Celestial Objects


[] The Sun [] The Moon [] Stars []
[] Planets & Satellites [] Black Holes []
[] Meteors [] Quasars [] Comets []

The Sun

The sun, a typical star, is an incandescent gaseous globe, 1.39 million km in diameter, with a mass of 2 x 1030 kg, an effective temperature of approximately 5800 K, and surface radiant power of 4 x 120 Mw. Earth intercepts only 17 x 1010 Mw, mostly as visible light and infrared radiation. For comparison, the total generating capacity of Canadian electrical plants is under 105 Mw.

The current theory states that the sun's power originates is nuclear reaction occurring in a hot (about 15 million K) core which contains half the solar mass in only 1.5% of its volume. Geological and astronomical evidence suggests that the reactions were triggered 5 billion years ago when the temperature and density at the centre of a condensing cloud of primordial interstellar gas rose to levels where hydrogen atoms fused into helium atoms. The heat released by this nuclear fusion creates enough internal pressure to counterbalance gravitational contractions. This equilibrium will last for billions of years before the sun's outflow of energy is drastically altered. This theory is being challenged because obstentational tests failed, so far, to detect this predicted flux of highly penetrating particles, which should be emitted from the sun's nuclear furnace.

The sun does not rotate as a rigid body about its axis: the solar equator rotates in 25 days, a solar parallel of latitude at 600 in 29 days. This differential rotation organizes the churning gaseous fluid in the sun's shell in a dynamo action, which creates the magnetic patterns characteristic of sunspot activity. The average number so spots grows and fades in an eleven-year cycle. Successive cycles can vary greatly in amplitude; however, extremely low activity can last almost a century as during "Maunder Millimum," from 1645 to 1715 AD. Solar activity may influence climatic changes on Earth, but no direct physical link has been identified.

Explosions called solar flares erupt when magnetic stresses stored in active regions are suddenly released. Terrestrial side effects of large flares include geomagnetic storms, enhanced northern lights, and ionospheric disturbances. In addition, high-speed streams in the solar wind, unrelated to flares or sunspots, strongly agitate the Earth's magnetosphere. These streams originate in "coronal holes," vast spaces of reduced temperatures and density, where coronal magnetic field lines are open to interplanetary space.

Canadian research in solar physics dates from the construction, in 1905, of spectrographic apparatus as in the Dominion Observatory, Ottawa, for application to solar eclipses and to the measurement of the sun's differential rotation. Solar radio astronomy in Canada began in 1946 at the Radio and Electrical Engineering Division of the National Research Council in Ottawa. Since then, NCR laboratories have daily monitored the flux of microwaves emitted by the sun at 2800 MHz, a measurement used world wide as an index of solar activity. NCR's Ottawa River Solar Observatory, established in 1970, records and analyzes fine chromospheric structures related to sunspot activity and solar flares. Observations of the sun's far infrared spectrum are made from balloons and high-altitude aircraft.


The Moon

The moon is a natural satellite of Earth with a mean diameter of 3476 km, and a mass of 7.28 x 1022-kg (1.23% of Earth's mass). Three moons of Jupiter and one of Saturn are larger; the planet Pluto is smaller. The moon's mean distance from Earth is 384,500 km, in an orbit that requires a 29.5306 days from one new moon to the next. The moon shines by reflected sunlight appearing as a crescent when it is within 900 of the sun. Except near its new moon stage, the moon is second to the sun in brightness.

Tidal effects of Earth have forced the moon's rotation to match its (the moon's) orbital period; hence, one side of the moon always faces Earth and only 59% of its surface is visible. Because it is so close, the moon has been important in religion and art from the earliest times, and was the basis of the lunar calendar.

Six American landings and several Soviet probes returned lunar soil and rocks for intensive study. The landings confirmed the absence of both a lunar atmosphere, and magnetic field; chemical studies of the rocks showed that the moon contains less metal than Earth, and is deficient in volatile materials. The formation ages of the rocks are between 3.1 and 4.42 billion years which accord with current estimates of the age of the solar system, nearly 4.6 billion years.

Historically, there are three main theories of the moon's origin; it was split off from Earth shortly after Earth's formation (fission theory); it resulted from the capture by Earth of one or more bodies that had formed elsewhere in the solar system; Earth and the moon were assembled in the same region as a double planet. A new theory has developed close to twenty years after the return of the first lunar samples. Known as the large impactor hypothesis, it suggests that the moon formed early in the solar system history as the result of a collision between Earth and another object of mass at least one-tenth of Earth's. In this theory, the moon is composed mainly of material from the impactor, heated by the collision, and the theory appears to explain dynamical peculiarities of the Earth-moon system as well as chemical anomalies revealed by the study of moon rocks.

Lunar craters are normally named after deceased scientists, and ten Canadians are among those honoured in this tradition: Oswald Avery, Sir Fredrick Banting, C.S. Beals, C.A. Chant, Reginald Daly, J.S. Foster, F.S. Hogg, Andrew McKellar, R.M Petrie, and J.S. Plaskett.



A star is a large, self-luminous sphere of hot gas held together by its own gravitational force. There are over a billion stars in each of the more than one billion galaxies in the universe; yet the sun, at a distance of 150 million km, is the only one close enough to show directly the details of its surface.

The masses of stars range from 0.1 x 1030 kg, to 100 x 1030 kg. The sun's mass is 2 x 1030 kg. A star's mass controls its basic structure, the most massive stars being the hottest, brightest, and largest. Most stars, including the sun, are called main sequence, or dwarf stars. A star is held together by gravity. Heat liberated by the conversion of hydrogen to helium inside the star results in high central pressure that prevents gravity from further compressing it.

Stars and gaseous nebulae can be chemically analyzed on the basis of the spectral lines present in their light. In most cases, hydrogen is overwhelmingly dominant(up to 99% of a star's mass). The chemical composition of the universe at its origen is unknown; however, since stars produce heavier elements out of hydrogen and as some of the stellar material is sent back into interstellar space by stellar winds, novae and supernovae, succeeding generations of stars have more heavy elements. The earliest formed stars have as little as 1% of the heavy elements present in the sun.

Stars are formed form clouds of interstellar gas and dust, which are pulled together by gravity until collisions between the molecules generate enough pressure to slow the contraction.Internal nuclear reactions have not yet started. The time required for contraction is a small fraction of the star's total lifetime; for example, the sun would have a contraction time of about 100,000 years, compaired to a main sequence lifetime of about 10 million years. The contracting star begins to shine during this relatively short stage. Contraction ceases and the star joins the main sequence when intenal nuclear reactions start. Rotation of a star arises from the spin-up of the clouds from which if formed. Larger stars rotate rapidly, some near the point of 'break-up, or materials spinning off their equators. Smaller stars rotate much more slowly because escaping mass gets caught in the magnetic field of the star. The 'magnetic brake' reduces the rotation of main sequence stars by about 2 each billion years.


Planets & Satellites

A planet is a nonluminous body that revolves in an orbit, around a star; a satellite is a body that revolves around a planet. In our solar system, these "worlds" range from Jupiter, nearly 145,000 km in diameter, to small lumps of rock less than 1 km across. Our knowledge of the physical and chemical nature of planets and satellites has increased rapidly since the landing of the first interplanetary craft of the 1960's.

Several centuries of tradition have given us names from Greek-Roman mythology for the planets and satellites themselves except for the satellites of Uranus. William Herschel first discovered this planet in 1781. The currently known satellites of Uranus are now 15 in number, thanks to the records of Voyager 2 made in January 1986, and in this case, all 15 satellites have been named after fictitious characters in the writings of Shakespeare and Alexander Pope.

As of 1987, 40 topographic names have been approved on 26 different interterrestrial worlds. After craters, the most frequent named features have been valleys, mountains, canyon ridges, and plains. Some 40 Latin terms are used to define the various categories of features. The Working Group for Planetary System Nomenclature has endeavored to bequeath to the cultural heritage in the names we used for other worlds. Over the years, the names of deceased scholars have been placed on the moon. Now we have outstanding individuals in the humanities such as Beethoven, Shakespeare, and Rachael on Mercury, feminine names such as Eve, Cleopatra, and Pavlova on Venus, and the deities of fire and volcanoes such as Ra, Rile, and Surt on Io. Craters on Mars have been named Hope, Chinook, Chapais, and Nain; taken from small towns in Canada.


Black Holes

The notion of black holes originated with the English physicist John Mitchell, and later with the French mathematician Pierre Simon de Laplace, who realized that if light was composed of particles, a sufficiently compact gravitating astronomical body could have such a high surface gravity that light particles, or photons, could not escape from its surface, resulting in a black star, more commonly known as a black hole. Einstein's General Theory of Relativity is used to study black holes, since the older Newtonian Theory of Gravity does not provide an adequate basis for discussing the curved space-time near them.

The black hole consists of a spherical surface called the event horizon, which separates the part of space accessible to an outside observer from the inside of the black hold from which nothing can escape. The radius of this sphere, called the Schwarzchild Radius, in honour of the German astrophysicist who derived the first black hole solution to Einstein's equations in 1916, is proportional to the mass of the object that co;;apsed to form the black hole. For an object with mass equal to that of the sun, this radius is about 3 km.

The existance of black holes outside the realm of theory has not yet been demonstrated. It has been assumed that a sufficiently massive star will not be able to resist its own self-gravitation forever and must eventually become a black hole. Most discoverers of black holes have based their claims on this assumption, including U of T's Thomas Bolton, who postulates a black hole in Cygnus X-1.

In 1974, Stephen Hawking of Cambridge U, England, demonstrated theoretically that a black hole radiates at a temperature inversely proportional to its mass. For a solar-mass black hole, the temperature of radiation is about 10-7Km much below obserbvable limits, but for a mass the size of a large mountain, the temperature is about 10-11K. This theory results in the consideration of such mini black holes as sources for highly energetic cosmic radiation. Primordial black holes, much less massive than these would porbably have had time to evaporate since the beginning of the universe. The size of a primordial black hole is such that the threories of gravitation and of quantum mechanics must both be used in its description, and it is hoped that this work may provide the long-sought link required to unify these theories.



The solar system contains many small objects travelling in individual orbits about the sun. When such a particle collides with Earth, interaction with the upper atmosphere produces a flash of light called a meteor, which typically endures for less than one second near heights of 90km. Large particles produce spectacular meteors, and in rare cases, part of the object survives to reach Earth's surface and is then called a meteorite. The atmosphere, and their violent collisions do not slow huge meteorites with Earth blast out 'impact' or 'meteorite' craters.

Except for lunar samples, meteorites provide our only chance to study material from space by laboratory techniques. Most meteorites are 'stones', with a thin, black,fusion crust; about 5% are 'irons', composed of a nickel-iron alloy; a smaller number are 'stony iron'. Analysis of mereorites yields vital clues about the early history of the solar system because some have had relatively simple chemical and thermal histories.

Most meteorites appear to be derived from asteroids by mutual collisions, but small ones are fragments blasted from the moon by mereorite impacts there, and a few are suspected to have come from Mars in the same manner. Their orbits appear to have been modified by Jupiter's gravitational field in tens of millions of years to permit collision with Earth. About 3000 different meteorites are known. Observations with a network of cameras in western Canada indicate that a meteorite of at least 100g falls somewhere in Canada daily, but very few are ever recovered.

Impact craters are formed by the expanding shock wave when a giant meteorite weighing hundreds to millions of tonnes strikes the ground at high velocity. The moon and several other planets and satellites retain impact craters for very long periods, but on Earth erosion usually removes the surface evidence in a few million years. Subsurface rock however, is permanently damaged by the shock wave and can be used to identify very ancient craters.

A major program to study impact craters was started during the 1950's by C.S. Beals. Two dozen features in Canada, ranging from 3 to 95 km in diameter, have been confirmed as impact craters in this pioneer study, of which the Nouveau-Quebec Crater is the most recent.



A quasar is an extraterrestrial object which emits radiation over a wide spectral range. Although the name is a contraction of 'quasi-stellar radio source,' these objects also radiate light, X-rays, and gamma rays. The term QSO (quasi-stellar object) refers to objects with many quasar-like properties, but no detectable radio emission. No quasar is visible with the unaided eye.

Even on photographs made with large telescopes they look very much like faint stars; hence, quasars were not recognized as distinct entities until the early 1960's, and it is still not clear what they really are. Examination of their colours and spectra has demonstrated that quasars are not stars. Most emit a larger proportion of their light in the ultraviolet and blue part of the spectrum than do stars.

Canadian scientists made the first direct measurements of the angular sizes of quasars using the 46 m Algonquin telescope and the 25 m radio telescope near Peniticton BC, to form a base-line interferometer. Such radio measurements, combined with distance measurements inferred with optical spectra, indicate that quasars have energies far exceeding those of any other objects. Measurements repeated over several years have shown distinct structural changes in a number of quasars. These quasars appear to consist of two or more regions, moving apart at speeds considerably faster than the speed of light. Such speeds are in contravention of well-established physical laws. This paradox is one of the most important unsolved problems in astronomy and physics.



A comet is an astronomical body orbiting the sun, which appears for a few weeks as a faint luminous patch moving slowly from night to night, relative to the background of stars. The comet may also have a luminous tail pointing away from the sun. In recorded history, abouit 750 comets have been observed well enough to allwo an approximate determination of their orbits. Of these comets, about 140 have short periods of 3 to 200 years, and have been observed more than once, so that about 1200 cometary apporitions have been observed in all. The remaining 600or so long-period comets have been observed only once and their orbital periods are known roughly or not at all.

Upon its discovery, a comet is assigned a temporary label consisting of the year of discovery, plus an alpha character indicating the order of discovery in the year. Later, when all orbits have been worked out, it is assigned a permanent label which includes the year, plus a Roman Numeral indicating the order of its passage throu perihelion. The comet is also named after its discoverer, for example, Comet Van den Bergh - 1974g - 1974 XII, means that this comet was discovered by Sidney Van den Bergh, and was the 7th comet to b discovered, and the 12th comet to pass perihelion in 1974.

A periodic comet such as Halley's bears several numeric designations such as 1835 III, and 1910 II. This means that since this comet has been observed at every passage since 240 BC, and was last seen from Canada in November and December 1985. It has become a spectacular subject for observers in the Southern Hemisphere in March and April, and was visible again in Canada in May 1986. Its passage will be visible again in July 2061.

Most comets are too faint to be seen with the naked eye,and not all develop tails. Occasionally, a large comet passing close to the Earth and sun produces a spectacular sight. such as the newly discovered comets of the 1970's; Comets Bennet, Kohoutek, and West.