Quiz of the Day
Time, Clocks & Timekeeping
Tuesday, 13 October 2026
Marking the International Meridian Conference that set Greenwich as the prime meridian (Oct 1884), covering calendars, time zones, and the history of clocks
1. In what year did the International Meridian Conference establish Greenwich as the world's prime meridian?
- 1884
- 1894
- 1864
- 1874
The International Meridian Conference met in October 1884 and voted to make the meridian passing through Greenwich the world's zero of longitude. Delegates from 25 nations attended, and the decision also laid the groundwork for a universal day and standardized time zones. France abstained and clung to the Paris meridian for decades afterward.
2. In which city was the 1884 International Meridian Conference held?
- Washington, D.C.
- Paris
- London
- Geneva
The conference convened in Washington, D.C., at the invitation of U.S. President Chester A. Arthur. Forty-one delegates from 25 countries debated where to place the prime meridian. Greenwich won partly because most of the world's shipping already used charts based on it.
3. The prime meridian was fixed at the site of which historic observatory?
- Paris Observatory
- Pulkovo Observatory
- Royal Observatory, Greenwich
- Palomar Observatory
The Royal Observatory in Greenwich, London, was founded in 1675 by King Charles II to improve navigation and astronomy. A brass line in its courtyard now marks longitude 0 degrees, where visitors famously stand with one foot in each hemisphere. Greenwich Mean Time was long the reference for clocks worldwide.
4. Because Earth turns 360 degrees in 24 hours, how many degrees of longitude does it rotate through in one hour?
- 20 degrees
- 15 degrees
- 10 degrees
- 24 degrees
Dividing 360 degrees by 24 hours gives 15 degrees of longitude per hour, which is exactly why standard time zones are spaced roughly 15 degrees apart. This neat relationship is the foundation of the global time zone system. It also means every 15 degrees you travel east or west shifts local solar time by about one hour.
5. Into roughly how many standard one-hour time zones is the Earth conventionally divided?
- 12
- 36
- 24
- 18
The globe is conventionally split into 24 time zones, one for each hour of the day. In practice there are more than 24 observed offsets because some regions use half-hour or 45-minute differences, such as India and Nepal. Political borders also bend the zones so that whole countries can share a single time.
6. What does the abbreviation 'GMT' stand for?
- General Meridian Time
- Greenwich Mean Time
- Global Meridian Time
- Greenwich Meridian Time
Greenwich Mean Time is the mean solar time at the Royal Observatory in Greenwich. The word 'mean' refers to averaging out the slight seasonal variations in the Sun's apparent motion. For much of the 20th century GMT served as the international time standard before being largely superseded by UTC.
7. The calendar reform of 1582 that most of the world uses today is named after which pope?
- Gregory XIII
- Julius II
- Pius V
- Leo X
Pope Gregory XIII introduced the Gregorian calendar in 1582 to correct drift in the older Julian calendar, whose leap-year rule made the year slightly too long. To realign the dates, ten days were simply dropped, so Thursday 4 October was followed by Friday 15 October 1582. The new rule skips leap years in most century years, keeping the calendar in step with the seasons.
8. How many days are there in a leap year?
- 366
- 367
- 364
- 365
A leap year has 366 days, one more than a common year, thanks to the extra day added as 29 February. Leap years occur because Earth actually takes about 365.24 days to orbit the Sun. Without the periodic correction, the calendar would slowly slip out of sync with the seasons.
9. Which ancient timekeeping device uses the shadow cast by the Sun to indicate the hour?
- Hourglass
- Astrolabe
- Sundial
- Sextant
A sundial tells time by the position of a shadow cast by an angled pointer called a gnomon. Some of the earliest known examples come from ancient Egypt more than 3,000 years ago. Because they rely on sunlight, sundials are useless at night or under cloud, which spurred the invention of water clocks and later mechanical clocks.
10. Who built the first practical pendulum clock in the 1650s, greatly improving timekeeping accuracy?
- Galileo Galilei
- Isaac Newton
- John Harrison
- Christiaan Huygens
The Dutch scientist Christiaan Huygens built the first working pendulum clock in 1656 and patented it the following year. The regular swing of a pendulum cut clock errors from minutes to seconds per day. Galileo had earlier sketched the idea but never completed a working model before his death.
11. Which English clockmaker built the marine chronometers that solved the longitude problem for sailors?
- John Harrison
- Edmund Halley
- George Graham
- Thomas Tompion
John Harrison spent decades building a series of precise sea clocks, culminating in his compact H4 of 1759. A clock that kept accurate time at sea let navigators calculate their longitude by comparing local time with the time at a home port. His work responded to the British Longitude Act of 1714, which offered a huge cash prize for a reliable solution.
12. The 'a.m.' in clock times comes from the Latin phrase meaning 'before midday.' What is that Latin phrase?
- ante mortem
- ante meridiem
- ante meridian
- anno meridiem
The abbreviation a.m. stands for the Latin 'ante meridiem,' meaning before midday, while p.m. stands for 'post meridiem,' after midday. The word 'meridiem' refers to the moment the Sun crosses the local meridian at noon. This is also why the north-south line of the prime meridian shares the same Latin root.
13. What does 'UTC,' the modern global time standard, stand for?
- Coordinated Universal Time
- Central Universal Time
- Universal Timezone Constant
- Universal Time Central
UTC stands for Coordinated Universal Time, the primary standard by which the world regulates clocks today. The odd letter order was a compromise between the English 'Coordinated Universal Time' and the French 'Temps Universel Coordonne.' UTC is kept within a fraction of a second of Greenwich-based solar time using occasional leap seconds.
14. Which type of clock provides the most accurate official time standard in the world today?
- Mechanical spring clock
- Quartz clock
- Pendulum clock
- Cesium atomic clock
The international definition of the second is based on the cesium-133 atom, whose radiation completes exactly 9,192,631,770 cycles per second. Cesium atomic clocks are so stable they would lose or gain less than a second over millions of years. Networks of these clocks around the world are averaged together to generate Coordinated Universal Time.
15. The International Date Line roughly follows which line of longitude, on the opposite side of the globe from Greenwich?
- 0 degrees
- 90 degrees
- 180 degrees
- 360 degrees
The International Date Line zigzags along roughly the 180-degree meridian in the Pacific Ocean, directly opposite the Greenwich prime meridian. Crossing it westbound advances the calendar by a day, while crossing eastbound sets it back a day. The line bends around island groups and nations so that neighbors are not split across two different dates.