In this month’s constellations highlights, we will discuss the Summer Triangle and the constellations of Lyra, Cygnus, Aquila, and Scorpius.
The summer triangle
High above, as seen in the late July twilight (which tends to last until close to midnight), are three very bright stars forming an inverted isosceles triangle:
- Vega (pronounced “Vee-gah”)
- Deneb (pronounced “Deh-nehb” with the “e” sounds used as in “they”)
- Altair (pronounced “All-tair” (last part as in “chair”)
While the Summer Triangle is quite notable, it is not recognized as an official constellation. From the city sky, sometimes it is the only thing you can see through the light pollution. However, in the often pristine skies visible in our parks, we can see many more constellations anchoring each of these stars.
Lyra the harp
Vega, a beautiful blue star, is the brightest in the small constellation of Lyra the Harp. The name “Vega” comes from Arabic. al nasr al waqi or “diving eagle.” The harp is said to be the instrument made by Hermes, son of Zeus, and used by Orpheus.
Lyra has two interesting items found within her kingdom. A beautiful double star (stars orbiting each other) lies just to the upper left of Vega: Epsilon Lyrae. Epsilon Lyrae is special because it is actually a “double double.” Two pairs of double stars, each orbiting the other!
The other interesting object is the annular nebula M57 (number 57 in Charles Messier’s catalogue). This smoke ring-like object is actually waste gas emitted by a star near the end of its life. The star’s core remains in the center, but you need a good telescope to see it.
Cygnus the swan: a bird of many feathers
To the east of Lyra is a much larger pattern of stars that forms a cross. Four stars running north to south from Deneb meet three stars running east to west. This pattern forms the “Northern Cross” that many people have learned to find. The name of the star Deneb comes from the Arabic ““Dhaneb” meaning “tail” (as in the bird’s tail).
So where is the bird?
There are at least two birds hidden within the same stars. The Anishinaabe people recognize a beautiful crane lying among these stars. The Deneb star is the tail of the bird and its body extends along the longitudinal axis of the cross. By adding a star to each side of the short axis of the cross, we complete the wings.
The ancient Greeks imagined these stars as a swan that represented Nemesis, in his flight from Zeus. The head of the Swan is marked by a star known as Alberio. Alberio is one of the most beautiful double stars in the sky. A blue and gold pair are visible with an even lower power telescope.
Crossing Cygnus is a band of light divided by some dark spots. This, of course, is the Milky Way. It is formed by the light of millions of distant stars. They are so far away that we cannot see the individual points of light, but rather the combined brilliance of their fused light.
A careful look with binoculars reveals the large number of stars it contains. Indigenous traditions recognize this region as a river along which their ancestors traveled in the afterlife. The stars of this area were the bonfires lit by those ancestors as they crossed the river.
Aquila the eagle
The last star of our summer triangle is Altair. The name Altair comes from the Arabic ““al nasr al tair” or “flying eagle.” Altair points to the eagle’s eye and the body extends downward and to the west.
Altair is a fascinating star because it spins incredibly fast: once every nine hours (compared to about 25 days for our Sun). The Milky Way continues to descend through Aquila towards Sagittarius. A binocular view through this area reveals many star groups and star clusters.
The time Machine
Perhaps one of the most surprising revelations discovered in recent years is that the brightness of a star does NOT indicate how close it is to us. In fact, some faint stars are quite close while some bright stars are quite far away.
Take the Summer Triangle as an example. All the stars appear to be approximately the same brightness but, as we will soon see, they are at very different distances.
Astronomers measure distances to stars in a unit known as a light year, or the distance a ray of light can travel in a year: just under ten trillion (10,000,000,000,000) kilometers. The star Altair is about 16.7 light years away. Vega is about 25 light years away. But Deneb is more than 2,500 light years away or 100 times farther than Vega.
Since nothing can travel faster than a ray of light, the light we see from Altair (16.7 light years away) left us 16.7 years ago. Let’s imagine a courier asking us to bring us a package from the star Altair. This intergalactic space messenger travels at maximum speed (the speed of light) and since Altair is 16.7 light years away, the messenger takes 16.7 years to reach us.
The light we see today from Deneb left the star about 2,500 years ago. One of the most distant objects that we can see in a dark sky is the Andromeda galaxy. 2.5 million light years away, the light we are seeing now left the Galaxy during the Early Stone Age! When we look at the sky, we look back in time, to the beginning of everything.
Scutum the shield
Below and to the right of Aquila the Eagle is Scutum the Shield. Scutum looks like a mini Corona Borealis (see June issue). The full name of the Scutum is “Scutum Sobiescianum” or “Shield of King Sobieski (of Poland).
Towards the lower right side there is a blurry spot. This is a beautiful open cluster known as M11 or the “Wild Duck” cluster.
Stars are born from interstellar gas clouds that have condensed into rotating balls of gas. Under the extreme pressures of the gas mass, the cores of stars become hot enough to fuse hydrogen into helium.
Eventually, over time, the original interstellar gas cloud disperses and what is often left behind is a loose cluster of a few dozen to several hundred stars. That’s what we see when we look at M11: the remains of star birth.
Scorpio the Scorpion
The final constellation of this edition is Scorpio the Scorpion. The bright red star Antares, meaning “rival of Mars,” marks the heart of the scorpion. Two claws extend to the right (west) of Antares and the body extends to the left (east) ending in a very well-formed stinger.
This is one of the most attractive constellations (in terms of looking like what it’s supposed to represent!):
The star Antares is a luminous red supergiant in the final stages of its life. It’s really huge. In fact, if we replaced our sun with Antares, the planets Mercury, Venus, Earth and Mars and much of the asteroid belt would be within the outer atmosphere of the star itself.
This is a very rich area of our Milky Way where gas clouds, newly formed star clusters and globular clusters are found en masse. When we look in this region, we are actually looking near the center of our galaxy, the Milky Way.
Are you inspired to stay up and watch these night skies?
Take a look at our monthly astronomical highlights for more information on what to look for.