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American Association of Variable Star Observers

American Association of Variable Star Observers
Related:  Astronomy&Astrophysics

How the Sun Shines by John N. Bahcall* What makes the sun shine? How does the sun produce the vast amount of energy necessary to support life on earth? These questions challenged scientists for a hundred and fifty years, beginning in the middle of the nineteenth century. Theoretical physicists battled geologists and evolutionary biologists in a heated controversy over who had the correct answer. Why was there so much fuss about this scientific puzzle? The sun's rays are the ultimate source of almost every motion which takes place on the surface of the earth. In this essay, we shall review from an historical perspective the development of our understanding of how the sun (the nearest star) shines, beginning in the following section with the nineteenth-century controversy over the age of the sun. The Age of the Sun How old is the sun? The older the sun is, the greater the total amount of radiated solar energy. Conflicting Estimates of the Solar Age Who Was Right? What was wrong with Kelvin's analysis? F.W.

Cosmigraphics: Picturing Space Through Time in 4,000 Years of Mapping the Universe Long before Galileo pioneered the telescope, antagonizing the church and unleashing a “hummingbird effect” of innovation, humanity had been busy cataloging the heavens through millennia of imaginative speculative maps of the cosmos. We have always sought to make visible the invisible forces we long to understand, the mercy and miracle of existence, and nothing beckons to us with more intense allure than the majesty and mystery of the universe. Four millennia of that mesmerism-made-visible is what journalist, photographer, and astrovisualization scholar Michael Benson explores with great dedication and discernment in Cosmigraphics: Picturing Space Through Time (public library) — a pictorial catalog of our quest to order the cosmos and grasp our place in it, a sensemaking process defined by what Benson aptly calls our “gradually dawning, forever incomplete situational awareness.” Contemporary thought is endangered by the picture of nature drawn by science.

If A Primordial Black Hole Hits The Sun...  Astronomers have so far discovered two types of black hole: supermassive ones at the centre of galaxies and stellar-mass black holes, which form when giant stars die. But there’s no reason why black holes of any size cannot form. In fact, many astronomers think that the variations in density in the early universe would have led to the natural formation of relatively small black holes. The smallest of these ought to have evaporated by now. Various theorists have suggested that we could spot primordial black holes by phenomena such as lensing effects as they pass in front of distant stars or by the gamma ray bursts they create as they flicker out of existence. Now Michael Kesden at New York University and Shravan Hanasoge at Princeton University in New Jersey say that the effect of a primordial black hole hitting the Sun ought to be easily observable. Such an event wouldn’t be as catastrophic as it sounds. That should generate a scramble.

Time delay The Astrophysical Journal, 521:L45-L48, 1999 August 10 © 1999. The American Astronomical Society. All rights reserved. Printed in U.S.A. A Method of Mass Measurement in Black Hole Binaries using Timing and High-Resolution X-Ray Spectroscopy A. Received 1999 April 21; accepted 1999 June 10; published 1999 June 28 In X-ray binaries, several percent of the compact object luminosity is intercepted by the surface of the normal companion and reradiated through Compton reflection and the K fluorescence. line and above the K edge of neutral iron. 106 s observation by a telescope with a 1000 cm2 effective area near 6.4 keV and with a 5 eV energy resolution. Subject headings: binaries: spectroscopic; X-rays: general; X-rays: stars The existence of stellar-mass black holes in our Galaxy is almost exclusively established by measuring the mass of the compact object in several bright X-ray binaries. is unstable and should collapse to form a black hole (Rhoades & Ruffini 1974; Chitre & Hartle 1976). is 2(c

A supermassive star, all alone A visible/infrared composite view of the Tarantula, with VFTS 682 at its centre. (Image: ESO/M.-R. The Tarantula Nebula is a gift that keeps on giving – if you’re into really massive stars, that is. Some of the region’s clusters contain the most massive stars we know today. The most massive stars form almost exclusively in clusters, as the clouds they form out of have to be so massive that many smaller stars are inevitably born in the process. Some scientists even propose that the combined winds from supermassive clusters like R136 could even be responsible for blasting heavy elements out of their galaxies entirely, into the intergalactic medium. The newly discovered behemoth star , named VFTS 682, is around a million times more luminous than the Sun, and around 150 times as massive. Our current modes of how massive stars form have no way of explaining the formation of a 150 solar star all on its own. References Joachim M. Norman Murray, Brice Ménard, & Todd A.

The Fundamentals of Stellar Astrophysics (by G.W. Collins II) Web Edition by G.W. Collins II Preface to the (2003) WEB Edition One may justifiability wonder why anyone would take the time to put a decade-old book on astrophysics on the WEB. Several events of the past few months have led me to believe that may well be some who wish to learn about the basics of stellar structure. The reader will notice that all the recommended reading is to books published prior to 1987. While I have been able to correct the errors resulting from the first production of the book, I am sure new ones have materialized during its regeneration. I have resisted the temptation to update the material since that would have been a monumental task approaching the original generation of the book itself with little increase in the reader’s depth of understanding. While the copyright for ISBN# 7176-1993-2) was returned to me by W.H. George W. Case Western Reserve University January 2003 Table of Contents

'Zombie' stars "Zombie" stars that explode like bombs as they die, only to revive by sucking matter out of other stars. According to an astrophysicist at UC Santa Barbara, this isn't the plot for the latest 3D blockbuster movie. Instead, it's something that happens every day in the universe - something that can be used to measure dark energy. This special category of stars, known as Type Ia supernovae, help to probe the mystery of dark energy, which scientists believe is related to the expansion of the universe. Andy Howell, adjunct professor of physics at UCSB and staff scientist at Las Cumbres Observatory Global Telescope (LCOGT), wrote a review article about this topic, published recently in Nature Communications. LCOGT, a privately funded global network of telescopes, works closely with UCSB. Supernovae are stars that have been observed since 1054 A.D., when an exploding star formed the crab nebula, a supernova remnant. "That's what our sun will be at the end of its life," he said.

Modified Julian Day Converter This converter requires the use of Javascript enabled and capable browsers. There are two converters in this script, the first converting from MJD to MM-DD-YYYY in the modern Gregorian calendar format. The second converts from the MM-DD-YYYY format to the MJD number. Modified Julian Date, MJD, is a modification of the Julian Date that is routinely used by astronomers, geodesists, scientists, financiers, and even some historians. Truncated Julian Date, TJD, is a truncated form of MJD.

“Impossible” Star Exists in Cosmic Forbidden Zone Want to stay on top of all the space news? Follow @universetoday on Twitter This ancient star, in the constellation of Leo (The Lion), is called SDSS J102915+172927 and has been found to have the lowest amount of elements heavier than helium of all stars yet studied. It has a mass smaller than that of the Sun and is probably more than 13 billion years old. Astronomers say a newly found star should not exist and is in the “forbidden zone” of a widely accepted theory of star formation. “A widely accepted theory predicts that stars like this, with low mass and extremely low quantities of metals, shouldn’t exist because the clouds of material from which they formed could never have condensed,” said Elisabetta Caffau (Zentrum für Astronomie der Universität Heidelberg, Germany and Observatoire de Paris, France), lead author of the paper appearing in this week’s edition of Nature. The team found the star with the X-shooter and UVES instruments on the Very Large Telescope. Source: ESO

Mario A. Jimenez I am an X-ray astrophysicist. I am interested in a mixture of experimental development work (X-ray optics for telescopes), observations with X-ray telescopes (X-ray spectroscopy of compact objects), and theory (numerical modeling of accretion disks around neutron stars and black holes). Here is a quick list of my interests: "Atomic X-ray Spectra of Accretion Disk Atmospheres around Kerr Black Holes," Jimenez-Garate, M.A., Raymond, J. C., Mauche, C. "Identification of an Extended Accretion Disk Corona in the Hercules X-1 Low State: Moderate Optical Depth, Precise Density Determination, and Verification of CNO Abundances," Jimenez-Garate, M. "Discrete X-Ray Signatures of a Photoionized Plasma above the Accretion Disk of the Neutron Star EXO 0748-676," Jimenez-Garate, M. "Thermal Forming of Glass Microsheets for X-ray Telescope Mirror Segments," Jimenez-Garate, M. "X-ray line emission from evaporating and condensing accretion disk atmospheres," Jimenez-Garate, M.