Observations

Predicting the visibility of the crescent Moon in May and June 2018

The calendar we use in civil society (the ‘Gregorian’ calendar) is a solar one – based on the time it takes for the Earth to orbit the Sun. Many religious calendars, however, are based on the phases of the Moon. These include the Catholic, Jewish and Islamic religious calendars. The dates of festivities, holidays and important events in the lunar calendar move by about 10 days every year within the Gregorian calendar.

The ninth month of the Islamic calendar, known as Ramadan, is the Islamic month of fasting. The Hilal, or crescent moon, marks the beginning of the fasting period. However, there are differences of opinion on how to define ‘crescent’. While some simply demand an unaided sighting by eye of the crescent moon, others are leaning towards using astronomical calculations to avoid confusion.

 

The following astronomical data concern the new and crescent moons in May and June of 2018.

The simplest useful criterion is the lagtime, or difference, between sunset and moonset. If that time is greater than 47 minutes (at the latitude of Sydney) the crescent moon should be visible to the unaided eye after sunset and before the setting of the Moon.

The most common method of prediction, however, is to use a scheme developed by Dr Bernard Yallop of HM Nautical Office and proposed in 1997. This scheme or algorithm involves the altitude difference between the Sun and the Moon; a calculated ‘best time’ to view the Moon; and the width of the crescent. The Yallop method is applicable to any location. More details of this method and maps displaying the Moon’s visibility are available here.

The new moon in May 2018 will occur at 9:48pm on Tuesday, May 15 (all dates & times are for Sydney and in AEST, i.e. Sydney time). On May 15 the Sun will set at 5:03pm and the Moon at 5:08pm. The lagtime is only 5 minutes so the crescent moon will not be visible to the unaided eye at Sydney’s latitude, and the Yallop method concurs. On May 16 the Sun sets at 5:02pm and the Moon sets at 5:54pm. The lagtime is now 52 minutes so the crescent moon should be visible (at Sydney’s latitude) to the unaided eye if the western sky is clear of cloud, and the Yallop method concurs.

The following new moon (marking the end of Ramadan and thus the beginning of Eid-ul-Fitr) occurs on Thursday June 14 at 5:43am. On June 14 the Sun will set at 4:53pm and the Moon will set at 5:27pm. The lagtime is only 34 minutes so the crescent moon will not be visible to the unaided eye at Sydney’s latitude, and the Yallop method concurs. On June 15 the Sun will again set at 4:53pm, but the Moon sets at 6:29pm. The lagtime is now 96 minutes so the crescent moon should be easily visible (at Sydney’s latitude) to the unaided eye if the western sky is clear of cloud, and the Yallop method concurs.

What about Australian locations other than Sydney?

If your latitude is within about a few degrees of Sydney’s latitude then the lagtime method of 47 minutes should work sufficiently well for you – but you will need to find the time of sunset and moonset for your particular location. Nevertheless, in 2018 the above conclusions for the dates of the beginning and end of Ramadan should hold for your location. For other latitudes different lagtimes may be required but these are beyond the scope of this article.

The Yallop method also draws the same conclusions (in 2018) for the unaided visibility of the crescent Moon on the above dates (May 15 & 16 and June 14 & 15) for all locations in Australia. In addition, on June 14, if you are north and west of a line that (roughly) joins Perth to Darwin, then the crescent Moon may be visible with binoculars or telescopes (but not to the naked eye). Please wait until after the Sun has set before using binoculars or telescopes to avoid the risk of eye damage.

22 responses to “Predicting the visibility of the crescent Moon in May and June 2018

  • Dear Andrew Jacob

    Thank you very much for taking time to provide these valuable information. Could you please let me when the new moon will born in August 2018 . Appreciate if you could provide a report such as this for August as well

    • Sheikh Muhammad SALEEM, We are pleased you find our posts useful. While we would love to be able to provide visibility times for the Moon all year round, our resources unfortunately do not allow for this. However, you can determine the visibility for yourself using the web site noted above. You could also calculate the lag-time using the Moon and Sun set times published in our Australasian Sky Guide, or finding those times from, for instance, TimeAndDate.

  • Hi Andrew.I hope this question isn’t too difficult. Just Wondering, on the 13th June 2018 is at at all possible to see the moon anywhere in Turkey after sunset or is it impossible.
    1- Will you be able to see the moon on 13th June in Turkey -with the naked eye or with some visual aid such as binoculars/telescope?
    2-Will you be able to see the moon on 13th June in Turkey- at the Observatory using equipment available at the Observatory in Turkey or any other Observatory.

    • Oussama, Thanks for your questions and I apologise for the delay in replying. For Sydney (according to the criteria in the post) the crescent Moon will not be visible on June 14 by naked eye nor by telescope. Unfortunately, we don’t have the resources to determine visibility for other locations – there are so many! But I encourage you to view the ‘Yallop’ maps which you can use to answer your questions. With regards to the lag time criteria, you can use the same lag-time criteria for Perth because it is at a similar latitude to Sydney, but for other locations other lag times are required. Again unfortunately, we don’t have the resources to determine these lag times. I wish you all the best for your viewings tonight and tomorrow!

  • Hi Andrew. Just Wondering, on the 14th June 2018 in Perth, Sun sets at 5:19pm and last light from the sun is at 5:46pm and the Moon sets at 5:58pm which is 12 minutes after the last light from the sun.
    1- Will you be able to see the moon on 14th June-with the naked eye or with some visual aid such as binoculars/telescope?
    2-Will you be able to see the moon on 14th June- at the Observatory using equipment available at the Observatory.

  • Hi Andrew. Just Wondering, on the 14th June 2018 in Sydney, Sun sets at 4:52pm and last light from the sun is at 5:20pm and the Moon sets at 5:28pm which is 8 minutes after the last light from the sun.
    1- Will you be able to see the moon on 14th June-with the naked eye or with some visual aid such as binoculars/telescope?
    2-Will you be able to see the moon on 14th June- at the Observatory using equipment available at the Observatory.

  • Hi Andrew. Just Wondering, on the 14th June 2018 in Melbourne, Sun sets at 5:07 and last light from the sun is at 5:36 and the Moon sets at 5:43 which is 7 minutes after the last light from the sun.
    1- Will you be able to see the moon on 14th June-with the naked eye or with some visual aid such as binoculars/telescope?
    2-Will you be able to see the moon on 14th June- at the Observatory using equipment available at the Observatory.

  • Dear Andrew,

    Thanks for your wonderful analysis. I am bit surprised that why people in Australia are attempting to do moon-sighting on 15 May 2018 when:
    – the age of the moon on the sunset time will be approximately 4 hours and 19 minutes; and
    – also the window to observe moon on 15 May is for 5-6 minutes only, i.e. between sunset and moonset.

    As per my understand the correct date to view moon for new Month is upon sunset of Wednesday 16 May 2018 between sunset 5:07 pm and Moonset 5:59 pm (approximately) . The age of the moon will be approx 19 hours and 20 minutes and will be above 9 degree angle.

    Your comments and guidance will be highly appreciated.

    Thanks

    Please note the timing info is given with reference to Canberra.

    • Farooq, I only include the information for May 15 (and June 14) so that everyone can see the whole story!

  • Thank you so much Andrew. Every year, I read your article to have a firsthand knowledge about the most authenticated information concerning the new Ramadan/ Eid moon .
    Really appreciate your effort.

  • Thanks Andrew like every year your information are very valuable, much appreciated. God Bless you. Abid

  • Many thanks Andrew, I have now learned the method, but still love to see your writings.

    Many Thanks.

  • Thanks Andrew for your contribution each year during this time of Islamic calendar. Just a little query -will the lag time on May 15, 2018 between sun and moon set 3 or 5 minutes?

    • Thanks Abdul, well spotted! Sorry for the basic maths failure there. I have edited the post to show the correct lagtime of 5-minutes on May 15.

  • Many thanks for your very valuable advice.
    It is very much appreciated, and May God reward you for your efforts.
    Oussama Magar

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