Clouds threaten Sydney eclipse viewing

Sydney "umbraphiles" are hoping clouds won't spoil their view of a partial solar eclipse in the nation's southern skies.

Tuesday afternoon's astronomical event has Dr Stuart Ryder from the Australian Astronomical Observatory very excited.

After more than 20 years of observing eclipses, the umbraphile, or eclipse enthusiast, is hooked.

"You never feel that you've had your fill," he told AAP.

"They're so short ... and there's just so much to take in."

The eclipse starts at 4.15pm (AEST) and at its peak, at 5.15pm, Sydney viewers could witness the moon cover 52 per cent of the sun.

That's if forecast cloud cover doesn't dampen the party.

"It would be ideal if it stayed as clear as it is this morning," Dr Ryder said.

"But even if it's partly cloudy it might result in some slightly more spectacular views."

A partial eclipse in clear conditions is not noticeable to the naked eye because the sun continues to provide close to normal daylight, he explained.

But a small amount of cloud obstructs the sunshine, making the eclipse more noticeable to people going about their daily routine.

Nevertheless, observers should not look directly at the eclipse regardless of cloud cover.

Andrew Smith from the Sydney Observatory says people should either wear special eclipse glasses or view the event through a solar telescope at an observatory.

Those viewing the eclipse from home can project it onto a white sheet of paper using a piece of cardboard pricked with a pin hole, he said.