This weekend, from 21 to 22 May on the night sky we will have the opportunity to see two major celestial events, Blue Moon and opposition of Mars.
As you can imagine, the blue moon is not really blue. The moon looks blue because of the dust particles from the ground into the atmosphere as a result of volcanic eruptions or fires. For this event better explains Bruce McClure of “Earthsky.org”, where he says that there are two definitions for Blue Moon.
Traditionally, blue moon means the third moon of the season with four full moons – the season is here defined as the time between the (solstice and solstice) and equinox, or vice versa. Usually there are only three full moons in a season, so when there is an extra, it is a blue moon and it is rare. The last time we had a blue moon in August 2013, and the next will take place on January 31, 2018.
Also there is another definition of a blue moon, and it is the second full moon in the same calendar month. But the definition of the fourth moon of the season is already rooted in history, so it is better to stick to it.
How occurs seasonal blue moon?
In both cases, the blue moon is a calendar oddity caused by the 19-year Metonic cycle. Have a 235 full moons in 19 calendar years, only 228 calendar months (or 76 monthly three seasons). Therefore, it is inevitable 7 of the 19 years to have two full moons in one calendar month and 7 of the 19 years have four full moons in a one season.
For this reason we have an extra full moon this weekend from 21 May (Saturday) from 21 hours and 14 minutes during which you can see around the world.
On 22 May (Sunday), Mars will be in opposition, which means that Earth passes directly between Mars and the Sun because it is expected to be extremely bright and red and can be seen from Earth during the next few weeks. About a week after opposition, Mars will be closest to Earth at a distance of 75.3 million kilometers, and that will be the biggest approaching of Red Planet to our Country from 2013.