Stargazers and astronomers looked to the sky this morning as the Moon became blood red in the longest total lunar eclipse in more than a decade.

Amateur astronomer Mike Salway says unlike solar eclipses, it is perfectly safe to view the lunar eclipse with the naked eye.

He says most Australians can see it by looking to the western horizon, but adds residents of Western Australia will get the best solar show.

"The partial phase will start around 4:30am (AEST) and the totality will begin probably about 40 minutes after that. And it will end when you can't see the Moon any more," he said.

"If you're in the eastern states - New South Wales, Victoria and Queensland - the Moon will actually set during totality, so it will go below the horizon while it's still in totality.

"If you're in Western Australia, you do get to see the whole eclipse... it will start around 2.30am and totality will be around 4.30am."

The eclipse is expected to last around 100 minutes for residents of Western Australia - the longest since July 2000.

Fred Watson, the astronomer-in-charge of the Anglo-Australian Observatory in New South Wales, says a total lunar eclipse occurs when the Moon passes through the Earth's shadow.

"The Moon goes around the Earth once in a month. So every month it sits on the opposite side of the Sun, and the Sun is on one side of the Earth and the Moon on the other," he said.

"Periodically you get a situation where the Moon actually passes through the shadow of the Earth as it's on the opposite side of the Sun, and that's what happens in a lunar eclipse.

"[Total lunar eclipses] are the more special kinds, where the Moon doesn't just graze the Earth's shadow to get a partial eclipse, it goes straight through the middle of the shadow, so all the direct light from the Sun to the Moon is cut off by the Earth and the Moon plunges into darkness."

Professor Watson says the refraction of the Sun's rays through the Earth's atmosphere causes the lunar orb to take on a spectacular blood-red colour during totality.

"The blue light from the Earth's atmosphere is scattered away in all sorts of directions and all that's left is the red light going through - it's why the Sun looks red sometimes when it's setting," he said.

"So you get this red light bathing the Moon's surface which has come from the Earth's atmosphere.

"If the Earth didn't have an atmosphere, the Moon would be invisible during a total eclipse of the Moon because there would be nothing illuminating it, but because we have an atmosphere you get this quite eerie red glow, which is quite spectacular."

He says if you could stand on the Moon and watch the total lunar eclipse, the view would be even more dramatic.

"You would see the Earth blocking out the Sun but with this really bright red ring around the Earth," he said.