If you step out and look at the moon right now this Saturday evening, you will see a reddish full moon (although Poornima, or full moon day as per the calendar is on Sunday, Oct. 16). Called variously 'Blood Moon' or 'Hunter's Moon', etc., the moon appears so because it is close to the horizon.
The moon also appears larger than usual, and is therefore billed a 'Supermoon', because it's at near perigee, the shortest distance between earth and moon in the latter's orbit. This combined -- 'blood moon' and 'super moon' phenomenon will be visible on October 15 and October 16 (it will reach its peak at around 9.53 am IST, so we in India won't see it at peak).
The 'Hunter's moon', which appears at the start of autumn equinox and is so called because it gives hunters and farmers extra moonlight to work by, also rises earlier than the moon usually does. The moon typically rises 50 minutes later each day in its cycle from new moon day to full moon day, but the Hunter's moon rises only 30-35 minutes later. The reason is because during autumn equinox, which is from late September to early December in the northern hemisphere, the moon's orbital path creates a narrower angle with the evening horizon.
So, why is it so reddish?
In reality, it's just the regular full moon, but it appears reddish due to an illusion created by the earth's atmosphere. According to EarthSky's Deborah Byrd, "The orange color of a moon near the horizon is a true physical effect.
It stems from the fact that - when you look toward the horizon - you are looking through a greater thickness of Earth's atmosphere than when you gaze up and overhead. The atmosphere scatters blue light - that's why the sky looks blue.
The greater thickness of atmosphere in the direction of a horizon scatters blue light most effectively, but it lets red light pass through to your eyes. So a full moon near the horizon - any full moon near the horizon - takes on a yellow or orange or reddish hue".
Being so close to the horizon also tends to create the illusion of the hunter's moon being bigger than a regular moon, and this weekend it's going to look even bigger than that, because the moon is now near its closest point to the earth in its oval-shaped orbit around our planet.
Bigger Treat in November
The full moon of November 14 will be the closest and largest in 2016 -- and it is also expected to be the largest full moon so far in the 21st century. Don't miss that!