Het Astronomie Topic #9

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Dit zijn de spectaculairste ruimtefoto's van afgelopen jaar

18 september wordt bekendgemaakt wie de astrofotograaf van 2013 is. In deze fotospecial zijn de spectaculaire foto's te zien van de genomineerden. Ook de Nederlandse fotograaf André van der Hoeven is genomineerd. De winnende foto's zijn vanaf 19 september te zien in het Koninklijk Observatorium van Greenwich te zien in Londen.

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Zesvoudige zwaartekrachtslens van quasar ontdekt

Een groep natuurkundestudenten van het Deense Niels Bohr Instituut heeft een quasar ontdekt, 11 miljard lichtjaar van de aarde verwijderd, waarvan het licht door een tussen de quasar en de aarde gelegen cluster van sterrenstelsels maar liefst zes keer is verbogen.

Die verbuiging heet een zwaartekrachtslens en is bijna honderd jaar geleden al door Albert Einstein voorspeld. Door het effect wordt het ene beeld van het verst verwijderde object meerdere keren verbogen en ontstaan extra beelden, meestal twee, drie of vier beelden. Maar nu hebben de vier studenten Anders Nielsen, Mikkel Kristensen, Mikkel Lindholmer en Thejs Brinckmann eentje ontdekt die zes keer is afgebeeld – op de afbeelding hierboven te zien als de objecten A, B, C, D, WD en Arc, G1 t/m G3 zijn delen van de cluster van sterrenstelsels op de voorgrond, genaamd SDSS J2222+2745.

De studenten hebben de quasar bestudeerd met behulp van de 2,56 m Nordic Optical Telescope (NOT) op het eiland La Palma. Door het licht van drie van de beelden tot spectra uiteen te rafelen, konden ze vaststellen dat ze één en dezelfde quasar lieten zien.

Hubble finds source of Magellanic Stream - Astronomers explore origin of gas ribbon wrapped around our galaxy [heic1314]

08 August 2013
Astronomers using the NASA/ESA Hubble Space Telescope have solved the 40-year-old mystery of the origin of the Magellanic Stream, a long ribbon of gas stretching nearly halfway around the Milky Way. New Hubble observations reveal that most of this stream was stripped from the Small Magellanic Cloud some two billion years ago, with a smaller portion originating more recently from its larger neighbour.

The Magellanic Clouds, two dwarf galaxies orbiting our galaxy, are at the head of a huge gaseous filament known as the Magellanic Stream. Since the Stream's discovery in the early 1970s, astronomers have wondered whether this gas comes from one or both of the satellite galaxies. Now, new Hubble observations show that most of the gas was stripped from the Small Magellanic Cloud about two billion years ago – but surprisingly, a second region of the stream was formed more recently from the Large Magellanic Cloud.

A team of astronomers determined the source of the gas filament by using Hubble's Cosmic Origins Spectrograph (COS), along with observations from ESO's Very Large Telescope, to measure the abundances [1] of heavy elements, such as oxygen and sulphur, at six locations along the Magellanic Stream. COS detected these elements from the way they absorb the ultraviolet light released by faraway quasars as it passes through the foreground Stream. Quasars are the brilliant cores of active galaxies.

The team found low abundances of oxygen and sulphur along most of the stream, matching the levels in the Small Magellanic Cloud about two billion years ago, when the gaseous ribbon was thought to have been formed.

In a surprising twist, the team discovered a much higher level of sulphur in a region closer to the Magellanic Clouds. "We're finding a consistent amount of heavy elements in the stream until we get very close to the Magellanic Clouds, and then the heavy element levels go up," says Andrew Fox, a staff member supported by ESA at the Space Telescope Science Institute, USA, and lead author of one of two new papers reporting these results. "This inner region is very similar in composition to the Large Magellanic Cloud, suggesting it was ripped out of that galaxy more recently."

This discovery was unexpected; computer models of the Stream predicted that the gas came entirely out of the Small Magellanic Cloud, which has a weaker gravitational pull than its more massive cousin.

"As Earth's atmosphere absorbs ultraviolet light, it's hard to measure the amounts of these elements accurately, as you need to look in the ultraviolet part of the spectrum to see them," says Philipp Richter of the University of Potsdam, Germany, and lead author on the second of the two papers. "So you have to go to space. Only Hubble is capable of taking measurements like these."

All of the Milky Way's nearby satellite galaxies have lost most of their gas content – except the Magellanic Clouds. As they are more massive than these other satellites they can cling on to this gas, using it to form new stars. However, these Clouds are approaching the Milky Way and its halo of hot gas. As they drift closer to us, the pressure of this hot halo pushes their gas out into space. This process, together with the gravitational tug-of-war between the two Magellanic Clouds, is thought to have formed the Magellanic Stream [2].

"Exploring the origin of such a large stream of gas so close to the Milky Way is important," adds Fox. "We now know which of our famous neighbours, the Magellanic Clouds, created this gas ribbon, which may eventually fall onto our own galaxy and spark new star formation. It's an important step forward in figuring out how galaxies obtain gas and form new stars."

Notes

[1] The "abundance" of an element is a measure of how common it is in its environment relative to other elements.

[2] The Magellanic Clouds can be used as a good testing ground for theories on how galaxies strip gas from one another and form new stars. This process seems episodic rather than smooth, without a continuous, slow stream of gas being stripped away from a small galaxy by a larger one. As both of the Magellanic Clouds are approaching our own galaxy, the Milky Way, they can be used to explore the dynamics of this process.
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Earth in crossfire on NASA hazardous asteroid map

Earth is near the center of a tangled mass of potentially hazardous asteroids. But there's little to worry about.


^{The orbits of all known Potentially Hazardous Asteroids (PHAs) as of early 2013 are shown here. But none are worrisome threats over the next century.
(Credit: NASA/JPL-Caltech)}

If you've been watching the skies for the spectacle of the Perseid meteor shower over the past few days, you've probably thought about some of the larger rocks up above.

A few are downright scary compared to shooting stars. This graphic from NASA shows the orbits of more than 1,400 Potentially Hazardous Asteroids (PHAs), objects measuring at least 460 feet across that come within 4.7 million miles of Earth's orbit.

It looks like a giant Spirograph drawing with Earth near the center, but NASA assures us that these giant boulders of rock and ice are not "a worrisome threat" over the next 100 years.

Of course, 4.7 million miles is really, really far away -- about 20 times the distance to the moon. But not all PHAs have been found. As one looks further into the future, the orbits of known PHAs become less predictable.

"By continuing to observe and track these asteroids, their orbits can be refined and more precise predictions made of their future close approaches and impact probabilities," NASA's Jet Propulsion Laboratory reported on its Photojournal page.

The recent discovery of the 10,000th near-Earth object (NEO) highlighted that there are a lot of marbles zooming around up there. NEOs are defined as objects approaching the Earth's orbital distance to within some 28 million miles.

Of greatest concern are the roughly 900 near-Earth asteroids that are at least 1 kilometer (0.62 miles) across. Judging by studies of mass-extinction events of the past, an impact by one of these could be a real bummer.

On NASA's NEO Program Sentry Risk Table of more than 400 near-Earth asteroids, only one is flagged as a yawn-inducing green on the Torino Impact Hazard Scale.

The asteroid known as 2007 VK184 is believed to be about 430 feet across and presents an unlikely chance of hitting us in 2048. Further observations likely will reduce that chance to zero.

But the threat of a big hit has prompted some scientists to hatch plans to deflect or destroy dangerous space rocks by using everything from nuclear weapons to huge laser guns.

What do you think? Do asteroids concern you? Or is the danger far too miniscule to care about?

Bright Nova Discovered in The Constellation Delphinus Visible To Unaided Eye



A star is shedding it’s material for all to see in a classic nova, which may be a rare event for one living on a planet. The nova is high up in the evening sky and visible to the unaided eye. Reports today indicate it is still brightening. How bright will it get? No one knows for sure but it is exciting.

Not much changes in astronomy. We see the same planets, stars, and deep-sky objects all the time. It can get boring to many. However, when things such as novas happen they become a treat to all who witness it. Try to locate it using the charts included in this article.

A classical nova happens in a special kind of tightly-orbiting binary star system: one where a relatively normal star pours a stream of hydrogen onto the surface of a companion white dwarf. When the layer of fresh hydrogen on the white dwarf’s surface grows thick and dense enough, the bottom of the layer explodes in a runaway hydrogen-fusion reaction — a hydrogen bomb in the shape of a thin shell roughly the size of Earth. The underlying white dwarf remains intact, and as new hydrogen builds up, the process may repeat in a few years to tens of thousands of years.

The nova was discovered by Japanese astronomer Koichi Itagaki of Yamagata, Japan.

[ Bericht 100% gewijzigd door Patriance op 17-08-2013 14:46:07 ]

Eleven Spacecraft Show Interstellar Wind Changed Direction Over 40 Years

<sup>by Karen C. Fox for Goddard Space Flight Center
Greenbelt, MD (SPX) Sep 10, 2013


The solar system moves through a local galactic cloud at a speed of 50,000 miles per hour,
creating an interstellar wind of particles, some of which can travel all the way toward
earth to provide information about our neighborhood.
Image Credit: NASA/Adler/U. Chicago/Wesleyan.</sup>

Like the wind adjusting course in the middle of a storm, scientists have discovered that the particles streaming into the solar system from interstellar space have most likely changed direction over the last 40 years. Such information can help us map out our place within the galaxy surrounding us, and help us understand our place in space.

The results, based on data spanning four decades from 11 different spacecraft, were published in Science.

Vestiges of the interstellar wind flowing into what's called the heliosphere -- the vast bubble filled by the sun's own constant flow of particles, the solar wind - is one of the ways scientists can observe what lies just outside of our own home, in the galactic cloud through which the solar system travels.

The heliosphere is situated near the inside edge of an interstellar cloud and the two move past each other at a velocity of 50,000 miles per hour. This motion creates a wind of neutral interstellar atoms blowing past Earth, of which helium is the easiest to measure.

"Because the sun is moving though this cloud, interstellar atoms penetrate into the solar system," said Priscilla Frisch, an astrophysicist at the University of Chicago, Ill. and the lead author on the paper.

"The charged particles in the interstellar wind don't do a good job of reaching the inner solar system, but many of the atoms in the wind are neutral. These can penetrate close to Earth and can be measured."

Frisch became interested in this subject when results in January 2012 from NASA's Interstellar Boundary Explorer, or IBEX, showed that the interstellar wind was entering the heliosphere from a slightly different direction than had been observed by NASA's Ulysses mission in the 1990s.

Frisch and her colleagues set out to gather as much evidence from as many sources as they could to determine whether the newer instruments simply provided more accurate results, or whether the wind direction itself changed over the years.

The earliest historical data on the interstellar wind comes from the 1970s from the U.S. Department of Defense's Space Test Program 72-1 and SOLRAD 11B, NASA's Mariner, and the Soviet Prognoz 6. While instruments have improved since the 1970s, comparing information from several sets of observations helped the researchers gain confidence in results from that early data.

The team went on to look at another seven data sets including the Ulysses information from 1990 to 2001, and more recent data from IBEX, as well as four other NASA missions: the Solar Terrestrial Relations Observatory, or STEREO, the Advanced Composition Explorer, or ACE, the Extreme Ultraviolet Explorer, and the MErcury Surface, Space ENvironment, GEochemistry, and Ranging mission, or MESSENGER, currently in orbit around Mercury. The eleventh set of observations came from the Japanese Aerospace Exploration Agency's Nuzomi.

"The direction of the wind obtained from the most recent data does not agree with the direction obtained from the earlier measurements, suggesting that the wind itself has changed over time," said Eric Christian, the IBEX mission scientist at NASA's Goddard Space Flight Center in Greenbelt, Md. "It's an intriguing result, which relied on looking at a suite of data measured in a bunch of different ways."

The various sets of observations relied on three different methods to measure the incoming interstellar wind. IBEX and Ulysses directly measure neutral helium atoms as they coursed through the inner solar system. IBEX's measurements are made close to Earth, while Ulysses' measurements reach out to the orbit of Jupiter.

The earliest measurements in the 1970s observed fluorescence that occurs when the extreme ultraviolet radiation coming from the sun scatters off the interstellar helium wind passing by the sun. Neutral helium atoms get caught by the sun's gravity, forming a focusing cone. As radiation from the sun bounces off these atoms, they give off light. Measuring the light provides information about the helium inflow direction.

The third technique to measure the helium wind relies on the fact that after this interaction with the sun's radiation, a fraction of neutral helium atoms gain an electron, and thus become charged. Many instruments in space are geared to study charged particles, such as instruments on NASA's STEREO and ACE. Such instruments can measure the longitudinal direction of the particle wind, providing one last set of historical observations to round out the picture.

The data from these diverse sources shows that the direction of the interstellar wind has changed some 4 to 9 degrees over the last 40 years.

"Previously we thought the local interstellar medium was very constant, but these results show that it is highly dynamic, as is the heliosphere's interaction with it," said David McComas, IBEX principal investigator at Southwest Research Institute in San Antonio, Texas.

While the reason for - and, indeed, the exact timing of - the shift is still unclear, Frisch pointed out that scientists know our solar system is close to the edge of the local interstellar cloud. Such an area of the galaxy might experience turbulence, and as we hurtle through space, the heliosphere could be exposed to different directions of wind.

While the scientists don't yet know for sure how the direction switch happened, the team believes that additional observations should ultimately explain its cause, giving us even more information about the galaxy that surrounds us.

http://www.nu.nl/wetensch(...)at-zonnestelsel.html

Ruimtesonde Voyager 1 verlaat ons zonnestelsel
De Amerikaanse ruimtesonde Voyager 1 heeft na 36 jaar vliegen ons zonnestelsel verlaten.

Foto: AFP/NASA/JPL-Caltech
Het is de eerste keer in de geschiedenis dat een bouwsel van de mens die grens overgaat en terechtkomt in de eindeloze ruimte tussen de sterren. Het historische moment gebeurde in augustus vorig jaar.
Dat heeft de Amerikaanse ruimtevaartorganisatie NASA donderdag bekendgemaakt. Het nieuws staat donderdag ook in het gezaghebbende wetenschapsblad Science.
Eerder dit jaar meldden wetenschappers ook al dat de Voyager 1 buiten het zonnestelsel was beland, maar dat werd toen nog afgezwakt door de Amerikaanse ruimtevaartorganisatie NASA.
De Voyager 1 vliegt op ongeveer 18,8 miljard kilometer van de aarde. Omdat de mens daar nog nooit is geweest, wisten de wetenschappers niet hoe het gebied eruitziet en wat ze moesten verwachten. Bepalen waar de Voyager 1 precies was, was dan ook erg ingewikkeld.
Plasmadeeltjes
Voor het definitieve bewijs kregen de wetenschappers hulp van de zon. Die slingerde in maart 2012 een enorme hoeveelheid plasmadeeltjes de ruimte in. Die zogeheten plasmawolk kwam 13 maanden later, in april van dit jaar, aan bij de Voyager 1. Uit metingen bleek dat de plasmawolk bij de sonde veel dikker was dan wat er eerder was gemeten aan de rand van ons zonnestelsel. Dat betekende dat de Voyager was aangekomen in een eindeloos gebied dat het interstellaire medium wordt genoemd.
Toen de wetenschappers oudere gegevens terugkeken, zagen ze dat dat vorig jaar ook al was gemeten. Op basis daarvan rekenden ze uit dat de Voyager 1 in augustus 2012 het zonnestelsel verliet.
De Voyager 1 is in 1977 gelanceerd. Na anderhalf jaar vloog het vaartuig langs de planeet Jupiter. Weer anderhalf jaar later bereikte de sonde de planeet Saturnus. In 2004 kwam hij in de buitenste schil van ons zonnestelsel terecht.
Tweelingbroer
De sonde vliegt met een snelheid van ongeveer 17 kilometer per seconde. Waarschijnlijk heeft hij nog genoeg stroom om te blijven werken tot 2025, 48 jaar na de lancering. Over ongeveer 40.000 jaar bereikt de Voyager 1 de dichtstbijzijnde ster.
Kort voor de Voyager 1 was zijn tweelingbroer gelanceerd, de Voyager 2. Die staat nu op 15,3 miljard kilometer van de aarde. Ook de Voyager 2 werkt nog altijd.

De mooiste foto's van het heelal

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Op zaterdag 14 september 2013 13:05 schreef Perrin het volgende:
De mooiste foto's van het heelal

[ afbeelding ]

machtig thanx

Mars kopen !!!!

Heeft iemand de ruimtevaart expo die momenteel in de jaarbeurs in Utrecht plaatsvindt al bezocht?

Is het de moeite waard en hoelang duurt het ongeveer om het meeste te kunnen zien?

Ja, ik heb hem bekeken. Best mooi! Volgens mij ben ik er 3 uur geweest ofzo.

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Op zaterdag 21 september 2013 09:15 schreef ExperimentalFrentalMental het volgende:
De meeste astronomen denken dat het universum in korte tijd extreem uitdijde, tot het ongeveer zijn huidige afmetingen had.

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De meeste astronomen denken dat het universum in korte tijd extreem uitdijde, tot het ongeveer zijn huidige afmetingen had.

Dat snap ik niet? Het heelal deed al zoveel miljard jaar uit?

Hoe snel gaat dat uitdijen eigenlijk?