Leading Museums, Museum Leaders

22-degree sun halo captured above Launceston

The 22-degree halo above Launceston’s clock town on Sunday. Picture: Phillip Biggs.

Isobel Cootes, A 22-degree sun halo captured above Launceston, The Examiner, 14 December 2020

If you happened to stare into the sky on Sunday in Launceston you may have seen an optical phenomenon – a sun halo.

A 22-degree sun halo to be exact. It is a large white ring formed when light is bent as it passes through million of high-altitude hexagonal ice crystals suspended in the atmosphere.

Optical phenomenon captured above Launceston.

The ring appears whitish, except for a narrow tinge of red on the inside and violet on the outside of a sun halo.

It gets its name as it’s equal in distance around the sun to the apparent distance between your thumb and little finger when your outstretched hand is held at arm’s length.

The Queen Victoria Museum and Art Gallery astronomer Dr Martin George said depending on where you viewed it from.

“It really depends on the ice crystals being in the atmosphere basically above where you are,” he said.

“So, for example, you might go some distance away to even another part Tasmania and you might not see anything, but if the ice crystals are suspended over a broad area, quite a number of people might see it.

“It is more of a local phenomenon and they are they can be very short-lived to.”

Dr George said there were two halo phenomenons, the 22-degree and the 46-degree halo, with the first being much more common.

“Now the reason we say 22 degrees, is that if you took the one, the line from the halo to your eye and back to the sun. If you can imagine drawing it on a bit of paper, the angle, it would be 22 degrees,” he said.

“It is one of many kinds of atmospheric phenomena. Of course, rainbows are very well known, but this particular atmospheric phenomenon is caused by ice crystals.

“You might notice in the photographs, the halo is red on the inside of the circle and it’s a bit bluer on the outside of the circle. That colour effect is caused by the fact that red light and blue light are bent at slightly different angles, which means that one part of the circle is a bit redder and another part is a bit bluer.”

Council of Australasian Museum Directors, c/o Ms Daryl Karp, Museum of Australian Democracy at Old Parliament House PO Box 3934 Manuka, Australian Capital Territory 2603 Australia, © CAMD 2021
Disclaimer: The content of this website is provided for information purposes only and is not intended as a substitute for professional advice. No claim is made as to the accuracy or authenticity of the content of the website. The Council of Australasian Museum Directors does not accept any liability to any person for the information or advice (or the use of such information or advice) which is provided on this website. The information on our website is provided on the basis that all persons accessing the site undertake responsibility for assessing the relevance and accuracy of its content. No responsibility is taken for any information or services which may appear on any linked web sites. Hostgator.
.