Without the moon to brighten the evening sky, mid-October’s a fine time for a dip with the celestial dolphin. All you need are your eyes to see one of the most delightful of the 88 constellations: Delphinus.
To get there, we begin around 8 o’clock and look high in the southern sky to find the three bright stars outlining the figure of the Summer Triangle.
The bottom star is first magnitude Altair (all-TARE) in Aquila the Eagle. Thrust your arm out and look one fist to the left of Altair for a small, rather faint group of five stars you can cover up with just a few fingers. That’s Delphinus.
The exquisite diamond shape is the dolphin’s body; the single star below it, the tail. Small telescope users should be sure to look at Gamma Delphini, a binary star of magnitudes 4 1/2 and 5 separated by 9 arc seconds. 35x will split Gamma into a bright, neat pair of golden stars.
Not far from Gamma in the same low power field of view is a slightly fainter, tighter pair of stars called Struve 2725. You’ll spot them perpendicular to Gamma and a short distance to the southwest. 50x will easily cleave both pairs.
Two gorgeous doubles in the same view – can it get any better? Well, maybe. That all depends on what you think of triple stars. Tucked between Rotanev and Zeta Delphini, the triple Struve 2703 curls a beckoning finger at the telescopic observer.
I confess that after years of looking at Gamma and Struve 2725, I saw Struve 2703 for the first time only this week. How I avoided it for so long is beyond me. Even 35x will split this overlooked gem into a skinny triangle of three 8th magnitude stars. You’ll love it.
All three multiple stars we’re talking about today are real, physical systems where each star in the pair (or triple) revolves around their common center of gravity. They travel through space together and are married for life.
If you’re feeling a measure of confidence at finding Delphinus, take the next leap to Sagitta the Arrow, a fist above Altair (see map above). It’s smaller and fainter but what it lacks in brightness it makes up in compactness and distinctive shape much like our dolphin.
Before we leave Delphinus, you must know about its two brightest stars – Sualocin (Alpha Delphini) and Rotanev (Beta). Many Westerners assume the star names are traditional Arabic. Not so. Instead they’re the words Nicolaus Venator spelled backwards.
Nicolaus Venator, whose real name was Nicolaus Cacciatore, worked as an assistant to the famous astronomer Giuseppi Piazzi at the Palermo Observatory in Sicily at the turn of the 19th century. It was Piazzi who discovered the very first asteroid Ceres in 1801. Cacciatore helped him compile an important star catalog of the time.
Cacciatore assured his name a measure of immortality during the catalog’s creation by naming two stars in Delphinus after himself. ‘Cacciatore’ means ‘hunter’ in Italian, which translates as ‘venator’ in Latin. So yes, we have Nicolaus Venator to thank for Sualocin and Rotanev! He did this quietly of course, and it was only uncovered later through the detective work of English astronomer Thomas Webb.