Scientists now believe that there are many galaxies and that clusters of many galaxies make our Universe. Continuing this trend of astronomical up sizing, the latest speculation among astronomers is that may be the Universe we know is only one of the many- and that there may be many Universes, making a vast Super Universe.
The difference between space and outer space is that means the whole the earth’s atmosphere ends extends on and on in all directions
Outer space is vast. Our terrestrial units of measurement hardly suit its dimensions. So we have evolved new units of measurement like the Light Year and the Astronomical Unit(AU). A Light Year is the distance covered by light in one year in vacuum travelling at a speed of 299,792.5 km per second. The
Astronomical Unit represents the mean distance between the Sun and the Earth. Distance within the solar system are measured in AU. Light travels this distance in 8.3 min approx. AU in terrestrial measurements is 149,597,870 km.
The distance between the Sun and Pluto, the outermost planet, averages 39 AU. In term of space dimensions, a light Year is made up of about 60,000 AUs.
The word is from the Greek astron meaning Star (and nautes meaning sailor). Astronomy is the scientific study of the heavens and all that is therein. It is not to be confused with Astrology-which lacks any kind of scientific basis and encompasses the belief that heavenly bodies affect human lives. Modern astronomy began with Italian astronomer Galileo. In 1609 Galileo heard of the telescope made by the Dutchman Hans Lippershey. It was this instrument, a refractor telescope, that heralded the era of optical astronomy. Galileo made several startling discoveries.
He found that the moon’s surface is rugged, and that Pleiades is a group of over 40 stars. He discovered four of Jupiter’s moons and observed the sunspots.
Galaxies are huge congregation of stars held together by force of gravity. They are so big that they are also called ‘island universe‘. Studies of distant spaces with optical and radio telescopes indicate that there may be about 1.3 trillion galaxies in the visible Universe. Galaxies seem to be scattered in space. Galaxies tend to be grouped together into clusters, and some clusters appear to be grouped into super clusters. All the galaxies we look at will display red shift in their spectra, indicating they are moving from us. Current data suggest that the galaxies are moving apart at the rate of 50-100 kps for every million parsecs of distance. A structural analysis of the known galaxies brings out three major forms-spiral, elliptical, and irregular.
Spiral galaxies which form 80% of the galaxies so far known, have a central nucleus with great spiral arms trailing round it. Elliptical galaxies, account for about 17% of the known galaxies and show purely elliptical shape without any spiral arms-ranging in shape from spherical ellipticals to extremely saucer-shaped ones. Irregular galaxies show no definite geometric pattern or shape.
The Milky Way
The Milky Way is our home galaxy.
Our galaxy forms part of a bigger cluster of 1000s of galaxies. This appears like a river of light – known as the Akash Ganga or Milky Way. It is a spiral galaxy. The main body is 100,000 light years across and its globular nucleus about 16,000 light years in diameter.
The Milky Way consists of hundreds of billions of stars rotating about its centre in a stately average period of some 230 million years. Our galactic nucleus is about 32,000 light years from the Sun.
There are many millions of stars in the sky. In the whole heavens, fewer than 6000 stars are bright enough to be visible; and at any time, less than 2500 stars are visible above the horizon.
Stars account for 98% of the matter in a galaxy. The rest of 2% consists of interstellar or galactic gas and dust in a very attenuated form. The normal density of interstellar gas throughout the galaxy is about one-tenth of a hydrogen atom per cubic centimeter(cm3) volume. Stars tend to form groups.
Going on their own are the exception in the Universe.
Do not number more than 25% and Double Star account for some 33% of the stellar population. The rest are multiple stars. Antares in Scorpio is actually two stars. Capella and Alpha Centauri comprise 3 stars each, while Castor consists of 6 stars.
Star which appear single to the naked eye are sometimes double star (binaries). These are two stars revolving around a common center of gravity. They are also found in orbital motion round each other, in periods varying from about one year to many thousands of years.
When the hydrogen in a star is depleted, its outer regions swell and redden. This is the first sign of age. Such stars are called Red Giants. Our star, the Sun is expected to turn into a red star of this type in another 5 billion years.
Red Giants are dying stars that has expanded greatly from its original size and gives off red light. They have gigantic dimensions. Betelgeuse, for example, has a diameter of 480,000,000 kilometers, about 350 times the diameter of the Sun. Mira, another red giant, has a diameter of 640,000,000 kms.
Black Dwarf is the tiny blackened corpse of a star like the Sun. Ultimately it disappears into the blackness of space.
White Dwarf is a tiny, dense, hot star, representing a late stage in the life of a star like the Sun. The matter in it is so incredibly dense that a single teaspoonful of it would weigh several tonnes.
Super Giants are huge stars, with all their hydrogen fuel used up in their core but continue to expand hundreds of times bigger than its original size before they finally die.
Novae and Super Novae
Novae and Super Novae are stars, whose brightness increases suddenly by 10 to 20 magnitudes or more and then fades gradually into normal brightness. The distinction between the two types has not been precisely explained. It would appear that they differ in degree and not in kind. The sudden increase in brightness is attributed to a partial or outright explosion. In novae, it seems that only the outer shell explodes, whereas in supernovae the entire star explodes. Novae occur more frequently than supernovae. Astronomers say that when the whole structure of the star is blown to pieces, it flares up in brilliance so that its intrinsic luminosity for the first 30 days following the explosion is equal to about 1000 million Suns in the Solar system.
They are stars that show varying degrees of luminosity. Delta Cephei, the first of this type of stars noticed in 1784 by English astronomer John Goodrich, has a regular fluctuation of brightness every 5 days and 9 hours. Stars of fluctuating luminosity, are called Cepheid Variables. In stars of this type, luminosity fluctuates between periods as small as a few hours to as long as 1000 days or more. Generally speaking, the slower the bright-dull-bright cycle, the higher the luminosity.
They are powerful quasi stellar sources of radio radiations.
Pulsars are variable stars which emit regular pulses of electro-magnetic waves of very short duration.
Strange things happen to a star at the end of its life if its mass is more than three times the mass of the Sun. It will collapse, becoming more and more compact. The collapse continues until the star becomes so dense that nothing, not even light, can escape from its gravity. Hence the object is dark and can’t be viewed directly. According to General Relativity, bodies of matter curve space. If the body of matter was very dense(tons of matter packed into a small space), it convulses space into an infinitely deep chasm, called a black hole. John Wheeler, a US physicist, first used the term ‘black hole’ for a completely collapsed star at a meeting at the Institute for Space, NY, in 1967.
Just a look at the sky will make us confused but if one gets accustomed, one can recognize the patterns, called constellations. It helps us find our way around the night sky and an order. All stars appear to circle around the Pole Star.
Other notable features of the northern hemisphere include Andromeda nebula, the Pleiades or Seven Sisters cluster. The circumpolar constellations include Ursa Major(Great Bear), Ursa Minor(Little Bear) and Cassiopeia.
Age of the Universe
The current estimate of the age of the Universe is about 13 billion years. The 60 odd-years following Hubble’s original findings have seen numerous revisions of the constant. HST’ main purpose was the measurement of the Hubble constant. The Hubble’s constant as measured by the space telescope was on the high side implying a rather young Universe-also depending on what theoretical mode is accepted. Scientists say the Universe could be just 8 billion years old if the Hubble constant is precisely 80.
Size of the Universe
No one knows whether the Universe is finite or infinite in size. Albert Einstein described the Universe as ‘finite but unbound,’ meaning that the frontiers cannot be observed even though they are definitely there.
EXTRA PLANETARY BODIES
About 18,000 asteroids are known at present, and orbits have been determined for about 5,000 of them. The first three asteroids discovered Ceres, Pallas, and Vesta- are the largest of the asteroids, with average diameters of 933,523, and 501 kilometers respectively. Daniel Kirkwood found rings in the asteroid belt where few or no asteroids were found. These depleted regions are known as “Kirkwood gaps”.
There has long been a suspicion that there may be yet another population of asteroids, orbiting in a dynamically stable zone near the Sun inside the orbit of Mercury. If the “Vulcanoids”. as they have been known, actually exist, they have so far escaped detection because they are small and could only be observed from the ground just after sunset or before sunrise, through the atmosphere.
Missions To The Kuiper Belt
The discovery of the first Kuiper Belt object was in 1992. The hunt for KBOs uncovered a large number of bodies in a wide range of sizes up to objects at least as big as Pluto.
KBOs are classified by their orbit:
“Plutinos” are trapped in some class of orbit resonance with Neptune. “Classical” KBOs have stable, non-resonant orbits. “Scattered disk objects(SDO)” have eccentric orbits, some ranging as far out as 1,000AU. Since 2008, they are referred to as “plutoids” by making it the archetype of an entire class of cosmic bodies.
THE SOLAR SYSTEM
Solar system means system of the Sun. All bodies under the gravitational influence of our local star, the Sun, together with the Sun, form the solar system. The largest bodies, including Earth are called planets. Often smaller cool bodies, called satellites or moons, orbit a planet. Bodies smaller than planets that orbit the Sun are classed as asteroids if they are rocky or metallic, comets if they are mostly ice and dust, and meteoroids if they are very small. Most comets release gases as they near the heat of the Sun, producing a luminous cloud called a coma and often a long tail. A meteoroid that burns in Earth’s atmosphere is a meteor, while one that reaches Earth without burning completely become a meteorite.
It is one of more than 100 billion stars in the giant spiral galaxy called the Milky Way.
It is the center of the Solar System. It’s mass is about 740 times as much as that of all the planets combined.
It continuously gives off energy in several forms-visible light; invisible infrared, ultra-violet, X-rays and gamma rays, cosmic rays, radio waves and plasma. The Sun generally move in almost circular orbits around the galactic center at an average speed of about 250 km per second.
It takes 250 million years to complete one revolution round the center. This period is called a cosmic year.
It’s energy is generated by nuclear fusion in its interior. It is calculated that the Sun consumes about 4 million tonnes of hydrogen every second. At this rate, it is expected to burn out its stock of hydrogen in about 5 billion years and turn into a red giant.
Photosphere(400 km thick) is the glowing surface of the Sun, which we see. Temperature: 4,226 to 5,726 0Celsius. The gases that extend away from the photosphere make up the chromo-sphere, which is about 2,500 kms thick. Chromosphere (10,000 km thick) is called so because of its reddish colour. From the bottom to the top the everage temperature rises from 4,226 to 9,726 0Celsius. The chromosphere merges into the corona, the outermost region of the atmosphere.
Corona is magnificiently visible during eclipses. The temperature of the corona, which extends far into space, is about 2,700,0000C, hot enough to emit ultraviolet and X-ray wavelengths. The corona extends millions of kilometers into space above the photosphere and is very hot-millions of degree Celsius.
Throughout the rest of the sun, temperatures drops as gases move away from the core. Outside the core is the convection zone. Here, turbulent motions of gases transport the energy generated in the core towards the photosphere. The visible white light of the corona is made up of a continuum of colors, such as violet, indigo, blue, green, yellow, orange and red. Super-imposed on the spectrum are hundreds of dark lines called the Fraunhofer lines. The different sets of lines constitute the signatures of the various elements that make up the Sun and their temperature.
Recent researches using satellites have shown that the solar wind is made up of plasma, that is, ionised gas, mostly hydrogen and helium, containing nearly an equal number of protons and electrons. It flows outward from the Sun at supersonic speeds,around 400 m a second. Apparently, this wind sweeps through the whole Solar System to a distance of 40 AUs from the Sun which coincides with the very limits of the planetary orbits. When these eruptions roll out of the atmosphere of the Sun for many kilometers, they are called solar flames. The solar flares are spectacular- hot ionised gas rolling out as enormous clouds, 20 to 40 times the size of the Earth at speeds of around 100 km per second through corona, the outer layer of the Sun’s atmosphere.
The surface of the Sun change continuously. Bright spots called plages and dark spots called sunspot frequently form and disappear. Gases often shoot up violently from the surface.
Solar activity has been observed to follow a 11-year cycle. Owing to the Sun’s rotation, the solar wind travels in spirals and carries with it magnetic fields. The Earth’s magnetic field-the magnetosphere-acts as a shield against the ever-blowing solar wind and deflects it away from the Earth. Nevertheless, particles of solar wind sometimes pierce the magnetic shield and enter the upper atmosphere, where, like the solar flares, they cause auroral displays.
The solar wind distorts the shape of the magnetosphere. The magnetosphere extends to a distance of 64,000 km above the Earth- 10times the radius of the Earth. On the part of the Earth exposed to the Sun(the sunlit side), the solar wind sweeps along the magnetosphere past the Earth. On the other side of the Earth(the night side), the solar wind converges again and compress the magnetic field into a plume or tail, more or less like what it does to comets. The tail thus formed extends to over 6 million km on the night side of the Earth.
Sunspots are dark patches noticed on the surface of the Sun. They appear dark surface they are cooler (around 1500 degree Celsius) than the surface of the Sun which has a temperature of about 6000 degree Celsius. The largest spot ever measured (April, 1974) covered 18,130 million sq kms or approximately 0.7% of the Sun’s visible surface. The life periods of these spots also vary. They may last from a few hours to many weeks.
Polar Auroras are two auroras, the Auroras Borealis or Northern Lights and the Aurora Australis or Southern Lights. These are lights that sweep across the sky in waves or streamers or folds. They are very often multi-colored and provide one of the finest spectacles in nature. They occur in the Arctic and the Antarctic regions respectively. But the Northern Lights can be seen as far south as New Orleans in America and the Southern Lights as far north as Australia.
The magnetosphere is the earth’s magnetic shield. It was at first called the Van Allen who discovered them in 1959. Van Allen, in analyzing the data from the earlier Explorer and pioneer rockets found two belts of high intensity radiation in the upper atmosphere. Pioneer 12 later showed that these belts were a part of a large band of radiation called the magnetosphere. It extended far out to about 64,000 kilometers from the Earth’s surface.
Comets probably derive their name from their tail, as in Latin ‘comets’ means “long-haired.” Comets may originate in a huge cloud called the Oort Cloud that is supposed to surround Solar System. Extremely bright comets such as Hale-Bopp are rare. Not all comets have tails. The tail takes shape only when the comet gets close to the Sun. When first viewed through a telescope the bright head of a comet, called Coma, looks like a hazy dot. Sometimes a coma contains a star-like point called a Nucleus. The nucleus of a comet is extremely small. Solar energy warms comet’s head as it moves sunward and vapourises the frozen-crystalised gases. These gases stream out and form a spectacular, glowing tail behind the comet’s head. As the comet approaches the Sun the solar wind, which consists of high-speed atomic nuclei, protons,and electrons, sweeps cometary gases away from the Sun, producing a straight tail of up to 150m km in length. At maximum size the tail may be 250m km in length and brightness soon after the comet has passed its perihelion. Some comets may become so bright as to be visible even in daylight.
Comet tails always point away from the Sun because of the force exerted by solar wind and radiation on the cometary material.
Comets have very low density. Although they are larger than any body in the solar System by volume except the Sun, their density is only one 10,000 millionth of the Earth’s.
EXTRA SOLAR PLANETS
The first planets outside our solar system were spotted in 1990, in orbit around a dying, radiation-showing star very different from our Sun. Starting in 1995 with “51 Pegasi b” the first extrasolar, or exoplanet, discovered around a normal star, scientists have found alien worlds that are large, gassy giants and rocky. Some are two-faced worlds of fire and ice, and some float eerily through space, bound to no star. In the dozen years since the discovery of 51 Pegasi b, the number of known and suspected exoplanets has climbed to nearly 230.
The definition of planets, as accepted on 24 August 2006 is: “The IAU resolves that planets and other bodies, except satellites, in our Solar System be defined into three distinct categories in the following way:
A Planet is a celestial body that-It is in orbit around the Sun.
It has sufficient mass for its self-gravity to overcome rigid body forced so that it assumes a hydrostatic equilibrium(nearly round) shape.
It has cleared the neighborhood around its orbit.
A “dwarf planet” is a celestial body that-
It is in orbit around the Sun.
It has sufficient mass for its self-gravity to over-come rigid body forces so that it assumes a hydrostatic equilibrium(nearly round) shape.
It has not cleared the neighborhood around its orbit.
It is not a satellite.
All other objects, except satellites, orbiting the sun shall be referred to as “Small Solar System Bodies”.
Mercury, Venus, Earth and Mars. The bodies chiefly consist of iron and dense rock and rare collectively called terrestrial planets(Earth-like)
Jupiter, Saturn, Uranus and Neptune are very big (sometimes called giant planets), with large satellite families. They are composed mostly of hydrogen, helium, ammonia and methane. These Planets are called Jovian.
As the Earth travels in its orbit around the Sun, it continually encounters meteoroids head-on. Sometimes, on a clear, dark night, an unusually large number of small meteors can be seen in rapid succession-perhaps more than 50 an hour-called a meteors shower. Because of their small size, these meteors generally burn up in the upper atmosphere and never reach the ground. Some meteor shower coincide with the passage of a comet.
Asteroids are smaller heavenly bodies generally found between the orbits of the planets Mars and Jupiter. They may be about 100,000 in numbers but their total mass is only a few hundredths the mass of the Moon. They include Vesta, Eros and Icarus. Some asteroids come closer to the Earth. Apollo, even cross Earth’s orbit. There are Bifurcated asteroids-two chunks of rock that touch each other. At least 10% of the asteroids approaching the Earth are bifurcated.
- Asteroid-mining telescope giving public access to outer space (king5.com)
- Earth May Still Lie In Path Of Potential Gamma-Ray Burst (GRB), Say Astronomers (forbes.com)
- Mysterious and Well-Preserved Oort Cloud Object Heading Into Our Solar System (universetoday.com)
- Citizen Scientists Help Astronomers Solve Space Mystery (spaceref.com)
- Outer Space (dlwh8.com)
- Watch: Earth’s Atmosphere Is Escaping into Outer Space (news.softpedia.com)
- Study: incoming Oort Cloud object is preserved relic of early Solar System (wired.co.uk)
- Star Mystery Solved: Stellar Twins Closer to Earth Than Thought (space.com)
- Search for Space Warps! Armchair Astronomers Can Now Scout the Universe (scienceworldreport.com)
- We Are Light (livingawarenessmeditation.net)