Clocks, Calendars and the Measurement of Time – answers and explanations
Here are the answers to all 15 questions in the Clocks, Calendars and the Measurement of Time quiz, each with a short explanation. From sundials to atomic clocks: test your knowledge of how we measure time. Haven't played yet? Take the quiz first and compare your score.
Play the quiz · 15 questions1. When daylight saving time begins in spring, what do clocks do?
Answer: Move forward one hour
When daylight saving time starts in spring, clocks are advanced one hour, which is why the rule is remembered as 'spring forward, fall back'. In the US the change happens at 2 a.m. on the second Sunday in March, in the UK and EU at 1 a.m. UTC on the last Sunday in March.
2. The International Date Line roughly follows which line of longitude?
Answer: 180 degrees
The International Date Line runs through the Pacific Ocean roughly along the 180 degree meridian, exactly halfway around the globe from the Greenwich prime meridian. It zigzags east and west of that line so that countries and island groups are not split between two calendar dates.
3. Under the Gregorian calendar, which of these century years was a leap year?
Answer: 2000
In the Gregorian calendar a century year is a leap year only if divisible by 400, so 2000 had a 29 February while 1700, 1800 and 1900 did not. This refinement, introduced by Pope Gregory XIII in 1582, keeps the average year at 365.2425 days.
4. In London's famous clock tower, what is 'Big Ben' actually the name of?
Answer: The great bell
Big Ben is strictly the nickname of the Great Bell of the Great Clock of Westminster, a roughly 13.7-tonne bell cast at the Whitechapel Bell Foundry. The tower housing it was simply the Clock Tower until it was renamed the Elizabeth Tower in 2012 for Queen Elizabeth II's Diamond Jubilee.
5. Which London district gives its name to the line of 0 degrees longitude?
Answer: Greenwich
The prime meridian, 0 degrees longitude, passes through the Royal Observatory at Greenwich in south-east London, agreed as the world standard at the 1884 International Meridian Conference in Washington DC. It also underpins Greenwich Mean Time.
6. Atomic clocks that define the second are based on atoms of which element?
Answer: Caesium
Since 1967 the SI second has been defined by the caesium-133 atom, as exactly 9,192,631,770 cycles of its ground-state hyperfine transition frequency. The first operational caesium-beam atomic clock was built at the UK's National Physical Laboratory in 1955.
7. Which pope introduced the calendar most of the world uses today?
Answer: Gregory XIII
Pope Gregory XIII issued the bull Inter gravissimas on 24 February 1582, reforming the Julian calendar into the Gregorian calendar now used worldwide. To realign the equinox, ten days were dropped: 4 October 1582 was followed by 15 October.
8. Which country was the first to adopt daylight saving time nationwide, in 1916?
Answer: Germany
The German Empire (with ally Austria-Hungary) became the first nation to introduce daylight saving time nationwide on 30 April 1916, to save coal during World War I. Britain followed in May 1916 and the United States in 1918.
9. Travelling west across the International Date Line, what happens to the date?
Answer: It jumps forward by one day
Crossing the International Date Line westbound advances the calendar by one day, while crossing eastbound subtracts a day. The line roughly follows the 180° meridian but zigzags to keep island groups and countries on a single date.
10. What is the name of the shadow-casting part of a sundial?
Answer: The gnomon
The gnomon is the raised part of a sundial that casts the shadow onto the marked dial plate; the edge actually casting the time shadow is called the style. The word comes from Greek gnomon, meaning indicator or discerner.
11. Which Dutch scientist built the first working pendulum clock in 1656?
Answer: Christiaan Huygens
Christiaan Huygens designed and built the first working pendulum clock in 1656, patenting it the following year; clockmaker Salomon Coster of The Hague constructed it. Accuracy jumped from about 15 minutes to roughly 15 seconds of error per day.
12. Despite its huge width, how many official time zones does China use?
Answer: One
China officially uses a single time zone, UTC+8, known as Beijing Time domestically and China Standard Time internationally, even though the country geographically spans about five time zones. The single standard was imposed in 1949 for national unity.
13. When Britain switched to the Gregorian calendar in 1752, how many days were lost?
Answer: 11 days
Under the Calendar (New Style) Act 1750, Britain and its colonies dropped 11 days in September 1752: Wednesday 2 September was followed by Thursday 14 September. The act also moved New Year's Day from 25 March to 1 January.
14. Besides Hawaii, which US state does not observe daylight saving time?
Answer: Arizona
Arizona and Hawaii are the only US states that skip daylight saving time, as allowed by the Uniform Time Act of 1966. Arizona stays on Mountain Standard Time year-round because of its summer heat, though the Navajo Nation within it does observe DST.
15. What does the abbreviation UTC stand for?
Answer: Coordinated Universal Time
UTC stands for Coordinated Universal Time, the world's primary time standard kept by atomic clocks. The odd abbreviation was a compromise between the English wording and the French 'temps universel coordonné'.