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Press Release

"Star Watching Network" - Implementation of 2005 Summer Star Watching and Result of 2004 Winter Star Watching

July 25, 2005

"Star Watching Network" is an activity of simultaneous nation-wide star observation by familiar means, such as with naked eyes or binoculars. This project is conducted twice a year (summer and winter) since 1988 aiming at stimulating interests of people toward clean and clear atmosphere without any light or air pollution.

The Ministry of the Environment (MoE) has tried to widely appeal the significance of clean air through this project. The MoE will foster favorable outdoor lighting set-ups through further promoting various measures such as diffusion of lighting installations with less spill light to upward in the air and with subdued lighting, eventually improving local air quality and preventing global warming. Star Watching Network activities are introduced in the MoE webpage for children (in Japanese).

1.2005 Summer Star Watching

Wednesday, July 27 - Tuesday, August 9, 2005
Participants are required to watch stars for more than one day during the period.

(2)Observation method
(a) Naked eyes
To observe the Milky Way in three different altitudes (in the vicinity of Cygnus, Scutum, and Sagittarius).
(b) Binoculars
To observe stars in a triangle-shaped area in Lyrae including first magnitude star (Vega) and check magnitude of stars observed.
(c) Photographing stars
To take photograph of the night sky near the zenith, using single-lens reflex camera utilizing reversal film (film for slides).

(3)How to participate
Apply to the authorities in charge of air quality management in prefectural, ordinance designated cities, or core city governments. Conduct the observation based on a Manual for 2005 Summer Star Watching and report the results to the authorities.

(4) Fixed point observation
The MoE appointed 24 locations at which observation is conducted consecutively by the same method as photographing stars mentioned (2)-(c) above to assess brightness of night sky. National Astronomical Observatory of Japan (NAOJ) in Mitaka, Tokyo is added as an observation point in 2005.

2.Results of 2004 Winter Star Watching

(1)Observation period
Saturday, January 1 - Friday, January 14, 2005
Participants were required to watch stars for more than one day during the period.

(2)Number of groups and individuals participated
Although 547 groups applied for participation, 359 groups conducted observation in 392 locations due to bad weather condition. The total number of individuals participating in observation is 3,788 (346 groups and 3,491 individuals participated in FY 2004 Winter Star Watching).

(3)Observation results
Participants observed the Milky Way in three different altitudes in the vicinity of Perseus (higher altitude), Gemini's (medium altitude), and Monoceros (lower altitude). There were differences in the visibility of stars according to the altitude. As the altitude lowers, the reporting rate of "not visible due to bright sky" is higher. It confirms that the artificial light influences the visibility of stars at lower altitude.
(a) Naked eye observation of the Milky Way
Participants observed visibility of the Milky Way in different altitude (in the vicinity of Perseus (high altitude), Gemini's (medium altitude), and Monoceros (low altitude). Visibility differs according to the altitude. As altitude lowers, more participants report "the Milky Way can not be seen due to bright night sky". This shows the night sky is affected more by artificial lighting as it get closer to the ground (Fig. 1).
(b) Binocular observation
Participants observed stars near racket-shaped area in Pleiades star clusters by binoculars. The result is compiled into an "Average Magnitude of Stars Observed" (an average of magnitude of stars which were visible) classified by the scale of cities (Fig. 2). The result indicates that visibility of stars is lowered as the scale of city increases, making only bright stars visible.
(c) Brightness of the night sky based on color slide photographs
Color slide photographing of the night sky near the zenith taken by groups with voluntary participation was reconvened from FY 2004. Assessment of brightness by slide photographs is very objective since it is conducted by third person, on the contrary, naked eye or binocular observation can not avoid deviation in the assessment since it is done by many different observers. In addition, observing points are fixed which makes the data to be more reliable as a long-term data. In general, observation shows that there is no large fluctuation. The stars are difficult to see in large cities with innumerable artificial lightings making night sky brighter. Although long-term observation for almost 20 years shows no major changes in the visibility of stars, there is a clear inclination that the visibility is lowering. (Tables 1 & 2, Fig. 3).


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