By Jim Kaler

As the days of northern autumn take us ever closer to winter's dark chill, it lifts the spirits to know that spring will follow. And what better way to tell of its coming than to watch great Leo rise as a morning figure, then follow his progress across the ever-earlier skies until you see the grand figure in evening as the trees and flowers begin their awakening. In mythology, he is the Nemean lion killed by Hercules as his first labor, the Hero's constellation rising much later far to the east.

More important to those who watch the skies, Leo is one of the dozen ancient animalistic members of the Zodiac, the band of constellations defined by the ecliptic, the path of the Sun against the stars. The Zodiac embraces the disk of the Solar System, including the planets as well as the Moon. Being the realm of the gods, it was thus sacred to the ancients. The Sun passes through Leo's modern boundaries between August 11 and September 16, allowing him to clear the Sun by early fall, and we are back to the opening of this story.

Ancient astrology took the meaning of the signs of the Zodiac from the natures of the constellations. In the early days, 2000-4000 years ago, the Vernal Equinox (the point where the Sun crosses the celestial equator on its way north to begin northern spring) was in Aries, which is why the Ram usually tops the astrological listings. The Earth, however, has (in addition to rotation and orbital revolution) a third motion, a 26,000-year axial wobble called "precession" that changes the pole star and moves the equinoxes and solstices westward against the stellar background. The Vernal Equinox (still called "the first point of Aries" and symbolized by a ram's horn) is now within Pisces, one constellation to the west, and around the year 2700 will cross over into Aquarius. The Vernal Equinox's opposite, the Autumnal Equinox (in ancient times in Libra, referring to the balance of days), now resides in Virgo. Next up is Leo, which will receive the gift of autumn about the year 2430 (the equinoctial crossing times not symmetrical because of the natures of the modern constellation boundaries).

Leo's charms are, like Gaul, divided in three: bright stars with companions, fainter variables, and a set of marvelous galaxies. Topping the list in the first category is Regulus (the "Little King"), which ranks 21st among first magnitude stars (second up from the bottom) and sits at the most southerly point of Leo's famed "Sickle." It makes a marker for the current Autumnal Equinox, which lies roughly between it and Spica. Just half a degree north of the ecliptic, the star is regularly (no pun intended) occulted by the Moon. Regulus's location as a class B7 dwarf well away from the Milky Way makes it a bit unusual, but its nearby distance of only 79 light years still places it well within the Galactic disk. Spinning madly at an equatorial speed of 317 kilometers per second, the star is notably oblate, a third again bigger through its equator than through its poles. Regulus is actually a quadruple star, orbited by a much fainter but double (K2-M4) dwarf 175 seconds of arc away that must take at least 125,000 years to orbit Regulus proper. Tucked in close to the bright star appears to be a white dwarf that takes a mere 40 days to go around.

Sharing the Sickle is one of the heavens' classic double stars, second magnitude Algieba ("the Forehead"), which is made of two helium-fusing giants (G7 plus brighter K1, classically called "bright orange and greenish yellow") just 5 seconds of arc apart and that orbit with a period of 500 years. What makes the system, better known as Gamma Leonis, most intriguing is a planet that orbits the brighter star with a period of 1.2 years in an path about the size of Earth's. But don't look for life, as it's a giant with a mass of at least nine times Jupiter's, so big it could be a low mass brown dwarf. At Leo's nether end lies second magnitude Denebola (the Lion's Tail), Beta Leo, an A3 dwarf. It was one of the first to be recognized as having a highly structured infrared-radiating encompassing dust-disk, a "Vega-type" star that may well possess planets, though none has been found as yet. Denebola appears to have three companions, but all are probably "optical" line-of-sight coincidences. One, Beta Leo B, a 16th magnitude star 40 seconds of arc away in the 19th century, seems to have "disappeared" and may be spurious or might even have been recovered as "C."

That brings us to the second category, the variables, of which R Leonis (in western Leo) usurps the title from Regulus as "king." This notably red M7-M9 giant is a well- known (the fourth discovered) Mira variable with a 312-day period, and is one of the few that reach naked-eye brightness. After hitting fifth magnitude, half a period later it sinks to tenth or even 11th. Two hundred forty light years away, with a temperature hovering around 3000 Kelvin, the star shines with the light of some 4000 Suns, making it as big as Earth's orbit. It's surrounding dusty cloud is the source of both silicon monoxide and hydroxyl masers that are pumped by the star's brilliance.

Continuing the variable-star trek, look first to a magnificent fourth-magnitude blue class B1 supergiant, Rho Leonis, which lies practically on the ecliptic to the southeast of Regulus. At least 3700 light years away, it must radiate at a rate (including a lot of ultraviolet light from its 24,000 Kelvin surface) of close to 200,000 Suns. Its location far from the Galactic plane suggests that it is a "runaway star" that was ejected from a binary system either by gravitational interaction or by a companion exploding as a supernova.

Surrounding it (on the sky, not in three-space) is a trio of subtle variables. Two degrees almost due west find the sixth magnitude semiregular red M3 giant DE (Flamsteed 44) Leonis. A thousand light years away, it changes by just a tenth of magnitude in a couple days. Then just a degree to the northwest and also nearly on the ecliptic lies sixth magnitude CX (45) Leo. This one is a class A0p magnetic variable in the mode of Alpha-2 Canum Venaticorum, one with peculiar abundances as a result of diffusion (settling of some elements via gravity, raising of others by radiation) enhanced by magnetism. At a distance of 420 light years, it also varies by a tenth of a magnitude or so over 1.44 days. Finally, just under a degree southeast of Rho sits TX (49) Leo, a subtle class A2 eclipsing binary 430 light years away with an Algol-like behavior that yet again changes by a tenth of a magnitude but over 2.5 days.

Now look to vaster distances. Lying well off the Milky Way and far from the "zone of avoidance," Leo is also famed for its groups of bright galaxies, which are highlighted by no fewer than five Messier objects. The best known assembly is probably the "Leo Triplet," which lies just south of Leo's eastern stellar triangle. It's made of three massive galaxies some 35 million light years away: the highly tilted and tidally distorted spiral M 65, M 66 with its asymmetric spiral arms, and NGC 3628, a spectacular edge- on spiral. Central Leo east of Regulus then features the M 96 group made of it (a disturbed spiral), M 95 (face-on), which along with many fainter systems comes in at about 38 million light years. They are aligned with M 105, an elliptical with a supermassive black hole nucleus. Then scattered within the eastern stellar triangle and elsewhere are hosts of NGC galaxies available for your enjoyment.

But one lion is a lonely lion. On Leo's back rides the modern constellation Leo Minor. Leo Minor's outstanding feature is that just one star carries a Greek letter. And it's fourth magnitude Beta; there is no Alpha. The luminary, also fourth magnitude, is instead Flamsteed's 46. The constellation was invented by Hevelius in the seventeenth century well after Bayer had placed the Greek letters in his famed Uranometria of 1603. Flamsteed's numbers came later while, later yet, Baily (of Baily's Beads fame) applied Greek letters. According to M. Wegman in his "Lost Stars" (McDonald and Woodman, Blacksburg VA, 2003), the others were too faint to be lettered, and Baily probably simply forgot to apply "Alpha" to 46 LMi. Making up for the lack, this common K0 giant does carry a proper name, "Praecipua," meaning "chief." The more interesting of the two, however, brings us back to Beta, a close binary made of a G8 giant orbited every 39 years by an F8 dwarf, the two just a fraction of a second of arc apart. It's all not much to say even for a minor "King of Beasts." Best to walk with Leo proper.

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 2012 Newsletter of the Lowestoft and Great Yarmouth Regional Astronomers, who are gratefully acknowledged.