Epsilon Aurigae

Epsilon Aurigae

Theory Proposes Planetary System Forming in Binary

Epsilon Aurigae, a long-standing puzzle star for astronomers, is the remarkable instance of a binary system in which a planetary system is currently forming, according to a theory proposed by two British mathematicians.

A third magnitude yellow supergiant star. Epsilon Aurigae is eclipsed every 27 years by a mysterious dark companion. The fact that this companion star is invisible has led to speculation that is a black hole, although this has not been borne out by subsequent x-ray observations.

Michael Handbury and Iwan Williams of the University of London suggest that Epsilon Aurigae is actually a very young star about nine times as massive as our sun, and still contracting onto the main sequence. Its dark companion is so young that it has not yet “switched on” to become a star. The companion is surrounded by a disk shaped nebula in which planets may be forming.

Epsilon Aurigae being eclipsed by a dark dust cloud. Source of the photo: astronomycentral.co.uk

The true shape and nature of the secondary companion to Epsilon Aurigae is revealed by the peculiar light curve of the eclipses it produces. The whole eclipse lasts a remarkable two years. Minimum light output, during which Epsilon Aurigae is dimmed by 50 percent, lasts 330 days.

To account for this behavior, Handbury and Williams believe the obscuring body cannot be a simple spherical star (or a black hole), but instead must be shaped like a flattened disk, growing transparent toward its edges. The obscuring disk is about one billion miles in diameter and contains approximately 10 solar masses. Most of the mass is concentrated in a forming central star, with the remainder collecting into a planetary system around it.

Because the two stars of the binary are so far apart – about two billion miles – planets can form in stable orbits, similar to the stable orbits of Jupiter’s satellites.

The Handbury-Williams model is particularly important because it means that the binary becomes one of the best candidates for observing solar system formation in action. So far, only RU Lupi, a star of the T Tauri variety, has looked as promising. In 1974, four Swedish astronomers suggested that RU Lupi was surrounded by a swarm of protoplanets.

Confirmation of planets in the Epsilon Aurigae system will settle the longstanding argument among astronomers of whether planets can ever form around double stars, with consequent implications for the existence of extraterrestrial life.

If the dark companion of Epsilon Aurigae is a star in the process of formation, it might become visible in the near future. Certainly, the next eclipse of the system in 1982 will be the object of a great deal of astronomical attention.

(History of astronomy. Astronomy Magazine, July 1976).

A Former Planet

A Former Planet

Comet Orbits Point To Former 10th Planet

An astronomer at the United States Naval observatory believes there is solid evidence that a giant planet existed between the orbits of Mars and Jupiter about six million years ago.

Dr. Thomas C. Van Flanders based his findings on the computer plottings of the orbits of 60 very-long-period comets that may have originated from the explosion of the giant planet.

In tracing the orbits of these comets – each has been seen only once from Earth – Van Flandern found there is a tendency for the orbits to intersect at a common point located in the asteroid belt. The asteroid belt, confined primarily to the area between the orbits of Mars and Jupiter, has been suspected since its discovery of being the by-product of a former planet.

Life on a planet. Did a biological life exist on a hypothetical former planet. Photo: Elena

Van Flandern said that although the orbits scatter all over the sky, they tend to cluster near 2.49 degrees ecliptic longitude. The clustering is statistically significant: at the center of the cluster, four orbits intersect within 0.01 cubic degrees.

The cause of the theorized giant planet’s break-up is unknown.

The results of Van Flandern’s work support the theory proposed in 1972 by University of British Columbia astronomer M. W. Ovenden. Ovenden said there were strong indications that a former planet existed in the asteroid belt between Mars and Jupiter with a mass 90 times that of Earth.

The idea that the break-up of a planet is responsible for the presence of the asteroid belt is not new. German astronomer Johann Bode devised a formula (Bode’s Law) two centuries ago for predicting the planets’ distances from the sun. His formula predicted that a planet existed between Mars and Jupiter, but none was found.

(History of Astronomy. Astronomy Magazine, August 1976).

Comet West

Comet West

Comet West to Yield Clues To Early Solar System

During the first two weeks of March 1976, comet West (1975n) put a show that rewarded the early riser with a glimpse of a special phenomenon that provided astronomers with important clues to the early solar system. Results of many scientific experiments will not be available for months, but armed with interpretations of past comets, we can look at a few of the comet`s characteristic features that anyone with an ordinary camera and small telescope could record.

Although comets share basic similarities, they also appear quite individual to the observer on Earth due to differences in orbital elements and viewing geometry, as well as intrinsic physical differences. According to early calculations by Brian Marsden of the Smithsonian Astrophysical Observatory, comet West is a long period comet traveling in a nearly parabolic orbit inclined about 43 degrees to the ecliptic. It approached from the south and had a perehilion distance of about 18.5 million miles.

The comet was bright enough shortly after perihelion (which occurred on February 25) to be seen with a six inch telescope in broad daylight. The reason was apparent a few days later: After moving away from the Sun’s glare, a highly structured dust tail was seen stretching more than 20 degrees behind the nucleus. The high, variable production of dust at perihelion produced synchrones whose change in position reflected the change of the comet’s position as it moved around the Sun.

Comet West. Photograph: J. Linder/SEO

A generalized scenario of what is thought to happen to a comet can help us interpret what was seen in comet West. First, the nucleus, believed to be somewhere between one and six miles in diameter, as an icy amalgamation of dust grains; some grains are silicates ranging in diameter from 0.025 inch to less than .000025 inch. The distribution of dust in the nucleus is unknown, but comet West appeared to display in inhomogeneous mixture. As the comet approached the Sun, it heated up and the ices (probably water, methane and ammonia) vaporized. The outgassing pressure drove the dust away from the nucleus. When the dust no longer collided with gas molecules, solar radiation pressure drove the dust particles away from the Sun to form the dust (or type II) tail. At the same time, some of the gases went through photodissociation and florescence processes. The produced gaseous ions were accelerated by the solar wind and associated magnetic field to velocities over 9,000 m.p.h.

The gas (type I) tail was viewed distinct from the type II tail because of its different positional angle. This “double tail” became more prominent as the type I component became more pronounced and was particularly striking in color photographs, since the type I tail was blue. A look at an objective prism spectrum shows why this was true.

When the light of the comet was broken into a spectrum, a series of emission features were present. The most common was due to carbon and cyanogen molecules (including the somewhat rare C3 molecule) in the coma and ionized carbon monoxide (CO+) in the type I tail. Overlying this is a solar continuum from solid dust particles reflecting sunlight. The relative intensities of the emissions vary from comet to comet. Whether this variation is due to intrinsic composition differences or age (how many times the comet has come close to the Sun and expended some of its volatiles) is unknown. The spectrum of comet West’s tail indicated well developed CO+ emission showed up as monochromatic straight tail images in the blue end of the spectrum. The type II tail simply shows a continuous spectrum with peak intensity around 5,500 angstroms. Comet Kohoutek did know show a good separation of its tails; color film was used to identify the comet’s tail. Comet West did not have this problem, since color differences were obvious, giving the comet an especially asthetic appeal.

The tails grew fainter as they diffused into space and the production rate of new material decreased as the comet moved away from the sun.

Small instruments showed daily changes in the come close to the nucleus. They were subtle changes, hinting at some kind of activity in the nucleus. Detail in the coma was nothing like the striking spiral structure observed in comet Bennett in 1970. The objective prism spectrum had emission features of carbon (both C2 and C3), cyanogen, sodium and methylidyne associated with the coma. Slit spectra obtained with larger telescopes showed much more. Perhaps the most spectacular phenomenon of comet West was the splitting of the nucleus into several pieces during and after perihelion passage. Several observers noticed a secondary nucleus which parted slowly from the primary.

By mid-March observers at New Mexico State University Observatory photographed four distinct nuclei slowly spreading apart. Photographs with the Mt. Lemmon Observatory 61 inch telescope showed their relative brightness changed by as much as 20 percent. Each nucleus developed its own tail, probably a gaseous one of CO+. Tracing the motions of the four bright, separate nuclei back in time, it appears that the nucleus first split around February 25. On March 9 or 10, the secondary piece broke again, leaving behind a piece almost motionless with respect to the first (all these motions in the plane of the sky, since there is no available radial velocity data).

This sort of observation is consistent with an icy conglomerate nucleus with an inhomogeneous mixture of volatiles that may produce fractures. Another consequence of inhomogeneous mixture might be jets of gazes that may be large enough to impart more spin and cause break-up. Observations argue against a loose sandbank model of particles rotating about a center of mass, since such a configuration could not break up into several well defined groups of nearly the same visual magnitude.

It appears that we witnessed a clump of primitive solar system material, kept intact in the deep freeze far from the disruptive forces of the sun, which was recently perturbed. There is still a great deal to learn from satellite observations made in the ultraviolet and application of new ground based techniques on the spatial and temporal distribution of the comet’s components. But, our understanding and appreciation of the “hairy” members of the solar system has deepened.

(Astro-News, Latest News from the World of Astronomy. Astronomy, August 1976)

Perseids

Perseids

Moon Subdues Perseid Meteors

Because the Perseids – the finest of all meteor showers – reach their maximum on August, this month is generally considered the prime time for meteor observation. Unhappily, this will not be the case in 1976, because of the presence during early morning hours of the waning gibbous moon. Observers might be able to assuage their disappointment somewhat with a look at Jupiter, once more in an excellent position for viewing.

Perseid Meteors

In years when skies are dark and moonless, the Perseids lay justifiable claim to the title of “year’s best meteor shower”. Beginning toward the end of July and extending through most of August, the shower peaks on the night of August 12-13, when 50 or more meteors per hour can be seen streaking from their radiant in the constellation Perseus.

Perseids Perseid Meteor shower in Austin, Texas. Photograph by Jared Tennant. This photograph is licensed under the Creative Commons Attribution 2.0 Generic license.

In the North hemisphere, when the moon reaches full phase in August, it will be in the sky the entire night. All through the predawn hours (the best time for observing meteors) of subsequent nights, the moon shines brightly in the sky, blottin out all but the brightest Perseids. In this period you should expect to see only those that reach second magnitude or brighter; the rest will be washed out in the glow from the moon. The Perseids may, therefore, yield in this moment the top prize to the Orionids, which reach maximum later, in October just before new moon.

Nevertheless, it may be worthwhile to attempt some observation of the shower precisely because only the brightest members will be conspicuous. The chance to see bright, reliable meteors should not be passed up. Photographs of individual Perseids – black and white or color, can be found on the Internet.

Star Dome in August

Star Dome In August

Star Dome: To some, our galaxy rises from the horizon on August nights like a boiling cloud of steam. We might see it as the smear left by a giant’s paintbrush, or – referring to our own name for it – a streaming puddle of spilled milk. Any such comparisons, however, pale beside the actuality of the Milky Way: our own spiral galaxy, composed of billions of stars and vast clouds of gas and dust.

Many bright stars dot the Milky Way as it stretches from Sagittarius to Cygnus ; most dominant are the three that comprise the summer triangle – Vega, Deneb and Altair. The constellation patterns themselves include some of the sky’s most distinctive groups: the Northern Cross in Cygnus, the teapot in Sagittarius, the row of three stars in Aquila, and the tiny figures of Sagitta the arrow and Delphinus the dolphin.

Another small constellation, set directly in the Milky Way, is Scutum the shield. Invented by Hevelius, its original name was Scutum Sobieskii; it was ‘placed” in the sky in honor of John Sobieski, king of Poland, who prevented the Turkish invasion of Vienna in 1683. Scutum is notable today not for any bright stars, but for the richness of the Milky Way within its borders.

August Sky. The Sky Dome rendering approximates the sky as it appears early in August. The same constellations are visible one hour earlier during the latter half of the mouth. To use this constellation finder, hold it overhead so the compass points up line with North, South, East and West in your backyard or viewing area. For example, to find constellations in the southern part of the sky hold the chart in front of you so the South compass point faces the southern horizon. Repeat this procedure for East, West and North. Since only the brighter stars are represented in this map, you should be able to trace out the geometrical shapes of the constellations with ease. To find planets, asteroids, etc., visible among the current month’s zodiacal constellations refer to the planet finder. Source of the photography : Stargazing.net

The Milky Way itself is the subject of innumerable legends and bits of folklore. Often depicted as a river, it has had many different names. In Arabia it was simply Al Nahr (the river); in ancient Mesopotamia it was river of the Divine Lady, wife of the heaven –god; in Japan, the Milky way was the Silver river. When the crescent moon was in the sky, the fish in the river were said to be frightened, believing the moon was a hook.

The most widespread conception of the Milky Way, however is that of the road. We find this idea in our own title, for the word “way” is an archaic synonym for “road” or “path”. The German Milch Strasse has the same meaning, as does the French Voie lactée.

Other nations, however, have or had different ideas about this road. In Sweden it is Winter street, and the Chinese know it as Yellow road. Among English peasantry it was called Watling Street, the name of an ancient highway stretching from Chester to Dover, while in Celtic countries, the Milky Way was Arianrod or Silver Street.

It follows naturally that if the Milky Way is a road, there should be legends concerning its travelers and their destinations. In summer, the Milky Way appears to rise from Earth toward the zenith; thus many stories tell how a road, rising from the edge of the world, leads to heaven. To the Norsemen, the Milky Way was the road that dead heroes followed to Valhalla, home of the gods (although in later times the rainbow assumed this function). American Indians had the same ideas, and the brighter stars along the Milky Way were the heroes’ campfires. Natives of Patagonia believed their dead friends were hunting ostriches along the way, and the early Hindus called it the path that Ahriman took to his throne in heaven.

In Northern India, the Milky Way is called the path of the snake, providing another example of widely separated peoples having similar sky legends; the Norse told of the Midgard serpent, a monstrous snake that surrounded the world. In some stories the serpent lived in the ocean, but elsewhere the Milky Way is either the home of the snake or the snake itself. The Akkadians also knew the galaxy as the great serpent.

A story from Finland tells of how the lovers Zulamith and Salai, wanting to be united in heaven, built a “starry bridge of light”; after they completed the task, they were joined together into the star Sirius. Another Finnish story returns us to the notion of the Milky Way as a river. To the Finns, Tuonela, the land of death, was surrounded by a wide river that has been identified by some as the Milky Way. On this river swam a black swan, singing a melodious mournful song. In order to win the hand of the daughter of Louhi, ruler of Pohjola, the hero Lemminkainnen was ordered to make his way to Tuonela and shoot the river-swan. The hero’s first arrow missed. Before he could aim another, a shepherd, determined to prevent the sacrilegious act, attacked Lemminkainen with his sword and killed the hero. After dismembering the body, the shepherd threw the pieces into the river, which carried them to the land of death.

Planet Finder. The chart shows the positions of the moon, planets and brightest asteroids for August. Letters within the cercles correspond to the letters beside each object in the data section above the map. Additional information about each object: R.A. = right ascension and Dec = declination, the two coordinates used to locate astronomical objects. Magnitude = a. The general coordianate system is indicated around the edge of the map

If the Milky Way is indeed the river surrounding Tuonela, it’s easy to see the swan (Cygnus) swimming down it, as well as Lemminkainen’s first arrow (Sagitta) narrowly missing the bird’s head.

The tale, incidentally, ends happily, for Lemminkainen’s mother wore a ring that turned chill when her son was in danger. Leaning in this manner of his death, she was able to restore her son to life and death by magic. The composer Jean Sibelius relates the story in his Four Stories for orchestra.

If Cygnus and Sagitta are the swam and the arrow, might Lemminkainen himself be in the sky? We could chose to see him in the constellation Hercules, in place of that hero. This would actually not be inappropriate, for Hercules has had more identifications in its long history that any other constellation. In fact, the name Hercules is a very recent title for this group, which originally had nothing to do with that greatest of Greek heroes. The Greeks themselves did not know the constellation by that name, and it was only during Roman times that Hercules finally found his way into the sky. The Greek called the group the kneeler – nameless man, bent on one knee with his other foot on the head of Draco the dragon.

The constellations may originally have been intended to represent the important occupations of the day: hunters, farmers or worriers. If so, Hercules’ identification has long been lost, because of the Greeks and early Arabs he was simply the anonymous kneeler. Aratos, in 270 B.C., wrote that “no one can clearly speak of him, no upon what task he is bent; but simply Kneeler they call him.” Also titled the leaper, the keen-eyed one, or the club wielder in Greek days , the man remained unnamed.

Why should this be so? We have seen that the Greeks were ingenious in devising stories to complement their sky figures. Yet there is a group that exists, so to speak, in a void. Today, of course, there are many constellations associated by legend with Hercules, but these are recent additions to skylore. Hercules’ upside-down orientation in the sky is yet another addition to the puzzle: no other constellation except Pegasus stands on its head in manner.

But if the Greek were reluctant to assign a name to a kneeler, other nations certainly were not. There is evidence that the group may have represented the Chaldeans’ great hero Gilgamesh. A Chaldean cylinder seal dating from about 3000 B.C. shows Gilgamesh resting on one knee, with the other foot propped on the head of the dragon Tiamat – the exact pose assigned the figure in the sky. The Greeks, in fact, may have adopted the figure of Gilgamesh into their own mythology, transforming him into Hercules in the process.

Later, Hercules was changed by the Arabians into the dancer, although the Arabian word is translated by some as posturer. Still other names for the constellations have been Prometheus, Theseus, Orpheus (fittingly enough, with Lyra the lyre nearby), and Ixion. The last is a name of a figure in Greek legend, who, after a crime committed against Zeus, was punished in Hades by being tide to a wheel that revolved forever. The constellation’s daily motion around the pole may even have suggested the story of Ixion to its inventors.

Surprisingly, there is no mention anywhere in old records of the famous globular cluster M-13. Its first appearance in any written record is in 1714, when it was first seen by Sir Edmond Halley. Since the cluster is visible to the naked eye on clear nights, it is remarkable that it successfully avoided recognition prior to Halley’s discovery.

Still one more mystery is associated with Hercules. The constellation is indistinct; the only easily recognizable pattern is the keystone, made up of third and fourth magnitude stars. Why, then, has the group been so important to so many nations? In old records, it is always one of the most prominent figures in the sky, despite its faintness and anonymity.

The checkered career of Hercules is something to puzzle over while observing it on a clear August night in the Star Dome.