Where You At Q2: How many days til the moon is full?


The supermoon of March 19th, 2011


The second question in the Where You At? bioregional quiz is:

How many days til the moon is full?

I’m not sure how good I would be at this calculation generally. I can’t remember seeing the moon lately but then I can’t remember looking at the night sky recently either. Today, Wednesday 11th April 2018, I’m pretty sure the last full moon was Easter Saturday – which was 31st March – which I think means that we are a few days off new moon – so perhaps it’s not surprising I haven’t seen the moon lately. The moon has a 28-day cycle, so the next full moon should be in about 17 days time – 28th April.

Ok, let’s check. The first result following Google search for “next full moon” is for the promising-sounding space.com and its 2018 Full Moon Calendar. This tells me that the next full moon is on April 30th at 01.58 UTC – so that’s 02.58 British Summer Time – not that the moon cares we put the clock forwards) – so my guesstimation of April 28th is close but off my two days – and new moon is in 5 days on April 16th. (The original quiz gave you slack of two days of scoring for this question – so I’ll take solace in that.) What I got wrong was the 28 days; while the moon does take about 28 days (27.3) to orbit the Earth, the synodic month which gives the cycle of the visible phases of the Moon is actually c.29.5 days.

In calculating when the last full moon was in relation to Easter, I was reminded that in the UK, Easter is the only holiday that moves with the moon – I couldn’t remember the relationship so looked it up:

Easter falls on the first Sunday following the first ecclesiastical full moon that occurs on or after the day of the vernal [spring] equinox.

Easter inherits the relationship with the moon from the Jewish festival of Passover as according to the Bible, Jesus Christ’s death and resurrection occurred around the time of the Jewish Passover. According to the Hebrew lunar calendar, Passover is celebrated on the fourteenth day of the Spring month of Nisan aka Aviv  – which means that it generally occurs on the first full moon following the vernal equinox.

Why does it though? One clue may be in the name of the month Aviv which means the time when the Barley becomes ripe. The days around the full moon following the vernal equinox would have provided the longest days for harvesting in that month (12 hours of the day plus the hours of the night lit by the moon). After the first harvest, the first bread of the year’s grain could be made.

The phase of the moon has few effects on my life – my office job doesn’t follow its cycles, and hunting down food in the supermarket of an evening does not demand moonlight. I knew the Easter moon because I had been planning a night walk for the week before and had scheduled it close to the full moon to benefit from the light in the remote location I intended to walk (bad weather forced a cancellation in the end) – but that’s not a regular calculation I have to make. Sometimes the moon creeps around the sky and shines brightly through our thin bedroom curtains which is charming/annoying depending on sleep disruptive we find it – but thicker curtains would dispel its influence entirely.

In Burnham-on-Crouch, the most relevant aspect of the moon phase these days is probably its effect on the tides – which are relevant to both the boating community and to the Environment Agency, who tend to close the town seawall flood barriers around new and full moons.

Mon 30 April Monday 04-30   Full Moon
High Tide: 01.20 5.1m
Low Tide: 07.47 -0.1m
High Tide: 13.44 5.3m
Low Tide: 19.55 0.1m


High tide at the Quay, Burnham-on-Crouch. New Moon January 18th, 2018


The population doesn’t seem to be bothered – memories of the great flood of 1953 are fading now and even fewer reflect on the fact that the storm which ostensibly caused the deluge crossed the North Sea two days after the full moon, interacting with the spring tides (when the gravitational pull of the Sun and Moon combines to create the highest tide of the lunar cycle). As the basal sea-level rises, and as the weather becomes more erratic – the moon phase and its tidal effects will become increasingly relevant on the sinking Essex coast.

Next up: I’ll try and answer – What soil series are you standing on?

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