James B. Kaler

Department of Astronomy, University of Illinois

First published in the Proceedings of the 44th Annual GLPA Conference, Milwaukee, WI, October 29-November 1, 2008, reprinted by permission.


The year presented us more with numerous small things rather than blockbuster events. There were exceptions of course, notably the Phoenix landing on Mars and the Mercury flybys. Highlights include the continuing Hubble saga, no or few spots on the Sun, the centenary of the Tunguska impact, the inscrutable Comet Holmes, the discovery of numerous superearths, a number of confusing anomalies, and quite a lot on supergiants and supernovae.

Passages (Us)

All must pass. Nothing, not even the stars, lasts forever. Not even GLPA talks. Before going on, I need to express my deepest thanks to one of the best groups of people I can imagine for an amazing 20-year run that has brought far more to me than I ever gave. Thanks to Dave Linton who got me started giving the Updates in 1989 and to Dave Leake for his continued ideas and encouragement. Thanks to Bob Bonadurer and Dave DeRemer for "The Stargazer." Thanks to Dale Smith for his editorial patience and to Jeanne Bishop for just about everything. Thanks for the opportunity to show my old hand-made planetarium in a real dome, and for granting me the Spitz Lecture. Thanks to the University of Illinois Department of Astronomy for the many years of helping to support these lectures. And above all, thanks for the friendship and bubbling enthusiasm from all.

Passages (Them)

We've traditionally started this review with comings and goings of note, and this year is no different. Among the saddest is watching the big old observatories of yesteryear fade into the twilight. Over the last couple years it was Yerkes, and now it's David Dunlap Observatory, which the University of Toronto wishes to close. It's hard to maintain a top institution within sight of a large community (and when I worked there once, a driving range). The family contends, so stay tuned.

Then NASA blew a FUSE, the Far UV Spectroscopic Explorer failing mechanically after an eight-year run. And Ulysses, the "over the top" solar satellite that examined the Sun's fast (750 km/sec) but constant polar wind (compliments of a gravitational boost from Jupiter), went to join the gods at Olympus, its transmitter going off for good. On the plus side, GLAST, the "Gamma Ray Large Area Space Telescope," mercifully renamed after Enrico Fermi, was successfully launched on June 3 and quickly bagged its first discovery, an all-gamma-ray pulsar.

Even more positively speaking, Salvation is at hand for one of the greatest scientific instruments ever built, the Hubble Space Telescope. Last October (clearly in honor of the GLPA meeting), Shuttle astronauts were to service the Imaging Spectrograph, the Advanced Camera for Surveys, the guidance sensor, all batteries and gyros, and then add the new Wide Field Camera 3 and the Cosmic Origins Spectrograph. Then the data transmission system went out (fortunately BEFORE the mission was launched), resulting in a new launch date in February of 2009. Farther out in the Solar System, the Pioneer Problem, in which the spacecraft motion indicated an unknown gravitational influence, is solved. Just uneven heating. No planet X, no dark companion, no DeathStar. No aliens. But we knew that.

Back on Earth, the Large Binocular Telescope (too bad not the Binocular Large Telescope, as then we could have had the BLT) saw first light last January with its twin 8.4 meter mirrors, which together give the light-gathering power of an 11.8 meter telescope and, as an interferometer, the resolution of a 22.8 meter.

The Sun

We tell all, "don't look at the Sun." Right now there is not even much point. There have been preciously few spots for over a year. Are we seeing just a long wait for the new cycle, or are we entering a new Maunder Minimum, wherein the lack of spots between 1645 and 1715 coincided with the Little Ice Age? That would certainly counter global warming. If so, though, we'd best prepare for when the cycle roars back. More mystery resides in the corona. In spite of unprecedented space imagery and measurement, we still do not know how the solar magnetic field heats the gas to such high temperatures.

We commonly define the "Solar System" by the extent of the planetary system, which stretches to 30 Astronomical Units, 40 if you count Pluto. It's more accurate, however, to include the Kuiper Belt of comets, which takes us to 55 AU or greater. Another definition involves the domain of the solar wind, which we are starting to breach. At a distance of 84 AU, Voyager 2 went through the "termination shock" (where the wind goes subsonic as it pushes against the interstellar medium), a lesser distance than for Voyager 1, which was 94 AU away. The system is clearly flattened. We hope the Voyagers' power supplies last long enough for them to hit the heliopause, where the wind finally slows a halt.


More here than usual. Long before it reaches the heliopause, the solar wind slams past Earth, it and the solar magnetic field seemingly carrying echoes of the five-minute solar oscillation. There is evidence of its imprint on undersea cable and cell phone communications. The effect -- if real -- is the ultimate subtlety in solar-terrestrial relations.

It's nothing compared with the whammy from the asteroid belt. Celebrate then the centenary of the mighty Tunguska impact, whose energy has been downgraded to a "mere" 3 to 8 megatons. (Celebrate more that it has not happened again!) That number of course pales in comparison to the K-T impact of 65 million years ago, the one that took out the dinosaurs. Orbital simulations (that include the "interplanetary superhighway," along which planets can toss things around in a predictable way) suggest that the impactor was a chip from the 198 Baptistina asteroid family (the main belt asteroid itself roughly 20 km in diameter and a piece of a once much larger one).

In a triumph of measurement, the GRACE polar satellites have measured the geoid (the Earth's real shape) to a precision of one centimeter, which allows us to see the rebound of Greenland from the glacial pressures of the last ice age.

Our oxygen isotopes do not match solar or meteoritic values. Nobody knows why. But at least the "faint young Sun" paradox may be resolved. At the time of solar birth, the Sun is calculated to have been only 70 percent as bright as now. How could life have begun on a frozen planet? Perhaps by greater solar magnetic activity caused by youthful fast rotation, or -- as posed recently -- by an increased carbon dioxide content and greenhouse effect, the new work finding that less CO2 is needed than once thought.

... and Moon

Water on the Moon or not? Ice at the poles, ice not at the poles, back and forth. Well, water has finally been found in microscopic amounts in glassy regolith from Apollo 15. So drink up. Then its on to the planets.


With the January and October Messenger flybys (needed to slow the craft down for orbital insertion in March of 2011), Mercury finally takes top billing. We see heavy cratering set within volcanic plains and mysterious radial cracks ("The Spider") at the center of the Caloris Basin, which seem to come out of a large crater at dead center (the latter likely coincidental). At just over 1500 kilometers diameter, Caloris is 20 percent bigger than thought. There is an argued possibility of Mercurian meteorites blasted off the surface. But that is nothing compared to the calculation that there is a 1-2 percent possibility that Jupiter could so change the orbit that whole dang planet could hit us. Fortunately, that would be long after the Sun, expanding as a red giant (5 billion years hence), vaporizes it. And maybe us as well.

Lightning on Venus? So suggests static observed by Venus Express, and originally indicated by the old Soviet Venera craft. New simulations show that our Sister Planet could have had oceans for its first two billion years. And thus maybe life. But all evidence for Venusians (whatever form they might have taken, if any) would have been destroyed by the planet-wide volcanic turnover that took place within the past billion years, not to mention the effect of the runaway Venusian heat.

Mars merits a book. Indeed, several books. So we will note just a few returns from the red planet. The Recon Orbiter sees huge holes, caves hundreds of feet wide, of unknown origin or depth, plus active avalanches across a kilometer-wide scarp and evidence for long-gone glaciers and clays in ancient river deltas. But there is a suggestion that early Martian water was just too salty for life. Back to now, is there a more dramatic picture than the one that spotted the Phoenix Lander coming down under its parachute? It then gave us a magnificent view of the northern Martian plains and more evidence for ice. And then Move Over Mercury, as Caloris pales beside the "Big One." The Martian hemispheric anomaly (volcanos, plains, in the north, cratered highlands in the south) can be explained by a 10,600-kilometer-long "crater" in the north caused by an off-center sideways collision with a 1900-kilometer-wide impactor some four billion years ago that ripped off part of the Martian crust.


Well, not really. Jupiter and Saturn are mostly liquid molecular hydrogen, whereas Uranus and Neptune contain not only H and He but a lot of water and other volatiles such as methane and ammonia. All of a sudden Jupiter had not one, but three red spots. But the GRS is eating the others. No wonder it's so big.

Saturn's ring system seems to have a lot more heft than thought, some three times the "old" mass and about triple that of Mimas. It's mostly the moons that make the press, though, topped by Titan's huge northern methane lake the size of Superior, with tributaries and all. The satellite's rotation suggests a 100-km- thick crust floating on a warmer ocean, reminiscent of Europa. Then we can't seem to get enough of the "tiger stripes" and the icy geysers of Enceladus. Not only have the geysers' origins been seen, but Cassini flew right through them, revealing relatively high temperatures and a complex mix of water and carbon compounds, all possibly the result of tidal heating. The phenomenon suggests subsurface liquid water. And Rhea's got subtle debris rings, the first satellite known to have them. Don't believe in "flying saucers"? You will when you see the nutty shapes of some of Saturn's small moons, which exchange particles with the rings, suggesting that the rings might not be as young as thought.

Speeding along past Uranus, we arrive at Neptune, whose south pole is weirdly hotter (10 K out of 60 K average) than the rest of the planet. Watch out for the resulting strong winds.

Pluto and the Iceballs

Comets, that is. And none captured attention like Comet Holmes. The thing is in a modest 6.9 year period with a perihelion of 2 AU. Who would expect an outburst that raised it from 17th magnitude to 3rd (an increase in visual brightness of a factor of more than a quarter million), whereupon it became an important modifier to Perseus (and a seeming threat to Alpha Persei!). It did the same thing in 1892. Nobody knows what could trigger such an event. Among the best iceballs of the past century, though, was Comet Hale-Bopp, which came to us from the vast Oort Comet Cloud and brought so many out to look. Even though it is now 26 AU out from the Sun and 20th magnitude, it's still puffing a coma. The stuff that the Stardust spacecraft returned from Comet Wild 2 adds to cometary mystery by revealing olivine, suggesting that comets -- at least some comets -- may not have formed so far out as thought.

Circulating among the comets in the Kuiper Belt is our "last planet," Pluto. Now comes along another near-Pluto-sized body, Makemake, touted as the next Plutoid. NOOOOOO, don't let that awful word catch on! Pluto, the first body of the Kuiper Belt, is to my mind an "honorary planet" if nothing else. We'll know more when New Horizons (which has passed the orbit of Saturn) gets there in 2015. (That's only 7 years from now, about a third of the time I've been doing the GLPA Updates.)

Interstellar Medium

Winter's coming, and so is the Orion Nebula. We have a new and improved distance from parallaxes of related small radio sources as found by the Very Large Array, which give 1350 light years good to 2 percent. I've had it at 1400 l-y, not bad. The Nebula is now seen as an ionization blister on the front side of the huge and very dark Orion Molecular Cloud, which lies in back of it, the ionizing radiation coming from the hot stars of the Trapezium (notably Theta-1 Orionis C). While the "OMC" is rich in molecules, the best place to find them is the "Heimat Source," Sagittarius B2 North, near the Galactic Center. Radio astronomers have now found it to contain acetonitrile (NH2CH2CN), a possible precursor to glycine (which was once discovered, then undiscovered). The total number of interstellar molecules is closing in on 150, and there are far more when isotopic variations are included.

Other Worlds

Among the most exciting discoveries since Galileo is the existence of other planets, and even planetary systems, around other stars. They are topped by 55 Cancri (a sixth magnitude G8 dwarf), which has (at least) five planets. The biggest news is the lowering of planetary masses into the realm of "superearths" as a result of dramatically improving technologies. The smallest in the 55 Cancri system carries only 11 Earth masses, while HD 40307 in Pictor has three such planets, the lightest of which carries but 4.2 Earth masses. It goes around its star in 4.3 days. And you think summer speeds by HERE. The current record is 3.3 Earths (in Sagittarius) for a planet found through gravitational lensing.

Brown Dwarfs

Going up the mass scale from planets takes us into the realm of the brown dwarfs, "substars" that cannot run the proton-proton fusion chain (though above 13 Jupiters they can fuse their natural deuterium.) At the low end it's difficult to tell these from planets, though planets are presumed to accumulate from proto- stellar disks, while brown dwarfs collapse directly from interstellar clouds. Or not. Remember that the spectral sequence is now OBAFGKMLT, where class M has a few BD's, class L lots of them, and ALL of class T is made of the little guys. We now have new, and lowest, brown dwarf masses for a T5.0/T5.5 binary of 0.029/0.027 solar masses, far below the 0.075 solar mass fusion cutoff. Each running about 1000 Kelvin, they are "visible" only in the infrared. But that's nothing compared to a new low record temperature of 620 Kelvin (657 degrees F, lower than your self- cleaning oven) for a star that seems to have ammonia bands and has been touted as the first of a proposed new and cooler spectral class Y (though it is more likely very late T).


Climbing the mass-mountain even higher, we arrive at real stars. Among the more interesting news notes is the re-determination of the Hipparcos parallaxes by Floor van Leeuwen, resulting in improved values and lower errors, especially for very distant stars.

Then there are various odds and ends that show fascinating progress in stellar techniques and research. Going more or less from lower masses on up, we encounter, for example, BO Microscopii, a K0 dwarf 145 light years away in which Doppler imaging (from the changing shapes of spectrum lines as the star rotates) actually revealed the location of a stellar flare. More dramatic is EV Lacertae, a red dwarf that popped a global flare that brightened it from 10th magnitude to a naked-eye fifth! So much for life and sunbathing under red dwarf skies. How would you like to see the Sun suddenly 100 times brighter! And since today is Halloween, we have to say "BOO!" Tau Boo that is, a class F6 dwarf/subgiant with a hot Jupiter, for which the stellar magnetic field was found to reverse -- rather like it does in the Sun.

Much higher on the mass scale we find familiar Regulus. Long known to be a wide double (triple, really, as its distant companion is also binary), we now see that it has a white dwarf companion with a 40-day orbital period, making it a quadruple star. Mass transfer from the evolving close companion to Regulus proper is suggested as the source of Regulus's rapid rotation and (as a result) its clearly oval shape (though there is nothing unusual about the rapid rotations of B stars).

White dwarfs evolve from stars with initial masses under 8 to 10 solar, and they are found in abundance not just in the general field, but, as expected, in clusters as well. A search for the oldest open clusters leads to an age for the Galactic disk. Among the oldest open clusters is NGC 6791 in Lyra. All the stars of a cluster are presumed to form at the same time. But two different sets of the cluster's white dwarfs give ages of 4 and 6 billion years, whereas the rest of the stars give 8 billion. Something is amiss, probably with the theory. If it's with the cluster, we clearly have an interesting problem to solve.

Specifically Supergiants

R Coronae Borealis stars are a collective form of carbon star without much in the way of hydrogen envelopes. The prototype, R CrB (a G0 supergiant), will suddenly drop from 5th magnitude to as dim as 15th as a dust cloud is ejected along the line of sight. Now we've confirmed the scenario by actually seeing such a cloud, compliments of RY Sagittarii. Of mysterious origins, R CrB stars may result from the mergers of double white dwarfs.

Are you ready for Epsilon Aurigae, the northernmost of Auriga's Kids? Every 27.1 years, a mysterious immense cloud that seems to surround an internal star or stars eclipses a class F0 supergiant, which is quite a feat. The next event begins in August of 2009 and lasts until May of 2011, during which time the star dims by nearly a magnitude.

Then look to the north for another supergiant, Polaris, the brightest Cepheid variable in the sky. Not that you would notice, since the amplitude of variation shrunk in the 20th century to almost nothing. We thought the star was converting itself from a first overtone 4.0-day pulsator to a 5.7-day fundamental mode, but no, the amplitude now seems to be increasing, making us all wonder what is going on. A much fainter Cepheid, RS Puppis, had its distance accurately measured at 6500 light years using the echo of its light from its surroundings. Such measures are deeply important in calibrating Cepheids for their use as primary distance indicators.

And are you ready for the coming variation in the grandest of all hypergiants, Eta Carinae? Every 5.5 years an unseen companion makes rather a mess of the Eta Car's wind, spectrum, and X-ray radiation as it loops past its periastron. Keep watch in January of 2009 (though you would need to go to the southern hemisphere and have a lot of fancy equipment to do it). This magnificent star is always worth watching. Around 1840, Eta Car erupted to become the second brightest star in the sky after Sirius as it released a vast cloud now seen as the famed Homunculus. Shining near 5 million solar luminosities, it is a prime candidate for a supernova, or an even greater hypernova.

We look at other galaxies to see active "starburst" star formation. But it's here too, as observed by Hubble in the spectacular open cluster/nebular complex NGC 3603, which lies 20,000 light years away in the Milky Way in Carina. Just two million years old, the cluster is loaded with class O3 and already-evolving Wolf-Rayet stars, which have stripped their hydrogen envelopes, allowing us to see by-products of nuclear fusion. (The nitrogen-rich variety is supposed to precede the carbon-rich, but in a nearby galaxy, IC 10, the former are mysteriously missing, suggesting we do not understand such stars all that well.) Measurement of a binary in the cluster gives us the most massive star known to date, 115 solar masses, topping the old value of 85 (and close to the old predicted maximum of 120). Such massive stars may need the heat from less massive "helper stars" to allow them birth, which means they can form only in clusters. This connection is supported by the Galactic motions of a large fraction of field O stars that take them back to their parent clusters. The best known of these is the second magnitude class O star, Zeta Puppis, which left a cluster called Trumpler 10 two and a half million years ago and is now some 8 degrees away from it.

Supernovae and their Leavings

Along with Eta Car, NGC 3603's O and WR stars are destined to develop iron cores that collapse into neutron stars or (in the case of the highest mass stars) into black holes. The remainder of the star is then blown apart in a grand supernova. A first: the SWIFT gamma ray burst telescope spotted the initial X-ray burst from Supernova 2008d in the galaxy NGC 2770 (88 million light years away), the first such observation ever.

A couple years ago, we introduced "RRATS" (Rotating Radio Transients), that can temporarily become the brightest known radio sources in their 0.1 to 1 second bursts. They are apparently another form of neutron star, whose variety boggles the mind. And now we have accurate measures of neutron star dimensions from relativistic effects on hot circumstellar X-ray emitting gas, placing them, as expected, in the range of 29-33 kilometers across. Then it's back to the galaxy IC 10, which contains an eclipsing binary that tells of the largest known stellar black hole, estimated at 24 to 33 solar masses.

Core-collapse ("Type II") supernovae are almost always exceeded in their power by the Type Ia variety, caused when white dwarfs are forced to go past the Chandrasekhar "degeneracy" limit of 1.4 solar masses and then flame out in gigantic nuclear bombs. There are (as seemingly always) two possibilities: overflow onto a massive white dwarf from a binary companion, or the merger of two white dwarfs. The first is the more accepted, but now we have good evidence from the spectrum of ultrabright supernova 2006gz of the merger scenario. Probably it's both, and it's important to understand because the Ia SN's are used as the principal distance indicators in demonstrating the acceleration of the Universe.

At the top are the GRBs, which are (we think) caused by high mass hypernovae, which, because of their increasingly fast rotation as they collapse, produce focused bi-polar bursts of gamma rays. These in turn light up their surroundings in visual "afterglows." That from GRB 089319B hit an all time record of visual magnitude 5.4 even though 7.5 billion light years away! All things being equal (which of course they are not), the absolute magnitude must have been around -35. Don't get too close. Eta Carinae may blast out an energetic GRB. The rotation axis, however, happily points elsewhere.

Mystery Objects

Well, just one. Hubble spotted a transient that went from fainter than magnitude 26 to 21 in 100 days, then disappeared. We have no idea where to place it within this presentation, so it might just as well go here.

Galaxies, Including Ours

The Spitzer infrared space telescope's observation of 110 million stars resulted in yet another, but greatly detailed, map of our Galaxy, clearly revealing its central bar. Yes, we are a barred spiral (a concept that goes back at least 40 years).

Galaxies build themselves up by mergers. We see, for example, the Sagittarius dwarf now passing through our own. The great globular cluster Omega Centauri seems to be the stripped core of a long- since merged small galaxy, and apparently contains a middling central black hole of some 40,000 solar masses. (Even the Large Magellanic Cloud, which we are tidally tearing apart, may have one. A hot star shot out of the LMC at 1000 km/s can be explained by a binary star being disrupted by passing a 1000 solar mass black hole.) There is also evidence that the mergers of spiral galaxies can create ellipticals. Will that happen to us if and when the Andromeda Galaxy hits us? Even multiple events can take place, Spitzer showing four distant galaxies merging at once within a cluster.

It's standard dogma that stars form within a galaxy's dense spiral arms. But apparently not always. We find stars being born also within thin, tidally-formed streamers. In the magnificent spiral galaxy M 83, star formation extends to vast distances out, more than five times distant from the center than the "edge" of the visible disk. But don't expect life. The low metal content of these outlier stars leads to excess ionizing radiation, which kills off interstellar molecules (as observed in M 101). That is, if interstellar molecules really have anything to do with life. And close to the center, we have too many supernovae, resulting in an intermediate ring that may be friendly to life forms. The bulges of spiral galaxies correlate with the masses of their central black holes. And now, so do the pitch angles of the spiral arms. Once more, nobody knows why.

BL Lacertae does it again. Once thought to be a variable star (hence the name), it's a quasar (now known to be a galaxy's central black hole) with one of its bipolar jets pointing right at us, which gives the light a relativistic boost. An ejected blob shows that twisted magnetic fields really do power the jets. And it's hard to ignore OJ 287, in which an orbiting star points to a central black hole of an amazing 18 billion solar masses.

Finally, out there in the great distance, more than 10 billion light years away, are ultradense galaxies that carry our Galaxy's mass but measure only a few percent of our size. No one knows yet what to make of them or how they fit in.

Dark Matter, Dark Energy, and Everything Else

We still do not know what the two "darks" are, though observations continue to point to dark matter as WIMPS (weakly interacting massive particles). From Hubble and the Chandra X-ray observatory, we see the results of yet another collision of galaxy clusters in which the normal matter is stripped and radiates X-rays, while the dark matter, whose distribution is given by gravitational lensing of distant sources, just sails on along with the parent clusters.

In the last category, further analysis of the Wilkinson Microwave Anisotropy Explorer (WMAP) observations of the variations in the cosmic background radiation produced by the Big Bang lead to an age to the Universe of 13.73 billion years, a Hubble constant of 70.1 kilometers per second per megaparsec, a baryonic (normal matter) contribution to the mass-energy of the Universe of 4.6 percent, dark matter and dark energy respectively coming in at 23 and 72 percent. Numbers may vary, depending on what set of observations one uses. The message, though, is clear. We don't understand 95 percent of it all.

Such is the excitement of our field. We never know what is going to turn up with the next observation. We may solve these problems, we may not, but if we do we'll surely encounter more. It's been an exciting and fun ride along the GLPA trail. Thank you for everything. Paraphrasing Edward R. Murrow, "Good Night and 217- 555-1212," we end with a lovely sunset that will surely turn for both of us into a golden sunrise.