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Thursday, 23rd August 2012

Astronomical Observations and Time Services - Continuation of Historical Missions

At the time of establishment of the Hong Kong Observatory in 1883, the time service was one of its three historical missions[1] . In that era, staff of the Observatory operated transit instrument (Figure 1) to determine the local time based on astronomical observations, and reported the time to mariners and local residents by lowering a time ball (Figure 2). Although time services nowadays in Hong Kong no longer rely on astronomical observations, the close relationship between astronomy and time services persists to date - both are still fundamental duties that the Observatory shoulders.

The annular solar eclipse on May 21 and the Transit of Venus on June 6 earlier this year were both very rare astronomical events. To strengthen the public's knowledge and to record the events for future references, the Observatory provided webcasts jointly with the Hong Kong Space Museum and the Ho Koon Nature Education cum Astronomical Centre. Our colleagues even conducted astronomical observations at Cape D'Aguilar, the southeastern tip of the Hong Kong Island.

In preparation of the first ever "location shooting", besides buying the instruments needed, colleagues also collected relevant information, sought advice from the experienced, and rehearsed on the rooftop of the Observatory's Headquarters several times to identify the optimal filter and settings of aperture and shutter etc. The night before the event, colleagues arrived at the Observatory before midnight for preparation, then proceeded to Cape D'Aguilar in the middle of the night. After arrival, the work to establish a mobile astronomical observatory commenced immediately. As soon as the astronomical instruments and network equipment were assembled, final tests were conducted to ensure smooth operations. Although the annular solar eclipse could not be recorded due to cloud coverage, magnificent photos were captured during the Transit of Venus (see extended reading), which brought the team into euphoria. Having to endure strong winds blowing into faces during the annular solar eclipse and the fierce sunshine during the transit of Venus, our colleagues worked hard without a murmur, reflecting their professionalism. (Figure 3 & 4)

For the leap second introduced on July 1, preparatory work to ensure proper operation of the Observatory's time services started a few years ago. In addition to procuring suitable instruments, it had also been stipulated that only instruments and computer programs shown to pass leap second tests repeatedly could be adopted for operational use. The handling of leap seconds was also emphasized in product developments to ensure that leap seconds could be correctly displayed on all time service instruments and web clocks. On July 1, colleagues closely monitored the operations of the instruments in the Observatory to ensure smooth transition and to record the responses of the instruments for future reference. Apprehensive while expecting the leap second, colleagues could not help acclaiming when the instruments properly showed up "59 minute 60 second" ! (Figure 5 & 6)

Be it an astronomical observation or a transition through the leap second, successful operations depend heavily on seamless co-operation between colleagues. Extraordinary teamwork was displayed in the astronomical and time service operations during the past few months. We wish the team spirit would continue and further contribute towards the promotion of astronomy and the development of time services.

Woo Wang-chun, Mok Hing-yim


[1] There other two being meteorological and geomagnetic observations.

Extended Readings:

- On the abolishment of leap seconds (Observatory's Blog)

- Leap second to be added on July 1, 2012 (Press Release)

- Don't miss the two forthcoming astronomical events (Observatory's Blog)

- Rare annular solar eclipse in Hong Kong on May 21 (Press Release)

- Partial lunar eclipse and rare transit of Venus in Hong Kong in June (Press Release)

- Transit of Venus on June 6 (YouTube)

- Transit of Venus on 6 June 2012 (Astronomical Photo Album on the Web)

Figure 1

Figure 1      Similar type of Transit Circle used by the Observatory for determining
time with astronomical observations in the 19th century.

Figure 2

Figure 2      The Time Ball Tower in use from 1 January 1885 to 1907, which still stands in "1881 Heritage",
the former Marine Police Headquarters at the junction of Canton Road and Salisbury Road.

Figure 3

Figure 3      Staff of the Hong Kong Observatory and of the Hong Kong Space Museum jointly shooting the
annular solar eclipse in front of the Cape D'Aguilar Lighthouse on May 21.

Figure 4

Figure 4      Colleagues of the Observatory shooting the Transit of Venus in front of the Cape D'Aguilar Lighthouse
early in the morning on June 6. The light spot in the sky was the moon.

Figure 5

Figure 5      The caesium beam atomic clocks of the Observatory correctly handled the leap second. The time
displayed on the atomic clocks is Coordinated Universal Time (UTC). Hong Kong Time is
eight hours ahead of UTC. Normally, 00:00:00 follows 23:59:59 immediately. When a leap
second is inserted, 23:59:60 succeeds 23:59:59, followed by 00:00:00.

Figure 6

Figure 6      The web clock of the Observatory successfully displayed the leap second as 07:59:60.

Last revision date: <17 Jan 2013>