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Leo lights up the night’s sky

February 22, 2011
By Aileen O’Donoghue,

Leo, the king of beasts, the great lion, has risen into our evening skies. As the diagram shows, Leo is one of the few constellations that actually looks like what it is supposed to be. When I point it out to people at star parties (as observing sessions for the public are called), I describe it as looking like the Sphinx and people are instantly able to pick it out. As shown on the diagram, the bright star Regulus (REGG-you-luss) marks the lion's elbow as he rests on his belly facing to the west (our right) with his front paws stretched out to Omicron (OH-mih-chron), his mane curling from Regulus through Algieba (Al-JEE-buh) to Ras Elased Australis (Rhas El-A'-sed Aus-TRAL-iss), his body stretching back to Zosma (ZOHZ-muh) and Chertan (CHUR-tun), and his tail stretched out to Denebola (Den-EBB-oh-luh).

Some claim that Leo was actually the model for the Sphinx, and indeed, the constellation had seasonal importance at the time the Sphinx was carved from a ridge of sandstone. Most Egyptologists argue the Sphinx was carved during the "Old Kingdom" between 2,600 and 2,100 BCE, when the great pyramids were also built. At this time, the Summer Solstice occurred when the sun was in Leo, so the lion would have risen at dawn on that important date. Other scholars who have examined the geology of the Sphinx claim its more eroded state indicates it is much older, thousands of years older, than the pyramids. In this much earlier time, perhaps as far back as 10,500 BCE, the Vernal Equinox that is now in Pisces would have been in Leo. In the centuries between these two eras, as Leo changed from the home of the Vernal Equinox to that of the Summer Solstice, the constellation would have appeared in the pre-dawn sky on the morning of the Summer Solstice, in view of the eastward-facing Sphinx. Since the Nile flood season began after the Summer Solstice, it was a very important date in Egyptian culture. With the likeness of the Sphinx so much like Leo, the importance of the sun in Egyptian culture and astrology and Leo rising before dawn as spring changed to summer, Leo having been the model for the Sphinx seems quite plausible.

Once you've seen him, the lion is fairly easy to pick out in the sky. His mane is an asterism, a recognized pattern of stars that is not a constellation, known as the Sickle. I generally describe it as a backwards question mark since few of my students would recognize a sickle!

Playing the part of the period at the bottom of the question mark is the bright star, Regulus. This "little king" is the 21st brightest star in the sky and 15th brightest star in the northern sky. It's one of only three bright stars, with Spica and Antares, that lie near enough to the Ecliptic to be occulted by the moon and planets. An astronomical occultation is when one object moves between us and a more distant one and thus hides or "occults" it. Back in 1959, Venus occulted Regulus, allowing astronomers to calculate the density of the planet's atmosphere. Regulus will be occulted by Venus again in 2044. I was not quite 1 year old when the previous occultation occurred and will be 86 at the next one. Given that my mom turns 90 this year, there's a decent chance I'll get to observe it!

In the meantime, Regulus will be occulted by the asteroid 163 Erigone (Air-RIG-oh-ee) on March 20, 2014. It will only be visible from a narrow strip of New York state stretching from New York City to Oswego and Ontario from Belleville past North Bay (a map is available on the Wikipedia site for Regulus). In 2017 and 2018, the moon's orbit will be aligned so that there will be multiple opportunities for viewing a lunar occultation of Regulus. Until then, the moon's orbit is south of the ecliptic in this part of the sky so watch for the waxing gibbous to pass between Leo and bright Alphard (AL-fard), the "solitary one" in the water snake.


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If you have any questions about astronomy, please visit the Adirondack Public Observatory web site at or e-mail Aileen at



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