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Archive Astronomy Questions of the Week - International Year of Astronomy 2009
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Jupiter

Where does a storm last for several centuries?


Week 26
The longest documented storm on Earth lasted for just five weeks. Last year, astronomers observed a storm on Saturn that lasted for more than five months. However, on Jupiter, scientists in the 17th century observed a gigantic 'red eye' - known as the Great Red Spot – that has been observed continuously ever since and can be seen with amateur telescopes.
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What are gravitational lenses?

What are gravitational lenses?


Week 25
Ninety years ago, Arthur Eddington undertook an expedition to West Africa to confirm Albert Einstein's general theory of relativity. Eddington was not, of course, an ethnologist or geologist but an astrophysicist and he observed the solar eclipse there on 29 May 1919. This enabled him to photograph stars in the region around the Sun - stars which would otherwise have been obscured by the Sun.
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Does the Sun have a surface?


Week 24
"Of course," we might answer, "what a question!" However, we should also consider that our Sun - like all other stars - is a ball of hot gas. This gas ball, with a diameter of 1.4 million kilometres, is held together by gravity alone. This means that the Sun does not have a firm surface.
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Will Lisa find gravitational waves and prove Einstein right?


Week 23
Space and time are no longer what they used to be – absolute dimensions of the universe without regard to anything external. That is how Isaac Newton described them in the seventeenth century. In 1915, Albert Einstein completed his general theory of relativity, which fundamentally changed our view of space and time.
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Where is all the antimatter?


Week 22
Everyone knows about matter; after all, that is what the world is made of (or at least a large part of it). Matter, in simple terms, is what can be touched – that is, physical bodies or objects – in contrast to energy or thoughts and ideas. 'Antimatter', on the other hand, sounds rather spectacular, like the stuff of science fiction.
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Asteroid

How can we prevent an asteroid impact?


Week 21
A critical emergency – an asteroid or comet is on a collision course with Earth. In principle, there are two ways to avert the impact or collision of an object that is near Earth: destroy the Near Earth Object (NEO) or move it into a safe orbit. But is this realistic?
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Asteroid

Can we predict when an asteroid will impact Earth?


Week 20
Objects with orbits that bring them near to Earth are potential killers. These objects, known as NEOs (Near-Earth Objects), are asteroids (see the astronomy question from week 19: Where is the planet between Mars and Jupiter?) or comets, which we can recognise when they are in the vicinity of the Sun by their characteristic tail. If these small heavenly bodies cross Earth's orbit while they are orbiting the Sun, it could lead to a collision – a so-called 'impact event'. Can such impacts be predicted?
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Ceres, Erde, Mond

Where is the planet between Mars and Jupiter?


Week 19
From ancient times, scientists have attempted to identify laws governing the orbits of the planets. In 1766, the physicist and mathematician Johann Daniel Titius developed a formula that can be used to derive the distances between the planets and the Sun. However, according to this formula another planet should be present between Mars and Jupiter. This prediction was an incentive for many astronomers to try to find this as-yet unknown heavenly body.
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Weltraumteleskop Herschel

Why do some space telescopes have to be cooled?


Week 18
It is cold in space, unimaginably cold for us. The temperature that prevails there and the temperature of the cosmic background radiation (see the astronomy question from week 10: Where is the coldest point in the Universe?) is around minus 270 degrees Celsius. This is only slightly above absolute zero, which is minus 273 degrees Celsius, the lowest possible temperature. In spite of this, some space telescopes have to be cooled - but not others. But why?
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Polarlicht

Why is the sky alight?


Week 17
There have been accounts of what are known as auroras – the eerie reddish and greenish flickering of light in the night sky – for the past 2000 years. The Vikings interpreted the luminous effect as being the shimmer of moonlight on the armour of the ghostly Valkyries as they rode across the sky. But why do auroras occur?
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Earth's path around the sun

Why do the times at which the Sun rises and sets not change evenly?


Week 16
The winter solstice, which occurs on 21 or 22 December, marks the shortest day and the longest night of the year. Following the winter solstice, the days – or, more exactly, the period between sunrise and sunset – get longer again. At first you hardly notice it, but it gradually becomes more and more obvious. This means that the Sun does not rise earlier by a fixed number of minutes every morning and set later by the same number of minutes. How can this happen?
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Großer Bär

Where did the Little Dipper and the Big Dipper go?


Week 15
The 'Little Dipper' and the 'Big Dipper' – even people without any knowledge of astronomy will at least be familiar with these names. The Little Dipper and the Big Dipper are both configurations of seven bright stars that look like a dipper (ladle or scoop). Four stars form the bowl of the dipper, the other three form the handle. By imagining a line between the two outermost stars of the Big Dipper – the ones furthest from the handle – and then extending it by five times, you almost immediately find the North Star (Polaris). The North Star forms the tip of the handle of the Little Dipper.
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Gregor XIII.

When is Easter?


Week 14
In 1582, Pope Gregory XIII decreed that a new calendar be used. This Gregorian calendar has, over the centuries, replaced most other calendars and nowadays it is used practically everywhere. The main reason for the introduction of this new calendar was that calculating the date of Easter proved problematic. Unlike Christmas or All Saints' Day, Easter – the celebration of the resurrection of Jesus Christ – is a moveable feast, which means that its date is not fixed to a particular day of the calendar year but instead changes from year to year.
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