Sunday, September 20, 2020

The Ecliptic runs through it

Looking Southeast 11:00 p.m., June 3. Submitted

Looking Southeast 11:00 p.m., June 3. Submitted

By Mike P. Usher

Tonight the Summer Milky Way is rising, almost looking like the beginning of dawn; just above it is the large, but fairly faint constellation of Ophiuchus. It is usually drawn as a man grasping a snake, and as one might expect the name in ancient Greek means “serpent-bearer.” Recently it has become famous (again) as the 13th zodiacal constellation for, as you can clearly see from the chart, the ecliptic runs through it. Every few decades the media treats it as a major discovery, but it’s been that way for all of human history. Ptolemy recorded it more than two millennia ago in his famous work The Almagest. To be fair, the official boundaries of the constellations were not established until 1930. Without official boundaries people were free to ignore Ophiuchus (and did). As an additional note, although the ecliptic does not run through these constellations, planets can appear occasionally in Orion, Perseus, Auriga and Andromeda.

Back before Roman times Libra (the scales) was considered part of Scorpius (the scorpion); the Romans found this inconvenient and split off Libra as its own constellation. Some trace of this remains in the names Zubeneschamali (the northern claw) and Zubenelgenubi (the southern claw). Please do not ask me how to pronounce these names! Besides the jaw-breaker of a name, Zubeneschamali has the distinction of being the only naked eye star with a greenish tint. Can you see it? I have never been able to. In the third century BC this star was recorded as being brighter than Antares and 350 years later it was recorded as being the same brightness as Antares. Both sources are considered reliable. Nowadays Antares is ten times as bright as Zubeneschamali!

A more recent change in this area of the sky occurred in 2000; in July of that year, Delta Scorpii (Dschubba), suddenly brightened. After untold centuries of being the fourth brightest star in Scorpius, it now was second – and not that much dimmer than Antares itself. It has been as bright as magnitude 1.6 compared with 1.09 for Antares. Since then Delta Scorpii has fluctuated between 2.0 and 1.6. For reasons not entirely clear the star has been ejecting great clouds of gas from its equatorial region. The study of variable stars like this one is a major branch of Astronomy; with a little practice amateurs can make significant contributions to the science.

See you next time!

Mr. Usher is President of the Everglades Astronomical Society which meets every second Tuesday at 7:00 PM at the Norris Center, Cambier Park, Naples.


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