A different kind of Corona

Right now, many of us are looking

for interesting things to do with

the kids or our spouses, literally in

our backyards.

Looking up can help you decompress and learn at the same

time. As a

child, back on

the farm and

with mom’s

guidance, I

spent a lot of time looking for

planets, stars, constellations, asterisms, etc. It can be tricky and it

takes time but if you start with the

moon and work your way up, it’s

pretty simple and lots of fun.

I’ve always found the moon to

be quite intriguing, regardless of

its phase or its position in the sky.

The fact that it can be seen during

the day makes it an interesting

celestial object. Observing the

moon is very educational and

can trigger conversations about

astronomy, astrology and meteorology.

The other day, Beverly Dewolfe

was out to get a glimpse of the full

pink moon. She had no trouble

finding it but as she stood there

admiring it, a cloud drifted by

and presented a set of coloured

rings. Beverly wanted to know

what caused the rainbow colours

to appear on the edge of the passing cloud.

Beverly was looking at a corona. In meteorology, a corona is

an optical phenomenon produced by the diffraction of sunlight or moonlight by very tiny

water droplets in a cloud.

In its full form, a corona consists of several concentric, pastelcoloured rings and a central

bright area called aureole. That

aureole is often the only visible

part of the corona and is usually bluish-white and fades to

reddish-brown toward the edge.

The diameter of a corona depends

on the sizes of the water droplets

involved — smaller droplets produce a large corona.

Last Sunday, many of you witnessed a lovely ring around the

sun — a solar halo. You might

be wondering if the corona is its

nighttime equivalent. It is not.

The night halo is a lunar halo.

Halos are also optical phenomena that appear around the sun or

moon, and sometimes near other

strong light sources like street

lights. They are caused by ice

crystals in cold cirrus clouds located anywhere between five and

10 kilometres above the ground.

In the case of a halo, the ring

is a result of diffraction from

comparatively large ice crystals.

A corona, on the other hand, is a

pastel halo around the moon or

sun created by the diffraction of

water droplets. The droplets in the

cloud must be almost perfectly

uniform for this phenomena to

occur.

Another interesting difference

is the colour sequence: from blue

inside to red outside in a corona

and the reverse of that in a halo.

Many of us were out admiring the full pink moon earlier this month. That's what Beverley Dewolfe had planned when she stepped outside in Terence Bay. Then, she was treated to a partial lunar corona. Beverley is curious about the science behind the colours.