What is Zodiacal Light ?
There are millions of objects orbiting the sun. These include planets, dwarf planets, asteroids, and comets. But there are millions more objects, much smaller than these, ranging downward in size to tiny grains of interplanetary matter, the size of sand grains or even smaller. These are too small to be visible as discrete points of light, but like the faint stars in the Milky Way, their combined light causes a faint glow in the night sky. Since these tiny objects cluster along the ecliptic, the path of the sun and planets across the sky, which the ancients called the zodiac, we call this glow the Zodiacal light.
I found there are no detail explanation of this phenomena in General Astronomy books, only few books discuss this, one of them is “A Survey of Radial Velocities in the Zodiacal Dust Cloud” by Brian May, famous guitarist of the Queen, he wrote this book in 2006 for Phd thesis long time after his career in music.
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Zodiacal Light (Left) and Milky Way Galaxy (Right). Credit Caroline Halderman on EarthSky
Zodiacal Light = Sahoor Time
In Islam, Hadith described zodiacal light in reference to the timing of the daily prayers, calling it the "false dawn"( الفجر الكاذب al-fajr al-kādhib) in which the Prophet Muhammad describes the difference between it (false dawn), and the light of the first band of horizontal light before sunrise, the "true dawn"
(الفجر الصادق al-fajr al-shadiq). According to the vast majority of Muslim scholars, astronomical twilight (the sun is -18 degree below the horizon) is considered the true dawn, but it is not correct. According to few articles, observations found that zodiacal light appear when the sun between -19 to -14 degree below horizon, then Fajr Shadiq follow to appear when the sun is -12 degree below horizon.
In Qur’an, Zodiacal Light time is called as Sahar (Q.S. 5434) and As-har (Q.S. 317 and 511, why Qur’an calling it like that? Possibly it’s word root same as 'Sihr' means to bewitch, magic, or illusion. Zodiacal light also called by False Dawn because sometimes it is illusion that people thought it is True Down. Interestingly, Hans Wehr in his book Dictionary of Modern Written Arabic, Sahr/Ashar also means Lungs, maybe because the Zodiacal light look like Human Lungs.
Muslim in Ramadhan recognize this time as Sahoor time, which is the time to have a light meal shortly before Fajar (as starting Fasting).
When I was child, I was curious why fasting starting from Imsak (me in Indonesia, it starting ten minutes before Fajr), What is the sign in the Sky for determine that time? During Prophet Muhammad life time, there was no clock watch to know when sahoor time or fajr start. The only way to know is looking at the sky. Jews starting fasting from Sunset until tomorrow Sunset again, so no problem with the timing sign. Qur’an in AlBaqarah 187 said that fasting starting from True Fajr until Night (not sunset), Fajr is easily known when the sky color starting bright, but muslim should eating sahoor before Fajr rise, the only sign is Zodiacal Light (Sahr/As-har time) at Prophet life time.
Again, interestingly Zodiacal light not always seen everyday for all day year round, for me this proof that Fasting Ramadhan always perform in September crescent moon in the Prophet Muhammad life time as I will discuss later.