The moon is expected to be bathed in a bright orange-red glow on Wednesday when the second total lunar eclipse of the year occurs – and Sydneysiders should have prime-time viewing.
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The cosmic event, often termed a blood moon, will begin about 9.25pm and last for an hour.
A dark sky and clear horizon is essential, but University of Sydney associate professor of physics, John O'Byrne, said predictions of scattered clouds on Wednesday evening should not deter amateur astronomers.
"You only need the spot in the sky where the moon is to be clear," he said.
"From a public point of view, it's the most visible astronomical event in the sky ... it's pretty hard to miss."
A total lunar eclipse occurs when the sun, Earth and moon become aligned, resulting in the Earth's shadow plunging the full moon into darkness.
While total lunar eclipses are not uncommon – there are usually one or two each year – the prospect of a red moon should draw eyes to the sky.
While moon-gazers should see a "orange-red" moon on Wednesday, Dr O'Byrne said, the exact colouring is difficult to predict as it "depends on how much dust there is in the Earth's atmosphere".
"As the amount of volcanic dust in the atmosphere increases, it typically dims the brightness but it also reddens it further," he said.
The red colouring occurs because some sunlight still manages to reach the moon, despite it being in shadow.
This light passes through the Earth's atmosphere, which bends the light so that a small fraction reaches the moon, Sydney Observatory astronomer Melissa Hulbert,. said.
"The Earth's atmosphere also filters out most of the blue-coloured light, which is why it goes red," she said.
Not to be confused with a solar eclipse, where the moon blocks the sun making observation dangerous, a lunar eclipse can be viewed with the naked eye and is safe.
