Probing The Stars (For Real)

ptsCanopus now belongs to the constellation Carina, the Keel, but the Keel was once part of Argo Navis, the Ship Argo. Provided a berth in the night sky as one of the 48 constellations cataloged by the Alexandrian astronomer Ptolemy, the starry Ship is now dry-docked and dismantled. In 1763, the French astronomer Nicolas-Louis de Lacaille split the old galley into several pieces for the convenience of more modern astronomy.

Canopus has been getting keelhauled at least since the third century B.C., when Aratus, the author of the oldest handbook of the heavens we’ve inherited from ancient Greece, called this star the Ship’s pedalion, or rudder. It hangs loose, he added, beneath the hind legs of Canis Major, the Great Dog. Identifying the ship by name, Aratus confirmed that this celestial vessel once transported Jason and his all-star crew of Argonauts to Colchis on the eastern shore of the Black Sea in the quest for the Golden Fleece. Later this year, several cruise ships will be following the wake of the Argo through the Bosporus on a quest for coronal fleece in a total solar eclipse that includes the Black Sea in an August 11th argosy of darkness.

Although Aratus did not use the name Canopus for the star in the Ship’s rudder, that name does appear in the Catasterismi. Its celestial myths probably reflect star lore of the same era. Canopus is not mentioned, however, in the Catasterismi’s chapter on Argo. It appears instead in the passage on Eridanus, the River. Placed below the River, Canopus “touches the steering-oars of the Argo.” The Catasterismi additionally suggests that Eridanus represents the Nile. The Roman mythographer Hyginus also identified Eridanus as the Nile, assigned Canopus to it, and described the star as “an island washed by the Nile river.”

A star as bright as Canopus understandably commanded attention in other parts of the world. Most of China could see it, and in China it was known as Shou xing, the Star of Longevity. Its southern disposition also prompted the Chinese to call it “The Old Man of the South Pole,” and China’s first emperor, Qin Shi Huang Di, offered sacrifices to it. Later, Canopus was personified as a cheery and bald old man who travels with a big peach, a symbol of long and rich life.

In New Zealand the Maori watched for the first predawn return of Canopus as a signal of the coming frost. They named it Atutahi and remembered its use by their migrating ancestors to navigate the Pacific from eastern Polynesia. Wilhelm H. I. Bleek and L. C. Lloyd included ideas about Canopus among the San people of South Africa in Specimens of Bushman Folklore (1911). The San sang to the star in winter and burned a stick toward it to coax a little more heat from the Sun. They associated Canopus with Sirius and said the two wink similarly.

Of course, you don’t have to travel as far south as New Zealand, South Africa, or even Alexandria to catch Canopus. If you are moored anywhere south of 37[degree sign] north latitude, you can spot it at this time of year.

Precession doesn’t alter the declination of Canopus very much. Located fairly close to the south pole of the solar system, it is more or less anchored in the current that shifts the stars’ positions in a 26,000-year cycle. Its visibility from places like Athens, Alexandria, and Rhodes hasn’t changed much in 2,000 years.

vpFrom Rome, too, Canopus still enjoys roughly the same level of southern hospitality it did when Vitruvius Pollio was compiling his 10 books of De architectura. Explaining how some constellations circle the south celestial pole and remain hidden beneath the ground from Rome, he wrote, “The star Canopus proves this. It is unknown to our vicinity; but we have reports of it from merchants who have been to the most distant part of Egypt, and to regions bordering on the uttermost boundaries of the earth.”

For the Romans, Canopus was almost synonymous with Egypt. In fact, a famous town with that name once operated as a Mediterranean port for the westernmost branch of the Nile. By legend, Canopus was named for the pilot who was shepherding King Menelaus and Helen back home. Their ship was driven by storm to the Egyptian coast, and thanks to a viper, Canopus died during shore leave. The ruins of old Canopus today are next to Abu Qar, a small village in the Nile Delta. An important council for calendar reform was convened there by Pharaoh Ptolemy III Euergetes I in 238 B.C., and the astronomer Ptolemy was headquartered there.

Canopus was just some 20 kilometers northeast of Alexandria. Operating as a pleasure spa, it also attracted pilgrims to its pagan shrines. Erotic rituals and libertine recreation helped maintain its notoriety and international appeal. Its celebrated temple to the god Serapis inspired the emperor Hadrian to build a replica in his summer retreat at Tivoli, just 26 kilometers east of Rome. Serapis was the Hellenistic version of Osiris, the Egyptian god who presided over cyclical renewal. Osiris also judged and ruled the dead, and as Serapis he acquired attributes of several Greek gods, including a talent for healing.

There is a puzzle in all this Canopus lore. According to the Greeks, the constellation Argo was Jason’s ship, and the star that marked its rudder was named for a legendary helmsman. Canopus, however, never sailed on the Argo. When the poet Pindar recited the ship’s roster in the first half of the fifth century B.C., Canopus didn’t make the list. Apollonius of Rhodes, who in the third century B.C. authored the most enduring account of the Argo’s adventures, said the ship’s first pilot was Tiphys.

Canopus was not shanghaied for an Argo tour of duty until later, in the first century B.C., when Greek writers like the geographer Strabo conscripted Canopus into the crew. In the earlier Greek star tales, however, Canopus was associated with Egypt. This connection with Egypt was later reinforced by the reassignment of a veteran of the Trojan War to Jason’s quest. Maybe we should be looking toward Egypt to understand how Canopus was insinuated into Greek astronomy.

Plutarch documented his understanding of the Egyptian gods in Isis and Osiris, and he reported the Egyptian belief that the star Canopus was named after the pilot who guided the ship of Osiris. The ship, he added, is the constellation Argo. Although we can’t independently verify Plutarch’s astronomical analysis, other information he provided about Egyptian gods and stars is supported by Egyptian antiquities. If Plutarch was right, this element of Egypt’s astral mythology may have been borrowed by the Greeks and reconfigured to commemorate their maritime adventures. By the time the stellar Ship had become known as Argo, constellational consistency enlisted Canopus to steer the Argonauts.

Check Out Mars, Man

commFrom temperate latitudes the Moon, planets, and Sun are always lower than the zenith, so backyard astronomers must contend with the presence of roughly 10 miles or more of air at ground density in their line of sight.

This air acts like a weak red filter (or a strong one when objects are really near the horizon). It reddens everything a bit, from blue-white stars to objects that are reddish to begin with. The British planetary observer Val Axel Firsoff, who often painted landscapes in watercolors, cautioned that when comparing the color of planetary features with familiar objects “we must not think in terms of our immediate surroundings but of horizon views, 7 to 10 miles distant and preferably seen through a telescope.” Under such circumstances dark markings will appear bluish (due to scattered daylight) and bright markings will appear reddish.

A Colorful History

For many years the most influential descriptions of Martian colors were those provided around the turn of the century by Percival Lowell, who observed with a 24-inch Clark refractor at his private observatory in Flagstaff, Arizona. The hues that he described were as vivid as his prose. The bright regions were predominantly “roseate ochre,” dappled here and there with “brick-red” and even “dragon’s blood.” Lowell compared them to colors in the Painted Desert near Flagstaff. The dark markings appeared “robin’s egg blue” but faded seasonally to “chocolate brown,” a phenomenon that he interpreted as the growth and decay of vegetation.

Another keen student of Mars during these years was Eugene M. Antoniadi, who observed with the 33-inch refractor at Meudon Observatory on the outskirts of Paris. Although he argued vehemently that Lowell’s observations of canals were hopelessly flawed, Antoniadi not only confirmed but even embellished Lowell’s palette of colors and their purported seasonal changes. In 1924 he wrote: “Not only the green areas but also the greyish or blue surfaces turned under my eyes to brown, lilac-brown, or even carmine. . . . It was almost exactly the color of leaves which fall seasonally from trees in summer and autumn in our latitudes.”

These vivid hues were literally in the eye of the beholder, the products of an optical illusion known as simultaneous contrast. This phenomenon was discovered in 1839 by the chemist M. E. Chevreul. The Director of Dyeing at the Manufactures Royales de Gobelins, France’s national tapestry workshop, Chevreul investigated chronic complaints about the fading of blues and violets in tapestries. To his surprise, he found that in many instances these colors were every bit as bright and unfaded as intended. The real nature of the problem was that the apparent intensity of a color depends on the hue and lightness of its surroundings. He wrote: “When the eye sees at the same time two contiguous colors, they will appear as dissimilar as possible, both in their optical composition and in the height of their tone. We have then, at the same time, simultaneous contrast of color properly so called and contrast of tone.”

Simultaneous contrast causes colored highlights to impart their complementary hue to any adjacent low-luminosity features. (Double-star observers are very familiar with this effect.) Viewed against a bright ochre background, a dark neutral gray marking will take on an illusory bluish green cast.

The relevance of this fact to Mars was not lost on several mid-19th century astronomers, notably William Herschel’s son John, a great astronomer in his own right. He often perceived greenish tints in the dark areas but suspected that they were merely an effect of contrast with their ruddy surroundings. There is no evidence, however, that either Lowell or Antoniadi ever considered simultaneous contrast as a possible source of error in their assessments of Martian colors.

It is a little-known fact that the greatest 19th-century observer of Mars, the Italian astronomer Giovanni Schiaparelli, suffered from red- green colorblindness. Those afflicted with this condition have a weakened perception of all colors that is most pronounced in the case of red and its complement, green, which both appear basically gray. Color vision in such individuals is best for yellow, but even then it is less sensitive than normal to gradations of hue. Ironically, this idiosyncrasy of Schiaparelli’s eyesight conferred immunity from the effects of simultaneous contrast, so his impressions of the dark markings as “mere reinforcements of the reddish color that dominates the continents” have proved quite accurate. On the other hand, colorblind individuals are more sensitive to contrast than those with normal vision. This may account for Schiaparelli’s proclivity to depict soft, indefinite shadings as hard-edged linear features, the very hallmark of the geometrical network of canali that he “discovered” in 1877.

Optical Illusions

oiIn addition, estimates of the colors made with large-doublet refractors like those employed by Lowell and Antoniadi must be regarded with skepticism. The chromatic aberration of large refractors almost always comes as a shock not only to observers accustomed to views provided by reflectors, but also to users of achromatic refractors of modest size. The color error of objective lenses made with conventional crown and flint glasses grows markedly with aperture. A time-honored rule of thumb is that the focal length of an achromat should be three times the square of its diameter in inches if its chromatic aberration is to be unobtrusive. Hence the color error of a 5-inch f/15 doublet is hardly noticeable, but achieving comparable correction in a 12-inch objective requires an unwieldy focal ratio of f/36, and a 40-inch lens demands an utterly impractical focal ratio of f/120.

Most large-doublet refractors, including those used by Lowell and Antoniadi, have focal ratios of f/15 to f/20. Their makers gave the shortest focal length to light in the yellow-green region of the spectrum (where the human eye is most sensitive) and made the focal lengths of red and blue light longer and coincident. Consequently, the image of a bright object like Mars is seen through a purple veil of “secondary spectrum” (defocused red and blue light) that mutes low- contrast markings and makes accurate assessments of color all but impossible.

At the dawn of this century the preeminent American planetary observer was Edward Emerson Barnard. For two decades he had tirelessly observed the planets with the largest refractors in the world, the 36-inch at Lick Observatory and the 40-inch at Yerkes Observatory. It is hardly surprising that his first views of Mars with the recently commissioned 60-inch reflector at Mount Wilson Observatory in 1911 proved to be something of a revelation. He found the reflector’s complete absence of secondary spectrum “very remarkable.” Mars looked “as if cut out of paper and pasted on the background sky . . . perfectly hard and sharp with no softening of the edges.” To Barnard’s amazement, the bright regions of Mars appeared “a very feeble salmon – almost free of color.” The dark markings looked “painted with a greyish paint supplied with a very poor brush, producing a shredded or streaky and wispy effect.”

Barnard’s impressions were confirmed in 1956 by Gerard Kuiper, who used an even larger reflector – the 82-inch Cassegrain at McDonald Observatory in Texas. Kuiper carefully compared the image of Mars to a color chart containing 200 different hues placed three feet away. During these observing sessions the interior of the dome was brightly illuminated so that his eyes remained daylight- rather than dark- adapted. He employed a beamsplitter binocular viewer equipped with a pair of matched eyepieces that gave a magnification of 900 [yen] . At this generous image scale the disk of Mars appeared no less than 6[degree sign] across, 12 times the diameter of the Moon seen with the naked eye.

Kuiper found the basic color of the dark markings to be “neutral grey . . . essentially the same hue as the adjacent deserts but diluted with black.” A few localities exhibited subtle tints ranging from “slightly brownish” to “a very dilute moss green.” There seemed to be a correlation between the quality of the seeing and the apparent color of the markings. When the atmosphere was turbulent, Kuiper found that his eye tended to wander rapidly over the roiling image, causing spurious colors arising from simultaneous contrast to become much more pronounced. But when the air settled down and the image became steady for several seconds, these colors all but disappeared.

Martian Blues

Few opinions on the subject of Martian colors should carry more weight than those of University of Arizona astronomer William Hartmann. A talented artist whose paintings of planetary landscapes are among the most realistic, Hartmann is extraordinarily discriminating when estimating and naming colors. In 1988 he observed Mars with a 24-inch Cassegrain reflector at the summit of 13,800-foot Mauna Kea. The bright deserts appeared “pale orange like what you might find at the junction of orange sherbet and vanilla ice cream.” Although the dark markings looked “bluish-grey” at the eyepiece, he subsequently found that, in “a textbook display of simultaneous contrast,” they could be very realistically depicted in an acrylic painting using only pigments on the warm (reddish brown) side of neutral.

If we’ve managed to convince you that seeing is disbelieving, we’ll close with a cautionary note that not every bluish tint seen on Mars is an illusion. During the opposition of 1858, Mars was extensively observed by the Jesuit astronomer Angelo Secchi with the 911/42-inch refractor of the Collegio Romano in Rome. Although Secchi described many of the dark markings as “ashen colored,” one of the most prominent was “a large triangular patch, blue in color” that he christened the “Atlantic Canale.” This was the first use of the fateful term “canale” (channel) that is often erroneously attributed to Schiaparelli. Secchi later called this feature the “blue Scorpion.” Today we know it as Syrtis Major.

The Mariner and Viking spacecraft revealed that Syrtis Major is a plateau. A low-relief shield volcano has been identified within its confines whose eruptions are widely believed to be the source of the dark materials that cover the area. Every Martian year around the time of northern-hemisphere summer solstice, a remarkable localized cloud forms over Syrtis Major and portions of the adjoining Libya basin and persists through early summer. Scattering by the cloud’s aerosols and ice crystals imparts a genuine blue color to the region. This recurring meteorological phenomenon was named the “Blue Syrtis Cloud” by the late Charles F. Capen.

The Northern Skies Are An Inspiration

tnsaiIn some ways, the Vela Supernova Remnant is the southern sky’s answer to the Veil Nebula in Cygnus. Located some 1,500 light-years away and covering 5[degree sign] of sky, it ranks as the largest supernova remnant in the sky. Roughly 12,000 years ago, a massive star exploded at this site. Today we see the gas in the collision zone between the material ejected by that star and the interstellar gas it has swept up, glowing as it is heated by shock fronts from the expanding shell. Many sources, including the Uranometria 2000.0 star atlas, incorrectly label this as the Gum Nebula, which is in fact a huge, overlapping emission nebula centered in Puppis.

A 13-inch telescope with a nebula filter gives an astonishing view of this supernova remnant, with strings of nebulosity lacing field after field. Look to the west of the 4th-magnitude star e Velorum for one of the brightest of these strands, elongated north-south and filling a 1[degree sign] field. Surprisingly, only one portion of this immense, beautiful complex earned a place in the NGC. Some 5[degree sign] east-southeast of the remnant’s center lies NGC 2736, which appears for all the world like the Veil Nebula near 52 Cygni – a twisted, writhing cigarette-smoke plume more than half a degree long.

Return now to Delta Velorum and scan 2[degree sign] north-northwest to find the naked-eye open cluster IC 2391. This sparse, nearby cluster lies approximately 500 light- years away. Only 30 stars shine brighter than 12th magnitude, but the main attraction is the handful of naked-eye stars that make this a good binocular target. Using 11×80 binoculars, IC 2391 displays six bright stars and another 13 stars down to magnitude 9.5 but with no obvious border. A telescope overwhelms this cluster, spreading its member stars too far apart.

Just over 1[degree sign] southeast of Kappa Velorum, the star at the tip of the False Cross, is the bipolar planetary nebula NGC 2899. A 12-inch telescope shows two bright lobes, each round and about 30″ across, connected by a bar traversing the center. Larger telescopes may show a fainter envelope that brings the size of the planetary up to 2′. Immersed in a rich part of the Milky Way at a distance of 2,800 light-years, the field surrounding NGC 2899 appears magnificently starry. Don’t expect to ferret out a central star though – it hasn’t been seen optically yet, even with professional telescopes. Some astronomers think that the responsible star may be hiding behind a binary companion.

Two degrees south-southwest of NGC 2899 and back in Carina lies another interesting planetary, NGC 2867. When John Herschel discovered this object with his 18-inch telescope, he at first suspected it might be a planet. He confirmed it lay far beyond our solar system by measuring its position relative to the nearby stars on successive nights and detecting no motion. The better optical quality of today’s telescopes reveals the planetary’s tiny annular disk that has a subtle north-south elongation.

nsNearly 6[degree sign] south of Iota Carinae and near the border with Volans dwells the impressive globular cluster NGC 2808. A 4-inch telescope barely shows its brightest stars, but the cluster springs to life with innumerable 13th- and 14th-magnitude jewels using 8 inches of aperture. Well concentrated to a sharp center, the cluster presents several hundred stars in an area about 10′ across. Radiating streamers appear to bring the overall size to 15′. Many observers rank NGC 2808 as the third-best globular cluster in the southern sky, trailing only Omega Centauri and 47 Tucanae, and among the five most beautiful in the entire sky.

Some 8[degree sign] northeast of this globular, in a portion of the Milky Way rich in competing open clusters, resides one of the most spectacular. NGC 3114 appears as a mist against an already bright background when seen with the unaided eye from a dark site. But turn an instrument that provides a 1[degree sign] or larger field of view on it and you will be truly impressed. A 4-inch telescope at 30x shows more than a hundred stars scattered about with no distinct center. In a 10-inch scope at 75x, it is difficult to contain the cluster’s 200 members brighter than 15th magnitude. At a distance of 2,800 light-years and an apparent size of 35′, NGC 3114 extends some 30 light-years across.

Writing in the European journal Astronomy & Astrophysics, J. E. Dyson and J. Ghanbari describe NGC 3199 as “an interstellar snow plough.” Lying 3[degree sign] northeast of NGC 3114, this nebula appears similar to the Bubble Nebula in Cassiopeia and the Crescent Nebula in Cygnus. Its distorted shape arises from a strong stellar wind blowing off a Wolf-Rayet star. A small telescope equipped with a nebula filter reveals the crescent shape of the nebula, which opens to the east and appears brightest at the south end. The eastern edge appears sharp while the western edge is diffuse throughout. A small trio of faint stars lies at the “focus” of the arc.

Heading south once again, to a point 6[degree sign] southeast of NGC 3114, brings us to an open cluster sometimes referred to as the “Southern Pleiades.” Centered on the 3rd-magnitude star Theta (q) Carinae, IC 2602 is a wonderful assemblage of a half-dozen stars visible to the naked eye covering a 1[degree sign] area. In an 8-inch telescope at 50x, IC 2602 shows 30 stars with no discernible boundary. Sweep less than a degree south to find the much fainter and smaller open cluster, Melotte 101.

Perhaps the highlight of this entire region is the Eta (h) Carinae Nebula (NGC 3372). Located 5[degree sign] due north of IC 2602 and spanning 2[degree sign], it ranks as the brightest emission nebula in the sky. It is a spectacular object whatever instrument you use. It appears as the brightest spot in the Milky Way to the naked eye – clearly a large, nebulous glow. Binoculars bring out its full extent and hint at the object’s enormous dust lanes. Through a telescope at 40x, the most prominent detail is this dark, V-shaped rift slicing through the nebula’s center. You can see scalloped detail where this edge meets the bright nebulosity, and the entire object is mottled with filaments of gas that a nebula filter will greatly enhance.

It pays to treat this object with reverence by very slowly increasing the magnification of your view. If you peer into the center of NGC 3372 at 100x you will see the Keyhole Nebula, a dark cloud with overlying nebulosity. Even the highest magnifications hold something of interest: the star Eta Carinae itself. A region of yellow nebulosity surrounds Eta Carinae, which has earned it the nickname “the Fried Egg.” This central blaze is more commonly known as the Homunculus, or Little Man. Under the steadiest seeing conditions, tiny spokes can be seen extending from the star.

A century-and-a-half ago, Eta Carinae was the sky’s second-brightest star, exceeding even Canopus. Since then it has varied irregularly and today glows at 6th magnitude, partially because the surrounding nebula obscures it. In fact, it is one of the most massive and most luminous stars in the entire galaxy, shining with the light of over 5 million suns.

From Eta Carinae it is only a 3[degree sign] sweep eastward to the great open cluster NGC 3532. Spanning a full degree, the cluster contains more than 100 stars brighter than 12th magnitude that shine across a distance of 1,600 light-years. Naked-eye viewers will notice an oval concentration brighter than the surrounding Milky Way, but optical aid brings the best view. Even 7×50 binoculars reveal 50 stars that are detached from the starry background. Through a 4-inch telescope, the central half-degree becomes packed with stars between 7th and 10th magnitude. Look for a prominent lane devoid of stars that runs along the northern edge of the cluster. Although the view in a wide-field telescope is most pleasing, a large aperture does reach the multitude of fainter members.

On the eastern edge of Carina south of NGC 3532 lies a nebulous complex known as RCW 57. Despite its rather obscure designation, don’t pass up this interesting target. It encompasses both NGC 3603, the densest concentration of very massive stars in our galaxy, and NGC 3576, a giant emission region excited by the hot, massive stars. It compares well with the Tarantula Nebula in the Large Magellanic Cloud. Although NGC 3603 appears bright, it is too small to be resolved or even identified as an open cluster. Faint emission nebulosity can be seen surrounding the bright mass of stars at the center. To the west, the area around NGC 3576 becomes spectacular when seen in a backyard telescope. Through a nebula filter at 100x, four bright glowing regions immediately come into view accompanied by two fainter ones to their south. All this activity happens in an area scarcely 10′ across.

Four degrees north of Eta Carinae, over the border and back into Vela, lies the pretty double star x Velorum. An easy split in binoculars, this pair shows a gorgeous contrast between orange and blue stars vaguely reminiscent of Albireo in Cygnus.

The loosely concentrated globular cluster NGC 3201 lies about 10[degree sign] north- northwest of x Velorum and actually climbs above the horizon murk when viewed from the southern United States. Only 16,000 light-years distant, close for a globular cluster, its stars glow brightly. An 8-inch telescope resolves about 100 members over an area 8′ across. Larger telescopes extend the size and number of stars slightly, but the concentration remains very loose and the edge is difficult to define.

On the northern edge of Vela, where it meets with Antlia, resides the planetary nebula NGC 3132. Also known as the Eight Burst Nebula, the first impression of this object is a planetary with a bright central star. Indeed a 10th-magnitude beacon lies at the nebula’s center. But this star isn’t the one responsible for illuminating the surrounding shell. The real candidate seems to be a 15th- magnitude star that lies 2″ from the bright star. NGC 3132 has a very high surface brightness, allowing you to view it at high magnification. A shell 60″ by 45″ in diameter surrounds the bright star. This shell dims gradually from the inner edge to the center, where patchy detail is subtly visible when the seeing permits.

Checking Out A Different Sort Of Atlas

coadsAs passingly interesting as VRLI’s interactive atlases were, I envisioned a much more utilitarian product for the Moon. It’s impossible to see the surface features of Venus, and the detail visible on Mars pales in comparison to what anyone with modest optical aid can view on our natural satellite. I imagine an electronic lunar atlas comparable to sky-atlas software. You should be able to click on a topographic feature to find out its name, characteristics, and history. Include as many or as few labels as you wish on a variable-scale map that’s north-up, south-up, or mirror-reversed to match your telescope. The program would account for libration for your observing location and show you what’s on the limb that night.

With today’s computer-animation technology, why not let people fly over the surface using their PCs? Since no one can see it from Earth, the representation of the lunar far side does not have to be as detailed as the near side. Selenophiles would nevertheless have an interest in those unseen features and the people their names commemorate.

Since I’m fantasizing, to broaden the interest of such a lunatic’s dream, my CD-ROM would also include utilities for eclipse and occultation predictions; bundle movies and results from space missions from Ranger to Lunar Prospector; add planetarium-program features so users could view the sky from anywhere on the Moon; and contain a cultural reference that highlights everything from lunar mythology to tales of science fiction.

Other Views

alI’ve been waiting for that lunar atlas for more than three years. What else do people want from their astronomy software? For some other viewpoints, I contacted several astronomy professionals for their thoughts.

Distant views. With the advent of the star catalogs from the Hipparcos satellite, astronomy software will have marked boosts in the accuracy of the positions, magnitudes, spectral colors, and proper motions of nearby stars. Now software can take us out of the solar system. For a couple of years SkyChart III, by Southern Stars Software, has been able to provide users with such an interstellar view, but others will surely follow suit by incorporating the Hipparcos catalogs. You’ll be able to set yourself on Alpha Centauri or elsewhere and look back at the home star. Advance time through millenniums and see if you can detect the Sun moving against the background stars. Or pretend you’re in the astrometrics laboratory of Star Trek’s starship Voyager and the computer monitor displays our neighborhood of stars with which you can pan and zoom around at will.

But why stop there? Science writer Jeff Kanipe notes that he’d like to see software that can provide a three-dimensional representation of our Local Group of galaxies and even nearby galaxy clusters. Deep redshift surveys are plotting the positions of thousands of galaxies in 3-D space. So let’s go on a super-relativistic flight through the cosmos! “Such information would be both instructional and fun,” he says, “and take us out of the Earth-centric bias.”

Research-grade assistance. Doing astrometry was a chore until Austrian amateur Herbert Raab’s Astrometrica made it simple (S&T: August 1997, page 72). Now amateurs can – and are – finding asteroids like the pros. Brian Marsden, of the Minor Planet Center and one of the primary beneficiaries of Raab’s software, hopes that some similarly pioneering software will help with photometry from CCD images. “Programs like Astrometrica and CCD Astrometry do a great job for deriving positions of comets and asteroids in CCD frames,” Marsden explains. “But I think we are still lacking convenient and reliable software for getting good magnitudes.”

ATM help. As Sky & Telescope associate editor Gary Seronik notes, one aspect of amateur astronomy that has been passed over by software developers is telescope making. Although ray-tracing programs exist that can help in defining a system of lenses or mirrors, they are largely overkill except for advanced optical experts. Why not have a package that can help design a telescope? The program asks a few questions about how you plan to use the telescope and your level of construction expertise. Then it suggests some designs that you can modify to your liking. Finally, it will output plans, blueprints, a parts list, and instructions.

Realism, please! Astronomy educator Andrew Fraknoi points out that he’s still disappointed with educational aspects of astronomical software. There may be spacey games, but he explains that the information they provide is limited if not wrong. “So many of the shoot-’em-up games have space and astronomy as their setting,” he says, “but then don’t even bother to make the slightest effort to get the science right or to teach the kids something while they are satisfying their destructive urges. And the educational software for kids in astronomy seems kind of boring and full of factoids instead of fun.”

Fraknoi also laments that computer graphics are perfectly suited to illustrate tricky astrophysical concepts, but he has yet to see any multimedia presentations of college-level material.

Imaging help. Laurence A. Marschall, former editor of CCD Astronomy, longs for a set of astronomy-based enhancements (called plug-ins) for Adobe Photoshop. He also wants “a simple Windows-based utility that converts all types (16- and 32-bit real and integer) FITS images to TIFF, GIF, JPEG, and also does the same for SBIG and other camera formats.” He explains, “There are elaborate image-processing programs that do this, but no simple dedicated utilities.”

Given the opportunity, Kanipe rattled off a laundry list of desires for a general planetarium program, including variable-star-magnitude estimates (and searching), orientations of double stars, accurate peaks for meteor showers, a “quantifiable” indication of twilight, and incorporation of the zodiacal light and gegenschein into displays.

Make It So

Of course, any dreamer can come up with ideas for software. The talent lies in the people who can actually follow through and create it. Adding features to existing software is always desirable to programmers who wish to improve their products and widen the user base. However, when it comes to developing a brand-new product of a specialized nature, I presume that unless a software author maintains a personal interest, it may never be realized. Yet many people have undertaken such private projects, and we all are the beneficiaries of such software as MegaStar Star Atlas, Astrometrica, and SkyChart III. So I’ll continue to wait for my “MegaMoon Atlas.”

April Is Killer For Constellations

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During the month, Venus continues moving north of the Hyades and lies 7[degree sign] north of Aldebaran on April 21. Through a telescope, Venus exhibits a shrinking phase – changing from an illumination of 80 percent to 69 percent over the course of the month. Its apparent diameter, although growing in size as Venus and Earth move closer to one another, remains tiny and only reaches 16″ by April 30.

Mars is at its best this month. The Red Planet rises in the east two hours after sunset and shines at a brilliant magnitude -1.1 on April 1. On April 24, Mars reaches opposition (opposite the sun in our sky) and will rise as the sun sets. By midnight the Red Planet is high in the southern sky and wandering through the stars in the constellation Virgo the Maiden.

Mars shines at a bright -1.7 magnitude at opposition, brighter than the star Sirius. Its red color is unmistakable in the evening sky. Watch Mars nightly as it wanders westward in its retrograde path against the stars of Virgo.

At this opposition, Mars will be within 54 million miles of Earth. The closest Mars can approach is 35 million miles. The next time such a close opposition happens will be in 2003.

As Mars and Earth move closer to one another, the Red Planet’s tiny disk grows in apparent size – from 14″ on April 1 to 16″ at opposition on April 24 (similar in apparent size to Venus on that same date). While this is large by martian standards, it represents a tiny disk through any telescope.

Patience is required when observing Mars. You must wait for those still atmospheric moments that allow startling detail to be seen. Only at those times of perfect seeing do the real delights of observing Mars pay off. Details such as Syrtis Major and the diminishing ice cap will be obvious to most observers. Subtler features such as Sinus Sabaeus, Aurorae Planum, and Solis Lacus require a good map of Mars to identify (see “Red Planet at Night, Observer’s Delight,” page 90).

While Venus and Mars dominate the evening sky of April, the stars also carry a few seasonal gems that should not be missed. Observers away from city lights will notice the Milky Way along the horizon. The final view of the winter Milky Way is carried toward the western horizon by the setting constellations Canis Minor, Gemini, Orion, Taurus, and Auriga. These “wintertime” stars will return to our skies during the early morning hours of autumn.

Because the plane of the Milky Way now rests along the horizon, it’s easy to look directly out of the galaxy into intergalactic space. Though a few stars from our own neighborhood are the most obvious objects to see, the galaxies beyond those stars are there, too. A good star atlas shows how many galaxies dot this region of the sky. Try looking in Ursa Major, Leo, Virgo, and Coma Berenices. Use a good atlas and telescope for many hours of enjoyable galaxy hopping.

Virgo is a major galaxy hideout. Not only does it harbor Mars in late April, but here too are the elliptical galaxies M59 and M60. Another galaxy on the must see list is the Black Eye Galaxy (M64), so called due to a dark dust lane near the core. Look for M64 in Coma Berenices not far from the constellation’s brightest star, Alpha (a) Comae Berenices. In addition, the 4th-magnitude globular cluster M53 is also in that region.

wgThe Whirlpool Galaxy (M51) is another fine object at which to point the telescope. This beautiful spiral is just over 3[degree sign] southwest of Benetnasch, the last star in the handle of the Dipper. The third Earl of Rosse, who lived at Birr Castle in Ireland, gave the galaxy its name. He was using a 72-inch reflector, the largest telescope of its time, to observe M51 when he saw its fine detail.

Four galaxy favorites can be found in pairs among the stars of Leo the Lion. First try M65 and M66. This twosome is separated by a scant 0.5[degree sign] and is located midway between Theta (q) and Iota (i) Leonis. Try moving from Theta Leonis two thirds of the way toward Rho (r) Leonis. There you will find the other fine pair galaxies, the spirals M95 and M96. Numerous other galaxies pepper this region. How many can you spot?

If you need a break from the late nights of observing, try a daylight lunar occultation of Regulus. The moon occults the 1.3-magnitude star in Leo on April 24 for regions east of Texas.

In Europe, the occultation takes place shortly after 9 p.m. GMT. In the United States, the occultation occurs in daylight and somewhat earlier, approximately 2:30 p.m. EST (detailed time predictions should be used for your particular location). The moon will be relatively easy to find during daylight hours, and Regulus should also be relatively easy to see in most small telescopes.

Returning to the night sky, look for the constellation Cancer the Crab just ahead of the Lion’s nose. The minor planet Vesta can be found there, continuing its path among those relatively faint stars. The asteroid begins the month just over 5[degree sign] north of the Beehive Cluster (M44), and its brightness fades from magnitude 7.2 to 7.6 as the month progresses. Even so, Vesta remains an easy object to spot in a pair of binoculars.

The Lyrid meteor shower, one of the year’s most reliable, occurs between April 19 and April 25. Lyrid meteors typically produce 10 meteors per hour, although rates of nearly 100 per hour have been recorded during the past 200 years, most recently in 1982.

Lyrid meteors peak on April 22, though reasonable activity can be expected for a day before and after the day of maximum. With the first quarter moon setting by 2 a.m. local time, conditions are good for early morning viewing of this annual shower.

Pluto is once again the farthest planet from the Sun. It regained its ninth planet status on February 11 when it crossed outside the orbit of Neptune. For the past 20 years, Neptune has been the most distant planet from the Sun.

Pluto can be found in Ophiuchus 1[degree sign] east-northeast of the bright star Zeta (z) Ophiuchi. It shines at magnitude 13.7 and is technically visible in an 8-inch

telescope under ideal conditions. Place the bright star just outside your field of view to reduce its glare. Pluto reaches opposition at the end of May when it will lie due north of 2.6-magnitude Zeta Ophiuchi.

Uranus and Neptune rise during the early morning hours and appear above the southeastern horizon well before dawn late in the month. Neptune is first to rise and lies toward the western end of Capricornus the Sea Goat. The 7.9- magnitude planet lurks about 1[degree sign] east of magnitude 5.3 Sigma (s) Capricorni.

Uranus appears about 2[degree sign] east of magnitude 4 Theta Capricorni. Uranus shines at magnitude 5.8, which is detectable in binoculars.

Mercury reaches greatest elongation (28[degree sign]) west of the sun on April 16, just three days after it passes through its aphelion point (the farthest orbital point away from the sun). However, Mercury’s southerly declination means it’s not well placed for Northern Hemisphere observers. On the other hand, Southern Hemisphere observers will get a fine morning view before dawn.