- by John Hlynialuk
When Galileo crafted his version of the "spy glass", he was constrained by the optical glass that was available in 1610. The lenses he made produced a telescope with a very small field of view (FOV), the size of the circle of visibility when you look through the device. For a simple comparison, imagine the view through a paper towel cardboard tube as compared to a plastic straw. If you look at the Moon through the former, you will see all of the Moon plus lots of surrounding sky, while through the straw, only a small part of the Moon can be seen.
Galileo's telescope had a field of view more like the straw (so do modern telescopes, for that matter) but a pair of ordinary binoculars have a much larger field of view that make them the instrument of choice for starting out in astronomy. They are by far a better initial investment in the hobby. As for their invention, we once again hear the name Hans Lippershey, the same Dutch optician who applied for a patent for the telescope. It is reported that he was asked by the patent officials to produce a binocular instrument when he presented the design for a single-tube telescope. Lippershey never produced this binocular but oddly, other records indicate that even Galileo may have devised a binocular instrument. It was a pair of telescopes mounted in a helmet and had the user sitting in a pivoting chair for use on ships. Historians still debate the veracity of this story, and personally, I just cannot picture Galileo swivelling around in a test model of the chair wearing a helmet with two lens tubes projecting out of it!
In any case, binoculars of the modern design have been around for over a hundred years and my guess is that just about everyone reading this column has access to a pair. I hope some of you tried them out on Venus and the Pleiades recently and will continue to do so over the next few months. Venus continues to guide us to additional astronomical objects that are best viewed with these marvellous hand-held double-barrelled telescopes! From May 18 to 22, Venus will be in the same binocular FOV as M35, a smaller open cluster like the Pleiades (aka M45). M35, a cluster of about 300 stars is located at the foot of the Gemini twin, Castor and, with binoculars you can see about 30 stars easily in the group.
Then on May 27, Venus sidles up to the star Mebusta (in the middle of Gemini) passing it so closely that you will be hard pressed to split the pair with the naked eye, but no problem in binoculars. Then from June 17 to 21, Venus passes a third star group, the Beehive Cluster (M44), a faint patch to the naked eye in the middle of Cancer but which, in binoculars, reveals 40 to 50 starts, -looking like bees swarming a hive, if you use your imagination. Coincidentally, Mercury goes through the Beehive as well on July 4.
As a finale, on July 9, look for Venus beside the bright star Regulus in Leo. The separation will be wider this time and Regulus is brighter than Mebsuta, but Venus and Regulus will be well within the FOV of most binoculars.
If you are looking to buy or upgrade your binoculars, there are many brands out there and I recommend your local camera store as a starting point. You can't go wrong with a brand like Canon or Pentax, and buying from a local camera shop will insure you get good service and advice. The most important information about binoculars are the magnification and the diameter of the front lens, or objective. Expressed as 8 X 30 or 10 X 50, these stand for magnification and the objective diameter in mm. Unlike a telescope where you can switch out the eyepiece to get different magnifications, binoculars have only a single power unless you get a zoom type which has a range of magnifications.
An interesting coincidence is that the first three objects viewed by Galileo with his telescope were Orion's Belt, the Pleiades and the Beehive. He provides the very first telescopic descriptions of these in his book "Sidereus Nuncius" (Starry Messenger) printed in 1610. All three are visible right now above the western horizon and Venus will guide the way over the next few weeks. Dust off the binoculars and do have a look! There are some nice views to be had with these handy devices.
Clear skies!
