James B. Kaler

Department of Astronomy, University of Illinois

First published in the Proceedings of the 43rd Annual GLPA Conference, Wheeling, WV, October 9-13, 2007, reprinted by permission.


The year was led by Cassini's Saturn and methane-filled Titan, as well as by Hubble, which will indeed get its repair (if all goes well) in 2008. And let's not forget the Rovers' Mars, on which the little guys continue to roam and discover. Plan on parties for Uranus's equinox on December 7, and for new views of Pluto in 2015. Pluto gets a minor planet number, but so too does Eris. Our planets and their debris remind us of the remarkable number of discoveries that bring the exo-planet count to 255 (and counting) that include a five-earth-mass measure. Brown dwarfs continue to fall from the sky, Altair now has an actual image, and a record super-supernova lit someone's distant sky. At least we do not have to be so afraid of a nearby gamma-ray burst. Dark matter is more real than ever, while we can now make out some structure in the time-history of dark energy. Huge surveys also begin to show us not just the nature of the Universe, but our place in it as well.


Though most passages are quick, others, like that of the Yerkes Observatory, seem to linger over the years. Now the deal with the developer (to whom the University of Chicago wanted to sell it), who was to maintain the Observatory as an educational site, fell through. Check back with these pages in 2008. The end of the story did, though, catch up with the Mars Global Explorer, which passed away to that great orbit in the sky as a result of a dead battery.

Now a piece of space junk, the MGS, is at least not orbiting OUR world, where debris is becoming a serious problem. Collision with even a small bit of the dregs of the space age moving at orbital speed can cause massive damage to a live satellite, let alone an astronaut. The Chinese government did not help the situation by destroying one of their own satellites, the mess from which added mightily to the danger. One hopes nobody else will try a repeat. It reminds one of the ancient Air Force's circa-1950 Project West Ford, in which it was proposed to launch 500 million copper needles to act as a global radio reflector. Hare-brained schemes are nothing new.

But all is not lost, indeed far from it. The infrared observatory SOFIA (built into a Boeing 747), though years behind schedule (the FAA seems to think that flying a plane at 40,000 feet with a huge hole in its side is unsafe), finally flew, and should be ready to make observations from the optical through 65 microns before long (in dog years). The best news, though, is of Hubble, which is to be serviced next year and outfitted with new cameras, gyros, batteries, coverlets, and so on, in the most complex Hubble repair mission yet. It's a "go" now for perhaps another decade.

To the rebirth of Hubble add two real births that involve our own star,

The Sun.

The Japanese satellite "Hinode" ("Sunrise") has risen to observe the Sun in the X-ray spectrum, where so much energetic action takes place. STEREO goes "one better." The observatory consists of TWO satellites that lead and follow Earth in orbit and that can then observe Sun and solar activity in three dimensions. While we are now within a long "sunspot desert" (nothing seen from August through at least mid-November of 2007) at the low end of the solar cycle, we did catch one flare last December that literally rocked the Sun as it sent a "tsunami" of massive proportions skimming around both sides of the solar sphere. Keep a watch, as the next cycle is on its way (remember the naked-eye pair of 2003?). It's predicted to be a whopper. Then let the Sun set, allowing us to admire

The Moon.

Not only does one face now point at the Earth, but it has odd bulges on it too. Rotation alone (before it became tidally locked to us) can't do it, but a once-high eccentricity might. Closer to us in the astronomically distant past, the tides raised by each upon the other must have been highly variable humdingers.

And here we go again with "ice" in shadowed craters at the lunar poles, where it is presumably mixed with the lunar regolith. Water ice has been discovered, undiscovered, and discovered once again. Now it's the undiscoverer's turn, wherein the ice does not show via radar reflection. Then again, who knows at this point. One thing for sure has been some sort of volcanic outgassing from crater Ina. Those who were once derided for seeing "flaring" on the Moon have been vindicated. We've even seen impacts from Leonids. Things DO happen there.

Inner Planets

As they do here and on our brother/sister rock-balls. Mercury leads us with more proof of a liquid iron interior. By rights, the huge iron core, which contains 60 percent of the mass, should be frozen, the result of small Mercurian size. Yet there is a magnetic field suggesting a fluid core. Radar observations of the planet's librations reveal the same thing. The core is probably "polluted" with something, sulphur perhaps, to maintain at least a slushy state. And let's hear it for last November's great Mercury transit.

Venus's nighttime side has long been seen to glow with the controversial "ashen light." It really does glow, though, in the infrared, with light from the recombination of atomic oxygen into molecular form, the O-atoms separated from their molecules by sunlight on the other side. More dramatic may be an explanation for the planet's backward rotation, which may have been the result of a pair of impacts that created two moons, one of which escaped, the other of which crashed into Venus and reversed its spin. Best idea so far. If you don't like ad-hoc collision hypotheses, just look at the huge basins on Mercury, the Moon, and Mars.

Speaking of which, someone could write a book on Mars. And they have. More than one. Someone could write a book just on the Mars Rovers, which have now exceeded their 90-day design lifetime by a factor of nearly 15. You'd like your car to do that, though you would have to drive in the slow lane. All we can do here is sample the news. The smoother northern hemisphere, which appears so different from the cratered southern, may not be so divergent, as lots of buried craters are being noted. The most amazing thing (among many amazing things) might be fresh running water, evidence for which lies in a crater-wall gully observed in 2005 that was not there in 2001. Magma intrusions make the planet even more earthlike. Except of course, for any evidence for life.

That leaves us, our Earth. Plenty of life here, and it's having an impact by continuing to warm our planet through carbon dioxide (and other) emissions. Summer arctic waters are in massive retreat, as are glaciers. "Global warming" seems to mean intensification of storm systems. And possible further humidification. But studies seem to rule out any sort of variable solar luminosity.

Big Planets

As big as Earth storms are, they pale beside those of the "big guys." Last year Jupiter's "Oval BA" turned itself into "Red Spot Junior." Though roughly a half the size of the Great Red Spot itself, RSJ is as big as Earth. Passing to the south in 2006, RSJ hailed its bigger brother without destruction, and it was still kicking in 2007 when New Horizons took a shot at it. The origins and colors of such spots are not understood.

Saturn is the outer "new Mars," not in terms of form, but as a result of massive information flow from passing and orbiting spacecraft. Cassini has simply transformed what we know about the planet and its satellites, enough for more books. A sampling is all we can do. The famed "spokes" in the ring system observed by the Voyager craft may be the result of electrical charge induced by lightning in Saturn's cloudy atmosphere. The rings are flat enough to disappear when edge on: not true, though, of the D ring, which is rippled, the likely cause of which was an impact with a small body a dozen or so years ago. A spectacular image taken with Cassini in Saturn's shadow, the planet eclipsing the Sun, revealed a distant Earth and Moon. The backlighting and resulting forward scattering of sunlight allowed the detection of very faint rings associated with the satellites Janus and Epimetheus at respective distances of 151,000 and 212,000 km. Light scattered from the rings is so bright that it lights Saturn's nighttime side.

Speaking of satellites, Saturn is up to 56 (not counting ring particles!), Jupiter to 63. And it is the satellites that are getting the press. The nitrogen-ammonia geysers of Enceladus are spraying from the "tiger stripes," which seem to be faults. Tidal flexure makes them rub against each other to produce the needed heat. Tethys and Dione also seem to be ejecting gas into Saturn's whipping magnetic field. And Sponge Bob lives! in the form of Hyperion, on which impacts onto a very low density object create a weird spongy-appearing terrain. That "leaves" Titan, a subject for yet more books. Among other discoveries were a huge cloud from which methane may rain, a low mountain range that may be like our mid-Atlantic ridge, a northern methane lake district, a lake that outranks Superior, sand dunes, and a probable "hydrological cycle." It's enough to wear one out.

On now to Uranus and party time, as the planet will see the Sun crossing its celestial equator next December 7. Voyager 2 saw only a drab cloud deck when the Sun shone overhead near the south pole, but as the Sun (from the planet's perspective) crept toward its equinox, Uranus has developed wonderful weather patterns and "storms." Since there is "nothin' for Neptune," we move on to Pluto.

Pluto and the KBOs

In spite of its new minor planet number 134340, most of us will remain calling the little body the "ninth planet." Sure, Eris (136108) is larger, and from Hubble observations of its satellite, 1.27 times more massive. But it's also a lot farther away (90 AU) and a lot fainter. Pluto indeed is a member of the Kuiper Belt of debris out beyond Neptune. Traditionally, Pluto has been a planet, and given its terrific importance as a transition body, surely can remain so, at least in our minds. We'll know more about it when New Horizons gets there in 2015. An eighth of the way out, the craft passed Jupiter and (as we saw above) took a good look at the colorful cloud belts and the dusty ring, which appeared greatly enhanced when backlit by the Sun (which allows for further exploration of particle size). Even Charon got into the act with the discovery of watery geysers.

The Kuiper Belt extends more or less between 30 and 50 AU from the Sun. More than 1000 Kuiper Belt objects are known, and it is estimated that there may be 70,000 with diameters of at least 100 km.


Discussion of the Kuiper Belt of course leads us to comets, as the Belt is the source of those comets with periods under a couple (or a few) hundred years. We've found that far from being monolithic, comets show great diversity. From observation of Deep Impact debris, we see processed matter: carbonates and clays. The return of "comet stuff" by the Stardust craft shows a body in which some 10 percent seems to have been formed under high-temperature conditions. If so, the finding supports the "X- wind" hypothesis, in which meteoric chondrules were heated near the primitive Sun and then flung outward in part through magnetic interactions with the inner solar nebula. Comet McNaught was great if you could see it. I didn't. (We'll do the extraordinary Comet Holmes next year.)


All of the above came from "out there," when the Sun was birthed from an interstellar cloud. Hubble's 17th anniversary picture was a fabulous 48-image mosaic of the amazing Carina Nebula, in which star formation and death go on at a frantic pace. At the head of the class is Eta Carinae, a binary that is among the most massive in the Galaxy and whose stars may be candidates for the creation of deadly gamma ray bursts (but see below) and black holes.

Contemplation of the interstellar medium brings us to the discovery of another eight interstellar molecules in Sagittarius B2 (the "Heimat [home] Source") near the Galactic Center. The count of all molecules everywhere, including isomeric variations, is up to 141. Not bad considering that the number was TWO when I was in grad school.

Another, though smaller, source is the Orion Nebula, whose distance (derived mostly from the assumed luminosity of the Trapezium stars) has long been somewhat uncertain. Radio parallaxes of young embedded T Tauri stars (stars in formation) nails them at 1350 light years (the nebula a bit farther than the stars), very close to the 1400-1500 light years generally adopted. The radiation from "killer O stars," like the one that lights Orion's nebula, and this year in IC 1396 (as seen with the Spitzer Space Telescope), acts to destroy the protostellar disks of lower mass stars. Don't expect any planets from stars born in the neighborhood.

One of the more contentious star-formation problems involves the creation of binary stars. The old idea that stars bifurcate through rotation is not correct. Binaries may come from fragmentation of the collapsing cloud, multiples from fragmentation of disks.


As Mars and Saturn are to their respective planetary groups, exo- planets are to stars, as there is so much new that we can but sample. As of October of '07, we've found a total of 255 planets. The main radial velocity technique has uncovered 242 planets in 207 systems that include 25 multiple planet systems. From transits we get another 28 planets, including 16 that Hubble nailed in one small area in the Galactic bulge.

Records fall every year. This year we get a "super-earth" of five (at least) earth masses orbiting the class M3 dwarf Gliese 581c every 12.9 days at a distance of 11 million km. Sandwiched between two other planets, (Gl 581b: 5.4 days, and Gl 581d: 83.6 days, the star itself Gl 581a), "c" may be in the life-giving liquid-water zone. Unfortunately, M dwarfs tend to be flare stars, which would not help life along very much. Oddly, M dwarfs with planets seem to have LOWER metal abundances than solar, rather than the usual higher metals as seen for more solar-type stars.

Then there are the puffy planets that are too large for their masses, planets in which hot spots are detected through infrared radiation, and famed Epsilon Eridani, for which a combination of radial velocity and proper motion variations show an orbital tilt similar to that of the dusty disk, firmly tieing planets and disks together.

Brown Dwarfs

Planets lead us on to failed stars, brown dwarfs with masses under about 0.075 solar, which are too small to fire thermonuclear fusion of hydrogen to helium via the full proton- proton chain. Their bottom limit is assumed to be 13 Jupiters, below which even deuterium will not fuse, but nobody knows, and they may well overlap planetary masses (planets forming from dusty disks from the bottom up, stars forming top down directly from interstellar clouds. Maybe).

Remember now that it's OBAFGKMLT. Gimme an "O" and all that. Young brown dwarfs may appear at first to be in class M, and then cool through L. All the T stars are BD's, the record for which is but a few hundred Kelvin. And there are a lot of them. There may be as many class L brown dwarfs as there are between class M7 and M9.5. Some are in binaries, and a tiny number reside in cataclysmic variables. (In a CV, a star donates matter drawn by tides into an accretion disk around a white dwarf. Instabilities in the disk cause flaring and a "dwarf nova." At the extreme, the accreted matter can explode to create a nova.) In an outstandingly odd case, we see an eclipsing binary with a star whittled down to the point in which it is making the transition to brown-dwarf-hood.


Now to more familiar territory, to some things we can go outside to see! Our local solar clone, Alpha Centauri A (in an 80-year binary orbit with Alpha B), seems to be losing its activity, hence its magnetic field, which is down by a factor of 80. Is the star going through a Maunder minimum, in which sunspots fell off between 1645 and 1715 and seem to have promoted a "little ice age"? Alpha Cen C, the M5 dwarf far better known as Proxima, turns out to have a solar cycle all its own of 1.2 years. Even with a long rotation period of 84 days, it's active and a flare star.

Hubble has directly imaged the disks of giants and supergiants (including Mira and Betelgeuse), and now we have an image (made by optical interferometry) of a famed dwarf, Altair, which directly reveals the oblateness that comes from its high rotation speed and short rotation period of 6.5 hours. To conclude naked- eye star news, Mira is trailing a 13-light-year long shock-heated tail from its wind as it plows through interstellar space.

Then there is the nutty eclipsing double in Orion with stars of similar mass, yet one is twice the size of the other. Nobody knows why. And the debris disk surrounding the central star of the Helix Nebula (NGC 7293). The hypothesis is that as the star rapidly lost mass in the creation of the nebula, chaotic motion in its orbiting bodies helped to stir up its Kuiper Belt, resulting in massive collisions and debris. And the perfect "Red Square" that seems to be a planetary nebula in formation. And a old shell around the dwarf nova Z Camelopardalis, which strongly indicates that it is an old nova and that the theory that dwarf novae (see above) eventually produce real novae when the white dwarfs accumulate sufficient mass for a surface nuclear explosion.

Clusters segregate stars according to their masses, higher mass stars sent to the center under the force of combined stellar gravity, lower mass ones to the outside where they can "evaporate" out of the cluster. Further proof of mass segregation was provided by the globular 47 Tucanae, in which more massive "blue stragglers" have sunk more toward the cluster's core.

Blue stragglers are stars the lie above a cluster's main sequence-to-giant turnoff, stars that should have evolved but have not. They are believed to be formed by binary star merger or even direct collision, which gives them their excess masses. And here it is:

Poor Blue Straggler

By Ol' Jim

To be sung to a blues tune.

I'm a poor blue straggler
On the HR diagram...
I don't know where I came from
And I don't know who I am...

Oh blue...poor blue blue blue straggler...

Too high on the main sequence,
Far above the giant turn...
I should now be brightening
My helium for to burn...

Oh blue...poor blue blue blue straggler...

Born in a collision
In an ancient glob-u-lar...
Or maybe by the merger
Of an old bi-nary star...

Oh blue...poor blue blue blue straggler...

When WILL I start evolving,
My stellar mates to join...
It could be in a billion,
With this core H yet to burn...

Oh blue...poor blue blue blue straggler...

Someday though I'll get there,
Be a big old AGB,
Pop a pretty neb'la,
And end degenerately.

Oh blue...poor blue blue blue straggler...
Oh blue...poor blue blue blue straggler.

Supergiants, supernovae, superdense

The wacky variable V838 Mon, the only evolved star ever seen to cross over into class L, still lights its surrounding nebula. In 2002, the star went from 12th magnitude to 6th, as it turned itself into a supergiant, and by reflection (a "light echo") illuminated a cloud of mass previously lost to the star through its wind. V838 is not understood, but with the discovery of another one in the galaxy M 85, it has now has a "class" as one of two "Luminous Red Novae." (See the 2003 update.)

Massive-star core-collapse (Type II) supernovae have left their mark in the Eagle Nebula (M 16) with hot dust revealed by Spitzer, the hot stars carving vast bubbles. These are supposed to be less powerful than the Type Ia supernovae (caused by white dwarfs in binaries exceeding the 1.4 solar mass limit), with absolute visual magnitudes of -17 to -19 as opposed to -19.5 for the Type Ia. Imagine everyone's surprise at seeing a core- collapse event in the galaxy NGC 1260 that hit an amazing -22. It remained brighter than the Ia maximum for nearly a third of a year. Could it be the first example of a "pair-production" supernova in a supermassive 100-150 solar mass star? In such an event, the core collapse is not caused by creation of an iron core, but by the creation of electron-positron pairs from gamma ray collisions that suck the energy from the core, leading to ultimate catastrophe. The result may be total annihilation

The nature of Kepler's Star of 1604 has long been contended. High iron and low oxygen content in the ejecta now clearly show it to be a Type Ia white dwarf supernova, as expected from its distance from the Galactic plane. The reality of the oldest recorded supernova (with an estimated apparent visual magnitude of -2), that of the year 185, has been contended too. Connection with its remnant, RCW 86, confirms that it really happened. To complete the supernova story, X-rays from Cassiopeia A (the brightest radio source beyond the Solar System) reveal particles accelerated by shocks, confirming it and other supernovae as sources of cosmic rays.

Type II supernovae collapse (so far as we know) into neutron stars (lower masses), black holes (in the tens of masses), or even into nothing (for the most massive stars). Don't take any of these limits too seriously. A neutron-star subset, the millisecond pulsars, are spun up to rotation frequencies of more than 700 spins per second by accretion of matter from a companion. It seems that black holes can do the same thing, one rotating 950 times per second as derived from the nature of the accretion disk. The X-rays from the accretion disk have also allowed the mass of the collapsed object in Cygnus X-1 to be nailed at 8.7 solar masses with an uncertainty of only 0.8 solar, confirming once again, that (given a mass greater than the neutron star limit of about three solar) it is indeed a black hole.

Gamma Ray Bursts

Core collapse in ultramassive stars seems to be responsible for ultrapowerful long-duration (more than two seconds) beamed gamma- ray bursts that more than once a day come from distant galaxies. One in our Galaxy even thousands of light years away could cause damage to Earth. But Hubble observations suggest that we might be safe, since the long bursts tend to take place in low-metal galaxies. High metals help produce strong stellar winds that whittle down high-metal supergiants to lower masses, hence lower supernova power. Short-duration bursts are not linked to supernovae. That and their presence in elliptical galaxies (where there are no massive stars) suggest that they come from mergers of binary neutron stars (or neutron stars and black holes). But then to cross it all up there was the long burst with NO supernova.

The Galaxy

The globular clusters of the outer halo have long been the oldest things known, 12 to nearly 13 billion years old. Now we have the oldest-known single star, which from thorium-uranium dating comes in at 13.2 billion years. Seemingly born only a few hundred million years after the Big Bang, the heavy element content (all from an earlier generation of supernovae) is quite low, a thousandth that of the Sun, though far from the lowest (which brings the age into some question).

Our Galaxy, and all the others, is a complex system. Not only was it apparently built from mergers, but collections of its supernovae blow superbubbles and chimneys of gas into the halo, from which it flows back. The nearest of these is found to be in Ophiuchus, 100 supernovae having blown a multi-million solar-mass bubble 13,000 light years into the halo.

Galaxies and their Clusters

While not an actual merger, some 200 million years ago, the Andromeda galaxy (M 31) seems to have taken a hit from M 32 that left ripples in its disk. Within clusters, individual galaxies apparently are swept of much of their interstellar star-forming gas from tides and from plowing through the hot intergalactic medium. Younger, high redshift, galaxies do not yet show the effect. Our own Local Group, not much as clusters go, is however growing, not with forming systems but with more discoveries. There may be as many as 50 dwarfs, though this number is far below that theoretically expected. Faint ones seem to be loaded with dark matter.

Active Galaxies and Quasars

The largest galaxies are centered on supermassive black holes, some of which may reach a billion or more solar masses. Accretion of surrounding matter leads to relativistic bipolar flows, the most famed of which is the jet coming out of the Virgo Cluster's M 87. If the jet comes more or less toward the observer, it's amplified by relativistic effects, and the counter-jet (the one going away from us) visually suppressed. M 87's counterjet has now been confirmed. The outbound flows are so strong that they are seen to power the entire cluster with filaments and loops that come from periodic outbursts that may even inhibit star formation. In another instance we can see the flow from the supermassive black hole in 3C 321 directly blasting and bending around a neighboring galaxy. A two-year flare in a distant galaxy revealed the central black hole to be swallowing a star. Even our own, as evidenced by X-rays, consumed a Mercury- mass some 50 years ago.

Mergers are a major paradigm in galaxy formation and maturation. We even sort of see the process producing bigger supermassive black holes from smaller ones. Ten billion light years off -- that far into the past -- is a triple quasar (quasars young, active, central black holes). Separated by but 100,000 light years, the trio seems to be in the act of merging to produce a more massive black hole. We've even learned how they can align themselves and their surrounding accretion disks so that they actually come together rather than slinging themselves apart.

Dark Matter and Energy

It's still dark. Nobody really has a clue. But dark matter, at least, is surely there. Colliding clusters of galaxies show that normal intergalactic matter was stopped dead, whereas the dark matter, revealed by gravitational lensing (in which dark matter distorts the light from more distant galaxies), stays centered on the clusters. Another huge ring of dark matter may be the result of yet another cluster collision, and seems to represent a DM- ripple much like a stone dropped into a pond. Using lensing, Hubble (with X-ray observations from XMM-Newton) even produced a three-dimensional dark matter map of two trillion solar masses that stretches from near here to halfway back to the Big Bang and reveals increasing clumpiness with time.

Dark energy (if real, as some think it can be explained by messing with gravitational theory) is accelerating the expansion of the Universe. Observations of distant Type Ia supernovae show that it goes back at least 9 billion years and took over from gravitational deceleration 5-6 billion years ago, shortly before the Sun was born.

The Whole Thing

Great distances pose anomalies and puzzles. Did Spitzer find the earliest objects, the mysterious Population III stars that were the first to come along? Spitzer's puzzling objects may also be accreting black holes. A redshift of between around 6 (age of Universe 900 million years) and 7 to 8 (700 million years) may be some sort of great divide, as there are many mature galaxies at the 900 megayear mark, but far fewer at earlier times. And of course there is the usual redshift record, up to 10 (a Universe only 500 million years old), using galaxies brightened by lensing.

Far out we do go. The Sloan survey now has 60,000 giant elliptical galaxies mapped to a distance of five billion light years. Farther yet, we see a huge void 6-10 billion light years away and a billion light years wide, in which there seems to be nothing, the void appearing as a dark spot on maps of the Cosmic Microwave Background.

At the end of story is AEGIS, the "All-Wavelength Extended Groth Strip International Survey" (whatever would we do without acronyms?). It's a 150,000-galaxy, 1.1 X 0.15 degree, panorama that takes us back to eight billion light years. In a different broad panoramic sense, we are one of them, as we can see what we were ourselves only a few billion years after our galaxy formed, giving us yet another dramatic glimpse of our place in the beauty of our wide-ranging and still-mysterious Universe.