Zenith Day’s shadowy story is set to hit the NT

Territorians will be treated to a bizarre astronomical phenomena on Saturday. Read what will happen.

Saturday will see the return to the Territory of Zenith Day, the twice-yearly solar phenomena that southerners never get to see.

At 12.35pm on Saturday, October 26th, the sun will be directly overhead and, according to NT amateur stargazer Geoff Carr, extremely close to the zenith position – or ‘top’ of the sky.

For a few minutes either side of the sun being directly overhead “a quirky thing happens”, Mr Carr said.

“Vertical objects such as poles and fences cast no shadows. Humans and animals can stand in their own shadow below them. It might sound like nothing special, but to see this happening is quite striking.”

Where have all the shadows gone? Zenith Day kicks in at 12.35pm on Saturday.

A long-time contributor to the Sunday Territorian, Mr Carr said of the many topics he discussed in his astronomy columns, Zenith Day was the one that generated most reader interest.

Zenith Day is restricted to locations between the tropics of Capricorn and Cancer and the dates vary depending on latitude. The first one each year occurs around Bombing of Darwin Day on February 19, when Wet Season clouds mask the moment.

While it would make sense that the phenomena occurred right on midday, Geoff explained that science isn’t always so neat.

“The Earth’s orbit around the sun is not circular, but slightly elliptical,” he said.

“When the Earth is nearer the sun its orbital speed increases slightly and the Sun is in front of civilian time.

Territory stargazer Geoff Carr.

“The opposite happens when the Earth is furthest in its orbit. This is called the Equation of Time and has to be taken into consideration when using a sundial, and the discrepancy in minutes is often marked on sundials, which are latitude dependant.”

Australia’s less than representative time zones also contributed to the 12.35pm zenith moment instead of it being noon, when it’s natural to assume the sun would be directly overhead.

“When time zones were being decided for Australia, Adelaide businesses wanted to

be more aligned to daylight in Melbourne and Sydney so Adelaide could continue their stock market trading,” Mr Carr said. “So they marked their solar time not with Adelaide, but much closer to the Victorian border, thus our Darwin clocks have a bigger discrepancy than just the Equation of Time.”

Mr Carr advised shadow-gazers to set an alarm to not miss the phenomena.

“But if you miss the exact time and date, no problem, the effect is very similar around the same time with days either side of October 26. For creative photographers it offers some interesting opportunities. Enjoy the spectacle.”

Originally published as Zenith Day’s shadowy story is set to hit the NT