WHY DO WE HAVE A LEAP YEAR?
Although you might think the Earth is still, it's actually moving in a track around the Sun rather like a circle. One complete trip round is what we call a year. As the Earth travels, it is also spinning, and each spin is what we call a day.
In a year, when the Earth comes right back around to where it started in relation to the Sun, it will have spun 365-and-a-quarter times.
This is a nuisance to our calendars - what can you do with a quarter of a day? So we just ignore it, which is why grown-ups sometimes say that there are 365 days in a year.
But if we continue to ignore that quarter day, the calendar would get out of step with where the Earth is. So every four years, we add up the quarters to one whole day and tag an extra day on to the calendar in February to bring us up to date.
Jonathan Betts, horologist (expert in time and time-keeping), Royal Observatory.
WHERE DOES THE WIND COME FROM?
Have you ever noticed that when it's cold outside and someone opens the front door of your cosy, warm house, the warm air from inside rushes out very quickly, which makes you feel chilly? Wind is made a bit like that.
When hot air from warm countries such as Spain bumps into cool air from places like England, the warm air rushes into the cold air and this movement of air is what we call wind.
If the air that meets is very warm and very cold, the cold air rushes very fast and produces a strong wind. But if the temperatures of the air are only a little different, the cold air moves slowly and we get just a light breeze.
Stuart Umbo, Science Museum
WHY IS THE SEA SALTY?
The sea is salty because the rivers that flow into it wash salts and other minerals out of the ground. These dissolve in the rivers and the rivers then flow into the sea.
Another source of salt is the sea bed. As the Sun evaporates the water from the sea to make clouds, it leaves the salts and minerals behind, so the sea is much saltier than rivers and lakes. Even though it rains on the sea as on land, this isn't enough to dilute the salt.
Roger Highfield, Editor, New Scientist
WHY DO YOU BLINK?
The very front of your eye is made of an extremely sensitive seethrough screen rather like the windscreen on your parents' car.
It's very important that it stays clean and moist so that you can see as well as possible. So every ten or 20 seconds, your eyelids close, spreading a thin layer of tears over your eye which washes off any bits of dust or anything else that may have got into it, like a car's windscreen wiper with squirty screen wash. If we didn't blink so much, we wouldn't be able to see properly, so it's lucky we do!
Dr Rob Hogan, president of the College of Optometrists
Regarding leap years -
ReplyDeleteThe Jewish and Chinese calendars are lunar/solar calendars. Because the lunar year is not the same length as the solar year, the calendars add an extra month in some years to match it up to the solar calendar.