Time
12 questions tagged Time — spanning every one of the seven Ws.
Where is the prime meridian?
The prime meridian, 0 degrees longitude, runs through the Royal Observatory in Greenwich, London.
Where is the International Date Line?
It runs roughly along the 180 degree meridian in the Pacific Ocean, zigzagging around islands and countries so they share one date.
What is a leap second?
A leap second is an extra second occasionally added to clocks to keep atomic time in line with Earth’s rotation.
Why do we have daylight saving time?
Clocks move forward in summer to shift daylight into the evening, first adopted widely to save fuel during World War I.
How Does a Sundial Tell Time?
A sundial tells time from the shadow cast by a pointer called a gnomon, which moves across marked hour lines as the Sun crosses the sky.
How Does a Pendulum Clock Keep Time?
A pendulum clock keeps time because a pendulum of fixed length swings at a very regular rate, and an escapement counts each swing to move the hands.
Why do clocks go clockwise?
Clock hands copy the movement of a sundial's shadow in the Northern Hemisphere, where mechanical clocks were invented.
What is a time zone?
A time zone is a region of the Earth that uses the same standard time. Time zones help coordinate daily life across different longitudes.
What is the International Date Line?
The International Date Line is an imaginary line near the 180° meridian where the calendar date changes by one day. Crossing it westward adds a day, and crossing eastward subtracts a day.
How does an hourglass measure time?
An hourglass measures time by letting a fixed amount of sand trickle through a narrow neck from one glass bulb into another at a steady rate.
How long does one year last on different planets?
A planet’s year is its orbital period: Mercury takes 88 Earth days, Earth 365 days, Jupiter about 12 years, and Neptune about 165 years.
How long is a day on the different planets?
A planet’s day is its rotation period: Jupiter spins in about 10 hours, Earth in 24 hours, and Venus takes about 243 Earth days to rotate once.