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The solar system still remains a defining part of many an amateur astronomer's interest in the universe. These days, however, actual viewing of these subjects is being subjugated increasingly to the more indirect experience of CCD imaging. Effectively, this has taken much of the human element, and more particularly, the ready accessibility of these subjects, out of the equation. Some spectacular close-up views from spacecraft also may have robbed amateur observers of some of the wonder they used to have.

However, it is not all over for the visual astronomer. We should never fail to make distinctions between live telescopic viewing, telescopic imaging, and scenes imaged by spacecraft on the surface of the planets themselves. These all remain distinctly different types of revelation, and they are all valid and valuable. However, the direct, live experience remains not only the most personally impacting, but in a busy world it is still the simplest and quickest way to access our celestial neighborhood. There is still nothing quite like the crisp refinement and breathtaking impact of the live view, something impossible to duplicate by any form of imaging, and certainly far less time-consuming.

The good news, therefore, is that our old solar system favorites can remain the core of our astronomy, if we so desire. Take advantage of the opportunities you have here, because once we leave our neighborhood and enter deep space it is no longer possible to have such intimate contact with anything. We still have no inkling at all how any destination in the greater universe would actually appear close-up in its own neighborhood! Thus, the entire realm of what has always been the amateurs' solar system is still meaningful in the most dramatic way. Regarding any thoughts we might have about participating in a useful scientific role, we must accept that while some forms of specific, if limited, continuing surveillance are indeed still feasible (such as that performed by networks of amateur organizations), in many of the traditional categories of observing, contributing in such a capacity is largely over for us. Regardless, the wonder of spending time in our astronomical backyard remains undiminished, but perhaps being mere sightseers serves to free us from the burdens and demands of being more serious students.

Although the new perspectives provided by visiting spacecraft have made the solar system a much more familiar place, we cannot pretend that this has had no effect on our own objectivity; it does, in fact, cause us to see things in an entirely different light. We should not ignore these insights. Although this does indeed make for a certain contradiction, it nevertheless provides the kind of reality we used to only dream of having, and one we cannot pretend does not exist. Spend a little time looking at the multitudes of images provided at the NASA web (see Chap. 16 “Astronomy via the Internet”), as they will provide unique perspectives. These sites are updated continuously, and between them feature the full range of space missions since the beginning of the Space Age, as well as extensive Caltech-related observatory imagery and descriptions. You will see that this goes far beyond merely the solar system!

Solar system viewing is a means for developing refined viewing skills, which will help you greatly in other areas of astronomy, too. It has to be said that developed visual abilities fuel a special appreciation all of their own, for it is those glimpses beyond the normal visual threshold where the greatest rewards lie. For our observations, we have already covered some of the most useful equipment, along with new and better products. However, despite all the apparent advantages offered by today's high-quality equipment, many observers are spending less time at the eyepiece! This is not because they have found how to accomplish more in less time, but rather they are using the telescope merely as a necessary interface to the computer screen. Not only does this destroy the entire live viewing experience but also virtually guarantees that fitting astronomy around a busy personal schedule will become impossible. (If you have already tried to do anything quickly on a computer you are probably already well familiar with this scenario!)

The Sun

The dominant force in our own existence, the giver and the taker of all things physical in our own realm, the only star near enough for detailed study, and the center of everything in this realm, is the mighty Sun (Fig. 9.1). Nevertheless, it is the one object that many observers remain uncomfortable exploring to any degree firsthand! Part of this “solar phobia” stems from earlier years when we did not have access to modern protective filters and other such modern equipment for our telescopes. A healthy respect for the Sun was drummed into us by all that we read and heard. Despite plucking up enough courage for the occasional peek or short session, many observers still find that they cannot overcome the fear that a compromised filter, Mylar film, a scratched glass objective shield, or the shattering of glass of any kind would bring their worst nightmares to life. If you do not share in these misgivings, you may find the Sun to be among the most compelling subjects in which to immerse yourself, and it will certainly deliver a great deal for limited time, opportunities, or constrained budgets.

Fig. 9.1.
figure 1_9

The Sun, SOHO image 1999, Extreme Ultraviolet Imaging Telescope Consortium (photo courtesy of NASA/JPL-Caltech).

Full size image

Being a unique subject (even the next nearest star lies at an almost unfathomable distance), obviously the Sun is prime fodder for study, and it is study that offers easy and generous access for busy lives. In having this unique opportunity to study an actual star close-up, it is a natural destination for the observer. A complete subject all unto itself, the Sun is worthy of an entire separate volume; indeed, some observers never concern themselves with anything else. Many of these enthusiasts spend their annual vacations traveling to far away places to observe total eclipses and will accept remarkable degrees of discomfort, expense, or inconvenience to do so!

Even today, many misconceptions still exist among average laymen regarding the most everyday fundamentals about the Sun, such as “it is a giant gas ball burning in space,” when, in fact, its heat and light is the result of a gigantic nuclear reaction. Many people do not even realize that the Sun is a star, and not a particularly special one at that. Even more naively, expectations that its output will remain forever at a constant amount, or that if it changes at all during anyone's lifetime this is abnormal, have lead the average layman (even many in the scientific community) to believe that humankind alone is responsible for apparent global climate change, the “hot” topic of our time. To discount the probable influence of the Sun, apparently a variable star, is shortsighted, to say the very least.

The misconceptions do not stop there, however. Many amateur astronomers, although easily able to explain such simple things as the Sun's movement across the sky, might be hard pressed to explain to the uninitiated why it appears to change direction in the opposing hemisphere, and more to the point, when exactly does this apparent decisive turnabout occur? Once we cross the equator, is there a sudden reverse in the Sun's direction across the sky? In case you, too, find yourself scratching your head, just visualize the position of the Sun as it gains altitude in the sky as we approach the equator. We are still turning in the same direction, regardless of which hemisphere we are in. Once we move ever more into the opposite hemisphere, it will appear to have crossed the highest point in the sky and drop lower into the sky in an arc opposite to that from which it was traveling before. We will now find ourselves turning around to view it because of its placement, and it will now appear to be moving in the opposite direction, even though only its relative placement in the sky has changed! Logically, we perceive the Sun's ‘movement’ by facing the arc of the sky in which it appears to travel, from our home base or any other. All in all, this is a pleasingly simple explanation for something that often leaves otherwise well-informed folks stumbling for words or clear mental visualization. There are, of course, many other examples of a similar nature that we will not cite here.

We cannot complain that insufficient light or too small an image scale is a problem with the Sun! An effective study of it may be undertaken, therefore, with relatively small telescopes. Even with fairly limited apertures and appropriate filters, some solar devotees have spotted remarkable amounts of Sunspot activity and detail. Even an untrained eye can see far more detail on the Sun more easily than almost anything else in space. This is not to say that grander results may not be obtained with ever-grander equipment. Indeed, a large, unsilvered primary mirror will provide miraculous projected views, but few observers will be prepared to equip their large telescopes with unsilvered optics, or to have another set of aluminized optics on hand for the rest of their viewing. The need for such measures is because the heat generated by the Sun via large highly reflective standard objectives would invite equipment catastrophe. And even such special mirrors may be subject to disaster. Large filters for the primary optics are neither sufficiently effective, reliable, or even available. Some dedicated solar telescopes made by amateurs project an enlarged image of the Sun onto a flat screen; many serious solar observers prefer these for their observing. However, perhaps an ideal situation is to use specially designed solar refractors (such as those originally made by Colorado Instruments). They would seem to be the easiest and best “Sun scopes” of all, and certainly best for enthusiasts without much time on their hands.

John Watson, formerly editor of astronomy at Springer, has made a substantial contribution to this book on solar observing and imaging in Chap. 13, “Daytime Astronomy.”

Rediscovering the Planets

Even more than with the Moon, it had been all too easy in recent years to dismiss the planets as astronomical “has-beens,” whose interest and meaning for us had been left behind in the wake of modern cosmology and the far-flung universe. Some of us never bought into such a status for the solar system, however, and continued to observe these traditional astronomical sights with undimmed enthusiasm. However, a sudden new energy in official scientific circles has come about now for the planets, due to the astonishing discoveries made by recent unmanned spacecraft. The direct ties that many scientists now see in the relationship between the solar system, the universe as a whole, and the formation of life here on planet Earth itself has given professional astronomers reason once again to return to these relatively nearby has-beens. More amateurs are returning, too, while some of us never left.

For amateur observers, three grand destinations form the mainstay of our observable planetary system, that is, Mars, Jupiter, and Saturn. These are ideal telescopic objects, and for many of us these three planets, and/or the Moon, were the reason we entered the hobby in the first place. Although there is something quite mystical about all of the planets' place in space, it was these three worlds in particular that kept many observers straining to extract complex detail, much of which was as yet unconfirmed, not understood, or even unknown. We could only speculate about the actual nature of much of what we were seeing, and we could only imagine far away fanciful landscapes.

However, there is another, less immediately obvious, consideration for spending time in this corner of the universe. The fact that we can see these particular objects with such refinement, in real time, and in full color is more significant than it may seem. Color is a rarity once we leave the solar system. It is not that it is not there; however, experiencing it to any noticeable degree at the eyepiece is usually not in the cards. Now, aside from the brilliant colors of many individual stars, which are often striking to be sure, we are referring to almost all of the much fainter large structures far outside the solar system - especially outside our galaxy - where all significant traces of color are largely lost on our eyes. At these very low light levels our eyes strain to register anything at all, let alone color; those few objects that do reveal it present only the vaguest suggestions in faint pastels, at best. So take advantage of all that is nearby!

The Use of Color Filters

Many things sound possible, even promised in all the descriptions we see about filters. In theory, at least, the concept of blocking parts of the viewing spectrum with the appropriate filter to emphasize details of coincidental spectral properties certainly sounds good. It seems logical that it should work, and sometimes to a small degree it actually does, although it is unlikely to come close to the level of anticipation you may have. You will find that, with just a little care, you can see the same details without their use, albeit sometimes a little less starkly, providing a far more natural and satisfying state of appearance. Sometimes filters succeed only in coloring whatever we are looking at! They will not magically transform any view and their use often results in something far less desirable than using no filter at all. And, oh yes, they usually produce enough “ghosting” as to ruin the performance of any good eyepiece! So, just as the practice of stopping down the aperture of a telescope is a questionable practice for improvements in planetary resolution, you may generally find that the live filtered view generally loses more than it gains.

Should you wish to explore this topic further, including finding possible resources on the Internet, see Chap. 16. The Internet resources should provide some helpful and detailed views on many specific filters from the standpoint of a true filter “disciple.” There is always the possibility that perhaps, correctly applied, they might work for you! Meanwhile, you will need to take into consideration the aperture of your telescope, because too dark a filter for some apertures will be just right for others, and vice versa. Various shades of green, even yellow, are widely held to enhance detail on Jupiter's equatorial zones, and paler varieties are claimed to provide specific enhancements of details on Uranus and Neptune. However, the slight and vague nature of the markings on these outer solar system subjects must be understood, together with the unlikelihood that you will never see detail revealed on their surfaces! For the inner planets, a violet filter certainly is useful for discerning details of the cloud system of Venus, although there still will not be much of that to be seen either, regardless! So always be realistic in what you expect any color filter to do.

Everything Else in the Solar Realm

Perhaps surprisingly, the planets inside Earth's orbit are much less accessible in terms of viewing than those outside. Searing hot inner planets Mercury and Venus circle the Sun so closely that their temperatures long ago eliminated the prospect of finding anything on them other than parched landscapes. Venus, because of the thick cloud layer enveloping it, and Mercury, with its greater distance, poor viewing placement, and diminutive size, seem to have always conspired to yield little detail through our telescopes. Fascinating morsels of imagery on their surfaces itself via spacecraft have unlocked some of the secrets of Venus's cloud shrouded surface, the hostility of this world confirmed in dramatic fashion. Infrared imagery has also shown us the entire planet's terrain, albeit less satisfyingly than if we could just get rid of the clouds and see it for ourselves! Because of its total lack of atmosphere, Mercury has been fairly well imaged from near its surface by unmanned probes. Suffice it to say, the surfaces of these two planets remain places upon which no human may ever set foot.

In the opposite extreme, far beyond the orbit of Saturn, far-flung Uranus and Neptune are only just beginning to give up their secrets, thanks again to space probes. However, again, just as with Venus and Mercury, it is likely that amateur observers will find these planets somewhat frustrating to study. Their great distances prevent amateur observers from seeing anything other than faint single-colored discs. Further yet, beyond Uranus and Neptune but still within our solar system reside numerous additional worlds, with new classifications that have become a red-hot issue within the scientific community. Minor planets and asteroids will not reveal any outline or detail, of course, but many amateurs find great satisfaction in searching arduously for the brighter members of the Kuiper Belt fraternity; image intensifiers may be of value here since we are seeking points of light, which are generally well shown in such viewing.

We must not forget comets, asteroids, and meteors; these are all part of the Sun's realm. For some observers, these subjects alone are sufficient to occupy all of their attention, although if your time is limited the requirements are such that they will probably eliminate any serious depth of study. Certainly, the mystical presence of a bright comet in the sky is something in which all people, astronomically inclined or not, will take interest. However, the study of these celestial visitors is often most effective with large binoculars. Leftover debris of various solar system events of antiquity, meteors also respond very favorably to image intensifiers, since they generate wide spectrums of light as they burn up in Earth's atmosphere. The various annual bright meteor showers always attract a wide assortment of devotees, who find great satisfaction in logging the number that fall in each hour. Most people, though, will find their biggest pleasure in merely watching the magnificent cosmic spectacles, nature's own fireworks displays, from a reclining chair. As always, dark, transparent skies are best, and you are almost always guaranteed to see at least one dazzling meteor, which may appear more as a fireball, during any night out in these conditions.

Occultations of stars by planets are also sources of great anticipation, although any chance of seeing a bright star eclipsed by a planet is rather rare. Many amateurs derive much interest recording the effect that a planet's atmosphere has on the light source by the speed in which it is snuffed out. It is possible to draw some important conclusions from the results, which may even have further scientific value, although this is another rather work-intensive occupation that may be of little practical value for you. It is a more common occurrence for the Moon to occult something bright, because of its greater size, and of course, the Moon has no atmosphere. For most of us, however, the result is more spectacle than anything else, because stars will disappear instantly; planets will do so a little slower, of course, because they have appreciable dimensions from our point of view. However, events such as these are still quite rare, and this highly specific viewing activity only occasionally develops into a fulfilling area of specialized study for someone. Needless to say again, for such specialized forms of observing, you may simply not have the time.

On Being Useful

These days, so much detailed and complex information concerning the solar system has been uncovered by advanced research that there is not much left to be contributed by the amateur, except in one area. Around the clock surveillance of the three most easily observed planets still does have a certain value, as there is as-of-yet no continually orbiting spacecraft or large terrestrial telescope capable of the full-time monitoring of every large climatic or other ongoing global aspect of these worlds. This leaves certain monitoring opportunities still within the field of study for the amateur observer. Again, though, this will necessitate more dedication of time than you may have. However, it is not always necessary to feel useful, as the pure enjoyment of gazing upon other worlds is always wide open to us. It is this wonderful ingredient that often gets forgotten, as some amateurs seem to always be looking for justification for the time they spend with their hobby. Just reveling in all that there is to see, and making the effort to be knowledgeable about what meets our eyes, ought to be justification in itself.

Now let us look more closely at our local solar system destinations. There is so much pleasure in watching and studying these worlds that we cannot help but ponder the reality that people will actually visit, or even colonize, some of them during the present century – especially Mars! If you are of the younger generation, then maybe one of these people will be you! Meanwhile, all of us can visit them in our own way and come to feel that we know them, even if we cannot actually go there. You already know that there is a wealth of frequently untapped potential for your personal explorations at the eyepiece beyond merely adding to the near endless parade of mediocre CCD planetary imagery. The best part is that much enjoyment may be obtained without a huge time commitment or imposition on your life.