1:45 PM - 3:15 PM
[O06-P84] Web camera exposures of the heavenly body in the blue sky of daytime
Keywords:heavenly bodys in the blue sky of daytime, Observation , circular polarizing light filter, double star, Saturn
As shown in Fan, Z. et al. (2021) and others, the blue sky near the zenith at a distance of about 90 degrees from the sun is polarized to about 50% of its light intensity. We made a demonstration observation based on the idea that rotating a polarization filter in the optical path of the telescope should reduce the brightness of the blue sky by 50%, making it easier to observe daytime celestial objects with low polarization. We attached a circular polarization filter to the 25cm aperture refracting telescope at the Nagoya High School Observatory and used a web camera to photograph the double star Albireo in the constellation Cygnus in the blue sky from August to December. The images showed not only the 3rd-magnitude main star but also the 5th-magnitude companion star. The 5th magnitude star was easily visible when observed between 4:00 p.m. and 5:00 p.m. when the Sun's brightness was decreasing. On a day in December when the atmosphere was stable and seeing was good, the 5th magnitude star was visible even at 12:00 p.m. in the afternoon. A report that a 5th-magnitude star was observed from 12:00 noon in broad daylight could not be confirmed by a Japanese-language search, and the observation by Nagoya Senior and Junior High School in 2022 was probably the first. Although limited to days with good seeing, a webcam as a digital eyepiece can be a candidate for observing 5th magnitude stars in the daytime. This is an important finding for groups that hold observing parties, and is reported as Nagoya Senior High School Earth Science Club (2023).
In order to confirm the effect of the circular polarization filter on astronomical observation, we took photographs of Albireo and Saturn at about the same time of day, with and without the filter, and compared the results. When observing the objects in broad daylight with the naked eye, the field of view was completely white without the polarizing filter, making it very difficult to see the fixed stars and planets. However, when the polarizing filter was attached and rotated, the field of view became darker, and when Albireo was observed at the center of the field of view, not only 3rd magnitude stars but also 5th magnitude stars were sometimes visible. When Saturn was observed at the center of the field of view, the structure of Saturn's rings and stripes sometimes became easier to see. Thus, with the naked eye, polarizing filters have a remarkable effect of making stars and planets easier to see because they darken the blue sky. However, when the objects were observed in broad daylight using a web camera, there was little difference between the observations with the circular polarization filter and those with the polarization filter. When Albireo was observed at the center of the field of view, the fainter 5th magnitude star was captured both with and without the circular polarization filter. The ring structure of Saturn was slightly different, but not significantly so.
When daytime stars are observed through a telescope, the sky becomes darker as the magnification rate increases, but stars (point light sources) do not become darker as the magnification rate increases. Also, by increasing the magnification, the contrast increases and daytime stars can be observed. According to this principle, any star, no matter how faint, should be observable as long as the magnification is increased. However, when the
magnification of the telescope at the Nagoya High School Observatory exceeds 64x, stars that are supposed to be point sources of light appear as jagged lumps of light. Therefore, although stars up to 5th magnitude can be observed by increasing the magnification, stars fainter than 5th magnitude cannot be observed because they appear dimmer than 5th magnitude.
The web camera used in this study is more sensitive in the infrared region than the naked eye. Infrared rays can reach farther than visible rays without being scattered in the atmosphere. In daylight, visible light is scattered by the atmosphere, making it difficult to see 5th magnitude stars with visible light alone. However, since infrared rays are not easily scattered by the atmosphere, a web camera could have captured the image of the star by infrared rays in that region and could have captured the 5th magnitude star without a polarizing filter. Polarization filters also reduce non-polarized light by about 20%. Therefore, we believe that the contrast increase by adding a polarizing filter may be offset by the contrast decrease by adding a polarizing filter, making both parts of the image visible to some extent.
In order to confirm the effect of the circular polarization filter on astronomical observation, we took photographs of Albireo and Saturn at about the same time of day, with and without the filter, and compared the results. When observing the objects in broad daylight with the naked eye, the field of view was completely white without the polarizing filter, making it very difficult to see the fixed stars and planets. However, when the polarizing filter was attached and rotated, the field of view became darker, and when Albireo was observed at the center of the field of view, not only 3rd magnitude stars but also 5th magnitude stars were sometimes visible. When Saturn was observed at the center of the field of view, the structure of Saturn's rings and stripes sometimes became easier to see. Thus, with the naked eye, polarizing filters have a remarkable effect of making stars and planets easier to see because they darken the blue sky. However, when the objects were observed in broad daylight using a web camera, there was little difference between the observations with the circular polarization filter and those with the polarization filter. When Albireo was observed at the center of the field of view, the fainter 5th magnitude star was captured both with and without the circular polarization filter. The ring structure of Saturn was slightly different, but not significantly so.
When daytime stars are observed through a telescope, the sky becomes darker as the magnification rate increases, but stars (point light sources) do not become darker as the magnification rate increases. Also, by increasing the magnification, the contrast increases and daytime stars can be observed. According to this principle, any star, no matter how faint, should be observable as long as the magnification is increased. However, when the
magnification of the telescope at the Nagoya High School Observatory exceeds 64x, stars that are supposed to be point sources of light appear as jagged lumps of light. Therefore, although stars up to 5th magnitude can be observed by increasing the magnification, stars fainter than 5th magnitude cannot be observed because they appear dimmer than 5th magnitude.
The web camera used in this study is more sensitive in the infrared region than the naked eye. Infrared rays can reach farther than visible rays without being scattered in the atmosphere. In daylight, visible light is scattered by the atmosphere, making it difficult to see 5th magnitude stars with visible light alone. However, since infrared rays are not easily scattered by the atmosphere, a web camera could have captured the image of the star by infrared rays in that region and could have captured the 5th magnitude star without a polarizing filter. Polarization filters also reduce non-polarized light by about 20%. Therefore, we believe that the contrast increase by adding a polarizing filter may be offset by the contrast decrease by adding a polarizing filter, making both parts of the image visible to some extent.