Back in February 2018 a beautiful astronomical event occurred – a super blood moon. We observed this from Kangaroo Ground near Melbourne, Australia. Much to our surprise many people had the same idea and had gone to the trouble of escaping the city light to enjoy the event in the cool night air. Some imbibed a cold ale.
The “Super” term is used to indicate the full moon will be larger than usual due to it being at its closest point to Earth its elliptical orbit. Some have referred to the event as a “Super Blue Blood Moon”. Here the term “Blue” refers to the fact that two full moons occurred in the calendar month. But let’s not get too carried away!
A blood moon occurs during a total lunar eclipse when the Earth blocks all direct light from the sun reaching the moon. The Earth’s atmosphere refracts light just like a lens or prism, so some of this refracted light reaches the moon. While blue light is refracted more than red light, it is also scattered more (which is why the day time sky is blue). This scattering effectively filters out much of the blue light leaving the refracted light with its distinctive reddish hue.
The amount of refraction and scattering is very dependent on atmospheric conditions around the rim of the Earth at the time of the event. For this reason, each blood moon will have is own character. This is what we observed …
These three images show the moon at its most “bloody”. As the moon’s orbit takes it into direct sunlight the top right corner begins to brighten.
Because the direct sunlight is very much brighter and whiter than the refracted light, it quickly tends to overwhelm the blood hued areas.
If the photos were to be exposed for a normal moon picture the coloured areas would become almost invisible.
The images were captured by an ordinary digital camera with a telephoto lens. The detail is not nearly as fine as can be achieved with a larger telescope, but the colour and sense of presence are real.
Knowledge makes life more interesting.