On 2 Nov 1868, NZ set a national time at 11.5 hours ahead of Greenwich Mean Time at the Greenwich Royal Observatory

All telegraph offices connected to Wellington struck noon at same time as previously there were differences across NZ

Greenwich Mean Time (GMT) is yearly average (or 'mean') when sun crosses Prime Meridian (0°) daily at Greenwich, London

The Greenwich Royal Observatory is located in Greenwich Park in S.E. London & overlooks the River Thames to the north

Meridians are imaginary lines from Nth to Sth Poles to show longitude (0-180° E or 0-180° W) with Prime Meridian at 0°

To indicate latitude, horizontal lines tell how far North (0-90° N) & South (0-90° S) of the Equator

On 30 Sept 1927, the Summertime Act introduced daylight saving with clocks put forward 1 hour (12.5 hours ahead of GMT)

Over the years, a series of Acts have amended the commencement & finish of the dates for daylight saving in NZ

On 1 Jan 1946, New Zealand Mean Time was adjusted to 12 hours ahead of GMT & daylight saving was discontinued

In 1974, NZ adopted UTC (Coordinated Universal Time) which had been used internationally since 1972 to replace GMT

UTC is based on International Atomic Time (IAT) which uses the readings of atomic clocks (first introduced from 1940s)

Daylight saving has met with mixed reactions throughout NZ

Previously, each NZ city & town had organised its own clock time & Government buildings often had a public clock

Christchurch time was 8 mins faster, Dunedin 17 mins faster, & Napier 9 mins slower than Wellington & Auckland

In 1862, Wellington's Inspector and Commissioner of Customs, Stephen Carkeek, proposed accurate time-keeping

He recommended an observatory to aid captains of vessels arriving at Port Nicholson, as well as the general public

The Wellington Provincial Council agreed to having an Observatory at the new Custom House to be built on waterfront

The Observatory to have a Time Ball mechanism, 2 pendulum clocks & time transit instrument (telescope)

Opening on 9 March 1864, the Wellington Provincial Observatory had Rev Arthur Stock appointed as 'Astronomical Observer'

(When Stock became Vicar of St Peter's in 1856, he'd erected an observatory behind his house as a hobby)

The Observatory's Time Ball was on top of a 28 foot pole on the Custom House's roof & dropped at noon except Sundays

The TIme Ball was dropped by an electrical discharging machine connected to the astronomical clock to set the time

With arrival of the telegraph between 1862-1866, time differences between post & telegraph offices became apparent

If an office's 5pm closing was prior to another office's 5pm, urgent telegrams weren't received until the next day

In Sept 1867, Invercargill’s postmaster adopted Wellington's time as there had been a time difference between both

Invercargill's time was 25 mins faster than Wellington

In Jan 1868, Postmaster-General John Hall instructed all telegraph & post offices in NZ to adopt Wellington's time

Confusion arose whether the whole city/town, not just it's telegraph & post office, would adopt Wellington's time

Queries also arose as to why Wellington's time chosen. (See article in Otago Daily Times, 23 March 1868)

In Sept 1868, Dunedin MP William Reynolds proposed a standard time to be adopted for NZ which was passed by Parliament

He had proposed "Christchurch mean time" be observed; then amended wording to "New Zealand mean time" after the debate

NZ time of 11.5 hours in advance of Greenwich Mean Time was selected by James Hector, Director of the Geological Survey

He'd selected the meridian 172° 30' which was within three minutes of NZ's mean longitude from the Nth to Sth Pole

Sailors could determine latitude (how far north or south) a vessel was but not longitude (how far east or west of land)

To aid the navigation of vessels, London's Greenwich Royal Observatory was commissioned by King Charles II in 1675

Built on hilltop site of former Greenwich Castle in Greenwich Park in S.E. London, it overlooked River Thames to north

The Observatory's Octagon Room with high windows & south-facing views was designed by architect Sir Christopher Wren

Wren was also former Savilian Professor of Astronomy at Oxford University (1661-73)

The Observatory's astronomers made a map of the heavens to find out the longitude (east or west) of places

To indicate longitude, imaginary lines (meridians) were used in a half circle from North to South Poles around the Earth

Greenwich used 0° longitude (called the Prime Meridian) as the starting point for measuring distance both east & west

As there is 360° in a circle, the meridian halfway around Earth from Greenwich is 180° longitude (called antimeridian)

The meridians are numbered up to 180° east or 180° west of the Prime Meridian

To indicate latitude, lines were run horizontal & parallel to the Equator which divides northern & southern hemispheres

Latitude tells how far North (0 to 90 degrees N) or South (0 to 90 degrees S) of the Equator

Astronomers noted the exact time each star crossed the Prime Meridian that ran through London, to build a map of the sky

The position of the Sun at noon was also marked on the meridian that runs between Nth & Sth Poles through London

As the planet Earth rotates 360 degrees on its axis every 24 hours, the sun was in the same position from noon to noon

Navigators used telescopes when at sea to observe the night sky & the Sun

(Capt. James Cook & Charles Green used a Gregorian reflector telescope to observe Transit of Venus from Tahiti in 1769)

Chronometers were used to calculate longitude by measuring difference between their local noon & noon in Greenwich

(Capt. Cook carried four chronometers on his second voyage to NZ in 1772–75) (Image: Wellington Museum exhibit, c.1820)

In 1868, NZ's time was calculated based on its longitudinal distance (median) being 172° 30′ east of Greenwich

As the Earth rotates 360 degrees on its axis about every 24 hours, NZ was approx. 11.5 hours ahead of Greenwich

(The Earth turns one degree of longitude in 1/360th of a day, or every four minutes)

On Mon, 2 Nov 1868, NZ adopted a standard time when all telegraph offices connected to Wellington struck 12 noon

Post offices, many of which shared the same building as the telegraph office, also adjusted to the same time

On 2 Aug 1880, UK Parliament officially adopted GMT, as introduction of railways needed a national time system

GMT was then adopted by US on 18 Nov 1883 when telegraph lines transmitted noon time signals to all major cities

Several other countries chose different meridians than Greenwich as their Prime Meridian (0°) for their navigation

However, with increased travel leading to increased trading, a demand for one international prime median grew

In Oct 1884, an international conference held in Washington designated there be one Prime Meridian - Greenwich (0°)

Since then, Greenwich was used as reference point for all other meridians of longitude between the North & South Poles

The Prime Meridian is marked by a metal line fixed in Greenwich Observatory's courtyard. (See image taken during WWII)

The line is lit at night by a laser beam from a point above the Airy Transit Circle telescope & can be seen c.20km away

In 1893, Greenwich began using a 28-inch wide lens refracting telescope which could move east to west

It was aligned with Earth’s axis & moved parallel to the equator; hence, was named 'Great Equatorial Telescope'

In 1909, MP Thomas Sidey introduced Local Time Bill for clocks to be brought forward 1 hr in Summer, which wasn't passed

He saw benefits as greater use of daylight in Summer; an extra hour for evening recreation; & saving on artificial light

Sidey reintroduced his Bill every year & it nearly became law in 1915 & 1926

The Bill had been accepted by the House of Representatives but was rejected by the Legislative Council

Increasing support for daylight saving portrayed by cartoonists

On 30 Sept 1927, Sidey achieved the enactment of his daylight saving measure as the Summer Time Act

Clocks advanced one hour between 6 Nov 1927 & 4 March 1928

Advancing clocks by 1 hr made NZ time 12.5 hours in advance of Greenwich time

Summer Time Act 1928, clocks were advanced only 30 mins & the period extended to 14 Oct 1928 - 17 March 1929

Summer Time Act 1929 enacted 30 mins on the second Sunday in Oct to third Sunday in March of following year

Summer Time Amendment Act (enacted 15 Dec 1933) extended daylight saving to last Sunday in Sept to first Sunday in April

In 1941, the Daylight Saving Emergency Regulations extended daylight saving for greater use of sunlight during WWII

Instead of finishing on last Sunday in April, clocks continued being put forward 30 min until the following Sept

In 1928, the term Universal Time (UT) was introduced by the International Astronomical Union (IAU) to refer to GMT

The IAU was founded on 28 July 1919 in Brussels, Belgium & is based in Paris, France

In 1955, the caesium atomic clock was invented which was more accurate than astronomical observations for UT

It measures time by monitoring the resonant frequency of atoms, & is based on atoms having different energy levels

The atomic clocks' readings led to concept of UTC (Coordinated Universal Time) being formed in 1960 by radio signallers

The concept was formed by the International Radio Consultative Committee which began using it the next year

In 1972, Coordinated Universal Time (UTC) replaced GMT as the time standard & was adopted in NZ with the Time Act 1974

The unit of UTC is the atomic second, & UTC is widely broadcast by radio signals which are used to set clocks

Map shows UTC's 24 time zones & the International Date Line (IDL) which passes through mid-Pacific Ocean

UTC is based on the International Atomic Time (TAI) which is maintained by over 450 atomic clocks worldwide

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