A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Position-Finding
From: Frank Reed
Date: 2018 Nov 29, 19:01 -0800
I wrote previously:
"We can't escape "declination", this bit of jargon, because it's everywhere, unavoidable, inescapable. We should define it, emphasize its interchangeability with "latitude", and then use it. That's how I teach."
I want to emphasize that I do insist that we need the word declination. Yes, it's jargon, and really it can be quite a puzzling bit of jargon to beginners. But in the context of celestial navigation, it has a beautifully simple equivalence to latitude. The declination of the Sun is the latitude of the sub-Sun point, or with only slight loss in clarity, the declinarion of the Sun is the latitude of the Sun.
Roger, you wrote:
"I agree with most of this, except it would be better to say (near the end) '...emphasize that it is analogous to latitude on Earth.' "
Calling it analogous, I think, dilutes the message. Two things that are analogous are similar but not equivalent. And there really is an equivalence between declination and latitude. In nearly every celestial navigation class that I teach, we look up the Sun's current declination and GHA at a certain moment in class, and then I take them (in Google Street View) to that latitude and longitude (I try to plan ahead on the timing of this so that there's something interesting in Street View ...it's a "good day" when the Sun is directly over Macchu Picchu at high noon in Connecticut!).
The declination is the latitude of the sub-Sun point. The GHA is the (west-measured) longitude of the sub-Sun point. Of course, we can always be more precise in our specification of things. For example, there are various different types of latitude out there, and we're really talking about astronomical latitude. The latitude that was measured for centuries was always astronomical latitude, so it's a rather fine distinction but an important one. These small details should not get in the way of teaching and understanding the equivalence between declination of a celestial body and latitude on the surface of the Earth.
"The problem is that in astronomy the declination and latitude of a star or planet are two distinct things. The latitude (ecliptic or celestial) is the angle measured north or south from the ecliptic, whereas declination is measured from the celestial equator. "
I agree that there's a small potential for confusion with certain select audiences, but I don't think this is worth worrying about. It's a Venn diagram thing: the circles barely overlap. The people who know "celestial latitude" will also already be familiar with declination. Those who are new to declination almost certainly have never heard of "celestial latitude" and won't suffer from any confusion, and thus they benefit from knowing that declination is latitude.
"Declination is also confusing because it has other traditional uses. There's the magnetic declination (variation) of a compass."
Yep! I agree completely that there are too many things called declination, but I'm afraid that these, the oldest of the physical sciences, are stuck with this problem. Yes, we can ditch the idea of sundial "declination" which serves no useful purpose except as that "barrier to communication" --jargon without benefit. There aren't enough sundial experts to worry about. And as I've noted, declination in astronomy (and celestial navigation) is the best example that I can find of jargon that will probably never be eliminated. But I'm afraid we're also stuck with it in discussions of the terrestrial magnetic field because it is overwhelmingly preferred in geology. Navigators say magnetic "variation" while geologists say magnetic "declination". It's the same thing except in name. Geologists also refer to magnetic inclination and sometimes call that dip, which is yet another source of confusion. Let's face it: navigators and geologists should never speak. There will be arguments! :)
I'll take the opportunity while I'm here to repeat my advice on the original question. Should you use "hack" as a verb? No. Don't use the word "hack" in its old time-keeping sense at all, unless you're engaged in a historical discussion, or unless you're required to by the special language of a service, like a military unit. Other than that, a word like "hack" does not communicate and merely builds barriers, moats, trenches around the subject and the practitioners of celestial navigation. Who are we trying to keep out?? Jargon suffocates education. Hack as a verb for time-keeping has passed away. The more recent meaning (really a double meaning) in computing and technology has completely superseded the former sense. The hack is dead. Long live the hack!