Additional of the Light Filter to the Telescope for Monitoring of the New Moon of the Hijri Calendar

Abstract Direct observation of the shape of the new moon as a sign of the beginning of the Hijri month, which currently uses more telescopes, is called the monitoring method. Observations of the new moon were carried out shortly after sunset, causing new problems in the monitoring process using telescopes due to the evening light. The optimization of the telescope for amplifying the wavelength of light from the new moon also strengthens the wavelength of the evening light. Therefore, this study aims to improve the quality of the new moon image observed with a telescope equipped with a light filter that can distinguish between the new moon's and the twilight's lights. The literature review of the experimental light filtered from a tungsten lamp, which is assumed to be close to the wavelength of the evening light, shows that the wavelength value for the red filter shows the highest value compared to orange and green 6.2936 x 10-7 and 5.0738 x 10-7 m, respectively. Applying a red-light filter made of plastic coats the clear glass on the front and back. The filter is placed on the objective lens of the SKYWATCHER BK909 NEQ2 telescope. The test results show that the unfiltered observation shows that the new moon tends to be thinner while the red-light filter tends to be thicker. Based on the results of the literature review and experimental tests that have been carried out, it is concluded that the red-light filter can reduce twilight light in observing the new moon on the Hijri calendar.