Blue moon, red planet will dominate weekend sky

This Saturday at 5:14 p.m., the moon will be 100 percent illuminated, better known as a full moon.

The old Farmer’s Almanac calls the May moon the “Flower Moon” in reference to the abundance of spring flowers. More practical Native American tribes called it the “corn planting moon” or “milk moon,” a reference to May as the month when calving season and pastures full of green grass sends milk production into overdrive.

You may also hear this weekend’s full moon described as a blue moon, or more specifically a seasonal blue moon, the third of four full moons in a single season. This is one of two definitions of blue moon.

The other was popularized in a 1946 edition of Sky and Telescope magazine in an article by James Hugh Preuett, an amateur astronomer who claimed the second full moon in a calendar month was the definition of a blue moon.

So which is the right definition? Both, neither, it really doesn’t matter. There really is nothing astronomically or calendrically special about either definition of a blue moon. They aren’t as rare as the phrase “once in a blue moon” might suggest. 2018 will have two blue moons by the monthly definition.

Blue or not, this weekend’s full moon will be worth stepping out and seeing. Like any other full moon, it rises at sunset. Look just 5 degrees, or the width of three fingers on your outstretched arm, to the right for bright, ruddy Mars.

The planet is unusually bright and big during May leading up to opposition of the planet just a few hours later at 7:10 a.m. Sunday morning.

During opposition, Mars and the sun are on directly opposite sides of Earth. Mars oppositions happen about every 26 months. Every 15 to 17 years, opposition occurs within a few weeks of Mars' perihelion (the point in its orbit when it is closest to the sun).

Ignore any Facebook or other social media postings claiming this weekend= to the be the biggest and brightest Mars will appear in some large number of years.

These are repeats from 2003 when Mars came the closest it had in nearly 60,000 years. That 2003 record will stand until August 2287 when Mars will come just a bit closer thanks to its orbit which is elongating over time.

Earth and Mars will continue to draw just a bit closer in their orbits until May 30 when they will be at their closest of the year, separated by just 46.8 million miles.

The next close approach of Mars will be July 31, 2018.