By Jim Kaler

Sounds like something out of Aesop, some fable about odd acquaintances that professes a moral. In a sense they do, but not one that would be recognized by the old storyteller. Instead, we find two constellations that have some curious things in common, and not just that they both begin with the alliterative "L." Lacerta (our Lizard) and Lynx (the eponymous Lynx) are modern constellations made of faint stars that the ancients did not much bother with. Both are the creations of Johannes Hevel (1611- 1687), who took on the more erudite moniker "Hevelius." His other inventions include Canes Venatici, Leo Minor, Scutum, Sextans, and Vulpecula (in addition to some, like Cerberus, the guardian dog of Hades, that are mercifully gone). While (to the comfort of the Lizard) the constellations are widely separated, their locations nevertheless have a connection. We watch the northern sky turn around the pole, the North Star of Ursa Minor, and tell the season and time of night by the locations of the Big Dipper (the Plough in Britain, formally part of Ursa Major) and Cassiopeia as they circuit the pole nearly opposite each other. As one rises the other falls. From under a dark sky, you see that our two modern figures behave much the same way, Lynx preceding the Great Bear, Lacerta preceding Cassiopeia. The Lizard is formed from a small squiggle of stars that might rather resemble the little creature, whereas the irregular line of stars that makes Lynx (one of the longer figures in the sky) hardly resembles a predatory cat.

Both constellations are rather dim, Lynx's third magnitude luminary (Alpha Lyncis) beating out Lacerta's fourth magnitude Alpha star. Both are among the most common of stars, Alpha Lyn an evolving class K giant 220 light years away, Alpha Lacertae an ordinary Sirius-like class A star 102 light years off. Of the two, Lynx has the only star with a proper name, Alsciaukat (31 Lyncis), which out of Arabic culture refers to a "thorn."

We can single a trio of other stars of particular interest within Hevelius's fine figures. While the telescopic view of single stars is not generally terribly interesting, 10 Lacertae is an exception. At fifth magnitude one of the brighter single class O stars in the sky (the hottest variety), through the telescope 10 Lac, heated to more than 30,000 Kelvin, glows with a strikingly beautiful diamond-like blue-white light. About a thousand light-years away, it radiates at the rate of nearly 30,000 Suns. Admire then a youthful star carrying somewhat more than 15 times the solar mass, one destined to explode some millions of years hence as a supernova.

Then in Lynx, let's add two fine double stars. Easily found right next to Alpha (providing you can find Alpha), lies 38 Lyncis, which Allen calls "Rho Lyn," a designation not from Bayer and no longer used (Alpha the only accepted Greek designation within the constellation). Through even a small telescope, the star -- 122 light years away -- breaks into two components 2.6 seconds of arc apart (the duplicity discovered by William Herschel himself). The brighter is a fourth magnitude A3 dwarf star, while the fainter (and cooler) sixth magnitude companion is something of a mystery. It's classified as A6, but the absolute magnitude implies it is nearly a full class cooler, F4. It may have unrecognized abundance problems that alter the spectrum. Even though no orbital motion is seen, the two stars have been tracking each other since at least 1780, showing the duality to be real.

The star epitomizes the colors of binaries as expressed in the nineteenth century. Though both components are really white, proximity and the brightness difference magnify a small temperature difference into greatly enhanced visual coloration, the two called "silvery white and lilac." At one time, astronomers were actually convinced that doubles glowed with different colors than did single stars. At separations of about one and three minutes of arc lie components C and D, but their motions show that they are just line of sight coincidences. Yet there is still hope for multiplicity. Interferometric observations reveal that 38 Lyn B is really two stars very close together, at best about 0.2 seconds of arc (at the star's distance, at least 8 AU). There is even similar evidence that the A component is a close double. So maybe we are dealing with a quadruple after all.

We can also call out 10 Ursae Majoris, another fine double, in which a sunlike G star is coupled to an F dwarf with a very-difficult-to-split half-second of arc separation, the two in mutual orbit with a period of 22 years. 10 UMa? Shifting boundaries since the stars were given Flamsteed numbers have placed many firmly within neighboring constellations, the "star from UMa" actually now making part of Lynx's sprawling pattern.

Now go truly "deep sky." Lynx is home to one of the most distant - - and massive -- globular clusters in the Galaxy, tenth magnitude NGC 2419. Lying 300,000 light years from us, it is one of six famed outlier globulars that fall far beyond the ordinary "boundary" (such as it is) of the Galaxy's halo. Some 320,000 light years from the Galactic center, NGC 2419 (the first of the six known) was once called the "Intergalactic Tramp." Only "Eridanus" (the globular, not the constellation), Palomar 3 and 4, and AM-1 are farther, the latter only 20 percent more distant from the center. As such, the set outlines a vast "outer halo." Among the most luminous of globular clusters, NGC 2419 contains close to a million stars and is comparable to 47 Tucanae and Omega Centauri (the latter now thought to be the core of a stripped galaxy that merged long ago with ours).

Now let's go MUCH farther. At the center of our Galaxy lies a bright radio source known as Sagittarius A, within which is a smaller dense knot, Sagittarius A*. Radio observations of internal variations show that it has a diameter less than half the size of Mercury's orbit, while orbiting stars allow a measure of its mass at three million or more times that of the Sun. We can conclude only that it is a black hole made bright by its heated surroundings as they are accreted into the black hole's maw.

Yet our nucleus is nothing compared with some others. At the center of Messier 87 in the Virgo cluster lies a supermassive black hole of three THOUSAND million solar masses. From it pours a variable jet at nearly the speed of light, making M 87 an "active galaxy" and the core an "active galactic nucleus," or "AGN." The jet is not pointed sideways, but is rather directed toward us at an angle, making it subject to a relativistic effect that greatly amplifies its light, while a dimmed counterjet goes off in the other direction. Many are the AGNs, some in spiral galaxies, others in ellipticals. They march off to the distant reaches of the Universe, where they are known as quasars.

Now enter BL Lacertae. Once thought to be a simple variable star, hence its name, BL varies erratically between 14th and 17th magnitude. In the 1960s, the telescope at the Vermilion River Observatory of the University of Illinois, then the second largest single collector of radio waves in the world, discovered a radio source that was labelled VRO 42 2201. The blue variable and the radio source were then found to be one and the same. Later still, BL Lac was observed to be at the center of a large, dim galaxy whose distance closes in a thousand million light years. It became the founding member of the "BL Lac Objects," or "blazars" as they are sometimes called. The variable jet turns out to be pointed right at Earth, and thus "blazingly" bright. The ejection of AGN jets has long been thought to be caused by twisted magnetic fields emerging from the central black hole's surroundings, a theoretical construct that has recently been dramatically confirmed in BL Lac by radio astronomers using (among others) the Very Large Array in New Mexico.

So back to the moral. While observing and contemplating the sights of Orion, Cygnus, and other prominent ancient constellations, we need reserve a bit of time for the treasures of these lesser figures, one of which is almost always visible as the Lynx stalks the Lizard around the pole.
Copyright © James B. Kaler, all rights reserved. These contents are the property of the author and may not be reproduced in whole or in part without the author's consent except in fair use for educational purposes. First published in the January/July 2009 Newsletter of the Lowestoft and Great Yarmouth Regional Astronomers, who are gratefully acknowledged.