Tag: Astronomy

Sciency Words: Antitail

~ J.S. Pailly ~ 6 Comments

Hello, friends!  Welcome to Sciency Words, a special series here on Planet Pailly where we talk about the definitions and etymologies of scientific terms.  In today’s Sciency Words post, we’re talking about the word:

ANTITAIL

Did you see the comet?  Pretty much everyone I know has been asking me that question lately.  Comet C/2022 E3 (ZTF) had a wild ride these last few weeks.  First, she started glowing a lot brighter and a lot greener than expected, leading to some people calling her “the green comet.”  Then, due to some intense solar activity, a gap formed in one of the green comet’s two tails.  Shortly thereafter, almost as if the comet were trying to compensate for the damage to one tail, an apparent third tail became visible to observers here on Earth.  This apparent third tail is what astronomers call an antitail.

Definition of antitail: Comets typically have two tails: a dust tail and an ion tail.  These tails are supposed to point away from the Sun.  They’re caused by the solar wind sweeping gas, dust, and other lightweight material away from the comet and off into space.  An antitail is an apparent third tail pointing toward the Sun.  At least antitails look like they’re pointing toward the Sun, but this is actually an optical illusion.

Etymology of antitail: The prefix “anti-” can mean several things.  In this context, it means “opposite,” because antitails point (or look like they point) in a direction opposite to the direction cometary tails are supposed to point.  Based on my research, I believe this term was first introduced in the late 1950’s, following the appearance of comet Arend-Roland.

Okay, I’m going out on a bit of a limb claiming that the term was introduced in the 1950’s.  I cannot find any sources explicitly stating that, but almost every source I looked at seems to agree that Comet Arend-Roland had the most famous and noteworthy antitail in the history of antitails.  In 1957, Arend-Roland developed a large and protruding “sunward spike.”  In photos (like this one or this one), the comet reminds me a little of a narwhal.

Arend-Roland cannot possibly be the first comet ever observed to have an antitail, but it does seem to be the most spectacular and most widely studied antitail in recorded history.  Crucially, I was unable to find any sources mentioning cometary antitails prior to 1957.  Ergo, I think I’m right that the term was first introduced around that time, in reference to that particular comet.  But I could be wrong, and if anyone knows more about this topic than I do, please do share in the comments below.

Regardless of how much of a first Arend-Roland’s antitail really was to the scientific community at the time, it was not much of a mystery.  Within a matter of months, scientists were able to offer explanations, like this explanation published in Nature:

No extraordinary physical theory appears necessary to account for the growth of the sunward tail […]  The sunward tail must almost certainly have resulted from the concentration of cometary debris over an area in the orbital plane.  Seen at moderate angels to the plane, the material possessed too low a surface brightness to be easily observed, but seen edge-on it presented a concentrated line of considerable intensity.

So several things have to happen in order for us Earth-based observers to see an antitail.  First, a comet needs to shed some debris that’s too big and heavy to be swept off by the solar wind.  This extra debris will accumulate along the comet’s orbital path, rather than billowing off in a direction pointing away from the Sun.  Second, Earth has to be in just the right place at just the right time to see this debris field “edge-on.”  Otherwise, the light reflecting off the debris will be too diffuse for us to see.  And third, this has to happen at a time when the comet’s tails don’t overlap with the debris field (i.e., the debris and the tails have to be pointing in opposite directions, as seen from Earth).  Otherwise, the glow of the tails will obscure the light reflecting off the debris.

Last week, I was lucky enough to see the comet, but I didn’t see her bright green color (she was a hazy grey in my telescope), and I certainly didn’t get a chance to see the antitail.  I’m pretty sure I was a few days too late for that, and besides, there’s too much light pollution where I live to see faint details like that.

Still, I consider it a great joy and privilege that I got to see as much of the comet as I did.  And for all the cool sciency stuff I couldn’t see for myself, I can always turn to my research if I want to learn more.

WANT TO LEARN MORE?

Here’s the 1957 report from Nature that I quoted above, explaining what “must almost certainly” have caused Arend-Roland’s “sunward tail.”

And here’s a more recent article about Arend-Roland, reviewing the comet’s discovery, observation history, and the appearance of his antitail.

Lastly, here’s an article from Live Science about the recent “green comet” and her antitail.

#IWSG: The Planets Make Me Write

~ J.S. Pailly ~ 22 Comments

Hello, friends!  Welcome to another meeting of the Insecure Writer’s Support Group, a monthly blog hop hosted by Alex J. Cavanaugh and co-hosted this month by SE White, Cathrina Constantine, Natalie Aguire, Joylene Nowell Butler, and Jacqui Murray.  To learn more about this amazingly supportive group, click here!

I read somewhere once that every writer has a “thing”—something that they’re desperately trying to say.  It’s something that’s hard to put into words, a feeling or an idea that defies the conventional use of language.  If this “thing” could be said in a simple and straightforward way, we writers would just say it and move on rather than spend the bulk of our lives writing.

What is that “thing” for me?  I wish I could tell you!  It would be so much easier if I could just tell you the “thing” that keeps poking at my mind, but of course I can’t.  All I can say is that my thing has something to do with the stars.  It has something to do with the slow and stately motion of the planets.  It has something to do with that feeling I get whenever I look up at the nighttime sky.

Is it curiosity?  A sense of wonder at the vastness of the cosmos?  I guess that’s part of it, but those words feel wholly inadequate.  Wonder and curiosity are nice, but there’s something more.  There’s so much more!  The planets and stars inspire something in me that simply must be said—something that must be put into words, no matter what—it must be!

But no words ever seem to express this “thing” well enough.  So I keep trying.  I keep writing, in the hope that maybe someday I’ll find a way to say the thing I don’t know how to say, and maybe somebody else will read my words and understand what I’m talking about.

So, friends, do you have a “thing” that you’re trying to say through your writing?  Care to give us a clue (if you can) about what your “thing” might be?

Sciency Words: Metal

~ J.S. Pailly ~ 13 Comments

Hello, friends!  Welcome to another episode of Sciency Words, a special series here on Planet Pailly that’s all about those weird words scientists use.  Today on Sciency Words, we’re talking about:

METAL

Yes, scientists use some very strange words.  You know the kind of words I mean.  Words that are hard to pronounce.  Words with definitions that only make sense if you understand differential calculus.  But you know what’s even weirder?  When scientists take words you already know and redefine them.  That’s what astronomers and astrophysicists have done to the word “metal.”

Approximately 75% of the matter in the universe is hydrogen.  24% of it is helium.  And the remaining 1%?  Ask an astrophysicist, and they’ll tell you the remaining 1% is all “metal.”  If that seems weird to you, don’t worry.  All the other scientists think it’s weird too.

For years now, I’ve been trying to figure out how this started.  Who gets credit (or blame) for first messing up the definition of metal?

I don’t know, but I do have a pet theory.  Perhaps certain chemical elements (like nickel or iron) are easier to detect in outer space than others.  And if you’re trying to study that 1% of the material universe that isn’t hydrogen or helium, perhaps those easier-to-detect elements (which happen to be metals) serve as a convenient proxy for everything else—including nonmetals like nitrogen, carbon, and oxygen.

According to the Oxford English Dictionary Online, the earliest documented usage of either “metal” or “metallicity” (in the astronomy sense of those words) is this 1969 paper on the molecular composition of stars.  Now I won’t pretend to have read the whole paper (it’s over 60 pages long), but based on what I did read, I can say this much: this cannot be the true first usage of the word metal (in the astronomy sense).

At one point, the authors, two astronomers from U.C. Berkley, categorize nitrogen as a metal.  No explanation is offered.  Clearly the authors expect their readers (i.e. other astronomers) to understand why nitrogen would be considered a metal, which suggests to me that most astronomers in 1969 already understood “metal” to mean “matter that isn’t hydrogen or helium.”

However, I can also say this: I think this paper supports my pet theory.  The paper describes a new technique for determining the molecular composition of stars.  In explaining this new technique, the authors focus on the spectroscopic signatures of three specific elements: sodium, magnesium, and calcium.  Those three elements are then used as a proxy for all the other non-hydrogen and non-helium elements that might be found inside a star.

Sodium, magnesium, and calcium are all—wait, let me double check the periodic table—yes, all three of those elements lie on the metal side of the metalloid line.  And thus through a process linguists call semantic generalization, the word metal is generalized to mean something more than it originally meant.

Next time on Planet Pailly, someone really wanted to pick a fight with me about life on Mars.