- Email: [email protected]
Selected selections
Last words past and present at newscientist.com/lastword
THE LAST WORD Clouding the issue Are there any wavelengths at which the sun still casts a shadow when the sky is full of clouds? Could I make a sundial that would work on a cloudy day?
n Some radio waves can go through clouds and the sun does emit radio waves, so it would be possible to build a sundial that works on shady days. But you would need a sundial that was large in comparison to the wavelength of the radio waves in question, otherwise the waves
“X-rays emitted by the sun can penetrate cloud and you could see where they fall using a fluoroscope” would simply refract around it and you wouldn’t get a shadow. The shadow would have to be detected by a huge array of antennas designed to pick up the sun’s radio waves. This is not simple. It took a long time before radio waves from the sun could be detected and it was not until 1942 that English physicist James Stanley Hey managed it. There is another option though. X-rays are also emitted by the sun and these would penetrate clouds too. It might be easier to build a sundial based on X-rays because there wouldn’t be the problem of diffraction, and you could see where the X-rays fall using a fluoroscope. Eric Kvaalen Les Essarts-le-Roi, France
The writers of answers that are published in the magazine will receive a cheque for £25 (or US$ equivalent). Answers should be concise. We reserve the right to edit items for clarity and style. Please include a daytime telephone number and an email address if you have one. New Scientist retains total editorial control over the published content. Reed Business Information Ltd reserves all rights to reuse all question and answer material that has been
n One way to work out the position of the sun – and thus to deduce the time – when conditions are overcast is to observe the polarisation of what light is available. This phenomenon is something that insects and birds exploit for navigation. In general, scattered light is polarised at right angles to the sun. So, when the sun is at its highest point, light is close to being horizontally polarised along the entire horizon. When the sun sets directly west, the sky will be vertically polarised at the horizon due north and south. In 1848, English inventor Charles Wheatstone presented the “polar clock”, a sundial-like device that could be used when it was cloudy. By angling the tube towards the North Pole, and turning a prism in the eyepiece until the light vanished, the relative angle of polarisation of available daylight could be deduced, giving the position of the sun and thus the approximate time. It has also been suggested that Vikings used crystal “sunstones” to locate the sun when it was obscured by clouds or just over the horizon. Mike Follows Sutton Coldfield, West Midlands, UK
This week’s questions Having a ball
We found this object (see photo, above) by a sea wall in south-east Thailand. The white substance
submitted by readers in any medium or in any format and at any time in the future. Send questions and answers to The Last Word, New Scientist, 110 High Holborn, London WC1V 6EU, UK, by email to [email protected] or visit www.newscientist.com/topic/lastword (please include a postal address in order to receive payment for answers). Unanswered questions can also be found at this URL.
paper, and then the bottom corners. Why is this? I’m using a black ballpoint pen on white A4 printer paper. Gurleen Kaur By email, no address supplied Selected selections
The only genetic changes in humans we ever hear about are those producing diseases such as cystic fibrosis. Has anyone identified any genetic changes within recent generations that make individuals possessing them “more fit” to thrive in today’s environment? Would we even know these changes if we saw them? And would we consider them normal for healthy humans? Colin Bamforth Altrincham, Cheshire, UK looks like a folded piece of fabric made out of limestone encrusted with glassy spheres. Only a tiny section of each sphere is attached to the limestone, but they are held firmly in place and cannot be removed with a fingernail. None of them has a surface scratch, which is impressive considering they must have been bashed by waves against the rocky sea wall. What are these tiny spheres? Natam Tonkul Bangkok, Thailand Everything but the curl
I’ve been making notes to revise for my exams, and as I write, the pages curl inwards first from the top corners of the
RAILING AGAINST IT?
Edinburgh finally got its tram system last year, which was over-budget and behind schedule. Most of the problems were due to having to lay the rails in the road.
“Why didn’t Edinburgh go for trolley buses powered by overhead wires instead of trams?” Why didn’t Edinburgh and other UK cities go for trolley buses – electric buses powered from overhead wires – instead of trams? Jim Logan Castle Douglas, Dumfries and Galloway, UK
Question Everything The latest book of science questions: unpredictable and entertaining. Expect the unexpected Available from booksellers and at newscientist.com/questioneverything
THE LAST WORD Clouding the issue Are there any wavelengths at which the sun still casts a shadow when the sky is full of clouds? Could I make a sundial that would work on a cloudy day?
n Some radio waves can go through clouds and the sun does emit radio waves, so it would be possible to build a sundial that works on shady days. But you would need a sundial that was large in comparison to the wavelength of the radio waves in question, otherwise the waves
“X-rays emitted by the sun can penetrate cloud and you could see where they fall using a fluoroscope” would simply refract around it and you wouldn’t get a shadow. The shadow would have to be detected by a huge array of antennas designed to pick up the sun’s radio waves. This is not simple. It took a long time before radio waves from the sun could be detected and it was not until 1942 that English physicist James Stanley Hey managed it. There is another option though. X-rays are also emitted by the sun and these would penetrate clouds too. It might be easier to build a sundial based on X-rays because there wouldn’t be the problem of diffraction, and you could see where the X-rays fall using a fluoroscope. Eric Kvaalen Les Essarts-le-Roi, France
The writers of answers that are published in the magazine will receive a cheque for £25 (or US$ equivalent). Answers should be concise. We reserve the right to edit items for clarity and style. Please include a daytime telephone number and an email address if you have one. New Scientist retains total editorial control over the published content. Reed Business Information Ltd reserves all rights to reuse all question and answer material that has been
n One way to work out the position of the sun – and thus to deduce the time – when conditions are overcast is to observe the polarisation of what light is available. This phenomenon is something that insects and birds exploit for navigation. In general, scattered light is polarised at right angles to the sun. So, when the sun is at its highest point, light is close to being horizontally polarised along the entire horizon. When the sun sets directly west, the sky will be vertically polarised at the horizon due north and south. In 1848, English inventor Charles Wheatstone presented the “polar clock”, a sundial-like device that could be used when it was cloudy. By angling the tube towards the North Pole, and turning a prism in the eyepiece until the light vanished, the relative angle of polarisation of available daylight could be deduced, giving the position of the sun and thus the approximate time. It has also been suggested that Vikings used crystal “sunstones” to locate the sun when it was obscured by clouds or just over the horizon. Mike Follows Sutton Coldfield, West Midlands, UK
This week’s questions Having a ball
We found this object (see photo, above) by a sea wall in south-east Thailand. The white substance
submitted by readers in any medium or in any format and at any time in the future. Send questions and answers to The Last Word, New Scientist, 110 High Holborn, London WC1V 6EU, UK, by email to [email protected] or visit www.newscientist.com/topic/lastword (please include a postal address in order to receive payment for answers). Unanswered questions can also be found at this URL.
paper, and then the bottom corners. Why is this? I’m using a black ballpoint pen on white A4 printer paper. Gurleen Kaur By email, no address supplied Selected selections
The only genetic changes in humans we ever hear about are those producing diseases such as cystic fibrosis. Has anyone identified any genetic changes within recent generations that make individuals possessing them “more fit” to thrive in today’s environment? Would we even know these changes if we saw them? And would we consider them normal for healthy humans? Colin Bamforth Altrincham, Cheshire, UK looks like a folded piece of fabric made out of limestone encrusted with glassy spheres. Only a tiny section of each sphere is attached to the limestone, but they are held firmly in place and cannot be removed with a fingernail. None of them has a surface scratch, which is impressive considering they must have been bashed by waves against the rocky sea wall. What are these tiny spheres? Natam Tonkul Bangkok, Thailand Everything but the curl
I’ve been making notes to revise for my exams, and as I write, the pages curl inwards first from the top corners of the
RAILING AGAINST IT?
Edinburgh finally got its tram system last year, which was over-budget and behind schedule. Most of the problems were due to having to lay the rails in the road.
“Why didn’t Edinburgh go for trolley buses powered by overhead wires instead of trams?” Why didn’t Edinburgh and other UK cities go for trolley buses – electric buses powered from overhead wires – instead of trams? Jim Logan Castle Douglas, Dumfries and Galloway, UK
Question Everything The latest book of science questions: unpredictable and entertaining. Expect the unexpected Available from booksellers and at newscientist.com/questioneverything