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Star Watching Network - Results of FY2006 Summer Star Watching

February 20, 2007

The summary of observation results of FY 2006 Summer Star Watching is as follows:

(1) Observation period:
August 15 to August 28, 2006
Participants were asked to watch stars for more than one day during the period.

(2) Number of groups and individuals participating
While 554 groups applied for participation, only 416 groups actually conducted observation in 439 locations, due to bad weather and other reasons. Total number of individuals participating was 7,541 (in FY 2005, 427 groups and 7,325 individuals participated in the Summer Star Watching).(Fig. 1)

(3) Observation results
The stars are difficult to watch in large cities, with innumerable artificial lights making the night sky brighter. Although the long-term observation results for almost 20 years show no major changes in the visibility of stars, it indicates the trend of decreasing visibility.

(a) Naked eye observation of the Milky Way
Participants observed the visibility of the Milky Way at different altitudes from the horizon (in the vicinity of Cygnus (high altitude), Scutum (medium altitude), and Sagittarius (low altitude)). Visibility differs according to the altitude above the horizon. The lower the altitude, the more participants reported that they could not see the Milky Way because of the bright night sky. This shows that the night sky is affected more by artificial lighting at low altitude (Fig. 2).

(b) Binocular observation
Participants observed stars in a triangle-shaped area in Lyrae, including the 1st magnitude star (Vega), with binoculars. The results are compiled into an "Average Magnitude of Stars Observed" (an average of magnitudes of visible stars) classified by the size of cities (Fig. 3). The results indicate that the larger the city, the harder it becomes to observe stars. In large cities, only bright stars can be seen.

(c) Brightness of the night sky based on color slide photographs
Figure 4 illustrates the brightness of the night sky based on the slide photographs taken at fixed observation points. Assessment of brightness using slide photographs is very objective. On the contrary, naked eye or binocular observation can not avoid deviation in the assessment since it is done by many different observers. Furthermore, since observation points are fixed, data obtained become more reliable as long-term data. Color slide observation shows that, in general, there is no large fluctuation in the brightness of the night sky.

All figures are in Japanese.

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