Comet West and Comet d'Arrest

Comet West and Comet d’Arrest

For those unfortunates – and they must be few in number – who missed comet West in March and April 1976, the close passage by comet d’Arrest of Earth in August 1976 will provide another chance at comet observation. The comet will be making its most favorable appearance in our skies since its 1851 discovery.

This does not mean, however, that comet d’Arrest will put on anywhere near as spectacular a show as West provided; at best, d’Arrest will be about sixth magnitude, visible in richest field telescopes, small telescopes, or (if you’re lucky) binoculars. Its nearest approach to Earth will take it to within about 14 million miles (about half the closest Earth-Venus distance). The comet will reach perihelion on August 12, 1976.

Comet West. These photos of comet West, taken one day apart, demonstrate the changes in the comet’s position and in tail structure that took place in a short space of time. At left, one bright streamer extends back from the nucleus in a photo taken on March 27, 1976. The next day (night), the streamer has shifted slightly toward the right as the comet itself has moved against the background of stars. In both pictures, the comet is located in the constellation Delphinus. A home built six inch reflector at f/6 was used for each of these 20 minute exposures on GAF 200 film. Photographs by Brad Wallis.

Comet d’Arrest is a periodic comet: its orbit has been accurately calculated and it returns to the vicinity of the sun on a regular schedule – every 6.2 years. Watch for it as it moves southeast through the constellations Delphinus, Aquarius and Sculptor. By early September, it will be fading and close to the horizon for United States observers. The comet’s predicted positions are given in the accompanying table.

Predicted Positions for Comet D’Arrest. Predicted magnitudes are approximate (table from Astronomy magazine, August, 1976).

Table, Comet D'Arrest, predicted positions

Satellites of Jupiter and M - 17

Satellites of Jupiter and M – 17

The four major satellites of Jupiter orbit the giant planet in periods ranging from just under 2 days to 17 days. They can be seen to change position from night to night. Sometimes their motions become evident after only a few minutes’ observation. Only a small telescope is required to detect all four of the satellites and several can frequently be seen in rigidly held binoculars. This table shows the approximate positions of the moons at about 3 a.m. (EDT) on the evenings indicated. First column of numbers identifies the moons and their positions relative to Jupiter’s disk. (1=IO, 2=Europa, 3=Ganymede, 4=Callisto, and 0=Jupiter’s disk.) The third column approximates a telescopic view of the satellites’ positions. The orientation of the satellites is shown inverted as seen in a standard astronomical telescope.

Galaxy M - 17

M17, variously known as the Horseshoe, Swan, Checkmark, or (most often) the Omega nebula, is one of the grandest sights available to telescopic observers in the summer Milky Way. Its brightest, rectangular portion has a mass about 800 times that of our sun, and more than 35 stars are embedded in the nebula. This photo, obtained with a cold camera designed by the photographer, is 1 17.5 minute exposer on High Speed Ektrachrome, through a 12.5 inch reflector at f/4.5 Photograph by Greg Griffith.

(By James Mullaney and Henry J. Phillips, Astronomy, August 1976)

August Satellite Jupiter. August Satellites of Jupiter 3:00 a.m. EDT. 12:00 p.m. PDT

Close-up on the Hercules Region

Close-up on the Hercules Region

“Dim but interesting” is an accurate description of Hercules, just past the meridian on August evenings. Although it contains no star brighter than third magnitude, this constellation holds within its boundaries a vast store of celestial bounty of the telescopic hunter. Altogether, Hercules encompasses 1,225 square degrees of the sky, ranking it fifth among the constellations in order of size. The heart of the of the figure is the well-known keystone, marked by the stars Eta, Zeta, Pi and Epsilon. Lines of stars outlining the arms and legs of the mighty hero radiate from this distinctive grouping.

Barns tells us that Hercules “discloses many rarities in radiant fields to the south and southeast”. The constellation contains a seemingly inexhaustible supply of the fine double stars, displaying every imaginable combination of magnitudes, separations and colors. Only some of the more attractive ones could be listed in our Table of Selected Objects. Indeed, it is somewhat of a mystery why this area of sky should harbor so many fair pairs while other regions are almost devoid of them.

Hercules also is home of several fine globular star clusters, as detailed in Eyepiece Impressions. One of these – M – 13, the famed Hercules cluster – is the finest representative of its class in the northern sky. Located 1/3 of the way from Eta to Zeta in the keystone, M – 13 glows at magnitude 5,7 and can be glimpsed with the unaided eye on a dark transparent night. Binoculars clearly reveal its fuzzy, non-stellar appearance. Halley, who discovered it in 1716, referred to it as a “little patch”.

Another naked eye feature of this constellation is the star Alpha, known as Ras Algethi (the kneeler’s head) and located south of the keystone. The reddish-orange giant of spectral class M is a semi-regular variable, slumbering fitfully between third and fourth magnitudes with no certain period. A good reference star to use in checking on Alpha’s variations is Delta Herculis, 10 degrees due north and shining at a constant 3.2 magnitude. The two stars nearly match in brightness on some nights, while on others Alpha is noticeable fainter.

M-13 Hercules Cluster. Photo: Bareket.astro.com

Hercules Region: Eyepiece Impressions

Zeta Hercules

We begin our telescopic survey of Hercules with a selection of four distinctly different double stars. The first of these is Zeta, marking the lower right corner of the keystone.

This binary star consists of 3.1 and 5.6 magnitude components, presently a tight 1.2 seconds of arc apart. With a period of just 34 years, this pair has completed more than five revolutions since its discovery by Sir William Herschel in 1782. As a result Zeta’s orbit is one of the best determined in the sky. At closest approach (as in March 1967), the star’s separation drops to just 0.5 seconds. The double is now opening fairly rapidly and will reach a maximum of 1.6 seconds in November 1990.

At least a six inch telescope is needed to clearly split the pair now, although tantalizing glimpses of elongation can be had even in a three inch refractor at 150 to 200 power in good seing. The components are yellow and red, and even when the stars are unresolved, their blended hues can be seen at high magnifications.

Try separating this tightly bound duo with your telescope the next clear tranquil night. Even you should fail now, keep watching Zeta from season to season as the stars move apart. Some night, when least expected, the pair will reach your resolution threshold and suddenly reveal itself.

Delta Herculis

Our second offering presents an interesting test of magnitude and color, rather than of resolution. This is Delta Herculis, southeast of the keystone and consisting of a 3.2 magnitude primary attended by an 8.8 magnitude companion about 10 seconds away.

Delta is an example of an usual class of objects known as optical doubles (two unrelated stars at different distances from us). The “companion” happens to lie in the some line of sight but is actually much more distant than the primary, a mere 100 hundred-years away. The gap between them is closing as the two stars appear to cross paths with each other, making Delta look more than ever like a real (gravitationally coupled) double star.

The faint star can be glimpsed in a 2.4 inch refractor at 35 power or more on a good night. At least a four inch at 90 power, however, is needed to detect this object’s color. With larger aperture, Delta becomes increasingly lovely as a magnitude contrast pair.

Barns called this double “a study in color” and rightly so, for countless hues have been reported. Most observers see the pair as cream and lilac. Nut green and purple, pale yellow and bluish green, green and ashy white, yellow white and azure, and even greenish white and grape red have been recorded! The actual spectral types of the stars are A0 and G2. What colors do you find for this “fake” but interesting duo?

Alpha Herculis

Those seeking a spectacular double to show visitors at the telescope are sure to be pleased with third magnitude (sometimes fourth) Alpha Herculis. Located south of the keystone, it is not far from second magnitude Alpha Opiuchi.

Alpha Herculis consists of stunning combination of third magnitude orange and fifth magnitude blue green suns, a comfortable 4.6 second apart. Unlike Delta, Alpha’s tints are strong and easy to see without guessing. A 2.4 inch refractor at 100 power nicely resolves Alpha, while three and four inch scopes give the kind of view we can appreciate. Larger telescopes simply add to already beautiful scene.

Smyth called this pair “a lovely object, one of the finest in the heavens”. Webb gives the primary as very yellow or orange, and the companion as blue, bluish-green or emerald on different occasions. Olcott simple states “orange and green” while Barns strangely makes no comment on the colors. The spectral types are M5 for the primary and G for the companion.

This stellar couple lies 540 light-ears from us; the stars are apparently in very slow and orbital motion about each other. The primary is a pulsating giant star, whose tenuous outer atmosphere has been found to actually engulf the companion sun. This small is known to be a spectrosonic binary with a period of 52 days, making Alpha at least a triple system. Quite a varied and beautiful spectacle must grace the sky of any planet there.

95 Herculis

Our forth pair provides one of the subtlest, yet most beautiful, combinations of celestial color anywhere in the sky. Found by drawing a line from Epsilon to Lambda and extending it its own length, the double 95 Herculis is one of a group of naked eye stars in Eastern Hercules.

The components of 95 Herculis are nearly matched fifth magnitude suns, 6.5 seconds apart. A 2.4 inch refractor at 35 power splits them nicely; 75 to 100 power makes the color contrast apparent. Larger instruments enhance the tints greatly.

The finest color notation for this pair is that given long ago by Smyth: “apple green and cherry red” – and so they look to most eyes. Other less charming terms such as pale (or yellow) red and pale (or yellowish) green have been recorded, amounting to the same thing. Not to be outdone, Barns christened the duo as “beryl and sardonyx”. These tints are delicate, but persistent in all apertures.

Webb agreed with Smyth’s colors and added that 95 Herculis “is extremely pretty”. He called attention to the strange discrepancies in color reported among early observers, when comments such” red the larger, green the brighter” were made. We should try to confirm such descriptions by actual observation at the telescope.

NGC-6210

For a change of pace, we next offer a little planetary nebula. Like most of its kind, location of NGC-6210 presents a test of observing skill. Lying slightly more than one degree southwest of fifth magnitude 51 Herculis, a line from Gamma to Beta also points to its neighbourhood. Sweeping with a low power, wide piece eyepiece will reveal a triangle of stars – one of which is actually the nebula.

NGC appears as an eerie, 9.7 magnitude blue-green egg, 20 by 13 seconds of arc in size. (Some observers make it as small as eight seconds). It is fun to see how low a magnification will distinguish the planetary from a star; 45 power on a three inch refractor will do for a trained eye in this case. A definite disk can be made out at about 75 power on three and four inch scopes. A six-inch reflector at 100 power gives a fine view, while eight inch and larger instruments at 150 power or more make this a real show piece.

NGC-6210 is one of a handful of small nebulae picked up by F.G.W. Struve during his double star searches. This planetary is one of the few notable objects overlooked by Herschel in his great sweeps of the heavens. Many observers have likened this “cosmic pea” to a star out of focus. Some owners of large reflectors report its disk as an intense blue in color, but most see green with only a tinge of blue. Large apertures at high magnification will also reveal a faint outer hale surrounding the bright disk itself.

NGC-6229

We complete our survey of Hercules with three globular star clusters. The first of these is the “misidentified” object known as NGC-6229, situated midway between two fifth magnitude stars – 42 and 32 Herculis.

Illustration Editor

Illustration Editor

New Position With Astronomy Magazine

We are accepting resumes and applications for the new position of Illustration Editor on the editorial staff of Astronomy. The following skills are required:

Thorough knowledge of theoretical and amateur astronomy.

Knowledge and experience with color, 4/C process and B&W lithographic production techniques.

Ability to specify caption and body copy length and create rough copy for captions.

Galaxy M-17. Galaxy M-17, variouly known as the Horseshoe, Swan, Checkmark, or (most often) the Omega Nebula, is one of the grandest sights available to telescopic observers of the Summer Milky Way. Its brightest rectangular portion has a mass about 800 times that of our Sun, and more than 35 stars are embedded in the nebula. Photo in public domain

Ability to expand the number of contributing artists to Astronomy and help them develop their talents in terms of the magazine’s needs.

Ability to choose, specify and/or assign photographs, diagrams, charts, tables, maps, paintings and artwork to illustrate articles in Astronomy as well as coordinate and implement complete issue layout.

Ability to communicate effectively with contributing artists and authors both orally and in writing.

Ability to smoothly coordinate illustration assignment/selection with issue production schedules.

We seek an individual who is willing to roll up his/her sleeves, dig in, and get the job done on time each month – prima donnas need not apply. Since this is a new position at Astronomy magazine, you will be responsible for developing job details necessary to accomplish your primary task of creating the overall layout – including placement of advertising for each issue of Astronomy by assigning or selecting appropriate illustrations, etc. You will also be responsible for writing/creating your own job description and for determining Astronomy’s future art-editorial staffing needs.

Astronomy, published out of plus new offices in downtown Milwaukee’s financial district, has a national circulation of more than 52,000 and is continuing the rapid growth it has experienced since it began in August 1973. We offer a full employee benefit package including health, life and dental insurance, sick days, 2 weeks paid vacation, employee parties, and a boss that’s dynamite to work for.

Compensation

$14,000 to $25,000 annually to start, depending on qualifications and experience. If you think you are worth less, don’t write. If you think you’re worth more, let’s talk about it.

Send applications/resumes to: Stephen A. Walther, Publisher. Astronomy Magazine. 411 E. Mason St. 6th Floor, Milwaukee, WI 53202

Infinite Mysteries of Venus

Infinite Mysteries of Venus

The absence of water on Venus may delay the colonization of that planet a few centuries at most. It would be necessary to import the water in the form of an ice asteroid several miles across from Saturn or beyond. Perhaps it could be smashed into the planet in such a way as to speed up the spin, power up the magnetic field, and set up some protective Van Allen belts. Then the blue-green algae (a special strain tailored in genetics laboratories and resistant to sulfuric acid) would get their chance.

New space probes are already being built to investigate the old and new mysteries of Venus. Every year and a half, Venus and Earth swing around into some relative positions, opening up a launch window of several weeks’ duration, permitting a three month voyage from one planet to the other. Given enough energy, we could launch to Venus at nearly any time, but this cycle is only concerned with the most economical opportunities.

The next Venus window will open near the end of 1976. Recent Soviet statements indicate they are still studying results of their last missions and will not have new vehicles ready until min-1978. Despite traditional heavy curtains of secrecy about future space plans, the future goals of Russian astronomers can be approximated from public statements during the last mission.

With orbiting probes essentially blinded by the clouds, and landing probes facing a quick death, Soviet Scientists have picked a third environment for exploration: the atmosphere. In cooperation with French scientists, they are building inflatable aerostats (balloon platforms designed to send to send back data via orbiting relay satellites over a period of days or weeks).

Venus as seen by Mariner. Global radar view of Venus (without the clouds) from the Magellan imaging between 1990 and 1994. Image in the public domain

The latest Venus probe data has pinpointed the most productive levels for exploration. Initially, the balloon (called Eos) would carry its 50 pound instrument package through the clouds at an altitude of 30 miles, where the temperatures and pressures are close to those of Earth’s surface. Batteries could provide power for a week; longer missions use solar cells (although corrosion a problem) or nuclear power.

Once the more hospitable regions of the atmosphere had been charted, the probe could release most of its buoyant gas (probably hydrogen as there would be no danger of fire in an atmosphere devoid of free oxygen), and descend to more interesting realms. Passing quickly through the region of the sulphuric acid rains, the probe would reach an area about 20 miles high, where temperatures had climbed to 300 degrees Fahrenheit and pressures were 10 times those of Earth. Survival at this level would be short, and the orbiting radio relay would be visible only for a few hours every other day.

The primary mission of this suicide altitude would be to photograph a panorama of the surface and of the under-side of the cloud layers in the near-infrared and visible wavelengths. Areas, miles on a side, would be visible during the probe’s slow drift.

One sought-after datum would be the frequency of small craters. Volcanos, vents and faults would be prime targets of discovery. Evidence of liquid flow (whether lava or water) would be sought, and actual pool of liquid metals or hydrocarbons might be seen. Most important on a planet like Venus, the probe could detect features that are completely unexpected.

Although there is no indication that the Soviets are working on it (and there are definitely no American plans for attempting it), one more instrument would certainly produce the most haunting perceptual input from space since the first photographs from other worlds began coming back a few decades ago. The instrument in question would be a simple microphone, tuned to subsonic and ultrasonic wavelengths beyond the range of the human ear.

What does Venus sound like? The density of the atmospheric ocean would provide acoustic conduction more akin to that of Earth’s deep seas than air. Would we hear the shriek of winds, the groan of strained rocks, or the roar of volcanos? Would we hear thunder or the bubbling of escaping gases in a liquid metal pool? Would we hear only the patter of sulphuric acid rain on the roof of the gondola carrying the microphone? Whatever sounds did come back to Earth would be powerful stimuli to Earthbound imaginations, as they complete the perceptual pattern of what it would be like to really be on another world.

Besides listening to the atmosphere a crucial requirement for future surface exploration would be to listen to the land. The use of a seismometer to detect internal earthquakes could tell an incredible amount about actual Venusian tectonics. A network of two or three active seismic stations would be more valuable. However, the Soviets haven’t yet landed a seismometer on any celestial object, and it could be 20 years before one is in service on Venus.

A family of six American space probes would be launched toward Venus in the window after next, which will be open during the summer of 1978. These Pioneer-class spacecraft will make investigations of the planet’s interior and of its atmosphere; there are no current American plans for surface exploration.

One probe, Pioneer 12, will go into a polar orbit around Venus late in 1978. It will dip to within 120 miles of the surface, searching for gravitational irregularities which can tell geologists about the internal layering of the planet and about its external shape and mass distribution.

Pioneer 13 is a quintuple spacecraft. When it arrives at Venus five days after Pioneer 12, it will already have broken up into five separate parts. The mother ship (called the bus) will have ejected three small and one large entry probes, targeted for widely scattered points across the face of the planet.

As they plunge into the atmosphere, the probes will measure pressure, temperature, deceleration, cloud extent, altitude and density, and the heat exchange between the sun and Venus. One probe will also carry a mass spectrometer and a gas chromatograph to provide details about the atmospheric components. The bus will also have a mass spectrometer for measuring the upper atmosphere before it burns up (it has no heat shield).

The three small probes will fall straight down to the surface, returning data to Earth until impact. The large probe will have a parachute to give it more time for making its detailed readings. Survival after landing is not planned, but it could occur as a bonus. The large probe in particular could make further readings on the composition of particles kicked up from the surface by its impact.

Later Venus probes in the Mariner series (perhaps a Mariner 13 could be scheduled early in the 1980s) might make radar maps on the surface. In the bistatic mode, a large parabolic antenna on the spacecraft could pick up echoes from radar beams transmitted from powerful stations on Earth. New types of radar could operate directly from the spacecraft, given a high power source.

There are two possible approaches to the problem of long term survival on the surface. Specialized equipment, capable of surviving for days exposed directly to 900 degrees Fahrenheit, could be designed. Alternately, refrigeration would have to be provided, requiring extremely advanced nuclear power supplies or contamination of surroundings by evaporative water – a short term solution in any case.

Balloon-borne probes promise profitable and productive halfway house, since they could float high enough to provide Earthlike environments. Complex robot laboratories controlled by computers and advised by scientists on Earth could analyze samples brought up from the Venusian surface.

Transportation between the ground and the aerostatic balloon might be relatively easy. The lander, designed to survive a quick dash to the surface, could inflate a hydrogen balloon and automatically load the sample canister into a small gondola. Rendezvous and docking between the propeller-driven mother craft and the sample balloon provides some intriguing engineering problems, but the results could well be worth it – especially if the rock samples came from the ocean basins which once may have cradled life.

The blank face of veiled Venus belies a planet of infinite mysteries. The answers to many of these puzzles may be crucially important to questions of life on Earth. Venus is neither simple nor boring. Like every other world which men have explored, it is full of unexpected wonders. The age of the interplanetary surprise is far from over; Venus will astound us again and again.

(James Oberg, Astronomy magazine, August 1976)