Venus, named after the Roman goddess of love, and Jupiter, named after the god of sky and thunder, and a three-day-old crescent moon appeared as a smiley face on the western horizon.

The celestial coupling won't take place again for five years, but those who watched marvelled at its symmetry.

Canberrans looking west after sunset could see the moon with two bright dots above it, the brightest was Venus, the other Jupiter.

Canberra Astronomical Society president Andrew White watched the planetary alignment from a vantage point on Red Hill.

The avid astronomer loves the history of light.

''It takes the sun's light eight minutes to travel to the moon. So every time you look at the sky it is the history of light. Every time you look at the sky it is the first time the light has ever been seen,'' Mr White said.

The 42-year-old's passion for the sky started as a child.

''I can't ever remember not being fascinated by the stars,'' he said.

It will be another five years before the happy formation of crescent moon, Venus and Jupiter appears again, but it was the first time Mr White has seen it.

Clouds obstructed the planets and moon throughout last night, but Canberrans who missed it can look forward to the repeat performance in 2013. Australian National University astronomer Paul Francis said the happy line-up was not unique.

''It's not that rare that the planets and moon line up but people will be able to see it with their naked eye,'' Dr Francis said.

''It's absolutely unmistakable and very bright. They will [be] the brightest thing in the sky once the sun has gone down, by a long way.

''It's always a spectacular thing to see.''

He said the moon Canberrans saw was actually the moon as it was 1.5 seconds ago.

The travelling time of the light to our eye from Venus was about eight minutes and Jupiter about 45 minutes.

''This one will be interesting because it's got the two brightest planets and the moon very close together in the evening sky.''

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