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Lonely Spica haunts spring nights.

Sometimes amateur astronomers seem to think there are only three cardinal directions. If you've been using a telescope for a while you can probably name them immediately: south, east, and west.

Beginners soon learn that an observing site benefits most from a good southern exposure (at least in the Northern Hemisphere). The south part of the sky is where most of the seasonal parade of constellations passes highest. This is also where the Moon and all the planets but Mercury and Venus are highest and best seen in a telescope. If trees or buildings block the south, the best parts of the parade go unseen.

What about east and west? In those directions we get our emotional first and last looks at constellations as they come and go with the seasons. Here we witness the exciting sky-happenings called risings and settings. East and west are also the doors of twilight between day and night. When those doors are opened at dawn and dusk, we often see brilliant Venus, innermost Mercury, and the incisive form of the slender crescent Moon. East and west are also where we are most likely to see a comet when it is nearest the Sun - as is happening this spring.

The west can claim superiority because it's where the action happens in the evening, when most people are awake. But an eastern view has its own unique importance. This is where planets shine during evening when they're at opposition and nearest to Earth.

And what about the north? Aside from 2nd-magnitude Polaris, it doesn't have much to compare. Observers may use Polaris to find directions and perhaps polar-align a telescope mount, then spend most of their time looking elsewhere.

But let's not completely neglect the northern sky - even if in winter we may prefer a tall windbreak of trees blocking that chilly direction! The Dippers and Bears; jagged Cassiopeia and her dim husband, Cepheus; the mighty, pole-en-coiling Draco dragon - they are always on display. Nor do they present a static scene of circumpolar sameness. They are a drama, circular though it may be.

On spring evenings it is the drama of the Dippers and the sidewinding Dragon ascending in the northeast. Queen Cassiopeia and King Cepheus are resting down near at the northern skyline. But their time will come, later in the night and especially later in the year, when they will get their cue and climb to play their scenes in the never-ending show.

THE SKY AT THE SPICA HOUR

What is the loneliest 1st-magnitude star, other than autumn's famous beacon of loneliness, Fomalhaut? For most readers it must be Spica, which shines highest at the time of our all-sky chart on the preceding pages. Whether you see Spica at its height on an April midnight or after dusk in May, we can agree to call the time the Spica Hour.

Spica is not tremendously far across the sky from brighter Arcturus. But when both approach the north-south meridian of the sky as they do now (Spica first, Arcturus second), what happens? Most readers will find Arcturus so much higher that they have to turn their faces up to it - and away from Spica.

Spica has no bright company of stars in its constellation, as does Antares now rising in the southeast. Spica shines near the middle of the long form of Virgo, the Virgin; only a few moderately bright stars sparkle here and there to adorn her. Spica lies almost halfway between its fellow 1st-magnitude stars Antares and Regulus, but what a long sweep it is between those two! Antares is just above the southeast horizon on our map, while Regulus shines high off in the southwest.

Having said all this, the fact remains that Spica doesn't truly rival Fomalhaut for solitude. The latter has no 1st-magnitude peer anywhere among the traditional autumn constellations, and no bright planet can ever come closer to it than about 20 [degrees]. Consider also that Spica has Corvus, the Crow, watching it and keeping it company. We can hardly look at Spica without noticing the four-star pattern of Corvus about 15 [degrees] southwest (lower right), looking like a tilted kite, or a sail, or the hunched figure of the Crow it is supposed to be.

This year an additional bright gem burns in the spring sky to keep Spica company: the planet Mars, positioned in the gap between Spica and Regulus and now dimming from week to week. Mars is on its way to paying Spica a close visit in early August, when both will be getting low in the southwest at nightfall.

Those of us with deep-seeing telescopes or deep-pondering imaginations also realize that the "blank" areas in Spica's region are hardly empty and lonely. They're crowded with galaxies, even clusters of galaxies, far in the background. The great Virgo Cluster north-west of Spica is centered something like 50 million light-years from us. Those galaxies might seem like an insubstantial fancy of the telescopist, hiding on the periphery of the naked-eye view that has bright Spica at its center. In reality, though, it is Spica, our Earth, our solar system, our galaxy, and even our proud Local Group of galaxies that are hiding on the periphery, or beyond the periphery, of the vast Virgo Cluster.

Turning away from this sky direction, there's much else to see at the Spica Hour, including some surprises. For instance, the entire summer complex of Ophiuchus and the two parts of Serpens (Caput and Cauda, head and tail of the Serpent) has already heaved entirely above the eastern horizon (even though Serpens Cauda is still low in mist and haze). It is also surprising that the supposedly winter constellations Auriga and Gemini remain standing side by side on the northwest to west horizon, their 1st-magnitude heads still above treelines and city skylines. And the lesser Dog Star, Procyon, barks light beside them due west.

Lie on a ground cloth or lounge chair, gaze up, and you'll see a big circle or spiral of mostly bright star figures encircling the zenith. Your eye can travel from Regulus and Leo to the Big Dipper and around to Arcturus in Bootes, and finally to Spica - not so alone after all.

THE SUN, MOON, AND PLANETS IN MAY

Comet Hale-Bopp hangs in the west-northwest after sunsets in early May. It's on its way down from its grand showing in the northwest during late March and all of April. For observers around 40 [degrees] north latitude, the comet's height at the end of astronomical twilight drops from about 13 [degrees] to 6 [degrees] between May 1st and 10th. By May 20th Hale-Bopp sets in twilight about an hour after the Sun and will probably be lost to all but experienced observers using optical aid.

But the opening week or so of May could be fascinating if the comet has not faded too much. The tail, no matter how long it may be in space, is pointing almost directly away from us and thus appears greatly foreshortened. We'll find it intriguing to watch the comet on May 6th knowing that it is plunging through Earth's orbital plane only about 10 million miles outside the January part of our orbit. Too bad we're not there now to see it from 20 times closer up!

The most tantalizing question is whether the comet will still be bright enough to be a noble sight on the evening of May 8th, when the crescent Moon floats about 4 [degrees] or 5 [degrees] to its lower left (as seen from North America). The two will be midway up the horns of Taurus.

Venus is far to the lower right of the comet in brightest part of twilight as May opens. Although the time from sunset to Venus-set increases to more than an hour by late May, the planet will still be mired very low in the afterglow and viewed with difficulty.

Mars doesn't have to be hunted for! It's the golden orange point of light shining high and obvious in the south at dusk, in the hind foot of Leo well to the left of Regulus. Mars moves lower to the southwest by late evening. It fades by a half magnitude during May, from -0.4 to +0.1, yet is still only a trace dimmer than Arcturus by the end of the month.

The bad news is that Earth is leaving Mars far behind. Consequently, the planet's apparent diameter dwindles from 11.4[inches] to 9.1[inches] during May, a major change for observers with small to medium-size telescopes. At least Mars is high at nightfall and thus can present a steady image on good evenings.

Pluto, at the border of Ophiuchus and northernmost Scorpius, comes to opposition on May 25th. This tiniest major planet is 29 times farther than Mars and some 35,000 times dimmer at magnitude 13.7. You'll need at least an 8- or 10-inch telescope and a highly detailed map, such as the one on page 84.

Jupiter rises around 2:30 a.m. daylight saving (summer) time at the beginning of May, and around 12:30 a.m. at month's end. But the giant planet is best viewed at dawn, when it's fairly high in the southeast. Jupiter shines brilliantly (at magnitude -2.3) near the eastern tip of the dim Capricornus pattern. It reaches western quadrature on May 11th.

Uranus and Neptune are not far west of Jupiter, where you can find them before dawn with binoculars and the finder chart on page 84.

Saturn rises in the east around dawn's earliest gleaming in late May, so it's poorly placed for viewing. Even worse is Mercury, which comes up later in bright morning twilight in late May, far to Saturn's lower left.

The Moon is a slender crescent closely to the upper right of Saturn before dawn on May 4th. A few hours later it occults Saturn during daylight as seen from most of North America; see page 85. New Moon occurs on May 6th. During daylight on the morning of May 8th the thin lunar sliver occults Aldebaran for some areas, and that evening it shines near Comet Hale-Bopp as mentioned above. The Moon reaches first quarter on May 14th, skips past Mars on the 15th and 16th, and is full on the night of May 21st. The Moon appears near Jupiter before dawn on May 28th and is at last quarter the next morning.

[TABULAR DATA OMITTED]
THE MOON
(Times and dates are Universal Time)

New Moon               Apr. 7, 11:02
First Quarter          Apr. 14, 17:00
Full Moon              Apr. 22, 20:33
Last Quarter           Apr. 30, 2:37
New Moon               May 6, 20:46
First Quarter          May 14, 10:55
Full Moon              May 22, 9:13
Last Quarter           May 29, 7:51
Greatest and Least Distances

      Apsis                      Distance         Diameter

Perigee   Apr. 5, [17.sup.h]    361,498 km   33[feet]03[inches]
Apogee    Apr. 17, [15.sup.h]   405,003 km   29[feet]30[inches]
Perigee   May 3, [11.sup.h]     366,626 km   32[feet]35[inches]
Apogee    May 15, [10.sup.h]    404,211 km   29[feet]34[inches]
Perigee   May 29, [7.sup.h]     369,788 km   32[feet]19[inches]


May Phases and Librations

The Moon's phase, orientation, and relative apparent size are shown for [0.sup.h] UT every two days in May. Celestial north is up, and a blue tick indicates the Moon's north pole. The red dot shows the point on the Moon's limb tipped into best view by libration; the dot's size indicates by how much. The maximum libration plotted is 8.5 [degrees] on May 9th; the minimum plotted is 0.8 [degree] on the 3rd. Adapted by Guy Ottewell from his Astronomical Calendar 1997. For more on libration see June 1992, page 670.

RELATED ARTICLE: Light-Pollution Notes: Fundraiser for IDA

Every astronomer should know what IDA stands for: the International Dark-Sky Association. For nearly 10 years this unique little organization has spread the facts about light pollution and its cures. Although small and underfunded, it has been remarkably effective at changing attitudes in government and the lighting industry about ending the waste light that needlessly spills from so many fixtures sideways and up into the sky.

Now the IDA is marking its first decade with a fund drive. Its goal is to hire its first full-time paid staffer and get a proper office and equipment. The IDA's success "has led to a greater demand for information about the problems and what can be done to solve them," noted David Crawford, its volunteer director. "The increased effort has produced a workload that is unsustainable over the long term on the mostly volunteer staff.... The solution is to evolve IDA into a more professional organization."

There simple would be no battle against light pollution - almost no laws regarding it or even recognition of it in the U.S. - without IDA. Every astronomer has benefited from it and should contribute to benefit more in the future. Tax-deductible donations can be made to IDA, 3345 N. Stewart Ave., Tucson, AZ 85716.

F.S.

Fred Schaaf welcomes mail at 681 Port Elizabeth-Cumberland Rd., Millville, NJ 08332, and e-mail at fschaaj@aol.com.
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Author:Schaaf, Fred
Publication:Sky & Telescope
Date:May 1, 1997
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