The recent lunar eclipse made me wonder what has happened to sensibility. I’m all for people learning about the night sky, but the comments I saw on social media were disheartening. Worse, many in the astronomical community were guilty of overhyping what shouldn’t need to be hyped in the first place.
The recent total lunar eclipse was one of eighteen occurring in the 20 year period 2001-20, so while these aren’t common, they aren’t rare, either. The total minutes of all these eclipses is nearly 1300, so if one happens to see a total eclipse, one will see it for a period of many minutes, sometimes more than an hour, unlike total solar eclipses which last fewer than 7 1/2 minutes, and in all of our lifetimes under six minutes, assuming one is in exactly the right place, and I mean exactly. For a lunar eclipse, being in the right place is on the night side of the Earth, which has a probability about one half. For a total solar eclipse, the probability is 0.5% just to be on the track, let alone in the right place. The Europeans and Asians will see a total lunar eclipse in July, and all of North America next January.
What bothered me was the blue, super, and blood appellation, along with “the first in 150 years.”
Some background: back on June 5, 2012, when there was a transit of Venus across the Sun, I showed it to a small group of people at the Pima County Medical Society’s office in Tucson. One individual commented that it was not very interesting, seeing the small dot of Venus against the background of the Sun, 30 times the diameter of Venus, viewed from the Earth. To me, this was an exceptionally rare event, which last occurred in 2004, and before then in 1882. The next will be in 2117. The rarity, the history of those who traveled great distances to see one, the fact that I was following in their footsteps were all important to me. Others don’t see the world (or other worlds) the way I do, however, and I accept that. The total solar eclipse last summer was a yawner for a few of my friends, although I actually convinced my brother to take the effort to see it, and he was not at all disappointed. The next solar eclipse to touch Oregon will be October 5, 2108, and barely reaches the Pacific coast. This past lunar eclipse lasted 76 minutes, which was worth mentioning; I’ve spent fewer than fifty minutes under the Moon’s shadow during the 17 total solar eclipses I have seen.
A blue Moon is when a full Moon occurs twice in one month. It’s a calendar phenomenon only. Between 2001 and 2020, nine occur. The exact dates differ, because of time zones, where the full Moon may occur a calendar day later in the eastern hemisphere. We have two blue moons this year, which is unusual, and yes, it is interesting, but it isn’t the stuff of which “I have to see this or I am missing out on something special and not likely to happen again.”
Supermoons are when the full Moon is relatively close to the Earth. Because of the shape of the Moon’s orbit and the behavior of the Moon, our satellite can be full and be within 360,000 km of us, one definition of a supermoon, at least twice and maybe three times a year. That’s like giving an gold star for attending class. The full Moon of New Years’ Day was actually 2500 km closer to us than this one. “Supermoon” is a recent term, dating only about three decades. Before then, we just admired full moons and did just fine. In part, the “horizon effect,” where seeing a full Moon rise against the horizon, something to compare it with, makes the moon appear large. It actually appears larger six hours later, when highest in the sky, because we are no longer looking at the Moon across the radius of the Earth but directly at it, 6500 km closer, give or take. I have had almost no success, either as an astronomy columnist or as an amateur astronomer, convincing people that rising full Moons are not unusually bright.
Then again, once I failed to convince a couple that the large red object that was a lunar eclipse wasn’t Mars. And when I was a kid, I called the crescent Moon “Venus,” because I had recently learned Venus can show phases. But unlike the couple I learned to change my mind in the face of convincing evidence–and appropriate public shaming.
A supermoon is about 0.28 magnitude brighter than a regular full Moon. Magnitudes are listed where negative means brighter; every 5 magnitudes is 100-fold difference in brightness. This translates into a supermoon being a quarter brighter than average, but brightness is relative. We don’t compare full moons that we see with other full moons unless we use a light meter. We usually compare them to what we have recently seen, like how the Moon appeared the night or two before full, also bright.
Still, full moons are special, 11 times brighter than a half moon and 10% brighter than the Moon the day before or day after. The apparent size of the Moon is larger, but again, without comparison to other full moons, such as photographically or in an eyepiece of a telescope in which one can calibrate size, is not appreciably different. One way to prove this is to look at a rising full Moon through a cardboard tube and then look at it high overhead. The size is the same to one’s eye.
The blood moon is a reference to the red color of the eclipsed Moon, because the only light that can reach the eclipsed Moon is from the red sunrises and sunsets around the eclipsing Earth. As Fred Espenak, “Mr. Eclipse,” put it, “people have been calling these lunar eclipses for two thousand years.” Of the three terms, replacing blood moon with “eclipse” would have been the most helpful.
There are many astronomical events every year. In my opinion, they don’t need to be hyped. There are many beautiful things above, on, and below the Earth, and they are there for those who want to look.
Next time around, my self-improvement goal will be to discuss the phenomenon without raising my voice. THAT would be a rare event.
Total lunar eclipse 27 September 2015, White Bear Lake, MN. The darkest part is the Moon that is deepest in the Earth’s shadow; the lighter is in the outer shadow.
Transit of Venus beginning, 5 June 2012, Tucson, AZ
Boreal B[l]og 