Blue moon and lunar eclipse to occur simultaneously Jan. 31

Katie Daniels

On Wednesday, Jan. 31, there will be the second full moon of the month, which will make it a blue moon. The next full moon will not take place until March 1, leaving February without a full moon at all. A lunar eclipse will also take place. 

The interactive display at the Hardin Planetarium asks “What month can never have a full moon?” The answer is February.

Since February only has 28 days, or at most 29, you can never squeeze in two full moons, which must always be 29 and-a-half days apart. This is also why February has no full moon at all this year. The full moon is the last day of January, and so there must be 29 and-a-half days before the next full moon and February only has 28 days.

There is little astronomical interest in the blue moon since it is simply another full moon occurring at its regular interval. The interest lies in the bizarre relationship between the cycles of the moon and the calendar.

“Astronomers don’t worry about blue moons,” director of Hardin Planetarium Richard Gelderman said. “It does nothing for us. You get a full moon every 29 and-a-half days, and another full moon 29 and-a-half days after that. We know that they don’t have anything to do with years, and that months are a completely arbitrary mish-mash of things trying to divide a year evenly up when it can’t be divided. Twenty eight doesn’t work, 29 doesn’t work; none of them fit into 365 and one-fourth.”

The Roman solution to this was to have twelve months of 30 days each, followed by a five-day holiday to keep the year from getting off-sync. This was eventually replaced by the Gregorian calendar we use today, with twelve months of varying lengths that have nothing whatsoever to do with the lunar cycle. This means that sometimes we can have two full moons in the same month.

The original blue moon had nothing to do with the calendar at all, but with seasons. Native Americans and early settlers called each full moon by a name, depending on where in the season it fell. There were four seasons, and each season had three full moons. However, most years have 13 full moons. When an extra moon appeared in a season, there was no name for it, so it was a blue moon.

In addition to the blue moon, Wednesday also marks a lunar eclipse.

The fact that they are coinciding is mostly coincidence,” Ron Kistler, Planetarium coordinator, said. “The blue moon must be a full moon, and so must a lunar eclipse.”

Lunar eclipses are often known as “blood moons” due to the red color of the moon.

“The cycle of eclipses is a much more complicated thing, but basically we have two lunar eclipses a year,” Gelderman said.  

Gelderman said that “sunsets are red because light that shouldn’t have reached us gets bent by the Earth’s atmosphere. [The lunar eclipse] is red because that same thing that makes sunsets red is bending it around the earth, and that light is getting bent around to where no light should be. It should be a perfect shadow, but instead the light gets bent around by earth’s atmosphere just like lenses bend lights.”

Those interested in observing the lunar eclipse will have to get up early to do so. The eclipse will only by partially visible in Bowling Green, beginning at 5:48 a.m. and continuing until the moon sets at 6:49 a.m. Those who simply want to glimpse the blue moon can do so any time after it rises at 4:24 p.m. Tuesday, Jan. 30.

For more information on moon viewing times visit

To learn more about the 2018 lunar calendar and the orbit of the moon, visit the Hardin Planetarium interactive lunar exhibit any time between 8 a.m. and 4:30 p.m. Monday through Friday.  

Reporter Katie Daniels can be reached at 270-745-6291 and [email protected].