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Archive Astronomy Questions of the Week - International Year of Astronomy 2009
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How old is the Universe?

Week 52
The International Year of Astronomy 2009 (IYA) is coming to an end. The German Aerospace Center (DLR) celebrated IYA with exhibition 'Out of this World – Wonders of the Solar System' in the Gasometer Oberhausen and the 'Astronomy Question of the Week'. Once a week, DLR experts answered a question. Many interested parties took the opportunity to use the special IYA website to ask questions. The final Astronomy Question of the Week is: "How old is the universe?"
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Why is it dark at night?

Week 51
Just like being in a large forest, where in every direction and in our entire field of vision we can see trees that are either somewhat closer or further away, in a Universe that is infinite and filled evenly with stars or galaxies, we would have to see a star in every direction, sooner or later. The night sky should actually gleam as brightly as the surface of the Sun. But why doesn't this happen?
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Where are the nearest islands of stars?

Week 50
Earth's home galaxy, the Milky Way, consists of more than 100 billion stars and its spiral arms extend across 100,000 light-years. As if these were not already virtually inconceivable numbers for humans, the Milky Way is only one galaxy among billions that can be seen in the visible Universe using modern telescopes.
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Black hole

How is a black hole discovered?

Week 49
Black holes are astrophysical objects with an almost unbelievably high mass per unit volume. Within a certain distance from the black hole this warping of space is so strong that absolutely no light or any other radiation can leave. Therefore, black holes cannot be observed. So how do astrophysicists know that they exist?
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Is there a photograph of the universe?

Week 48
The concept of 'universe' means the totality of all things, including space and time. So, logically, there can be no 'outside' to the universe from which a photograph of it could be taken. However, the famous Hubble Ultra Deep Field image gives a glimpse of its most distant parts.
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Sonnenfinsternis vom Mond aus gesehen

What happens on the Moon during a lunar eclipse?

Week 47
Today, solar eclipses are seen as a fascinating natural phenomenon. In the past, people saw them as something threatening, because the Sun is a source of light and heat which life on Earth depends on. There are also lunar eclipses. What actually happens on the Moon during such an event?
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What are shooting stars?

Week 46
A bright line of light appears across the night sky – and popular wisdom would have us believe that any person witnessing a shooting star is entitled to make a wish. With eyes closed, that person must then make their wish, but not tell anyone else what it is. Science also takes an interest in these optical phenomena in the atmosphere, and calls them meteors.
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Voyager and Pioneer

How far into outer space have space probes penetrated?

Week 45
Outer space, a place of enormous distances: for more than 30 years, unmanned spacecraft have journeyed to learn more about the depths of space, its planets and the nature of interplanetary space. Now, billions of kilometres from Earth, space probes are entering areas never before explored by humankind.
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When did the first German satellite go into space?

Week 44
The first German satellite, AZUR, was launched 40 years ago. On 8 November 1969 at 02:52 Central European Time (CET), which was 7 November at 17:52 Pacific Standard Time (PST), a four-stage American Scout-B rocket took off from the launch site at Vandenberg Air Force Base in California – with Germany's first scientific spacecraft on board.
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What happens when stars play hide-and-seek?

Week 43
Astronomers know the answer and would therefore have been able to answer the One-Million-Euro question in the 250th episode of Günter Jauch's hit TV show 'Wer wird Millionär?' (Who wants to be a millionaire?): What is an eclipsing binary?
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Simplified Hertzsprung-Russell Diagram (HRD)

What does the 'family tree' of stars look like?

Week 42
Not all of the stars in the Universe are the same – differences in brightness and colour can be recognised even with the naked eye. In the 19th century, star spectroscopy developed into an important method of analysis in astronomy. With its aid, astronomers were able to divide the stars into what are known as spectral classes.
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How do we know that planets exist outside our Solar System?

Week 41
Even in ancient times, people observed the planets that orbit our Sun. Nowadays we know that there are many trillions of other stars in the Universe. It seems likely that planets orbit many of these stars too. The evidence that extrasolar planets exist was obtained for the first time in the 1990s. However, these planets are small, non-luminous bodies that are light years away – how are we able to prove that they exist?
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Das Sonnensystem

Why is Pluto no longer a planet?

Week 40
It happened on 24 August 2006: instead of the nine planets it had up to that time, our Solar System suddenly had only eight – the planet Pluto was no longer a planet. What happened?
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