Astronomical Musings

Done any hurtling lately?
A recent headline on Forbes cited a journal article in the Royal Astronomical Society:

“Milky Way will collide with nearby galaxy,
hurtling solar system into space, report says”

The phrase appears again in the article: “The impact could send our solar system hurtling into space.”

So tell me, where is the solar system now? To quote Wikipedia:

The Solar System is traveling at an average speed of 828,000 km/h (230 km/s) or 514,000 mph (143 mi/s) within its trajectory around the galactic center, a speed at which an object could circumnavigate the Earth’s equator in 2 minutes and 54 seconds; that speed corresponds to approximately 1/1300 of the speed of light.

And according to Speed of the Milky Way in Space – The Physics Factbook, “… [O]ur galaxy and its neighbors, the so-called Local Group, are moving at 600 kilometers per second (1.34 million miles per hour) in the direction of the constellation Hydra.” If that isn’t “hurtling through space,” what is?

Calling the Moon Names
And speaking of space, have you heard all the hype about the upcoming “super blood wolf moon total lunar eclipse”? This string of adjectives makes it all sound pretty ominous. But what do they actually mean?

As you may recall, the moon’s orbit around the earth isn’t a perfect circle. Rather, there are times when it’s closer to earth, and times when it’s farther away. We call the point at which the moon is closest to the earth “perigee” and when it’s farthest away “apogee.” (The earth’s orbit around the sun isn’t a perfect circle either, only there the terms are perihelion and aphelion, as “helion” refers to the sun.)

How much does this distance vary? At the next perigee, the moon will be 357,342 km / 222,042 miles from earth. At the following apogee, not quite two weeks later, it will be 406,555 km / 252,622 miles away. That’s enough of a difference for the moon to look noticeably larger or smaller to us here on earth.

A “super” full moon occurs when the moon happens to be full (that is, it’s on the opposite side of the earth from the sun) at the same time that it’s at perigee. It appears “super” huge to us. The next super moon will happen January 20 – 21, 2019. (The opposite—a full moon coinciding with apogee—is called a “micromoon,” but that doesn’t garner the same attention.)

What’s a wolf moon? It’s simply a name given to the first full moon of each year. According to Time and Date.com, “The first Full Moon of the year is named after howling wolves. In some cultures, it was known as Old Moon, Ice Moon, Snow Moon, and the Moon after Yule.” So we could just have easily said we’re going to have a “super blood snow moon”—only wolf sounds scarier.

Finally, we have a “blood moon” and a total lunar eclipse. The moon’s orbit  around the earth doesn’t lie exactly over the equator. Rather, it’s on a slightly different plane. Thus, the sun, moon, and earth don’t always perfectly align to produce a total lunar eclipse. This month, however, they do. Over a period of several hours, sky watchers in North and South America, Europe, and western Africa will watch the earth’s shadow come between the moon and the sun. At totality, the moon will appear reddish—a “blood” moon. So a blood moon and a lunar eclipse are essentially the same thing.

Instead of all the hype, you could just say that the eclipse of January 20 – 21 will be the “point at which perigee coincides with a total lunar eclipse in January”—but that doesn’t make a very good headline.

2 thoughts on “Astronomical Musings

  1. We had a blood moon last fall! It was a pretty dull red here. I found it very interesting… I thought we would not be seeing one again in my life! I wonder if I was not well informed!

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