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Archive Astronomy Questions of the Week - International Year of Astronomy 2009
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What is dark energy?


Week 39
Exactly what is dark energy? Astrophysicists would also like to know the answer to this question – it determines how the Universe will develop. Cosmologists are fairly sure that it has been expanding since the Big Bang. What is still uncertain is whether this expansion will continue forever or whether the Universe will one day begin to collapse again.
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How quickly is the Universe expanding?


Week 38
In the 1920s, Edwin Powell Hubble was analysing the distances between Earth and various galaxies using the Mount Wilson Observatory in California. In the process, he measured the electromagnetic radiation of the galaxies and discovered mostly what are known as 'redshifts' in their spectra; that is. in the distributions of the various wavelengths. In 1929, Hubble published the outcome of his investigation – almost all galaxies are moving away from us and their speed increases in a linear relationship with their distance from us.
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How far is 'unimaginably far'?


Week 37
We often speak of 'astronomically high prices' – 'astronomic' is a common way of describing anything that is extremely large. As a matter of fact, units of measurement are used in the field of astronomy that are far greater than the scale we are used to in everyday life. The nearest star – Proxima Centauri – is around 40,000,000,000,000 kilometres away. This example already shows that the unit of length that we are familiar with, the (kilo-) metre, is completely unsuitable for describing distances in the Universe – but what units are more suitable?
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Sind wir aus

Are we made of 'stardust'?


Week 36
Of course, the human body is not made of dust; it comprises mainly water, proteins, fats and mineral nutrients. These substances are in turn made up of chemical elements, or different 'atom types', which are primarily hydrogen, oxygen, carbon and nitrogen. But where did these chemical elements come from – how were they created?
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Andromeda

How can there be clouds in space?


Week 35
There are many different kinds of clouds in space, but none of them have anything to do with what we know as clouds on Earth – which are made out of tiny droplets of water. Originally – before the invention of the telescope – astronomers referred to all the shining, extended structures without clearly defined edges that they saw in space as ‘clouds’ (nebulae in Latin). Since even entire galaxies can appear to be cloudy patches to the naked eye, they were also called ‘nebulae’.
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Space debris

Is space debris dangerous?


Week 34
On 10 February of this year the flight path of the Iridium 33 communications satellite crossed that of the retired Russian military satellite Kosmos 2251. Both satellites were completely destroyed and about 700 pieces of debris were distributed along their paths. Such collisions cannot always be avoided and space debris has become an expensive problem.
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Saturn

How did Saturn get its rings?


Week 33
Saturn’s ring system was discovered as long ago as the seventeenth century. The French astronomer Cassini quickly suspected that the rings consisted of individual particles. Saturn’s rings are indeed not a single entity but consist of chunks of ice and rock that are orbiting the planet.
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Planetenrotation

Why do the planets break ranks?


Week 32
Our solar system is in motion – the planets orbit the Sun and at the same time rotate around their own axis. However, the direction of the axes of rotation is different for every planet. Why is that?
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Ceres

Why aren't all celestial bodies spherical?


Week 31
The heavens were divine in origin and, as a consequence, had to be perfect in structure and form; hence the astronomers of antiquity sought to discover perfect geometrical forms in the celestial bodies and their movements – spheres and circles. Today, we still look at the stars, planets and their moons as spherical bodies. But smaller celestial bodies such as asteroids and comets are often irregular in shape and tend to look more like potatoes. Why is that?
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Galaxien-Kollision

Whither goest thou, Milky Way?


Week 30
As the young god Heracles forcefully suckled the breast of the Greek goddess Hera, she pushed him away and a spurt of her breast milk spilled across the sky. The name of our home galaxy, which does in fact appear in the night sky as a milky band, originates from this Greek legend. The term 'galaxy' stems from the ancient Greek word for milk, 'gala'.
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Sonnenfinsternis

When do Solar and Lunar eclipses occur?


Week 29
The new century has just begun and already the longest solar eclipse that will occur in the 21st century is about to take place – on 22 July the Moon will completely eclipse the Sun for up to 6 minutes and 39 seconds. This event will, however, only be observable in parts of India, China and the Pacific region.
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Mondenstehung

How was the Moon created?


Week 28
Forty years ago, on 21 July 1969 at 03:56:20 (Central European Time), Neil Armstrong became the first man to set foot on the Moon. All (six to date) Moon landings took place between 1969 and 1972 and a total of 12 people, all of them American astronauts, have walked on the Moon's surface. They brought rock samples from the Moon back to Earth with them. The analysis of this rock was supposed to resolve the question of how the Earth’s relatively large Moon was formed.
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Life cycle of the Sun

How long will the Sun continue to shine?


Week 27
A shining and 'well functioning' Sun is critical for our survival on Earth. The Sun was formed almost five billion years ago. At that time, a gas and dust cloud became so condensed due to its own gravity that hydrogen nuclei began to merge with each other and release huge amounts of energy in a process known as nuclear fusion. Fortunately, the Sun's supply of hydrogen is so great that it will continue to shine for another five billion years. However, the intensity of the solar radiation will increase in the future and this will be fatal for life on Earth. As early as two to three billion years from now, the oceans will evaporate and it will become impossible to live on Earth.
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