Two eyes are better than one. That's been my astronomical gospel ever since I got hooked by this hobby because of a homework assignment to view a total lunar eclipse. I watched the eclipse unfold through a pair of 7×35 binoculars and was transfixed by what I saw.

Those 7×35s helped introduce me to observational astronomy. Although those binoculars are long gone, my enjoyment for binocular astronomy has never waned. The binocular universe is a very personal one to me. I never head out to view through any telescope without a pair of binoculars flung over my shoulder.

What about you? Do you bring a pair of binoculars with you when you head outside for a night under the stars? If not, you really should! You might be surprised how much of the universe they will show you.

As it dutifully circles the north celestial pole, the Great Bear, Ursa Major, offers a picture window into the depths of the universe. Thousands of galaxies lie within its borders, although nearly all are beyond the range of most binoculars. Except for two, that is.

M81 and M82 (Figure 3.1) form one of the most famous pairs of galaxies found anywhere in the sky. The former has already been described in the previous chapter, where it is listed as naked-eye Challenge 1. We return to M81 again here, as seeing it along with companion galaxy M82 is a good test for suburban binocularists.

Telescopes in the 3- to 5-inch aperture range can be divided into three wildly diverse groups. On one hand, we have an overabundance of small instruments that are marketed toward unsuspecting newcomers to the hobby. These are often sold through department stores, consumer-club warehouses, toy stores, hobby shops, online auctions, and other mass-market outlets like television shopping networks. Two underlying traits are shared by the vast majority of these instruments: mediocre optical quality and shaky mounts.

On the other hand, we have some nice, middle-of-the-road economy instruments that serve their owners well. These instruments excel as grab-and-go telescopes, allowing their users to spring outside at a moment's notice without the burden of carrying massive mountings and huge tube assemblies.

Finally, we have some of the finest instruments sold today. Small-aperture refractors from well-known companies like Tele Vue, Takahashi, and Astro-Physics delight and entertain amateurs who are looking for the highest-quality optics, top-notch mechanics, and superior portability. They share the same spur-of-the-moment freedom as the middle group, while delivering top-notch images.

Giant binoculars, defined here as anything 70 mm or greater in aperture and 10× or more magnification, are also included in this chapter's mix. Owing to their lower magnifications, some of the challenges here are beyond their capability, while others are made to order.

Regardless of which instrument you are using, the challenge objects gathered here will test its limits, and yours.

The first “good” telescope I ever owned was an 8-inch f/7 Newtonian reflector known as the RV-8. It was made by the Criterion Manufacturing Company of Hartford, Connecticut, and given to me by my parents as my sole Christmas gift in 1971. I have received uncountable gifts at Christmases since, but none will stand the test of time like that telescope. True, I had owned a couple of smaller telescopes beforehand, but the RV-8 was not just a telescope. It was a spaceship that catapulted me out into the real universe for the first time.

Here are a variety of challenging targets suitable for intermediate apertures that will take us both into the real, and sometimes, surreal universe.

Although it is one of the faintest constellations along the zodiac, Cancer the Crab hosts a variety of targets to test our mettle during the early spring. Spotting M44, the Beehive Cluster, by eye alone may prove very challenging for suburban observers, while the Crab's underappreciated second open cluster, M67, may also reach naked-eye visibility from more rural environs. While the constellation boasts a variety of challenging galaxies, in the test here, we will try our luck with one of the constellation's prettiest binary stars, Zeta (ζ) Cancri.

Many “best of” lists include Zeta as a spring showpiece target, so there is a good chance that you have already crossed paths. Zeta's two brightest suns, known as Zeta-1 and Zeta-2, were discovered in 1756 by German physicist/astronomer Johann Tobias Mayer.

We now enter the realm of double-digit apertures and step into the full depths of the deep-sky ocean. It wasn't that long ago that a 10-inch telescope was considered large by amateur standards. Bringing one to a club star party was a sure way to be the center of everyone's attention, as it stood alone amidst an ocean of 6-inch and smaller telescopes. A 12- or 14-inch telescope practically deified its owner.

Times have changed. Today, these same scopes are no longer the big kids on the block. But that doesn't change the fact that each can still bring its owner a lifetime of enjoyment. Indeed, there are so many challenging objects for these telescopes that trying to settle on the best-in-class is difficult to do. The targets included here represent some of my favorites, but you may well have others that you find equally demanding.

Several of the challenges in the last chapter involved hunting down tiny planetary nebulae. Many planetaries appear very small as seen from Earth, which can make them difficult to tell apart from surrounding stars. This also works in our favor, however, since their small size focuses all of the available light into small disks with high surface brightnesses. Their existence is also accented nicely by using narrowband and oxygen-III filters, which help suppress light pollution. That's why planetary nebulae are far better targets for urban observers than some other types of objects.

Trying to draw up a finite list of challenging objects scattered through the infinite universe is an almost insurmountable task. That became all too apparent as this book evolved. In fact, when I wrote the “Challenge Object” column in Deep Sky magazine back the 1980s, targets that I thought were difficult tests back then have subsequently proven to become old friends that I visit often. Others, however, proved to be so difficult back then that they jumped up an aperture class, if they are included in this book.

It would be a very easy task to assemble a volume 2 to this book simply from the leftovers that I chose not to include here for one reason or another. Indeed, the Cosmic Challenge could become a multi-volume set. But, rather than do that, I leave the task of developing volume 2 to you, the reader.

As you explore the objects discussed here, you will undoubtedly bump into other targets that are just as challenging, and perhaps even more so. Prompted by those, began to compile your own favorite list of cosmic challenges.

Perhaps your challenges favor Solar System targets. If so, begin with the Lunar 100 list of targets. Created by Charles Wood and first appearing in the April 2004 issue of Sky & Telescope magazine, the Lunar 100 offers, in Wood's own words, “a selection of the Moon's 100 most interesting regions, craters, basins, mountains, rilles, and domes; to provide Moon lovers with something akin to what deep-sky observers enjoy with the Messier catalog.

With those words, Garret Serviss embarked on his book Round the Year with the Stars. Published in 1910, Round the Year with the Stars brought readers to sights that few had ever seen before. Serviss was one of his generation's best-known astronomical authors, with several previous titles to his credit. Indeed, he was almost apologetic for writing this latest work. “The writer's only real excuse for appearing again in this particular field is that he has never yet finished a book, and seen it go forth, without feeling that he had overlooked, or cast aside, or of necessity omitted a multitude of things quite as interesting and important as any he had touched upon.”

That is my excuse, as well. In the 100 years since Serviss's book first appeared, there have been hundreds, if not thousands, of observing guides published. I have written a couple of them myself. Some were general guides intended to introduce the reader to the sky's finest objects. Others paid homage to only certain classes of objects, restricting their discussion to only deep-sky objects or perhaps members of the Solar System.

“It's going to be clear tonight,” you think to yourself as you stare out of the window. “I can't wait for the Sun to go down!” Your mind immediately leaves whatever it is you're doing at the time, be it work, chores, school, or something else, and flies into the cosmos.

Shhh, did you hear that? That's the universe calling you.

As amateur astronomers, we aren't content to sit home at night, watch television, or drive to the local multiplex cinema to take in the latest movie. We won't have any of that. We're explorers. That's what drew us into astronomy in the first place: the idea that we can explore this marvelous universe of ours right from our backyards.

But then, hours later, as you're gathering your observing gear for a night under the stars, you stop dead in your tracks. “What am I going to look at?”

Has that ever been you? Probably. In fact, that may have been you just last night. Let's face it, if you've been involved with observational astronomy long enough, there is bound to come a time when you've seen “everything” your telescope can show you. All of a sudden, that show on television is beginning to sound tempting.

Okay, now stop right there! I'm not going to let you do it. You're an explorer. You're a pioneer. As amateur astronomers, we share a unique perspective on life.

This final chapter throws down the gauntlet. Today's largest backyard telescopes, defined here as 15 inches in aperture or larger, have the capacity to show us sights that only a few years ago were either unknown entirely or, at the very least, not understood. All require good viewing conditions, whether that is excellent transparency, steady seeing, freedom from light pollution, or a combination of all three.

How many of these ultimate challenges can you see?

One of my favorite binocular open clusters in the entire sky is M44, the Beehive Cluster or Praesepe, in Cancer the Crab. It's a wonderful target through just about any pair of binoculars. Even the smallest, cheapest pair will show a rich vault of stars. Nine of the brightest stars near the center of the cluster form a distinctive V asterism that is sometimes called the Heart of the Crab. The Heart points toward the southwest and always attracts attention.

Hidden among the stars of M44 are no fewer than eight distant galaxies. Until 1987, most of us knew nothing of them. That was the year when the Uranometria 2000.0 star atlas was published. It showed the sky to a depth never before captured in a convenient star atlas format, and immediately shed light on thousands of objects that no amateurs, except possibly for a few extreme deep-sky hunters, even knew existed.

The biggest problem in spotting the galaxies beyond the Beehive is not their dimness, although that is clearly a factor.

Of all the challenges presented in this book, this chapter should be considered the great equalizer. All of the objects to come in later chapters require some level of auxiliary equipment – binoculars or a telescope – in order to be seen. But not these. The targets described below require only one piece of optical equipment: your eyes. That's right, we're about to go nude stargazing together!

While some readers will enjoy distinct advantages over others in the chapters to come in terms of equipment, here we are as close to on a level playing field as possible. That's the fun of it. It's amazing just what can be seen by eye alone when you really make a concerted effort under dark skies.

Has anyone ever asked you “What is the most distant object visible to the naked eye?” Probably? It could have been someone at a club star party or maybe a family member at a reunion who is bemused by your interest in astronomy, but most astronomers have been asked that question before. What did you tell them? More likely than not, most city slickers would give the stock answer that we have all used: M31, the Andromeda Galaxy (naked-eye Challenge 11), which by modern reckoning is 2.5 million light years away. Those who live farther from civilization, without the pall of light pollution shrouding their sky, may have answered M33, the Triangulum Galaxy (naked-eye Challenge 12), which is 2.9 million light years away.

An observer with much experience with eclipses, Steve Edberg, gazed silently at the Sun when its corona appeared near midday on July 11, 1991. Just stared. Even though he had seen the corona several times before, he was overwhelmed with its size and beauty. This was to be a long total eclipse – almost seven minutes of totality – so he had the chance to preserve this moment. “Well now,” he muttered after the moment. “Perhaps I should take a picture or something?”

No matter how well you prepare for it, unless you are a person of extreme discipline, the onset of totality will drag you away from your planned program. You just want to gaze at it. That is actually the right approach, and no matter how much or how little time totality will last, you do want to have some time for just taking it all in. If totality is long, as it was in 1991 and in 2009, then you have some time for this. If totality is short, then make the time. The shortest totality I've ever experienced was the hybrid eclipse, annular in places and total in other places, in April 2005. Even then I gave myself about five of the 29 seconds of totality to enjoy the view before I resumed my plan.

It is possible that the single most delightful observing session can happen when there is a penumbral eclipse of the Moon. Such an event is as far removed from a total solar eclipse as one can get, and still have an eclipse of some sort. In a penumbral lunar eclipse, the full moon enters, travels through, and then exits the outer shadow of the Earth. This part of the shadow is called the penumbra, and its effects can range from absolutely nothing to, at best, a slight darkening of one edge, or limb, of the Moon. For almost all observers, that is all. For Thomas Hardy, whose wonderful poem “At a Lunar Eclipse” appears at the start ofChapter 13, the total eclipse he saw in 1903 was preceded by a penumbral shading.

However, for me there is much more. At no other time do the rays surrounding the younger craters, like Tycho and Copernicus, appear so obviously. These big craters are certainly not young by human standards; Tycho was formed about 100 million years ago by the sudden impact on the Moon of a comet or an asteroid, and Copernicus is a bit older, but both are young geologically. The Moon's oldest craters were formed probably by impacts mostly during a period about 3.9 billion years ago, and is remembered today as the period of late heavy bombardment.