The moon and Venus visit the 'Heart of the Lion' this week. Here's how to see it

Sometimes an unusual celestial sight will take place at a rather ungodly hour.

As a budding young amateur astronomer living in the Bronx, I remember the bemused look on my mother's face when I told her I was setting my alarm for 4 a.m. so that I could get a look at a meteor shower or lunar eclipse. "How come these things don't happen at a more convenient hour?" she would ask.

In retrospect, that was a good question, for it seems that most of my nightly forays to observe something interesting tend to occur in the hours after midnight. We have one such event coming our way early on Thursday morning, Sept. 19. But I assure you it will be something well worth getting up for.

A preview of winter

Probably the best month for stargazing is September. After the stretch of hazy, warm and humid summer nights running from June through August, September brings us cooler temperatures and generally clearer and more transparent skies. My good friend, George Lovi (1939-1993), who for many years penned the "Rambling through the Sky" column in "Sky & Telescope" magazine and was a colleague of mine at New York's Hayden Planetarium, was also a railroad buff. At the start of the summer season, in June, the brightest stars of Gemini the Twins, Pollux and Castor appear side by side low in the northwest twilight, bringing up the rear of the winter stellar procession in much the same way as the twin marker lights on a caboose bring up the rear of a train.

And during this week at around 9:30 or 10 p.m., if you look low down toward the north-northeast horizon, you'll see what George often referred to in his planetarium shows as the "headlight,": the brilliant golden-hued star Capella. If you want to watch the emergence of the rest of the "celestial train," then stay up all night. By the break of dawn, the southeastern sky, dominated by Orion and his winter retinue, will be magnificent.

Incidentally, if you don't mind the late hours, this is the time to observe the winter stars in comfortable temperatures. Compare September predawn temperatures in the 40's and 50's to mid-winter subfreezing (or in some parts of the country) subzero readings!

Ghostly lunar ball

And speaking of the break of dawn, that happens nowadays at around 5:15 a.m. local daylight time. And that's the time for when you should set your alarm clock Thursday morning, to see a tight gathering of three celestial objects: the moon, the brightest planet, and one of the brightest stars in the sky.

One prerequisite here is that you should have an unobstructed view of the east-northeast horizon. This "celestial summit meeting" will appear rather low — just 10 degrees above the horizon. As we have noted many other times, your clenched fist at arm's length measures roughly 10 degrees in width. So, this celestial array will be sitting roughly "one fist" above the horizon.

The first object to catch your eye will be the moon. It will be a slender waning crescent, only 6 percent illuminated by the sun and just two days prior to the new phase. In addition, you may be able to see the full globe of the moon, appearing as a thin arc of yellowish-white light enclosing a ghostly ball glowing with a bluish-gray hue interposed between the sunlit crescent and not much darker sky. This vision is sometimes called "the old moon in the young moon's arms." Leonardo da Vinci (1452-1519) was the first to recognize it as earthshine.

That faint bluish-gray light is light from the Earth reflected back to the moon. The Earth's light of course is reflected sunlight, so earthshine is really sunlight which is reflected off Earth to the moon and reflected back to Earth. The season of year and an observer's latitude determine the angle a line joining the crescent moon's cusps make with the horizon and on this morning this line is more nearly horizontal, making the crescent looking more like a cup that might hold water — call this a "Wet Moon" if you want to follow old-time tradition.

Queen and a king get together

The next object that stands out is the planet Venus; queen of the planets. It shines with its usual powerful radiance, though in telescopes it is now a rather small and featureless gibbous disk. Venus blazes at magnitude -3.9 and on the morning of Sept. 19, it will sit less than a degree to the lower right of the moon and itself will be positioned a half-degree to the upper left of the 1st-magnitude star Regulus, the brightest star of Leo the Lion. Venus outshines the star by a factor of 120 to 1, and yet their proximity for several mornings intensifies the contrasting yellow-white of the planet and bluish white of the star.

Copernicus has been credited with giving Regulus its name, a diminutive of Rex, or "king" which may relate to the four "royal stars" (with Aldebaran, Antares and Fomalhaut) about 90 degrees apart in the sky. Arabic astronomers gave the star the name "Qalb al-Asad," or "Heart of the Lion." Ancient Greek astronomers also referred to it by the same name, "Kardia Leontos."

As the brightest star in Leo, Regulus has been almost universally associated in ancient cultures with the concept of royalty and kingly power. This star lies in the handle of the so-called "Sickle of Leo," a star pattern resembling a large reversed question mark. The Sickle, when rising and climbing the sky at dawn, as it is doing now, is seen cutting upward. To modern sky-watchers the Sickle outlines the majestic head and mane of a great westward-facing lion.

Illusion of perspective

These three celestial bodies will appear to be "scrunched" in a line measuring less than 1 and a half degrees in length. Binoculars will accentuate the beauty of this alignment and will make the Earth-lit moon seem like an eerie three-dimensional ball. Keep in mind that what you will be witnessing will be an illusion. The moon will be positioned just 242,000 miles (388,000 km) from Earth. But Venus will be 153.1 million miles (217.3 million km) away, while Regulus is 79 light years distant.

So, the light you're seeing from Regulus now, started on its journey toward Earth in 1946, one year after the end of the second World War and the year of the premiere of the movie "It's a Wonderful Life" and the introduction of the term "bikini."

Joe Rao serves as an instructor and guest lecturer at New York's Hayden Planetarium. He writes about astronomy for Natural History magazine, Sky and Telescope and other publications.