Tag Archives: Q&A

Why is Pluto not a planet?

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In 1930, Clyde W Tombaugh completed the search for Planet X, the outermost planet at the far reaches of the solar system.  This object was named Pluto.  Then, on 24 August 2006, the IAU (International Astronomy Union) formally voted on a new definition of the word ‘Planet’, which excluded Pluto.  For seventy-six years, our solar system had been understood to have nine planets, then suddenly it went back to eight.  The response was furious. Both the astronomical community and the … Continue reading →

Will an astronaut explode if he takes off his helmet?

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We’ve all seen it happen in science fiction films. The expendable character is outside the space ship, or trapped in the air-lock.  The space suit is damaged, or the helmet is removed.  His friends frantically bang on the glass as we get a nice close-up of his face as it blows up like a balloon.  And then… well it depends on the film.  Sometimes he freezes solid and shatters like glass, other times he explodes in a messy shower of … Continue reading →

Why can’t you see any stars on the moon?

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Ah, but you can if you wait till night time!  You can’ t see any stars in photographs taken from the Apollo missions because they were all taken in broad daylight.  As any photographer will tell you, a camera can only cope with a narrow range of brightnesses, so that the aperture setting and shutter speed are very important if a photograph is not to be over- or under-exposed for given lighting conditions.  In this age of automatic point-and-click digital … Continue reading →

How far away is the Sun?

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Earth orbits the Sun at an average distance of 149,598,000 kilometers.  Astronomers refer to this distance as 1 Astronomical Unit (AU), which is a handy unit for measuring distances within the Solar System.  But the actual distance changes every day, because the Earth’s orbit is elliptical and not perfectly circular.  On the 3rd of January each year, Earth is at its closest point to the Sun, with a distance of 147,098,074 km.  It is at its furthest point (152,097,701 km) on … Continue reading →

Phases of the Moon

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Everybody knows that the Moon changes its face.  Sometimes we have Full Moons, other times it’s a Half-moon, or a crescent, or there’s no Moon at all.  And everybody knows that these are called the phases of the Moon.  But not everybody knows that these faces follow a regular cycle, or that the common descriptions are misleading at best.  A proper understanding of what’s actually happening to make the moon show different faces, and the nature of the “Dark Side … Continue reading →