This weekend the night skies will feature a rare spectacle – a blue micromoon. We take a look at what the phrase means and how to catch a glimpse of the event. What is a blue moon? There is more than one definition of a blue moon. “Probably the more common one that’s used at the moment, the one that’s better known, and certainly the simplest, is a so-called monthly blue moon,” says Dr Greg Brown, an astronomer at the Royal Observatory Greenwich. “This is where you get a second full moon in one single calendar month.” That is unusual because the moon takes 29 and a half days to cycle through its different phases – the different shapes we see from Earth – meaning a full moon typically occurs once a month. “But occasionally you’ll get two, and the second one is referred to as a blue moon,” Brown says, noting that this is the type of blue moon occurring this weekend. A second type is known as a “seasonal blue moon”.…