Old News in Astronomy

Old News In Astronomy

Meteorite Falls In China

The 3,894 pound Kirin meteorite is shown with some of the fragments which broke off on impact. The fall, which took place around 4.p.m. on March 8, scattered fragments over a 200 square mile area. The Kirin meteorite broke the previous world’s record of 2,372 pounds which was attributed to a 1948 meteorite which fell in a cornfield in Norton County, Kansas.

Meteorite

X-Ray Nova Sources Growing in Number

X-ray novae are a new class of x-ray sources that must be added to the growing list of such objects. The first source, Cen X-2, was spotted in Centaurus in 1967. Last year a spectacular x-ray nova appeared in the constellation Monoceros and became the brightest x-ray source in the sky. In addition, during April 1975 an object near the Crab nebula, AO535 + 26, was observed to pulsate once every 104 seconds. The latter source faded in July, reappeared in August and faded again, and then reappeared in November 1975.

Two MIT scientists, Philip Morrison and Kenneth Brecher, have suggested that these new sources be divided into two groups. Sources like the brilliant one on Monoceros are “soft” x-ray objects that may generate radiation be ejected gases being excited by shock waves traveling through the nova. On the other hand, “hard” sources like AO535+26 may emit x-rays in the manner of neutron stars, by the excitation of matter falling onto a magnetized, rapidly rotating collapsed body.

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

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.