Broome's 'staircase to the moon' effect a unique combination of tides, location and cosmic angles
https://www.abc.net.au/news/2022-05-20/ ... /101081984
Broome's staircase to the moon phenomenon draws thousands of people from around the world to Roebuck Bay annually, but the science behind the spectacle is just as fascinating.
The effect creates what appears to be a glowing staircase over the mudflats leading to a full moon, a combination of location and conditions unique to Western Australia's north.
"During dry season, three times a month, there's an alignment between the Earth, the sun and the moon which creates big tides, or spring tides," Broome astronomer Greg Quicke said.
"That means we've got high tide at lunch time and low tide in the evening [so] all the mudflats are wet.
"The ripples in the mud have water in them, and they create a direct reflection of the moon as it appears over the horizon."
This is what gives the reflection its "staircase" appearance.
Location makes it special
Mr Quicke said the location of Roebuck Bay made the occurrence possible.
"Broome is blessed to sit on a peninsula that's 10 kilometres long and 4km wide," he said.
"Roebuck Bay faces the east, and that's where the Earth turns to the part of the sky that the moon is in, at a particular time.
"Tonight, it's 6:27pm, or something."
"Every one of them is different; you never know what you're going to get."
A tourism drawcard
Long-time Broome tourism operator Robyn Maher said people came to Broome to coincide with the natural phenomenon, from March through to October.
"If you're in Broome for the three dates, make sure you see the staircase each evening," he said.
"There might be a bit of cloud this evening, but the next two nights the colours might be different.
"If there's a bushfire, the moon might be bright red."
But there is more to Broome's sky show than its staircase to the moon.
Yawuru singer-songwriter Steve Pigram said the constellations of Orion and Scorpio signified the changing of the seasons.
"The constellations signify the coming of winter, of Barrgana season, and that's also when the south-east starts to blow," he said.
"It signifies the coming of the blue nose salmon.
"They start to run and all the locals go out and catch them in the bay."
Mr Pigram said the staircase to the moon did not hold much significance when he was a child.
"It wasn't made a tourist attraction 'til the 70's or maybe 80's," he said.
"Sometimes, when you're in your hometown, you don't really know what you've got 'til someone else says, 'Hey, that's pretty good mate'."
- The reflective effect is a dream for keen photographers.(James Curry via ABC Open Pilbara WA)
- broome moon.jpg (65.97 KiB) Viewed 963 times
