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Press Release

Star Watching Network - Implementation of Winter Star Watching and Result of Summer Star Watching For FY 2004

December 17, 2004

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 participants toward clean and clear atmosphere without any light or air pollution.

The Ministry of the Environment (MoE) tries to widely appeal the significance of clean air through this project. The MoE will further promote various policies for fostering favorable outdoor lighting sets-ups, global warming prevention and improvement of local atmospheric environment, such as diffusion of lighting apparatus with less light leakage to up in the air and with subdued lighting. Star Watching Network activities are introduced in the MoE webpage for children at (in Japanese).

1.    FY 2004 Winter Star Watching

(1) Duration
Saturday, January 1 - Friday, January 14, 2005
Participants are required to watch stars for more than one day during the period.
(2) Observation method
  (a) Naked eyes
Observe the Milky Way in three different altitude (in the vicinity of Perseus, Geminids, and Monoceros).
  (b) Binoculars
Observe stars near racket-shaped area in Pleiades star clusters and check magnitude of stars observed.
  (c) Photographing stars
Photograph 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 Winter Star Watching Network for FY 2004 and report the results to the authorities.
(4) Fixed point observation
The MoE appointed 23 locations at which observation is conducted consecutively by the same method as photographing stars mentioned (2)-(c) above to assess brightness of night sky.

2.    Outline of observation results for FY 2004 Summer Star Watching

(1) Observation period
6 – 9 August, 2004
Participants were required to watch stars for more than one day during the period.
(2) Number of groups and individuals participated
Although 594 groups applied for participation, 466 groups conducted observation in 456 locations due to bad climatic condition. The total number of individuals participating in observation is 7,690 (456 groups and 7,044 individuals participated in FY 2003 Summer Star Watch).
(3) Observation results
The stars are difficult to watch 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, it indicates the inclination of decreasing visibility.
  (a) Naked eye observation of the Milky Way
Participants observed visibility of the Milky Way in different altitude (in the vicinity of Cygnus (high altitude), Scutum (medium altitude), and Sagittarius (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 more affected by artificial lighting in the part closer to the ground (Fig. 1).
  (b) Binocular observation
Participants observed stars in a triangle-shaped area in Lyrae including 1st magnitude star (Vega) 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 as the scale of city increases, stars are hard to be observed with only bright stars being visible.
  (c) Brightness of the night sky based on color slides photographs
The MoE analyzed the color slides photographs of the zenith in night sky taken at 23 fixed observation points in Japan. It shows that darker stars were visible when the value of "brightness of night sky (mag/?": magnitude per square seconds angle)" is large (Fig. 3).

Fig. 3 illustrates brightness of night sky based on the slides photographs taken in the fixed observation points. Assessment of brightness by slides 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.

Note: The result of photographing of stars by groups with voluntary participation which reconvened from this observation shall be publicized after the next observation, since assessment of slides photographed is taking much more time than expected.


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