Of the 88 constellations that can be seen from the earth, Delphinus the Dolphin is the 19th smallest. Equuleus the Little Horse is the second smallest. The two constellations are nestled together in Rochester's southeastern evening skies this month.
I love showing Delphinus to folks at my stargazing parties. It’s made up of a small but distinct sideways diamond of stars that outlines the torso and head of the little dolphin, and a single star just to the lower right of the diamond marks the tail. Currently, Delphinus is swimming high in the southeastern skies as evening begins.
The best way to find Delphinus is to use the famous Summer Triangle as a guide. The Summer Triangle is nearly overhead at the end of evening twilight — just look for the three brightest stars that you can see in the high southeastern sky.
This trio of bright stars is made up of stars from three separate constellations, each being the brightest star in their respective constellation. If you face toward the southeast, you’ll see Vega, the highest and brightest star in the Summer Triangle. It's also the brightest star in the constellation Lyra the Harp.
On the lower left corner of the triangle is Deneb, the brightest star in the constellation Cygnus the Swan. On the lower right corner is Altair, the brightest luminary in the constellation Aquila the Eagle.
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It’s from Altair that you can search for the dolphin. Just gaze slightly to the left of Altair for that little diamond that makes up the body of the dolphin.
Even though the five main stars that outline the body and tail of Delphinus the Dolphin are fairly faint, each one of them is much larger and produces more light and energy than the sun, our closest star.
The stars in Delphinus are faint because they're so far away. They range in distance from 95 light years to more than 360 light years away — one light year equals six trillion miles.
Finding Equuleus the Little Horse will be a challenge because it’s less than half the size of Delphinus, and its stars are just as faint. About all there is to Equuleus are four stars that make a skinny, lopsided trapezoid that is allegedly the head of the horse.
Both Delphinus and Equuleus are two of the original 48 constellations listed by the famous astronomer Ptolemy in the 2nd century. As with all constellations, different cultures have their own names and mythology associated with them.
Equuleus the Little Horse was thought by some to be the little brother of the famous, winged horse, Pegasus. There’s a story among the Greeks about a battle for power between Poseidon, the god of the sea, and Athena, the goddess of wisdom. When Poseidon struck his trident against a rock, out popped the little horse Equuleus.
The Greek mythology tale of Delphinus also involves Poseidon. When Poseidon decided to get married, he set his sights on Amphitrite, one of the many nereids that occupied his domain. According to legend, nereids were like mermaids that they provided safety and protection for sailors and fisherman.
Despite Poseidon’s charm, Amphitrite was not interested in the god of the sea. After he kidnapped her, she managed to escape and swim away.
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Poseidon then sent Delphinus to search for Amphitrite. When he found her, Delphinus persuaded her to give Poseidon a chance; she did, and Poseidon and Amphitrite later married. As a reward, Poseidon placed the dolphin in the heavens as the constellation we still see thousands of years later.
