The most recognizable grouping of stars in the sky of the northern hemisphere, the Big Dipper
actually not a constellation at all, though many people think of it as such.
The Big Dipper is actually what we call a Asterism
, which means it's a group of stars
that most people are able to quickly identify, but are only part of a constellation, or even made up of stars from more than one constellation (such
as the "Summer Triangle").
The seven stars that make up the Big Dipper, are actually part of the constellation known as Ursa
(meaning "Larger Bear"). That constellation is also known as the "Great Bear" or "Charles' Wain" ("Wain" means "Wagon").
So why do people look at this constellation and settle on just the "Dipper" part? There are several reasons actually:
1) Popular media (TV, Films, Videos) normally only show the seven stars of the Big Dipper and refer to it as such.
2) Light Pollution. The stars that make up the Big Dipper, are the brightest stars of the constellation Ursa Major. The other stars in the
constellation are easily washed out by city night lights.
3) Navigational Aid: parts of the Big Dipper are used to locate other areas in the sky, such as being used to find the North Star (Polaris) or in
beginning astronomy, the arc of the "Handle" of the Big Dipper is used to help locate the star Arcturus ("Follow The Arc To Arcturus").
The Big Dipper is also known by several other names. In parts of the United Kingdom and Ireland it's reffered to as the "Plough" or "Butcher's
In Hindu astronomy it's referred to as Sapta Rishi, meaning The Seven Great Sages.
The Big Dipper (as we'll refer to it from here on out), is made up of seven stars, and has several deep space objects. Let us take a closer look at
Here is a list of the names of the seven stars that make up the Big Dipper:
Megrez 3.3 mag 58 lightyears
Mizar 2.1 mag 78 lightyears
Merak 2.4 mag 79 lightyears
Alioth 1.8 mag 81 lightyears
Phecda 2.4 mag 84 lightyears
Alkaid 1.9 mag 101 lightyears
Dubhe 1.8 mag 124 lightyears
If you've read my other thread on the constellation Orion, you'll notice right away that all these stars are a lot closer to us. Indeed, the
farthest star in the Big Dipper is closer to us than the nearest star in the constellation Orion.
Yet many of them have the same brightness. Why? Shouldn't they be brighter?
The answer lays with how big these stars are compared to the stars that make up Orion. These stars in the Big Dipper a much smaller than the
supergiant stars that make up Orion, and thus have a lower luminance. However, because they are so much closer, it makes them look just as bright.
One of my own pictures I took of the Big Dipper:
One of the unique things about the Big Dipper is, unlike most constellations or other asterisms, is that the majority of the stars that make up the
Big Dipper are actually related and believed to have formed together from a protostellar nebula about 500 million years ago. So the following stars
from the list above that are part of this group are:
Megrez, Mizar, Merak, Alioth and Phecda. The stars Dubhe and Alkaid are not part of this group. The group of stars is known of the Ursa Major Moving
Group and the 5 stars I named are joined by 9 other stars, 8 of which are also part of the constellation Ursa Major.
By observing these star's proper motions and using parallax, Richard A. Proctor back in 1869, noticed that these stars all seem to be moving towards
a common point in Sagittarius. The Hipparcos satellite was able to not only confirm this, but improve upon the measurements.
As I did in my other thread about Orion, I showed how the stars would look from a different perspective from far above the Earth, to show how the
stars are not right next to each other. Here we go again for the Big Dipper:
Surprisingly, there is not as much Pop Culture trivia associated with these stars like there was with the stars of Orion. However, there is some, and
there are some deep space objects too.
One of two stars in the Big Dipper used to find the "North Star" or Polaris.
It's a spectral class "K" star and has a companion star that is also a "K" class star.
This star is the official star of the state of Utah. The US Navy had a ship named after it, the USS Dubhe, ID-2562 back in 1918.
The Danish Navy has a ship named after it with the hull number of MHV 806.
(this is a picture of the Antares. The Dubhe looks the same however.)
The second of the two stars in the Big Dipper that are used to find the "North Star " or Polaris.
It's a spectral class "A" star that has 2.7 times the mass of our sun and is about 3 times the size of our sun. It is also about 68 times brighter
than our sun. It's a typical main sequence star and is somewhere around 500 million years old.
Observations of Merak in infrared suggest the presence of a circumstellar debris disk orbiting around the star.
The US Navy had two ships named after it, the USS Merak which was sunk by German U-boat U-140 in 1918 (sorry, no images) and the USS Merak (AF-21)
which served during WW2 as a cargo ship:
In the classical Star Trek episode "The Cloud Minders", the crew of the Enterprise pay a visit to Merak II
Wow! If that is how the ladies dress on Merak II, I think I need to see about getting a dress for my wife from there!
Phecda is a spectral class "A" star that is about 2.6 times the mass of our sun and about 3 times it's size. It's about 300 million years old.
Phecda is featured in the old computer game Elite II: Frontiers, as one of the most dangerous planets to venture to due to pirates in that system.
Deep Space Objects
There are several deep space objects located near the Big Dipper that are visible through small and modest telescopes:
The Whirlpool Galaxy, M51a
which is located near the star Alkaid:
The Pinwheel Galaxy, M101
which is located near the star Mizar:
M108 barrel galaxy
which is seen almost edge on from Earth, located near Mizar:
And also near Mizar we have the Owl Nebula, M97
Hope you enjoyed the thread!