Observations

Predicting the visibility of the crescent Moon in May and June 2019

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 2019 for Australia.

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 2019 will occur at 8:45am on Sunday, May 05 (all dates & times are for Sydney and in AEST, i.e. Sydney time). On May 05 the Sun will set at 5:11pm and the Moon at 5:38pm. The lagtime is only 27 minutes so the crescent moon will not be visible to the unaided eye at Sydney’s latitude, and the Yallop method concurs. On May 06 the Sun sets at 5:10pm and the Moon sets at 6:16pm. The lagtime is now 66 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 occurs on Monday June 03 at 8:02pm, but this is already after sunset so the Moon will not be seen on this night. On June 04 the Sun will set at 4:54pm and the Moon will set at 5:43pm. The lagtime is 49 minutes so the crescent moon should be visible (at Sydney’s latitude) 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 a degree or so 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 2019 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 2019) for the unaided visibility of the crescent Moon on May 05 & 06 for all locations in Australia.

However, using the Yallop method the situation on June 04 is more complicated. If you are north of a line that (roughly) joins Wollongong to Mount Gambier (in South Australia) then the crescent moon should be visible to the unaided eye if the western sky is clear of cloud. If you are south of this line (i.e. in most of Victoria and all of Tasmania) then the crescent Moon may be visible to the unaided eye, but only after you have found it with binoculars or a telescope. Please wait until after the Sun has set before using binoculars or telescopes to avoid the risk of eye damage. By June 05 the crescent Moon should be readily visible from all locations in Australia.

16 responses to “Predicting the visibility of the crescent Moon in May and June 2019

  • Hey mate,

    I just wanted to know that is the crescent aftee 30 days a bit thicker than the crescent sighted on 29th?

    • Muj, I’m not quite sure what you are asking. Do you mean 29 (and 30) days after the time of New Moon? This doesn’t quite make sense because the whole lunar cycle of phases only takes 29.5 days. At 28 days old the crescent is thicker than at 29 days old, but by 30 days we are into the next lunar month already.

  • Hi Andrew. I have a query: on the night that the moon is said to have been born i.e. tonight, Sunday 5th May, woukd it be visible to the *aided* eye? Would it be visible through a telescope that is?

    • Syeda Waqeea Chaudhry, For this particular case the Yallop method says the Moon would not have been visible to the aided eye, it was just too close to the Sun and to the horizon. However, in some years it can be seen with the aided eye (i.e. through a telescope or even binoculars) even if not to the unaided eye.

  • Thanks Andrew like every year your article is very informative and valuable for us. God bless you.

  • Thank you very much for a very accurate regarding the Crescent Moon for the blessed month of Ramadan in May 2018.

    Our community and I always use your report for the beginning and end of Ramadan and we fast based on your report.

    It is saving us lots of frustration.

    Please keep publishing this report, as it is helping lots of Australian Muslims.
    Kind regards
    Zia Kabir

  • Dear Andrew,
    Thanks for the article yet again. I wait for your article each year for the last 4 to 5 years. I found all these years your predictions are spot on. Thanks for your good work.

  • Hi Andrew,

    Thank you for your article which I always look forward to since the last few years.

    Mustaqeim (Perth)

  • I understand that the correct date to observe the new moon in Canberra or anywhere in Australia through naked eye or (using any other visual aide) is upon sunset of Sunday 05 May 2019 (for Canberra between sunset 5:17 pm and Moonset 5:44 pm approximately).

    Would the Sydney latitude be applicable for Canberra also and therefore no chances of visibility in Canberra.

    • Farooq, The Sydney conclusions should generally work fine for Canberra also. For Canberra, the lagtime is still just 27-minutes (too short), and the Yallop method also says the crescent won’t be visible on May 5, just as for Sydney. But, again as for Sydney, it should be visible on the 6th from Canberra.

  • Thanks for the article. I have a question. What is the possibility of moonsighting from Perth on Sunday evening?

    • Mohammed, Given Perth has almost the same latitude as Sydney we can use the same lagtime as for Sydney. For Perth sunset is at 5:35pm, moonset is at 6:05pm giving a lagtime of only 30-minutes, too short for the Moon to be visible that night. However, it should be visible on Monday night, if the sky is clear.

  • Dear Andrew,
    Many thanks for your very timely report which is very much appreciated and which we wait for each year to help us determine the beginning of Ramadhan.
    Oussama Magar

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