Leo


Transit Date of principal star:
22 February


The first on the list of Heracles' labours was the task of killing the Nemean Lion, a giant beast that roamed the hills and the streets of the Peloponnesian villages, devouring whomever it met.

The animal's skin was impervious to iron, bronze, and stone. Heracles' arrows harmlessly bounced off the lion; his sword bent in two; his wooden club smashed to pieces. So Heracles wrestled with the beast, finally choking it to death. He then wrapped the lion's pelt about him; it would protect him from the next labour: killing the poisonous Hydra.

As the story goes, the lion found its way to the heavens to commemorate the great battle with Heracles. Yet this isn't all there is to the story. For even in antiquity, long before the Greeks began telling stories, the lion was an ancient symbol of power.

Approximately three thousand years before the Christian era carvings and sculptures showed kings flanked with rampant lions. Indeed, the archaeological evidence suggests that at about this time the lion had already replaced an even earlier "sacred" symbol, the bull.

It has been suggested that this transfer of power from a horned animal to the lion was a change-over from a lunar-based to a solar-based religion. That is, instead of drawing their inspiration from a night-time symbol with a monthly cycle--a symbol which dealt with the fecundity of the earth and of its animals--the new rulers identified with an animal of strength and power, and with a heavenly body that ruled the day. Thus, as the bull had been identified with the moon, the lion was now associated with the sun. To assert this new religion, or new political structure, the lion was made to kill the bull. Its place in the heavens was therefore critical.

An intriguing theory, put forth thirty years ago by Professor Willy Hartner, eloquently describes the result. Briefly put, at about 4000 BC, the Lion is seen chasing the Bull over the horizon, announcing the end of winter and the beginning of spring. I shall quote Professor Hartner's descriptive words:

"The constellation Leo would have been directly overhead, standing at zenith and displaying thereby its maximum power [as it] kills and destroys the Bull trying to escape below the horizon, which during the subsequent days disappears in the Sun's rays to remain invisible for a period of forty days, after which it is reborn, rising again for the first time (March 21) to announce Spring equinox." [See W. Hartner, "The Earliest History of the Constellations in the Near East and the Motif of the Lion-Bull Combat" JNES 24(1965)1-16.]

Thus Leo, slayer of Taurus, dominated the summer skies, the time that the sun passed through this constellation. Due to precession, the sun currently passes through Leo at the end of summer, from mid-August through mid-September.


Leo is a fairly compact constellation and, unlike so many other constellations, it is readily recognisable. Alpha Leonis is named "Regulus" because it was seen as the Heaven's Guardian, one who regulated all things in the heavens. While the name Regulus was given us by Copernicus, the star was better known in antiquity as Cor Leonis, the Lion's Heart.

Regulus is a multiple binary, discussed below. Also, because Regulus lies so close to the ecliptic, the moon often passes close by, and even occults the star on very rare occasions.

Like other ancient constellations, many of the stars in Leo are named.
Beta Leonis is called "Denebola": the Lion's Tail.

Gamma Leonis is "Algeiba", Arabic for forehead, but more correctly named Juba, meaning mane.

Zeta Leonis is "Aldhafera", the meaning is uncertain;

Epsilon Leonis and mu Leonis go under the name of "Al Ashfar", the eyebrows.

Delta Leonis is "Zosma", a Greek word meaning girdle.

Lambda Leonis is Alterf, apparently meaning "extremity". It's located right at the tip of the lion's mouth.


Double stars in Leo:

Alpha Leonis (Regulus) is a multiple system. Component B is very wide: (8.1m, PA 307 degrees, 177"), and this star has its own companion ("C"), a very faint 13m dwarf, with a period of about 2000 years, now approximately 2.6" and a PA of about 86 degrees.

A fourth companion, D, is only optical. That is, there is no gravitational bond with the others, but before that was established, it too became a part of the group. It is found at 274 degrees, and 217".
Gamma Leonis is a notable binary with a slow orbit. While Burnham lists three possible periods (407y, 701.4, and 618.6) we have settled on the latter as the most probable, and based its orbit on this period.

Presently the companion is very gradually drawing away from the primary. The current values are: PA 124 degrees and separation 4.4".
Iota Leonis is a more rapid binary, with a period of 192 years. Its orbit shows that the 6.7m companion is slowly increasing its distance (now at PA 122 degrees and separation 1.62").

Variable stars in Leo:

R Leonis is the only variable of note in Leo. This isn't your typical Mira-type long-period variable. First of all, it's usually a very faint 11.3m star, which grows to an extremely bright 4.4m every 309.95 days. In 2000 the maximum should arrive in the last week of February.

Secondly, its colour is an unusually deep red, approaching purple. Surrounded by a number of white stars (18, 19, 21 Leo.) its own colour is even more pronounced. Thus R Leonis has become a favourite subject for many variable star observers.


Deep Sky Objects in Leo:

Leo has five Messier objects: M65, M66, M95, M96, and M105.

M65 (NGC 3623) and M66 (NGC 3627) make a splendid pair of spiral galaxies in the same field, between theta Leonis and iota Leonis.

This is a fine binocular duo, or use a small telescope. M66 is the one to the east. Both galaxies are elongated north-south; M65 has a tighter spiral and is perhaps the more noticeable.

About a degree north, hovering just between M65 and M66, is NGC 3628, a galaxy seen edge-on. Actually this is larger than either Messier object, but much dimmer because it is seen edge-on.

M95 (NGC 3351) and M96 (NGC 3368) form another nice pair, although farther apart. The two are found is a group of galaxies midway between alpha Leonis and theta Leonis, and just slightly to the south.

Of the two, M95 is to the west. This is a curious round object, with a very faint circular bar. M96 is a tight spiral galaxy, much brighter than its neighbour. Both this pair and M65/M66 are considered to be about 30 million light years away.
M105 (NGC 3379) is a much dimmer galaxy to the north-north-east of M96. Along with NGC 3384 and NGC 3389, which lie just to the east, this object forms a small triangle of galaxies.
Then there is NGC 2903, which somehow escaped Messier's telescope. This deep sky object is judged to be a visual magnitude of 8.9, which makes it brighter than any of the above Messier objects, and covering a larger area as well. It is an elongated multiple-armed spiral located directly south of lambda Leonis, one and a half degrees.

Indeed, there are many more galaxies in Leo to explore. Most of them lie between alpha and beta Leonis, with a smaller group scattered around gamma Leonis. Most of them are 10-12m, so the larger the telescope the more favourable the viewing.


If you wish a real deep sky challenge, try Wolf 359. This is an extremely faint red dwarf, and the third closest star, at 7.65 light years. It has a visual magnitude of only 13.53, which renders it all but lost among the millions of other stars. Only as large as Jupiter, it has a luminosity about 1/65,000 of the Sun's; its absolute magnitude is calculated at 16.7m.

Its Epoch 2000 values are: right ascension 10h 56m, declination 07 degrees, one second. If using Tirion's SkyAtlas 2000.0, while this chart doesn't show the star, you can easily find the region. Locate 56 Leo (west of sigma Leonis) then place a mark on the ecliptic just above this star. (The ecliptic is the dotted line running north of this star). This is where you'll find Wolf 359. Now you'll need Burnham's finder (on his page 1072), a nice dark sky, and plenty of patience.


The Leonid Meteor Showers

The Leonids are meteor showers which appear every 16-17 November, so called because their radiant point is in the Sickle of the Lion.

While Leo is only visible very early in the morning at this time of year, the meteors stream across the west, through Hydra, Canis Minor, and even Orion.

The meteors are debris from the Tempel-Tuttle comet, which orbits the sun every 33 years. While the showers usually bring 10-20 meteors per hour, three times a century the meteor shower is particularly dense, several hundred per hour with a quick burst of 1000 or more per hour.

These denser showers usually occur in years ending in 33, 66, and 99. The 1966 display was one of the better, with around 5000 meteors in one span of twenty minutes. By contrast, 1999 saw a very brief burst of around 2000 meteors as recorded by observers in the Middle East, while North American residents would only view several dozen per hour.


For a more detailed appreciation of Leo, visit the Binocular Section.


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