2021, May 20: Morning Summer Triangle


May 20, 2021:  With two bright planets in the southeast before sunrise, the Summer Triangle – Vega, Altair, and Deneb – is high in the south as daylight approaches.

Chart Caption – 2021, May 20: The Summer Triangle – Vega, Altair, and Deneb – is high in the southern sky during the morning. It is visible during the evening hours from May through December.

by Jeffrey L. Hunt

Bright Planets Jupiter and Saturn are in the southeast before sunrise.  A little earlier, as twilight begins, look high in the southern sky to locate a large triangle.  It is known as the Summer Triangle, made by Vega, Altair, and Deneb.

Jupiter outshines all the bright stars in the sky this morning, but Vega is brighter than Saturn.

The Summer Triangle moniker is an informal name to this stellar trio.  It appears just above the horizon in the evening as summer begins and ends the night high in the southern sky.

Each bright star belongs to its own constellation.

Vega, “the falling eagle,” is part of the small constellation Lyra the Lyre (Harp).  The small constellation is made of a parallelogram attached to a triangle.  If a musical instrument, the harp’s strings are strung along the long dimension of the parallelogram.  One could consider Vega as a sparkling gem on the frame.

A star named Epsilon Lyrae (ε Lyr on the chart) is known as the “Double-Double.”  Through a binocular, a single star splits into two stars – a double star.  With some magnification through a telescope, each of those stars is a pair of stars – a double-double star.

Vega is in the sun’s neighborhood.  It is the third brightest star visible from mid-northern latitudes and the second brightest in the northern half of the sky.  The star is about 25 light years away. At this distance it shines with a brightness of about 100 suns.

During the 19th century, an attempted measurement of the star’s minute annual wiggle was intended to demonstrate that Earth revolves around the sun.

Vega roughly marks the direction that the sun is traveling in space through the Milky Way galaxy, known as the solar apex.

Altair, “the flying eagle,” is the southern-most corner of the triangle.  The star is closer than Vega, over 15 light years away. It shines with a brilliance of about 20 suns.  It is the eighth brightest star visible from the mid-northern latitudes and the sixth brightest in the northern half of the sky.

Altair is part of Aquila, the Eagle.  The stars seem to resemble that shape.  The brightest star is the bird’s head, while the two wings extended are marked by two triangles below it.  A line of stars extending downward could be the tail.

Likely, one of the brightest stars in the sky is Deneb, “the hen’s tail.”  The star is the brightest in Cygnus. The star is thought to be about 1,400 light years away.  To shine as the 20th brightest star visible from Earth, it is about 100,000 times brighter than our sun!

The constellation’s nickname is “The Swan.” The pattern is informally known as the “Northern Cross.”

As a swan, the long axis extends from the tail to Albireo, at the nose of the cross.  The shorter axis makes the wings.  In a dark sky away from city lights and bright moonlight, the Swan appears to be flying southward along the Milky Way.

Through a telescope, Albireo splits into two stars, one gold and the other is blue.  “They are two jewels on the black velvet of space,” says an observing associate J. Packard.

Besides seeing Saturn through a telescope’s eyepiece, Albireo is a special request to see from the telescope’s owner.

Find the Summer Triangle in the sky during late Spring, and during summer and autumn evenings.


Leave a Reply Cancel reply