Astronomical Distance Scales

Some Common Distance Units:

• Light Year: the distance that light travels in one year (9.46 x 10^17 cm).
• Parsec (pc): 3.26 light years (or 3.086 x 10^18 cm).; also kiloparsec (kpc) = 1000 parsecs and megaparsec (Mpc) = 1,000,000 parsecs.
• Astronomical Unit (AU): the average separation of the earth and the sun (1.496 x 10^13 cm).

Some Representative Distances:

• The Solar System is about 80 Astronomical Units in diameter.
• The nearest star (other than the sun) is 4.3 light years away.
• Our Galaxy (the Milky Way) is about 100,000 light years in diameter.
• Diameter of local cluster of galaxies: about 1 Megaparsec.
• Distance to M87 in the Virgo cluster: 50 million light years.
• Distance to most distant object seen in the universe: about 13 billion light years (13 x 10^9 light years).

 

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Hubble's constant (Hubble's Law)

The Hubble constant H is one of the most important numbers in cosmology because it may be used to estimate the size and age of the Universe. Hubble constant indicates the rate at which the universe is expanding. Although the Hubble "constant" is not really constant because it changes with time (and therefore should probably more properly be called the "Hubble parameter"). The Hubble constant is often written with a subscript "0" to denote explicitly (clearly) that it is the value at the present time, but we shall not do so. 

The Hubble Expansion Law

In 1929, Edwin Hubble announced that almost all galaxies appeared to be moving away from us. This phenomenon was observed as a redshift of a galaxy's spectrum. This redshift appeared to have a larger displacement for faint, presumably further, galaxies. Hence, the farther a galaxy, the faster it is receding from Earth. The Hubble constant is given by
H = v/d where v is the galaxy's radial outward velocity, d is the galaxy's distance from earth, and H is the current value of the Hubble constant.

(Note -  In physics, redshift happens when light or other electromagnetic radiation from an object moving away from the observer is increased in wavelength, or shifted to the red end of the spectrum. In general, whether or not the radiation is within the visible spectrum, "redder" means an increase in wavelength – equivalent to a lower frequency and a lower photon energy, in accordance with, respectively, the wave and quantum theories of light. Redshifts are an example of the Doppler effect.)

Determining the Hubble Constant

Obtaining a true value for H is complicated. Two measurements are required. First, spectroscopic observations reveal the galaxy's redshift, indicating its radial velocity.

The second measurement, the most difficult value to determine, is the galaxy's precise distance from Earth. The value of H itself must be derived from a sample of galaxies that are far enough away that motions due to local gravitational influences are negligibly small (these are called peculiar motion, and they represent deviations from the Hubble Law).

Units for Hubble's Constant

The units of the Hubble constant are "kilometers per second per megaparsec." In other words, for each megaparsec of distance, the velocity of a distant object appears to increase by some value. For example, if the Hubble constant was determined to be 50 km/s/Mpc, a galaxy at 10 Mpc would have a redshift corresponding to a radial velocity of 500 km/s.

Current Value of the Hubble Constant

The value of the Hubble constant initially obtained by Hubble was around 500 km/s/Mpc, and has since been radically revised because initial assumptions about stars yielded underestimated distances. For the past three decades, there have been two major lines of investigation into the Hubble constant. One team, associated with Allan Sandage of the Carnegie Institutions, has derived a value for H around 50 km/s/Mpc. The other team, associated with Gerard DeVaucouleurs of the University of Texas, has obtained values that indicate H to be around 100 km/s/Mpc.

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What are the smallest particles in the Universe?

For many years, the only known subatomic particles were protons, neutrons and electrons. By the 1960s, however, advancements in particle accelerator technology had shown evidence of hundreds of smaller constituent particles. By studying these particles -- all part of what is known in particle physics theory as the standard model -- physicists can try to explain all of the forces and matter existing in the universe.

These smallest particles fall into several main categories, most notably fermions, hadrons and bosons.

Fermions

Fermions are the building-block particles. There are two types of material fermions: quarks, which work to hold the nucleus of an atom together, and leptons, which do not. Fermions can be broken down even further: There are different types of quarks, and for each, an anti-quark. Quarks are found in groupings, but leptons are found alone. Electrons and neutrinos are examples of leptons. Fermions have a half-integer spi.

Hadrons

Hadrons are composite particles made of smaller particles. A proton, for example, is a hadron made from a combination of different quarks. Strong interactions bind the hadrons together and they always have charges, but no color. Protons and neutrons are the most stable hadrons. Hadrons come in two classes: baryons and mesons.

Quarks

Quarks are the fundamental constituents of hadrons and interact via the strong interaction. Quarks are the only known carriers of fractional charge, but because they combine in groups of three (baryons) or in groups of two with anti-quarks (mesons), only integer charge is observed in nature.

Leptons

Leptons do not interact via the strong interaction. Their respective antiparticles are the anti-leptons which are identical except for the fact that they carry the opposite electric charge and lepton number. The antiparticle of the electron is the anti-electron, which is nearly always called positron for historical reasons. There are six leptons in total; the three charged leptons are called electron-like leptons, while the neutral leptons are called neutrinos. Neutrinos are known to oscillate.

Bosons

Bosons are subatomic particles that carry force. They help particles interact with one another without touching, much like the forces of gravity or magnets. Unlike fermions, bosons have integer spin. The Higgs boson is believed to be the tiny particle that likely provides mass to all matter. Yet scientists aren't even sure that the Higgs boson exists.The Higgs boson remains one of the key questions remaining in physics and in wrapping up the Big Bang theory. If scientists can identify and study the particle that gives mass to all others, they can explain how the universe started from a seemingly invisible field.

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Astronomy - August 2013 (40th Anniversary Issue)

Look forward to studying the starry night sky? Revel in seeing if you can locate and connect the Big Dipper and the brightest North star? If you're a star gazing enthusiast, you'll love Astronomy. You'll learn more about exploring the universe in your own backyard with the most popular amateur astronomy magazine.

• Astronomy - August 2013 (no ADS) 40th Anniversary Issue
• English | PDF | 83 pages | 36.6 MB

FEATURES :-

• 26 COVER STORY - 40 greatest astronomical discoveries
• Astronomers' biggest breakthroughs have lifted the veil on our universe. RICHARD TALCOT T
• 32 40 greatest mysteries of the universe
• Astronomers know more about the universe than ever but still have much to learn. SARAH SCOLES
• 38 Where will astronomy be in 40 years?
• The future involves larger collaborations, computers, and telescopes. DEBRA MELOY ELMEGREEN AND BRUCE G. ELMEGREEN
• 44 The Sky this Month
• Neptune's summer surge. MARTIN RATCLIFFE AND ALISTER LING
• 46 StarDome and Path of the Planets
• RICHARD TALCOTT; ILLUSTRATIONS BY ROEN KELLY
• 52 40 years of amateur astronomy
• We live in our hobby's golden age - just look at what's happened in the past four decades. MICHAEL E. BAKICH
• 58 Astronomy magazine's path to "stardom"
• From its modest beginnings, the publication now leads the astronomy hobby as the most
• popular magazine of its kind in the world. DAVID J. EICHER
• 68 Ask Astro
• Refracting light.
• 70 40 deep-sky targets in Sagittarius
• The Archer contains a dizzying variety of dazzling objects. MICHAEL E. BAKICH
• 72 Hunt down summer's best dark nebulae
• For a totally new observing experience, ignore the bright and aim for darkness. MICHAEL E. BAKICH
• 76 A backyard imager advances science
• An unexpected email opened the door for this astroimager. R. JAY GABANY
• 80 Prime time for Neptune and Uranus
• Late summer and early fall are the best times to track down the solar system's distant planets. RICHARD TALCOTT

COLUMNS :-

• Strange Universe BOB BERMAN 11
• Observing Basics GLENN CHAPLE 14
• Secret Sky STEPHEN JAMES O'MEARA 18
• Cosmic Imaging TONY HALLAS 24

QUANTUM GRAVITY :-

• Snapshot 9
• Breakthrough 10
• Astro News 12

IN EVERY ISSUE :-

• From the Editor 6
• Letters 11, 18,24
• New Products 84
• Web Talk 84
• Advertiser Index 87
• Reader Gallery 88
• Final Frontier 90

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Is the sun dying?

Without sun's existence, there wouldn't be life on Earth. In the grand scheme of things, however, our sun is simply another star among star among the other hundreds of billions of stars in the universe.Officially, the Sun is a class G2V star- in other words,a main-sequence yellow dwarf have a temperature range of 5,000 to 6,000 degrees Celsius and their mass is about 80-120 percent of the mass of the sun. That means that the Sun is one of the biggest yellow dwarfs in the group.

Like other yellow dwarfs, the Sun converts hydrogen to helium in its core through nuclear fusion,which generates massive amounts of energy and light.The Sun fuses about 620 million metric tons (683 million short tons) of hydrogen per sec. Based on the speed, astronomers believes that the sun is about halfway through its life cycle. About 40 percent of the hydrogen has been converted,leaving another 3 to 5 billion years before the Sun evolves into the next stage in its life cycle:a red giant.

 

But let's start at the beginning.The Sun formed approximately 4-5 billion years ago, at the same time as the rest of the solar system. At this time a spinning molecular cloud of dust, hydrogen and helium flattened out into a disk, With a gaseous sphere at its center that contained most of the mass.This sphere had a gravitational pull that attracted dust and other materials from the disk,which caused the sphere to compress until it begin converting the hydrogen to helium.A star-in this case, Our Sun-was born.

The Sun can't keep fusing hydrogen indefinitely, though - there's a finite supply. Nuclear fusion occurs in the Sun's core due to gravitational pressure, which heats the core to 15 million degrees (27 million degrees  Fahrenheit) and splits the hydrogen atoms.There's dedicates balance,known as 'hydrostatic' equilibrium 'between the inward compression exerted by gravity and the outward pressure from the energy created by nuclear reaction.As the Sun's hydrogen supply is used up,the nuclear fusion in its core will decrease, and the core will contract. The core will heat up to a temperature of 100 billion degrees Celsius and begin fusing helium into carbon.The outer layers of the Sun will expand as it become a red giant.This means that the Sun's radius will be 250 times larger than its current radius,and it will swallow the Earth.

       Astronomers once thought that because the Sun's gravitational pull will weaken when it becomes a red giant, the associated planetary movement outwards away from the Sun might spare our planet. However, the most recent projections show that Earth would likely still be in the outer layer of Sun,where it will be pulled in and vaporized.Even if the Earth itself is spared,astronomers still believe that the increasing heat from the Sun will eliminate life on Earth about one billion years from now.

Source - How it Works Book and Internet

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What are Saturn’s Rings Made Of?

Saturn's rings are made of billions of pieces of ice, dust and rocks. Some of these particles are as small as a grain of salt, while others are as big as houses. These chucks of rock and ice are thought to be pieces of comets, asteroids or even moons which were torn apart by the strong gravity of Saturn before they could reach the planet.

Galileo Galilei was the first to observe the rings of Saturn in 1610 using his telescope, but was unable to identify them as such.

Ring theory and observations

In 1655, Christiaan Huygens became the first person to suggest that Saturn was surrounded by a ring. Using a 50 power refracting telescope that he designed himself, far superior to those available to Galileo, Huygens observed Saturn and wrote that "It [Saturn] is surrounded by a thin, flat, ring, nowhere touching, inclined to the ecliptic" Robert Hooke was another early observer of the rings of Saturn, and noted the casting of shadows on the rings. 

In 1675, Giovanni Domenico Cassini determined that Saturn's ring was composed of multiple smaller rings with gaps between them; the largest of these gaps was later named the Cassini Division. This division is a 4,800 km-wide region between the A Ring and B Ring.

In 1787, Pierre-Simon Laplace suggested that the rings were composed of a large number of solid ringlets.

In 1859, James Clerk Maxwell demonstrated that the rings could not be solid or they would become unstable and break apart. He proposed that the rings must be composed of numerous small particles, all independently orbiting Saturn. Maxwell's theory was proven correct in 1895 through spectroscopic studies of the rings carried out by James Keeler of Allegheny Observatory.

The rings are named alphabetically in the order they were discovered. The main rings are, working outward from the planet, C, B and A, with the Cassini Division, the largest gap, separating Rings B and A. Several fainter rings were discovered more recently. The D Ring is exceedingly faint and closest to the planet. The narrow F Ring is just outside the A Ring. Beyond that are two far fainter rings named G and E. The rings show a tremendous amount of structure on all scales, some related to perturbations by Saturn's moons, but much unexplained.






Saturn is sometimes called the ”Jewel of the Solar System” because its ring system looks like a crown. The rings are well known, but often the question ”what are Saturn’s rings made of” arises. Those rings are made up of dust, rock, and ice accumulated from passing comets, meteorite impacts on Saturn’s moons, and the planet’s gravity pulling material from the moons. Some of the material in the ring system are as small as grains of sand, others are larger than tall buildings, while a few are up to a kilometer across. Deepening the mystery about the moons is the fact that each ring orbits at a different speed around the planet. 
 
Saturn is not the only planet with a ring system. All of the gas giants have rings, in fact. Saturn’s rings stand out because they are the largest and most vivid. The rings have a thickness of up to one kilometer and they span up to 482,000 km from the center of the planet.

Below is a list of the main rings and gaps between them along with distances from the center of the planet and their widths.

To view Image Right Click on Image and Select View Image

• The D ring is closest to the planet. It is at a distance of 66,970 – 74,490 km and has a width of 7,500 km.
• C ring is at a distance of 74,490 – 91,980 km and has a width of 17,500 km.
• Columbo Gap is at a distance of 77,800 km and has a width of 100 km.
• Maxwell Gap is at a distance of 87,500 km and has a width of 270 km.
• Bond Gap is at a distance of 88,690 – 88,720 km and has a width of 30 km.
• Dawes Gap is at a distance of 90,200 – 90,220 km and has a width 20 km.
• B ring is at a distance of 91,980 – 117,580 km with a width: 25,500 km.
• The Cassini Division sits at a distance of 117,500 – 122,050 km and has a width of 4,700 km.
• Huygens gap starts at 117,680 km and has a width of 285 km – 440 km.
• The Herschel Gap is at a distance of 118,183 – 118,285 km with a width of 102 km.
• Russell Gap is at a distance of 118,597 – 118,630 km and has a width of 33 km.
• Jeffreys Gap sits at a distance of 118,931 – 118,969 km with a width of 38 km.
• Kuiper Gap ranges from 119,403 -119,406 km giving it a width of 3 km.
• Leplace Gap is at a distance of 119,848 – 120,086 km and a width of 238 km.
• Bessel Gap is at 120,305 – 120,318 km with a width of 10 km.
• Barnard Gap is at a distance of 120,305 – 120,318 km giving it a width of 3 km.
• A ring is at a distance of 122,050 – 136,770 km with a width of 14,600 km.
• Encke Gap sits between 133,570-133,895 km for a width of 325 km.
• Keeler Gap is at a distance of 136,530-136,565 km with a width of 35 km.
• The Roche Division is at 136,770 – 139,380 km for a width 2600 km.
• F ring is begins at 140,224 km, but debate remains as to whether it is 30 or 500 km in width.
• G ring is between 166,000 – 174,000 km and has a width of 8,000 km.
• Finally, we get to the E ring. It is between 180,000 – 480,000 km giving it a width of 300,000 km.

As you can see, a great deal of observation has been dedicated to understanding and defining Saturn’s rings. Hopefully, having the answer to ”what are Saturn’s rings made of” will inspire you to look more deeply into the topic.

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How the Seasons Work?

It turns out that the elliptical orbit of the Earth has little effect on the seasons. Instead, it is the 23.45-degree tilt of the planet's rotational axis that causes us to have winter and summer.
The diagram below demonstrates what happens.

In this diagram, you can see the axis of rotation and the equator. The Northern Hemisphere (at the top) is currently experiencing winter, and the Southern Hemisphere is experiencing summer. By looking at how sunlight is landing on the planet in the diagram, you can clearly see two things:

• The Southern Hemisphere is getting about three times as much sunlight as the Northern Hemisphere.
• The North Pole is getting zero sunlight, which is why it experiences 24 hours of darkness in January.

That huge difference in the amount of sunlight reaching the ground in the different hemispheres is what causes the seasons.

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How do orbits work?

We might take it for granted, but why do stars, moons, planets or any celestial bodies constantly move around one another?

 What an Orbit Really Is

The drawings at the right simplify the physics of orbiting Earth. We see Earth with a huge, tall mountain rising from it. The mountain, as Isaac Newton first envisioned, has a cannon at the top. When the cannon is fired, the cannonball follows its ballistic arc, falling as a result of Earth's gravity, and it hits Earth some distance away from the mountain. If we put more gunpowder in the cannon, the next time it's fired, the cannonball goes halfway around the planet before it hits the ground. With still more gunpowder, the cannonball goes so far that it never touches down at all. It falls completely around Earth. It has achieved orbit.
If you were riding along with the cannonball, you would feel as if you were falling. The condition is called free fall. You'd find yourself falling at the same rate as the cannonball, which would appear to be floating there (falling) beside you. You'd never hit the ground. Notice that the cannonball has not escaped Earth's gravity, which is very much present -- it is causing the mass to fall. It just happens to be balanced out by the speed provided by the cannon.   

How do orbits work?

Although we don’t encounter orbits day to day, it’s common knowledge that in space, satellites, asteroids, moons, planets and even stars move around other celestial bodies in a seemingly perpetual dance. With the right conditions, anything will fall into orbit around Earth. But what are those conditions?

A terrestrial orbit is actually a freefall along the curve of the Earth’s gravity that never touches down. The basic physics is the same for any planet or star, no matter its size. For an Earth-like planet, if an object is at the right altitude so that the thinner atmosphere doesn’t drag too much – around 160 kilometres (99 miles) up – and the acceleration is enough – about 28,080 kilometres (17,450 miles) per hour – it will continue to tumble around the planet.

To put a satellite or shuttle into a circular ‘high’ orbit, the craft makes use of boosters to go from low orbit into a transfer orbit to achieve the required height, technically known as its apogee. Left to its own devices, the spacecraft would fall into an elliptical orbit, so an additional rocket motor called an ‘apogee kick’ (AKM) fires at the appropriate point. This gives the vessel the extra boost it needs to remain at that specific altitude in a high orbit.

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When does sky become space?

The Kármán line (Karman line) is an official boundary between the Earth’s atmosphere and space, lying 100km (approximately 62 miles) above sea level. The governing body for air sports and aeronautical world records, Federation Aeronautique Internationale (FAI), recognizes it as the Line where aeronautics ends and astronautics begins.   

The line was named after Theodore von Kármán, (1881–1963) a Hungarian-American engineer and physicist who was active primarily in the fields of aeronautics and astronautics. He first calculated that around this altitude the Earth's atmosphere becomes too thin for aeronautical purposes (because any vehicle at this altitude would have to travel faster than orbital velocity in order to derive sufficient aerodynamic lift from the atmosphere to support itself, neglecting centrifugal force). There is an abrupt increase in atmospheric temperature and interaction with solar radiation just below the line, which places the line within the greater thermosphere.

Thin air also explains why the Earth‘s sky looks blue and space is black. Atmospheric gases scatter blue light more than other colours, turning the sky blue. At higher altitudes, less air exists to scatter light.

Some people (including the FAI in some of their publications) also use the expression "edge of space" to refer to a region below the conventional 100 km boundary to space, which is often meant to include substantially lower regions as well. Thus, certain balloon or airplane flights might be described as "reaching the edge of space". In such statements, "reaching the edge of space" merely refers to going higher than average aeronautical vehicles commonly would.

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Astronomy - July 2013

The world's best-selling astronomy magazine offers you the most exciting, visually stunning, and timely coverage of the heavens above. Each monthly issue includes expert science reporting, vivid color photography, complete sky coverage, spot-on observing tips, informative telescope reviews, and much more! All this in an easy-to-understand, user-friendly style that's perfect for astronomers at any level.

• Hardcover: 80 pages
• File size: 27.2 MB   |  File Format: PDF

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Hardcover: 1622 pages

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Physics for Scientists and Engineers with Modern Physics (9th Ed)

Book Details:

• Hardcover: 1622 pages
• Publisher: Cengage Learning; 9 edition (January 17, 2013)
• Language: English
• ISBN-10: 1133954057
• ISBN-13: 978-1133954057
• File Size: 45.0 Mb | File Format: PDF

Book Description:
Achieve success in your physics course by making the most of what PHYSICS FOR SCIENTISTS AND ENGINEERS WITH MODERN PHYSICS has to offer. From a host of in-text features to a range of outstanding technology resources, you’ll have everything you need to understand the natural forces and principles of physics. Throughout every chapter, the authors have built in a wide range of examples, exercises, and illustrations that will help you understand the laws of physics AND succeed in your course!

Table of Contents

Part 1: Mechanics

Ch 1: Physics and Measurement
Ch 2: Motion in One Dimension
Ch 3: Vectors
Ch 4: Motion in Two Dimensions
Ch 5: The Laws of Motion
Ch 6: Circular Motion and Other Applications of Newton’s Laws
Ch 7: Energy of a System
Ch 8: Conservation of Energy
Ch 9: Linear Momentum and Collisions
Ch 10: Rotation of a Rigid Object About a Fixed Axis
Ch 11: Angular Momentum
Ch 12: Static Equilibrium and Elasticity
Ch 13: Universal Gravitation
Ch 14: Fluid Mechanics

Part 2: Oscillations and Mechanical Waves

Ch 15: Oscillatory Motion
Ch 16: Wave Motion
Ch 17: Sound Waves
Ch 18: Superposition and Standing Waves

Part 3: Thermodynamics

Ch 19: Temperature
Ch 20: The First Law of Thermodynamics
Ch 21: The Kinetic Theory of Gases
Ch 22: Heat Engines, Entropy, and the Second Law of Thermodynamics

Part 4: Electricity and Magnetism

Ch 23: Electric Fields
Ch 24: Gauss’s Law
Ch 25: Electric Potential
Ch 26: Capacitance and Dielectrics
Ch 27: Current and Resistance
Ch 28: Direct-Current Circuits
Ch 29: Magnetic Fields
Ch 30: Sources of the Magnetic Field
Ch 31: Faraday’s Law
Ch 32: Inductance
Ch 33: Alternating-Current Circuits
Ch 34: Electromagnetic Waves

Part 5: Light and Optics

Ch 35: The Nature of Light and the Principles of Ray Optics
Ch 36: Image Formation
Ch 37: Wave Optics
Ch 38: Diffraction Patterns and Polarization

Part 6: Modern Physics

Ch 39: Relativity
Ch 40: Introduction to Quantum Physics
Ch 41: Quantum Mechanics
Ch 42: Atomic Physics
Ch 43: Molecules and Solids
Ch 44: Nuclear Structure
Ch 45: Applications of Nuclear Physics
Ch 46: Particle Physics and Cosmology

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Time,Space,Stars and Man-The Story of the Big Bang

• Hardcover: 496 pages
• Publisher: World Scientific Publishing Company (April 2009)
• Language: English
• ISBN-10: 1848162723
• ISBN-13: 978-1848162723

Most well-read, but non-scientific, people will have heard of the term 'Big Bang' as a description of the origin of the Universe. They will recognize that DNA identifies individuals and will know that the origin of life is one of the great unsolved scientific mysteries. This book brings together all of that material. Starting with the creation of space and time - known as the Big Bang - the book traces causally related steps through the formation of matter, of stars and planets, the Earth itself, the evolution of the Earth's surface and atmosphere, and then through to the beginnings of life and the evolution of man. The material is presented in such a way that an intelligent non-scientist can comprehend it, without using formulae or equations but still preserving the integrity of the involved science.This book does not solve the mysteries of what initiated the Big Bang or how life evolved from inanimate matter, but it does make clear the nature of those problems. The reader will be left with a sense of wonderment that he or she actually exists!

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Space - From Earth to the Edge of the Universe

• Hardcover: 360 pages
• Publisher: DK Publishing (October 4, 2010)
• Language: English

Featuring a wealth of incredible astronomical photographs, Space is perfect for anyone interested in astronomy, space imagery, and the history of space exploration. Space takes us on an imaginary journey that starts on a launch pad, goes toward the center of our Solar System to see the inner planets and the Sun, and then flies outward past the outer planets and on to the fringes of the Solar System.

Space – From Earth to the Edge of the Universe by editors Carole Stott, Robert Dinwiddie, David Hughes and Giles Sparrow; Dorling Kindersley(DK) Publishing; New York, New York; $40.00 (hard cover); 2010.

Space is big…but so is this large format book. This is a captivating and nicely packaged volume that includes a wealth of space exploration and astronomical imagery.

The editors and senior art editors and designers clearly worked together here to pull together a picture-perfect look at the origins of human space exploits, current status, and the unknown unknowns awaiting discovery and investigation within the Universe at large.

Just the table of contents gives you an eyeful that will set you page turning. From launch pad Earth and our neighboring worlds to beyond the asteroid belt into a galaxy of stars and a universe of galaxies to the outer limits.

One thing that truly stands out in this book is not only how much exploration has been started, but also how much is ahead of us.

Right up front, the reader will find a quote from Stephen Hawking, world renowned cosmologist: “I don’t think the human race will survive the next thousand years, unless we spread into space.”

This volume will help you book your travel plans, be it to the Moon or Mars – or to help satisfy your hunger for deep space travel.

This over 350-page book comes complete with a very generous reference section and glossary.
But the real eye-catching value of this work is the layout and explanatory graphics and text. It’s laden with descriptive artwork that provides expert and novice alike a new appreciation for the complexities of astronomical surveys and human and robotic space exploration.

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Astronomy for Entertainment (by Yakov Perelman)

Astronomy is a fortunate science; it needs no embellishments, said the French savant Arago. So fascinating are its achievements that no special effort is needed to attract attention. Nonetheless, the science of the heavens is not only a collection of astonishing revelations and daring theories. Ordinary facts, things that happen, day by day, are its substance. Most laymen have, generally speaking, a rather hazy notion of this prosaic aspect of astronomy. They find it of little interest, for it is indeed hard to concentrate on what is always before the eye.

Everyday happenings in the sky are the contents of this book, free from professional terminology with easy reading. Its purpose is to initiate the reader into the basic facts of astronomy. Ordinary facts with which you may be acquainted are couched here in unexpected paradoxes, or slanted from an odd and unexpected angle solely to excite the imagination and quicken your interest. The daily aspect of the science of the skies, its beginnings, not later findings that mainly form the contents of Astronomy for Entertainment. The purpose of the book is to initiate the reader into the basic facts of astronomy. Ordinary facts with which you may be acquainted are couched here in unexpected paradoxes, or slanted from an odd and unexpected angle. The theme is, as far as possible, free from "terminology" and technical paraphernalia that so often make the reader shy of books on astronomy.

Books on popular science are often rebuked for not being sufficiently serious. In a way the rebuke is just, and support for it can be found (if one has in mind the exact natural sciences) in the tendency to avoid calculations in any shape or form. And yet the reader can really master his subject only by learing how to reckon, even though in a rudimentary fashion. Hence, both in Astronomy for Entertainment and in other books of this series, the aurhor has not attempted to avoid the simplest of calculations. True, he has taken care to present them in an easy form, well within the reach of all who have studied mathematics at school. It is his conviction that these exercises help not only retain the knowledge acquired; they are also a useful introduction to more serious reading.

This book contains chapters relating to the Earth, the Moon, planets, stars and gravitation. The author has concentated in the main on materials not usually discussed in works of this nature. Subjects omitted in the present book, will, he hopes, be treated in a second volume. The book, it should be said, makes no attempt to analyze in detail the rich content of modern astronomy.

Unfortunately Y. Perelman never wrote the continuation he had planned for this book, as untimely death in warbound Leningrad in 1942 interruped his labours.

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Clown Face Nebula (Eskimo Nebula)

A planetary nebula, also known as the Eskimo Nebula, in the constellation Gemini, position RA 07 h 29.2 m, dec. +20◦ 55 . It is bluish, 13" in diameter, and of ninth magnitude, with a tenth-magnitude central star. The bluegreen nebula’s hazy outer regions are thought to resemble an Eskimo’s hood or clown’s ruff.

The formation resembles a person's head surrounded by a parka hood. It is surrounded by gas that composed the outer layers of a Sun-like star. The visible inner filaments are ejected by a strong wind of particles from the central star. The outer disk contains unusual light-year long filaments.

 The nebula was discovered by William Herschel on January 17, 1787, in Slough, England. He described it as "A star 9th magnitude with a pretty bright middle, nebulosity equally dispersed all around.

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Gum Nebula discovered by C S Gum

Gum, Colin (1924–60) - Australian radioastronomer, mapped the southern sky for radio sources and emission nebulae, and discovered the Gum Nebula in the Vela Puppis region.

Gum Nebula - A very large, near-circular emission nebula, approximately 36◦ in diameter, in the constellations Puppis and Vela. The largest known nebula in the sky, it was discovered by the Australian astronomer C S Gum (1924–60), and is believed to be an ancient supernova remnant, with an age exceeding a million years. It is a convoluted mass of nebular wisps and loops, many of them very faint, but there are also numerous brighter parts. Its distance has been estimated at 1300 light-years, indicating that the nebulosity is approximately 840 light-years across. Within one of its brightest regions both the brightest-known Otype star ζ Puppis (spectral type O5f) and the brightest Wolf–Rayet star γ 2 Velorum (type WC8), are found. The much more recent Vela pulsar and supernova remnant also lie within the Gum Nebula, which for many years has rivalled the Crab Nebula in interest for astrophysicists.

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Crab Nebula

The Crab Nebula is a supernova remnant and pulsar wind nebula in the constellation of Taurus. Corresponding to a bright supernova recorded by Chinese astronomers in 1054, the nebula was observed later by John Bevis in 1731.

The Crab Nebula was first identified in 1731 by John Bevis. The nebula was independently rediscovered in 1758 by Charles Messier as he was observing a bright comet

It was named by Lord Rosse for its superficial resemblance to a crab. The Crab is 6 by 4 in extent and of eighth magnitude. Its outer regions consist of twisting filaments of hydrogen expelled by the supernova, appearing red on photographs and traveling outward at over 1000 km s−1. The inner region glows with the pale yellow light of synchrotron radiation triggered by electrons emitted by the Crab Pulsar at the center, the
core of the star that exploded as a supernova. This inner region makes the Crab Nebula the best-known example of a plerion—a supernova remnant with a ‘filled’ center. The Crab emits strongly in radio waves and x-rays.

• Distance to Earth: 6,523 light years
• Age: 1,000 years

At the center of the nebula lies the Crab Pulsar, a neutron star 28–30 km across, which emits pulses of radiation from gamma rays to radio waves with a spin rate of 30.2 times per second. The nebula was the first astronomical object identified with a historical supernova explosion.

At the centre of the Crab Nebula are two faint stars, one of which is the star responsible for the existence of the nebula. It was identified as such in 1942, when Rudolf Minkowski found that its optical spectrum was extremely unusual.The region around the star was found to be a strong source of radio waves in 1949and X-rays in 1963, and was identified as one of the brightest objects in the sky in gamma rays in 1967.Then, in 1968, the star was found to be emitting its radiation in rapid pulses, becoming one of the first pulsars to be discovered.

Pulsars are sources of powerful electromagnetic radiation, emitted in short and extremely regular pulses many times a second. They were a great mystery when discovered in 1967, and the team who identified the first one considered the possibility that it could be a signal from an advanced civilization.However, the discovery of a pulsating radio source in the centre of the Crab Nebula was strong evidence that pulsars were formed by supernova explosions. They now are understood to be rapidly rotating neutron stars, whose powerful magnetic field concentrates their radiation emissions into narrow beams.

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Orion Nebula Discovered by Christiaan Huygens

The Orion Nebula is a diffuse nebula situated south of Orion's Belt in the constellation of Orion. It is seen as the middle "star" in the sword of Orion, which are the three stars located south of Orion's Belt. It is one of the brightest nebulae, and is visible to the naked eye in the night sky. There are supersonic "bullets" of gas piercing the hydrogen clouds of the Orion Nebula. Each bullet is ten times the diameter of Pluto's orbit and tipped with iron atoms glowing bright blue. They were probably formed one thousand years ago from an unknown violent event.

The Orion Nebula is an example of a stellar nursery (A spiral galaxy like the Milky Way contains stars, stellar remnants , and a diffuse interstellar medium of gas and dust.) where new stars are being born. Observations of the nebula have revealed approximately 700 stars in various stages of formation within the nebula.

• Distance to Earth: 1,344 light years
• Age: 3 million years 

 

 
The red hue is well-understood to be caused by Hα (H-alpha (Hα) is a specific red visible spectral line in the Balmer series created by hydrogen with a wavelength of 656.28 nm, which occurs when a hydrogen electron falls from its third to second lowest energy level) recombination line radiation at a wavelength of 656.3 nm. The blue-violet coloration is the reflected radiation from the massive O-class(Most stars are currently classified using the letters O, B, A, F, G, K, and M, where O stars are the hottest and the letter sequence indicates successively cooler stars up to the coolest M class) stars at the core of the nebula.

Interstellar clouds like the Orion Nebula are found throughout galaxies such as the Milky Way. They begin as gravitationally bound blobs of cold, neutral hydrogen, intermixed with traces of other elements. The cloud can contain hundreds of thousands of solar masses and extend for hundreds of light years. The tiny force of gravity that could compel the cloud to collapse is counterbalanced by the very faint pressure of the gas in the cloud.

Whether due to collisions with a spiral arm, or through the shock wave emitted from supernovae, the atoms are precipitated into heavier molecules and the result is a molecular cloud. This presages the formation of stars within the cloud, usually thought to be within a period of 10-30 million years, as regions pass the Jeans mass and the destabilized volumes collapse into disks. The disk concentrates at the core to form a star, which may be surrounded by a protoplanetary disk. This is the current stage of evolution of the nebula, with additional stars still forming from the collapsing molecular cloud. The youngest and brightest stars we now see in the Orion Nebula are thought to be less than 300,000 years old, and the brightest may be only 10,000 years in age.

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Horsehead Nebula discover by Williamina Fleming

The Horse Head Nebula (also known as Barnard 33 in bright nebula IC 434) takes its name from the horse head shape in its middle. The first human to discover it was Williamina Fleming in 1888 at Harvard University. It is one of the most identifiable nebulae because of the shape of its swirling cloud of dark dust and gases, which bears some semblance to a horse's head when viewed from Earth.

The Horsehead Nebula is a dark nebula in the constellation Orion. The nebula is located just to the south of the star Alnitak, which is farthest east on Orion's Belt, and is part of the much larger Orion Molecular Cloud Complex.

• Constellation: Orion
• Distance to Earth:1,500 light-years

The red glow originates from hydrogen gas predominantly (Mainly) behind the nebula, ionized by the nearby bright star Sigma Orionis. The darkness of the Horsehead is caused mostly by thick dust, although the lower part of the Horsehead's neck casts a shadow to the left. Streams of gas leaving the nebula are funneled by a strong magnetic field. Bright spots in the Horsehead Nebula's base are young stars just in the process of forming.

 The nebula is a favorite target for amateur and professional astronomers. It is shadowy in optical light. It appears transparent and ethereal when seen at infrared wavelengths. The rich tapestry of the Horsehead Nebula pops out against the backdrop of Milky Way stars and distant galaxies that easily are visible in infrared light.

                                                                             The nebula is part of the Orion Molecular Cloud, located about 1,500 light-years away in the constellation Orion. The cloud also contains other well-known objects such as the Great Orion Nebula (M42), the Flame Nebula, and Barnard's Loop. It is one of the nearest and most easily photographed regions in which massive stars are being formed.

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