March 2014 Touring Taurus with Binoculars
Hi everyone I’m Darrell Heath with the UALR College of Science, welcome to The Night Sky.
When most people think of astronomy they think of telescopes as the essential piece of equipment needed to explore the night sky. But this isn’t quite true, you can actually see a lot of splendid things with just a pair of binoculars. In fact, many amateur astronomers recommend beginning with binoculars before purchasing a telescope.
There are good reasons for starting out with these basic bits of optical equipment: binoculars are much more affordable than a telescope, they are far more compact and portable than a telescope, allowing you to just grab and go whenever and wherever you want, plus they are easy to use and have a wider field of view than does a telescope, allowing you to see far more area of the sky.
You will be amazed at the range of celestial objects you can see through binoculars: the moon, Venus, Jupiter, and comets are fantastic solar system objects for binocular observing. Deep sky objects such as star clusters, nebulae, and even a few bright galaxies are also within reach of many binoculars.
But before we begin our night sky explorations let’s get acquainted with binoculars in a bit more detail.
The first thing you need to be aware of is that every pair of binoculars will have two important sets of numbers that are displayed somewhere on the body of the binoculars, something like 7×35 or 10×50. LetOs use the numbers 7×35 as an example to explain what the numbers mean. The first number describes the magnification power of the ocular lenses. The ocular lenses are the back pair of lenses that you hold up to your eye. Thus a 7x pair of binoculars will magnify objects 7 times their original size. The second number, in this case 35, tells us the aperture size of the objective lenses in millimeters. The objective lenses are the large lenses on the front end of the binoculars. Of the two numbers the second number, which gives the objective size, is the most important when considering binoculars for stargazing as the bigger the number the larger the aperture and the more light you can gather from very distant and very faint celestial objects.
Most stargazers use a minimum of 7×50 or 10×50 as this is about the maximum size that you can hold steady in your hand without getting too much of a shaky image. You can of course buy much larger and more expensive binoculars that are dedicated for stargazing but these will have to be mounted onto a tripod. In fact you might even consider a tripod mount for the 10×50’s if your hands are prone to shaking after holding binoculars of this size for an extended period of time. For most children a pair of 7×35 binoculars will work just fine.
While any pair of binoculars will reward you with good views of the heavens, some designs are better suited than others. LetOs talk about two different binocular designs, roof prism binoculars and porro prism binoculars. Binoculars are essentially two glass-lensed telescopes bolted together. In order to keep the barrels short and compact binoculars use a set of prisms inside them to fold up the path of light coming in through the objectives. Binoculars with a roof prism design folds the light path four times before it emerges from the oculars and enters your eye. These are great for terrestrial viewing such as birdwatching or use at a sporting event but not so good for stargazing.
Binoculars with a porro prism are the best for stargazing use. This design folds the light path three times before entering your eye and this design is often used for binoculars with the largest objectives and remember that we want to have large objective lenses to gather as much light as possible when looking at distant objects in the night sky.
To distinguish between roof prism binoculars and porro prisms just look at the shape of the binocular barrels or tubes. Roof prism binoculars have sleek, straight-shaped barrels while porro prisms are housed in barrels that give the binoculars a distinct step-sided appearance.
Now that we have a basic understanding of binoculars lets take them outside and do a bit of celestial exploration within the constellation of Taurus the bull. I’ve selected two targets for you, both of which are quite easy to find. The objects I have in mind for our binocular tour are two star clusters. All stars are born in multiples, or litters if you will, within vast clouds of hydrogen gas and dust. Astronomers recognize two basic types of star clusters: open clusters and globular clusters. Open clusters, the category to which our two objects belong, are loose aggregates of stars that were all born from the same interstellar cloud of gas and dust. Such clusters are only a few millions of years old and may contain anywhere from several dozen to hundreds of stars. Open clusters are located within the disc and spiral arms of our galaxy. Globular clusters on the other hand are tightly packed balls of stars that contain thousands or even millions of stars all gravitationally bound to one another. These huge masses of stars are quite ancient; some are suspected to be around 12 billion years old, almost as old as the universe itself. We usually find globular clusters within the outer halo of our and other galaxies.
Now, let’s get back to Taurus and our two open start cluster targets.
Taurus is one of the zodiacal constellations and according to Greek mythology the star pattern represents the bull shape that the god Zeus adopted when he kidnapped the Princess Europa of Phoenicia. The constellation is right next door to Orion the Hunter and can easily be found by extending an imaginary line from the belt stars of Orion up and to the right until you come to a bright reddish-looking star. This is Aldebaran, an red giant star that marks the eye of Taurus. Taurus is best seen during winter and early spring. On March evenings just step outside and face southwest. During the early parts of the month the constellation is very high in the early evening sky but with each passing night it gets lower and lower and by April it is just above the western horizon at nightfall.
Now that we have located Taurus lets break out those binoculars and begin our tour.
Our first stop will actually be right around Aldebaran itself. Just beneath Aldebaran you will see with the unaided eye a faint V-shaped pattern of stars that make up the face of the bull. With the unaided eye you might see a few dozen stars but take your binoculars and use them to roam around the V-pattern. With just a little bit of optical aid you will see that there are actually hundreds of stars here. This is the Hyades cluster. Astronomers have been able to determine that the Hyades cluster is about 150 light years away making it the closest open cluster to Earth.
As you enjoy the spectacle of seeing all of these stars through your binoculars be sure and pay special attention to a pair of stars just south of Aldebaran (And by the way, Aldebaran itself is not really a part of the cluster, it just happens to lie along our line of sight). This lovely pair is comprised of widely spaced double stars known as Theta 2 Tauri and Theta 1 Tauri. Their most distinctive feature is their strongly contrasting colors: Theta 1 is a red orange giant while Theta 2 is a blue-white giant. Side by side they look like two beautiful celestial gemstones.
Over the course of a single human lifetime the stars appear to be fixed and unchanging upon the sky but in fact, over much longer periods, they can make very noticeable changes in their positions. While the Hyades are currently within a loose cluster they will slowly disperse out into space after many millions of years of having been together.
Collectively the stars that make up the Hyades are also all drifting eastwards while Aldebaran is moving towards the south. After another 50,000 years the bull will have lost his distinctive V-shaped face and at some point will probably look more like the face of Pablo Picasso’s bull in the famous 1937 “Guernica” painting.
The next stop on our binocular tour of Taurus takes us a little further to the right of Aldebaran and the Hyades. Even within moderately light polluted skies you should see a hazy patch of about 6-7 faint stars forming what appears to be a small dipper-shaped pattern (no relation to the famous Little Dipper in the northern part of our sky). This is another open star cluster known as the Pleiades. With the naked eye you will only see the six or seven stars but with binoculars this regions of the sky suddenly transforms itself into many young, hot blue stars that often remind me of glittering diamonds spread across black velvet cloth.
According to one Greek legend the Pleiades are seven nymphs who are being pursued by a rather amorous Orion whose constellation is adjacent to Taurus. The goddess Artemis placed the nymphs in the sky for protection and to this day Orion still vainly chases them across the heavens.
If you took A long exposure photograph of the Pleiades, it would reveal a ghostly looking cloud of ionized gas and dust surrounding the stars that was once thought to be a remnant of the nebula from which the stars within the Pleiades were born. more recent evidence seems to indicate it is nothing more than an interstellar gas cloud that just happens to be passing in front of the star cluster.
I’m always interested in how some celestial objects have managed to enter into our culture in ways that we may not even be aware of. Take the Pleiades for example. In Japan the cluster is known as “Subaru” and sure enough if you look at the corporate logo of the car manufacturer you will see an emblem containing six stars.
Binoculars are a fun and inexpensive way of exploring the night sky. Be sure to check online and with your library or bookstore to find more information on binocular astronomy.
Until next time I encourage to grab your binoculars, head outside, look up, and wonder.