Australian Weather Calendar: May 2020

May photograph by Phil Hart

Smooth sailing

Well accustomed to shooting the night sky, astrophotographer Phil Hart found himself photographing dark skies of a different kind while on a sailing trip in Tasmania. 'We'd chartered a yacht in the D'Entrecasteaux Channel and looked at the 5 o'clock weather forecast and saw the wind had swung a little bit more southwesterly, and thought, "this isn't going to be the most comfortable spot to spend the night!"' The crew motored to a more sheltered bay and bunkered down as the storm passed. 'Skies cleared up around sunset and there was some amazing texture in the clouds. I'd packed the camera gear with the idea that I'd do some night photography and possibly capture some aurora activity if conditions were right, but when these amazing storm clouds and double rainbow appeared I couldn't resist.' As well as astronomy and sailing, Phil's other passion is weather—which he says he’s inherited from his meteorologist father. 'Anybody on a yacht is looking at the weather regularly, but even more so when you've got a passionate meteorologist and his son! I'm always checking the marine forecasts and warnings, because when you're sailing you're completely at the mercy of the wind,' Phil says. You can’t choose the weather (or your parents!), but it’s moments like these that have Phil thanking his lucky stars.

The science

Rainbows are formed when sunlight is refracted (bent) and reflected while passing through raindrops in the atmosphere. Blue light refracts at a greater angle than red light, resulting in the separation of the colours in the spectrum of white light. Sometimes a dimmer, secondary rainbow is visible, as shown in this photo. A secondary rainbow forms when light reflects twice inside the raindrop as opposed to once for the primary bow. The intensity of light is reduced by the second internal reflection, so a secondary bow is always fainter than the primary bow. The order of colours in a secondary bow is always the reverse of a primary bow. This is because the second internal reflection within the raindrop changes the angle at which the light is refracted, and the observer sees the different coloured light in reverse order.