Media

The largest ever database on night sky brightness
HK urban night sky can be 1,000 times brighter than the darkest standard

19 Mar 2013

Light pollution is a severe environmental problem in a crowded metropolitan such as Hong Kong. The public is growing acutely aware of this issue as reflected from the increasing number of complaints to the authorities. The Hong Kong Night Sky Brightness Monitoring Network (NSN) was developed by physicists at the University of Hong Kong (HKU) to monitor the light pollution condition.  Over 5 million night sky brightness measurements were collected since the inception of the project in May 2010, making it the largest single database on night sky brightness ever collected in the world.  The HKU scientists found that manmade outdoor lightings are indeed the major contributor to light pollution, with the sky found to turn significantly darker in later evening when these lightings are turned off during the night.  The Hong Kong urban night sky was found to be 100 to 1,000 times brighter than the international dark sky standard between 8:30-11:00pm, making it one of the most light-polluted cities in the world.

Local urban night sky can exceed 1,000 times brighter than the international standard
It is found that the night sky measured at Hong Kong Space Museum in Tsim Sha Tsui between 8:30pm–11pm is on average over 1,000 times brighter than the international standard of dark sky, caused by the large number of signboards and floodlights nearby.  The standard is established by the International Astronomical Union and refers to the brightness of a night sky not under the influence of manmade light pollution. Even a relatively remote location such as the Wetland Park is on average over 100 times brighter than the standard.

The NSN consists of 18 monitoring stations distributed around Hong Kong, measuring the night sky brightness continuously every night.  Real time data are transmitted to HKU via mobile phone network.  The NSN is fully automatic and the research team can provide real-time night sky conditions for everyone concerned. “This represents a great advancement over our pervious method,” commented Mr Chu Wing SO, the project manager of NSN, “as we are not bound by limitations of manpower.  We can measure the night sky accurately and continuously even in remote area which was not possible in the past.”

Light pollution is swiftly destroying the few remaining dark sites
The research team concluded that night sky brightness is closely related to land utilization near the monitoring stations.  Excluding effects from meteorological or astronomical factors, the 12 urban stations recorded a night sky between 8:30pm–11pm on average almost 10 times brighter than that for the 6 rural sites.  In particular, the night sky at King’s Park in Kowloon was on average 33 times brighter that of the Astropark in the Sai Kung Country Park in that same period.  “This conclusively shows that manmade outdoor lightings is the dominant factor in determining the extent of light pollution,” argued Dr Jason Chun Shing PUN, the principal investigator of NSN.  He also notices that “even though the Astropark is the darkest station in our study, its night sky is still at least 20 times brighter than international dark sky standard before 11pm; light pollution is swiftly destroying the few remaining star-grazing locations in Hong Kong.”

The HKU team also found that the night sky dims progressively when public and commercial lightings are being turned off during the evening.  The Hong Kong Space Museum in Tsim Sha Tsui, for example, suddenly gets darker near 11pm, 12am, and 1am every night, which duplicates the timing patterns of the outdoor lightings nearby by.  This no doubt proves that human lighting is the source of light pollution.

|The NSN was funded by the Environment and Conservation Fund of the Environmental Protection Department, and the HKU Knowledge Exchange Fund.  Results of the project will provide the scientific basis for the Government in related to possible developments of regulations on outdoor lighting usages.  “In addition to regulations, we as a society have to make a commitment to stop abusing the use of outdoor lightings, and to limit its adverse effects to the environment,” stressed Dr Pun.

The Earth Hour organized by the World Wide Fund for Nature (WWF) will be held this year at 8:30pm on March 23. This is a collective environmental action event to promote a sustainable low-carbon future by encouraging people to turn off non-essential lightings for one hour.  In support of this event, HKU will organize the Light Pollution Science Roadshow that evening in the Avenue of Stars, Tsim Sha Tsui, to promote the importance of dark sky and energy conservation to the public. Participants will have a chance to measure light pollution with provided equipment on-site and read the light pollution data collected around Hong Kong via mobile phones.

For more details about the research findings, please visit:http://www.cpao.hku.hk/media/130319science.e.pdf

Details of “Hong Kong Night Sky Brightness Monitoring Network” can be found from
http://nightsky.physics.hku.hk/ , or mobile website http://nightsky.physics.hku.hk/m.
Illustrations and videos can be obtained by internet via http://www.scifac.hku.hk/news/media?page=1.

For press enquiry, please contact:
Ms Cindy Chan, Communication Manager of Faculty of Science, at 2241 5286/  6703 0212 or by email at cindycst@hku.hk, or the principal investigator of NSN, Dr Jason Chun Shing PUN by email at jcspun@hku.hk, or Miss Rhea Leung, Manager (Media) Communications and Public Affairs Office, at 2857 8555 / 9022 7446 or by email at rhea.leung@hku.hk.

Dr Jason Chun Shing Pun of the Physics Department, the University of Hong Kong, says that the Hong Kong urban night sky was found to be 100 to 1,000 times brighter than the international dark sky standard between 8:30 to 11:00pm.

The Hong Kong Night Sky Brightness Monitoring Network (NSN) developed by physicists at the University of Hong Kong (HKU) monitors the light pollution condition since the inception of the project in May 2010.

Dr Jason Chun Shing Pun (left) and Mr Chu Wing SO, the project manager of NSN, indicate that light pollution is swiftly destroying the few remaining dark sites.