Monday 03 February 1997
Q Why don't stars appear in pictures from the Apollo landings on the Moon?
A The lunar surface is very bright, and reflects a lot of light. The television cameras on the Moon compensated for this by reducing the amount of light let through the lens. As a result, stars were not bright enough to be seen.
Q Why, if you shut one eye, do you still see in 3-D?
A You don't, really, but your brain supplies the missing information, so you get the impression that you are still seeing an image with depth. Depth perception still isn't fully understood, but our brain can use pictorial clues such as the angle an object covers on our retina. Other clues include the brightness of the object; if it is brighter, it will usually be nearer, so light and shade can also be important. There are also physiological clues such as when you focus on something close, the shape of the actual lens changes. To check if you are really seeing in 3-D when you have one eye shut, try moving your head from side to side, or touching objects at varying distances.
Q How far does the Earth travel round the Sun?
A About 570 million miles (900 million kilometres). The first measurement was made by Aristarchus of Samos in about 270BC. He measured the position of the Sun relative to the Moon when the Moon was half full. From this, he worked out the distance to the Sun (since the Earth's orbit is nearly circular, the distance travelled is 2p multiplied by the radius). The number he got was 20 times too small, but very early astronomers often did worse.
Q Stars twinkle because of the Earth's atmosphere. Why don't planets?
A Stars are so distant that they appear as point sources of light, so any disturbance in the Earth's atmosphere is easily visible. Planets, being closer, appear more as a disc than a point of light. Any disturbance is less visible because if the central part of the image is distorted as it passes through the atmosphere, that distortion probably won't reach the edge of the disc - so the planet won't seem to twinkle.
Q What is the strongest plant fibre?
A A fibre called ramie is the strongest. Its fibres are eight times as strong as those of cotton.
Q Do fish blink?
A No. Like snakes, they don't have moveable eyelids. Instead, they have a transparent eye protector permanently in place. Fish have excellent eyesight and can see parts of the spectrum we can't. They rely heavily on visual signals for species recognition, choosing a mate and territorial defence.
You can also visit the technoquest World Wide Web site at http://www.campus.bt. com/CampusWorld/pub/ScienceNet
Questions for this column can be submitted by email to firstname.lastname@example.org
- 1 Rarest Beanie Baby of them all could be sold for £62,500 on eBay
- 3 Driving while dehydrated can be just as dangerous as drink driving, study suggests
- 4 Farmer told to tear down mock-Tudor castle after hiding construction behind hay bales
- 5 One Direction: Louis Tomlinson launching his own record label, has already 'signed two acts'
Isis video purports to show beheadings and execution at gunpoint of 30 Ethiopian Christians and destruction of churches in Libya
Rarest Beanie Baby of them all could be sold for £62,500 on eBay
Professional big game hunter Ian Gibson crushed to death by elephant during hunt
Driving while dehydrated can be just as dangerous as drink driving, study suggests
Ben Affleck asked TV chiefs to hide slave-owning ancestry, new hacked Sony emails published by Wikileaks claim
If I’m being racially abused I don’t need a stranger with a saviour complex to rescue me
The only black face in the Ukip manifesto is on the page about overseas aid
Ukip is the only main political party to not address LGBT rights in its manifesto
Food banks: One million Britons will soon be using them, according to Trussell Trust
Religion isn't growing, it is becoming vigorous in its demise, says philosopher AC Grayling
BBC election debate: The one photo that summed up the whole 90-minute leaders debate
£18000 - £23000 per annum: Recruitment Genius: They work with major vehicle ma...
£16500 per annum: Recruitment Genius: A Chiropractic Assistant is needed in a ...
£18000 - £26000 per annum: Recruitment Genius: They work with major vehicle ma...
£28000 - £30000 per annum: Recruitment Genius: This company provides coaching ...