Wednesday, 8 June 2011

Total lunar eclipse across Australia (or what is a syzygy)

Today I learnt a new word.


A syzygy is a straight line configuration of three celestial bodies (such as the Earth, Sun, and Moon), and on Thursday 16 June, if you can get yourself up before dawn, you will witness a syzygy - in this case a total lunar eclipse - above the western horizon as the Moon passes through Earth’s shadow. This syzygy ends at sunrise in all states but Western Australia. It has been something of a star and planet watcher's dream recently, with four planets having lined up in the sky during May.

The eclipse begins at 3:25am AEST and enters its darkest phase at 05:22am AEST when the transformation to a blood-red Moon should begin. The colour of the eclipse depends on the amount of dust in the Earth's atmosphere. The red colour comes about because sunlight reaching the Moon passes through the Earth’s atmosphere where it is scattered. Shorter wavelengths (blue) are scattered more by  air molecules and dust particles than longer wavelengths (red), and so by the time the light has passed through the atmosphere, the light is mainly red. In extra-solar planets - planets in other solar systems - lunar eclipses can be used to determine the content of the planetary atmosphere. You might remember back to 2009 when Sydney was covered in dust and turned red to gauge a feeling for what the colour could be like - check out that article for a fuller description of the physics involved as it is similar.

If you are keen enough to not only get out of bed but to leave your house, Sydney Observatory is hosting a special breakfast viewing which includes tea, coffee, croissants and “blood-red” jam. Book at the Sydney Observatory website.

This material came from the Sydney Observatory.


  1. Syzygy is really strange for a word but it is justified.

  2. This is amazing. I wish it can be seen from Southeast Asia too.

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