April finds Leo the lion leaping above the eastern horizon at nightfall. Remarkably, this zodiacal formation actually resembles the beast it’s supposed to portray--a rare species in the sky’s largely imaginary zoo. The key part of the constellation is the sickle, a distinctive backward question mark that forms the heart and mane of the animal and leads Leo across the sky. At the base of the sickle shines Regulus, the lion’s brightest star. These nights this intense blue sun provides a vivid color contrast with the planet Mars, a brilliant orange guest in the Lion’s hind legs, and the sky’s brightest star after 8 p.m.
Mars and Regulus will perform a spectacularly tight conjunction this summer. But for now, watch how rapidly Mars changes position and brightness among Leo’s stars as Earth pulls away from the planet at the rate of half a million miles a day, following last month’s close rendezvous. This minuet creates the baffling retrograde motion and striking nightly mutations that have thrilled observers since antiquity.
Telescope owners can point any size instrument above Regulus to Algieba, the brightest star in the sickle’s curve. One hundred magnification shows why it’s special: suddenly there are two of them! Algieba is one of the night’s finest double stars, a pair of deep yellow jewels separated by about three times the distance between Earth and Pluto.
Algieba lies some 85 light-years from us. Curiously, that’s also the distance to Regulus, and to Delta Leonis, the next brightest star in the sickle--as if Leo reserved that region as a private parking space. That’s also the distance to most stars in the nearby Big Dipper, which makes it likely that they all belong to the same association, or loose star cluster. Its members occupy a big chunk of our sky because it’s the nearest star group of any kind. (Mention of the Dipper suggests a great tip for finding Leo: the Big Dipper’s two pointer stars traditionally guide us to the North Star, but if followed the wrong way--south--they point directly to the Lion.)
Algieba also marks the spot from which the amazing Leonid meteor shower radiates. Last November the Leonids coughed up a shooting star every few minutes, a lukewarm display. But in just two more years, on November 17, 1999, Earth will plow into the head of the defunct comet from which the Leonids were born. There’s an excellent probability that in several hours, more than 30 meteors per second will radiate from Algieba’s vicinity like fiery spokes streaming from the hub of a wheel.
The last piece of Leo to rise is its tail, marked by the star Denebola, a jumping-off place for much deeper prey. Draw a line downward from Denebola to the rising constellation of Virgo and you will have located the nearest great cluster of galaxies, the famous Virgo group. Those with telescopes under dark skies will find this region peppered with innumerable smudgy blobs, each an intriguing city of billions of suns. Several of the brightest spill into Leo itself, very near the Lion’s hind legs. This picture window into intergalactic space has been polished clear: when we look toward Leo’s tail we’re gazing 90 degrees (straight up) from the plane of our own Milky Way. No foreground dust or gas obscures our line of sight.
Comet Hale-Bopp, in the northwest right after sunset, deserves attention. But when the comet sets, Leo’s silent roar from the opposite side of the sky reminds us that its varied treasures and color contrasts easily make it this month’s most fascinating constellation.