The general public has many misconceptions about astronomy. Now and then newer astronomy enthusiasts also reveal some confusion that makes the rest of us realize that what we considered common knowledge may be new information to a newbie. Here are a few misconceptions with clues as to how they may arise.
Distant Objects - Cosmological distances are difficult for the human mind to fathom; mankind began to get a fairly decent grasp of this only within the last hundred years or so. Everyone knows the starry band of the Milky Way is our home galaxy. But precisely where other deep sky objects are located can be confusing, especially since our senses don't provide useful information about distances that are so great. On one occasion, a newcomer asked me whether a certain galaxy was in the Milky Way. On another occasion someone asked whether a bright nebula was in our galaxy. The simple answer is that all galaxies are distinct objects far removed from the Milky Way. But with very few exceptions, the stars, nebulae, and star clusters that we see through our telescopes are all located within the Milky Way. For many years, galaxies were referred to as "island universes", but that description has fallen out of favor because the term universe commonly encompasses all that exists, well beyond single galaxies.When Planets are Visible - A new amateur astronomer referred to Saturn as a "wintertime object". And indeed it would seem so, since during the past few years Saturn has been making its appearance mainly during the colder months. But as seen in our sky, the planets all move sequentially through the various constellations of the ecliptic as they follow their orbits in the Solar System ... but at different rates. The inner planets, Mercury and Venus, come and go pretty quickly in our sky and never stray very far from the sun, leading to their being called "morning" or "evening" objects. But the farther a planet lies from the sun, the longer it takes to complete its orbit and the slower it moves in our sky. This is explained in Kepler's Laws of Planetary Motion. So a planet like Saturn appears to dwell in the same general region of the sky for a long time. Someone who has recently developed an interest in observing may not have paid much attention previously to where the planets were to be found, but in the past few years probably has started to take notice of when they're visible. Relax. Saturn will soon be visible during a season when conditions are more comfortable!
Color - A few months ago, I received an e-mail message from a chap who had read one of my articles on the Internet and was planning to buy a good-sized telescope. Here is the issue he posed: "... my most burning question is whether or not we will actually see any color? Having been dazzled and spell-bound by Hubble images, I wonder what to expect in detail and color from a 12" Dob?" Preconceptions may cause many entry-level stargazers to be disappointed when first seeing deep sky objects in a telescope. Those awesome color images are a result of the sensitivity and light accumulation properties of the digital medium - the human eye simply can't detect those colors. There are a very few deep sky objects (emission-type nebulae) that will show some color visually due to the strength of their radiation, but I had to tell him that almost all objects will appear a uniform gray when seen through even a fairly large telescope.
Dobsonian vs Newtonian - At one of our club meetings I was discussing Newtonian telescope optics with a member who is fairly new to astronomy. After explaining what I knew about the subject, he asked whether it also applied to a Dobsonian, which is what he owns. It dawned on me that in his mind a "Dobsonian" referred to a telescope design. He didn't realize that the term Dobsonian refers only to a type of alt-azimuth mounting that is generally used with a telescope of Newtonian design. As one example of where this confusion might originate, the description of the XT series of telescopes in the Orion catalog refers to them only as "Dobsonians". And unwittingly we all perpetuate this by simply referring to this type of scope as a "Dob". Orion does a good job of comparing the different telescopes, but their overview section is somewhat vague, noting that a "Dob" consists of a conventional reflector optical tube mounted on a cradle-type base instead of a tripod. Newcomers might wonder what the heck is a "conventional reflector".
The Bottom Line - Newcomers to astronomy are confronted with some unfamiliar concepts. Add to that what their experiences have told them plus some jargon the rest of us toss in, and it's easy to see the sources of their confusion. Sometimes you can even read about a subject and still not grasp the full implications of what you've read. So those of us who are well versed shouldn't take for granted what we consider "common knowledge" when discussing a topic with those new to the hobby.Published in the June 2007 issue of the NightTimes