Brightness and color variation for evening and morning twilights at Bahria of Egypt IV

Hassan, A.H.; Abdel-Hadi, Yasser A.; Issa, Islam; Hassanin, N.Y.

doi:10.1016/j.nrjag.2014.02.004

Cited by 6 publications

(1 citation statement)

References 10 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In addition to the naked eye observations which recorded on four locations in Egypt; Matrouh, Bahria, Kottamia and Aswan and all had the same results. In 2014, Hassan et al (2014aHassan et al ( , 2014b concluded that there is a good agreement between the photoelectric measurements and the naked eye observations of the beginning of morning twilight (true dawn) in four locations in Egypt (Issa and Hassan, 2008a, 2008b, 2008cIssa et al, 2009Issa et al, , 2011Hassan et al, 2013Hassan et al, , 2014aHassan et al, , 2014bHassan and Abdel Hadi, 2015). All the above mentioned results are summarized in Table 5.…”

Section: Comparison Between the Current Results And The Preceding Resmentioning

confidence: 88%

Twilight observation by the naked eye of the dawn sincere at Hail and other areas in Saudi Arabia

Khalifa

Hassan

Taha

2018

NRIAG Journal of Astronomy and Geophysics

Self Cite

View full text Add to dashboard Cite

Naked eye observations of morning twilight phenomenon at Hail and other areas of Saudi Arabia are recorded. During the interval from 2014 to 2015, about 80 morning twilight observations were carried out in Hail at longitude λ = 41°42′E and latitude φ = 27°31′N for a desert background. The phenomena was followed over azimuth angles ranged from 0°to 20°of solar vertical direction and from 0°to 10°along the altitudinal range. By selecting 32 days with a very good visibility, it was found that Sun depression, D o , lies in a range between 13.48°a nd 14.69°with an average of 14.014°± 0.317. The difference between our obtained value and that one which is currently applicable in Saudi Arabia is about 4°. The results indicate that dawn (white thread browser) occurs at a sun vertical depression angle D o = 14.66°(mean + 2SD) according to the normal eye estimations. The results at different areas in the deep desert in KSA showed that the beginning of morning twilight and true dawn is at sun vertical depression D o = 14.88°(mean + 1SD). The current study shows significant results, which are comparable with both naked eye observations and photoelectric measurements of true dawn in both Egypt and Libya for desert background.

show abstract