VICTOR HABBICK VISIONS/Science Photo Library/Alamy
Herman D’Hondt
Sydney, Australia
This is easy, as long as you accept that Earth is a rotating sphere. If you are standing at the equator, you move west at about 1670 kilometres per hour. At my location in Sydney, we move somewhat slower, at only 1400 km/h.
If I were to hop on a fighter jet, I could fly west at those speeds and keep the sun at the same elevation in the sky for as long as the fuel lasted. As long as I am moving west, my day (as measured by the sun) will always be longer than 24 hours. Near Earth’s poles, a slow walking speed would be enough to get the same effect at lower latitudes.
As for skipping a day, any time you cross the international date line, you either gain or lose a day, depending on your direction of travel. Take, for example, a flight between Los Angeles and Sydney. Say it leaves Los Angeles at 11.05pm on 9 May. It will arrive in Sydney, after flying non-stop for 15 hours, at 7.05am on 11 May. What happens to 10 May?
The first to experience this were Ferdinand Magellan’s sailors. On their return home, they found that their log was one day behind the time in Spain. An apocryphal story has it that they were very worried by this: if the missing day was a Sunday, they would have skipped mass and committed a capital sin.
Finally, we must consider Albert Einstein’s theory of general relativity. For anyone who moves, the time will pass slower than for someone who doesn’t.
Similarly, if you are high up on a mountain, time will go faster for you than for someone in a valley. While these effects are tiny, GPS systems must account for them. GPS satellites move very fast and are very high up. The effects of speed and altitude are opposite, with speed slowing time and altitude speeding it up. However, they don’t fully cancel out. The difference is only 38 microseconds per day, but that amounts to 11 km. After a couple of weeks, your phone would put you in the next country!
David Craig
Edinburgh, UK
In Catholic Europe, 4 October 1582 was followed directly by 15 October (skipping 10 days) to align future dates of 21 March with the spring equinox and Easter. After 200 years, the UK and US followed suit, skipping from 2 September 1752 to 14 September 1752.
To answer this question – or ask a new one – email lastword@newscientist.com.
Questions should be scientific enquiries about everyday phenomena, and both questions and answers should be concise. We reserve the right to edit items for clarity and style. Please include a postal address, daytime telephone number and email address.
Â鶹´«Ã½ retains total editorial control over the published content and reserves all rights to reuse question and answer material that has been submitted by readers in any medium or in any format.
Ìý
