If you walk outside on any evening between now and late May, face roughly south and look up, you will be looking in the direction of the constellation Leo the Lion.
The shape of this constellation, as shown in the image in the photo gallery, consists of a raised hook (or sickle) to the right — like a backwards question mark — which is the lion’s head, and a right angled triangle to the left, which represents the hind quarters and tail.
Leo is one of the few universally known ancient constellations. The Babylonians in 4,000 B.C. recognized this pattern of stars as a lion. The Greeks associated Leo with the Nemean lion killed by Hercules during his return from Troy. The Hindus and Persians also recognized a lion in this grouping of stars.
Many of the stars forming the constellation of Leo are fascinating in their own right. The brightest star, at the base of the lion’s head, is Regulus, (“the little king”). Most other ancient cultures associated Regulus with royalty.
The 21st brightest star in the sky, located 77.5 light years from Earth, Regulus actually consists of no less than four stars all gravitationally bound to one another, separated into two pairs of stars.
The brightest of them is Regulus A, with a mass 3.4 times that of the sun and 140 times the visible brightness of the sun, which is very tightly bound to a white dwarf star.
This pair swing round one another every 40 days and are separated by a distance less than that from Venus to the sun. This pair can never be seen as distinct stars using telescopes — the second star has been detected only through careful analysis of the spectrum of light coming from Regulus A.
A small telescope shows a dim third star, Regulus B, and a large telescope shows a fourth star, Regulus C, near B. B and C orbit each other with a period of some 2,000 years.
At the opposite end of Leo, the last star at the tip of the triangle forming the tail, is Denebola (“lion’s tail”). This is a very young star, with an approximate age of 400 million years, producing about 12 times the energy of the sun.
Denebola is about 36 light years from Earth. Infrared observations suggest the presence of a dust cloud orbiting Denebola which may eventually form a system of planets.
Two other stars in Leo demonstrate the effects of distance on the apparent brightness of stars. The star in the lion’s head directly above Regulus is Eta Leo.
This star of modest apparent brightness is 1,275 light years distant, with an actual visible light output of over 5,500 times that of the sun. Eta Leo is a white supergiant star, with a diameter about 27 times greater than the sun.
If this star were at the distance of Regulus from Earth, it would outshine the planet Jupiter in our skies. On the other hand, Leo also contains the star Wolf 359, which is the third nearest star to our sun at a distance of 7.8 light years.
This star is invisible to the unaided eye, and requires a rather large telescope to be seen at all. Wolf 359 is a red dwarf star — small in size, low in mass, and low in temperature. The contrast to size and distance of the very visible Eta Leo is striking.
The constellation Leo is located in a direction from Earth almost perpendicular to the Milky Way, the disk of our home galaxy.
As a result, looking in the direction of Leo, we look past a relatively few Milky Way stars and into the vastness of intergalactic space.
Over 15 relatively nearby galaxies are located in the constellation Leo, and many of these are popular targets to be viewed by amateur astronomers using telescopes of modest size. The photograph shown with this post I took through my 10” Newtonian reflector of the "Leo Trio" of galaxies.
Lastly, but certainly not least, if you look just below the line connecting Regulus and Denebola, you will find a very bright reddish "star." This is the planet Mars, currently the easiest of the planets to find in the evening sky. (Venus can be seen near sunset in the West and Saturn is above the horizon at sunset in the East, but with typical Connecticut tree lines, these may not be readily visible).
Mars is the second closest planet to Earth after Venus, and is the most heavily explored object in the solar system after the moon. Through binoculars or a small telescope, Mars can be seen as a distinctly round small reddish dot.
Depending on how stable the atmosphere is on any given night, you may be able to see a whitish spot near the edge of Mars — this would be a polar ice cap — mostly of frozen carbon dioxide, or dry ice.
This completes our tour of the constellation Leo, one of the most easily recognized spring constellations. When you have a chance this month, get out and take a look for the great Lion of spring!