June 26, 2019

17.08.09: A Ramadan Moon.

Slender New crescent Moons are always a fun and interesting challenge to spot…but this week’s crescent Moon is special. For the astronomy challenge of the week, I give you a Ramadan Moon. The Muslim calendar is one of several that are lunar based, meaning that it follows a cycle of complete phases of the Moon through one synodic month, which is 29 days 12 hours 44 minutes and 3 seconds long, respectively. This means that any given lunar calendar falls about 10-12 days per year out of sync with the Gregorian solar based one. Ramadan, (“or Ramazan,” as its known in Turkey) begins at sunset with the sighting of the Hilal or crescent New Moon and is the ninth month of the Islamic calendar.

This was the month that the Qur’an was revealed to Muhammad, and Muslims fast from sunrise to sunset to concentrate on faith and spirituality. I remember living in Turkey in the early 90′s and waking to the sound of the village Ramazan drummer who would stir families for an early meal before fast! This year, Ramadan is generally listed as starting at dusk on Saturday, August 22th… However, there is a chance this year that the New Moon could be sighted on Friday night. New Moon falls on Thursday, August 20th at 10:02 UT, making sightings from the Middle East just do-able at an age 30+ hours… believe me, anything under 24 is tough, and requires pristine skies. Here from Astroguyz HQ in Florida a sighting should be achieve-able at 38+ hours; I urge you to give this fun (and easy, sans equipment) naked eye observation that has its roots in antiquity a try!

This weeks astro-term is Danjon Limit. Not to be confused with the Danjon number, which is a rating scale for the color of lunar eclipses, the Danjon Limit is the theoretical minimal separation between the Moon and Sun at which the slender crescent Moon can be seen. Proposed by French astronomer Andre Danjon in the 1930′s, it’s value was set at 7 degrees of separation and was thought to be the product of a rough lunar surface reflecting the Sun at a very oblique angle. Of course, you’re also viewing the New/Old Moon through a very thick layer of the atmosphere at a very low angle of elevation, and against a bright sky to boot! A fun test would be to apply the Danjon Limit for a crescent sighting of the New Earth on the airless Moon… hopefully we can blog about that firsthand one day. And where does the actual record for a naked eye sighting of the Moon stand? At 14 hours 51 minutes, at about 7.5 degrees of separation achieved by students from the New Mexico Institute of Mining and Technology in May 1989. The Danjon limit provides that this could still be improved on, up to about 12:45, which has been done with optics.


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