretty well until we looked at them closely (a common astronomical complaint). Look, for example, at MyCn-18, the "Etched Hourglass." There is an inner "hourglass" inside the outer one, and the star is not centered. Neither observation is understood. Nor are the concentric rings around the "Cat's Eye," NGC 6543. Nor is the formation of the World's Largest Planetary, KjPn 18, which is 13 light years long and has another planetary in the middle. One suggestion is that two stars produced two planetaries at about the same time, which seems highly unlikely.

And how about those titanium carbide nanocrystals, anyway. The tiny things have been observed in the ejecta of carbon stars (which create carbon-rich planetary nebulae). To get them, the wind flows had to be a lot larger than previously assumed, further confusing the issues of how the nebulae form.

And how about too that Nova in Aquila last year? Naked-eye novae are not all that common, and it was fun to see another. Novae result from the thermonuclear explosions of matter deposited on white dwarfs by tidally stretched companions, while white dwarfs are the end of the line for intermediate mass stars, and the successors of the planetary nebulae. In badly written books, white dwarfs turn into invisible "black dwarfs." However the Universe is not old enough for that ever to have happened, making the end of the white dwarf sequence a good indicator of Galactic Age. Long thought just to get redder and redder as they cool, the coolest can actually get bluer (for a time), the result of the formation of molecular hydrogen in their atmospheres. Best not to tell this to beginning students.

Higher Mass Star Death

High mass stars do not make white dwarfs. Instead, they explode as supernovae that make neutron stars or even black holes. It seemed to be getting clearer that the leading candidate for a Galactic supernova (100-solar-mass Eta Carinae) is a binary, and that it might be a Wolf-Rayet companion that in the last century belched the "homunculus" cloud that now surrounds the star. (Wolf-Rayet stars are massive stars with stripped hydrogen envelopes and weird high-nitrogen or high- carbon compositions.) The companion is inferred from spectral changes, and is purported to have an eccentric orbit and a 5.5 year period, winds from the two stars fiercely colliding. Other astronomers, however, hold out for the single-star model, and say that the 5.5 year period is caused by oscillations. Controversy rages on!

Further controversy involves the actual masses of these great stars, the "O3 stars" at the top end of the main sequence. The mass-luminosity relation found from double stars does not observationally extend all the way to the stars with the highest luminosities. Theoreticians have suggested that these stars may have masses as high as 120 times that of the Sun. However, the accumulation of observational data suggest that the upper mass limit may is much lower, maybe 55 solar masses or so. No explanation or resolution is yet available.

We do know that such stars indeed blow up, as witnessed by the Large Magellanic Cloud's Supernova 1987A, which came from a class B (Ia) supergiant. The expanding debris has hit the surrounding ring of previous ejecta, which is continuing to brighten. It is not a good idea to let such an explosion go off too close to the Earth (like we can stop it). Ocean sediments contain the iron-60 isotope, a by-product of high-temperature stellar explosions. Its existence on Earth shows that a supernova went off less than 100 light years away maybe only four or so million years ago. Close explosions might damage the atmosphere and affect life on the ground.

Lower-mass high mass stars (which really does make sense), those between say 10 and some limit well above that, seem to make the neutron stars and pulsars (obliquely rotating neutron stars). Explosions are off center, which kick the resulting pulsars away at high speeds. Observations of the Crab and Vela pulsars show the directions of motion to be along the rotation axes. Again, nobody knows why.

As the pulsars radiate their energy away, they slow, and eventually disappear. The observational cutoff for the "pulses" (the rotation period) is around 5-6 seconds. As a surprise, nature gives us an 8.5 second pulsar, with of course no explanation to go with it.

The highest mass stars should provide black holes, although no one can prove it. Our observational knowledge of these strange bodies, from which light cannot escape, comes from black holes in X-ray binaries in which mass falls from the companion into a heated disk surrounding the hole. One, X-ray nova Nova Scorpii 1994, a leading candidate for a binary with a black hole companion, has a visible star contaminated by supernova debris, rather nicely showing that black holes really might be made by supernovae. The nearest such candidate is only 1600 light years away, about the distance of Deneb.

The "collapse of rotating massive stars into black holes" is now a leading theoretical candidate for the explanation of the gamma ray bursts that Compton observed for so long coming from great distances far outside the Galaxy. The gamma rays might be sent outward in tight beams, reducing the energy requirements (which are huge if that much energy has to be radiated over an entire sphere).

Galaxies (Including Ours)

Globally, our Galaxy more and more seems to be a barred spiral, though little is known about the bar itself. Ours has also long seemed to have a massive, million solar mass black hole at its center, the source of the Sagittarius A* radio source. In fact, all large galaxies may have central black holes, which are inferred by size and mass measurements. There are now enough data for statistical studies. The masses of the central black holes seem to correlate not with the masses of the prominent galactic disks, but with the masses of the galactic bulges, the masses of the black holes about 0.2% that of the bulge masses. The disks have nothing to do with it.

The black holes may be older than the galaxies that host them, and may be among the first things formed in the Universe. The accumulation of such black holes and their associated galaxies and quasars may also be responsible for the general X- ray background of the Universe (quasars being distant, ultrabright galactic nuclei in which the surrounding faint galaxies are very difficult to observe).

The galactic black holes create huge jets that were thought to be magnetically confined. Observations of the famed M 87 jet (which pours from a three billion solar mass black hole) with high-resolution very-long-baseline-interferometry now confirm that suspicion, the jet seemingly wrapped in a spiral magnetic sleeve. Presumably, the magnetic field is made by the rotation of the disk surrounding the black hole, the disk that feeds the "monster in the middle." M 87 might also be the source of very high-energy cosmic rays. How, nobody knows (I seem to be saying that a lot, which of course is what makes astronomy the fun it is).

Dark Matter

Most dark matter is confined to vast halos around galaxies, the so-called "dark matter haloes." Merged images of galaxies taken in the Sloan Digital Sky Survey allow the study of the distribution of matter in such dark matter haloes. A typical spiral would have 5 trillion solar masses of the stuff within a volume a million light years wide centered on the galaxy.

Yet for all the mapping, we have no idea what the stuff is. It certainly is not an accumulation of brown dwarfs, unless we are missing an awful lot of them. Could it still be white dwarfs in the galaxy haloes? Or just ordinary molecular hydrogen? The search goes on. And on. And on.

And Now... the Universe

We have to have a new record; it would not be a "year" without one. This one is a quasar with a redshift of 5.8. (That is, spectrum lines are shifted in wavelength to the red by a factor of 5.8, showing the light to be coming from the quasar when the Universe was 1/6.8 its present size). There is even a faint suggestion of a galaxy of some sort with an unconfirmed redshift of 12. Hold that in abeyance, however.

The great AAT (Anglo-Australian Telescope) redshift survey goes on, the point of it to map the nearby Universe to see the distribution of galaxies. So far they have bagged 160,000 redshifts out of a planned 250,000 (a few more than your Messier Marathon). The purpose of the study is to be able to compare actual galaxy distributions with the originating fluctuations in the Cosmic Background Radiation.

Not quite finally, we have a "best" value for the Hubble Constant. Of course we did last year too, and the year before... Now it is 74 plus or minus 7 kilometers per second per megaparsec. Maybe. There are some concerns. From observations of eclipsing double stars, the Large Magellanic Cloud, which is the basis for the calibration of the distance scale, appears 12 percent closer than usually adopted, which raises the Hubble constant by a like fraction. On the other hand, the Cepheids observed in other galaxies, Cepheids that allow the calibration of the Type Ia supernovae that are used to probe the distant Universe, might be contaminated with unresolved stars. (A Type Ia supernova is caused by the explosion of a white dwarf in a double-star system after it is somehow pushed beyond the limit at which it can support itself.) The Cepheids would then be fainter, the host galaxies would be farther away, and the Hubble constant would go down. Then again, observations of water masers in the galaxy M 106 (the comparisons of radial velocities against proper motions, the latter motions being those across the line of sight) suggest that the galaxy is 20 percent closer than indicated by the Cepheids, so the Hubble constant would go back up. All these issues must be clearly resolved before there is a true definitive value.

Observations of the distant Type Ia supernovae suggest that the Universe's expansion is accelerating, but there are lingering doubts that the distant supernovae are really like those nearby, from which we learned the supernova characteristics. We are going to have to go farther out yet (past a redshift of 1) to know what is really happening. We do know that off in the distance, which is also distant in time, that galaxies formed quickly, some astronomers suggesting only 300 million years after the Big Bang.

Perhaps the most exciting discovery in this field is that from the Boomerang balloon experiment. The fluctuations in the Cosmic Background Radiation suggest that the Universe is indeed "flat," that Omega (the density of the Universe vs. the density needed to close it) is 1. But the observed density of matter (which provides but 1 percent or so of closure) plus gravitationally detected dark matter (which provides 25 percent) is insufficient. We also need "density" in the form of energy from the vacuum, that which seems to be making the Universe accelerate. It all rather fits together, yet the uncertainties are enough to give one pause as to whether we have really found the truth. Time only -- combined with further investigation -- will tell.
See main page for copyright statement.