Starting at sunset on June 17, Muslims around the world will be looking for the new crescent moon, or young crescent to return to the evening sky. Its sighting ushers in the Holy Month of Ramadan, ninth month of the Islamic year. Will this date mark the beginning of Ramadan? The answer is likely no, because this month’s new moon was June 16 at 14:05 UTC. On June 17, the moon will be close to the horizon and will set soon after sunset. Thus the young moon’s sighting – which marks the start of Ramadan – is by no means assured.

If it isn’t seen on the evening of June 17, the start of Ramadan will wait until the evening of June 18.

Read more: What’s the youngest moon you can see with your eye alone?

Ramadan, the month of fasting from dawn until sunset, continues until the appearance of next month’s young crescent moon.

It’s our understanding that the month of Ramadan can start on different dates, depending upon one’s geographical location. On June 17, you’re more likely to see the whisker-thin crescent moon from South America than in the United States, Canada, Europe, Africa, Asia or Indonesia. So possibly Ramadan could start on the evening of June 17 for Muslims in South America, but not until the evening of June 18 for their counterparts elsewhere around the world.

The Islamic calendar is strictly lunar. The lunar month represents the time between successive new crescent moons: 29 to 30 days. The lunar year, consisting of 12 lunar months, totals 354 or 355 days. That’s roughly 11 days shorter than the seasonal year on which our Gregorian calendar is based.

Because of this difference between lunar and seasonal reckoning, the date of Ramadan comes about 11 days earlier every year. Not a fixture of any particular season, Ramadan backtracks through all 12 calendar months in cycles of thirty-three years.

Bottom line: The start date for Ramadan in 2015 will vary with location. South America might catch the thin crescent moon on June 17. The evening of June 18 might mark the date for much of the rest of the world.

© 2014 Earthsky Communications Inc

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