Perfessor Friar finds his True North

Polaris, known as the “north star”, or “pole star“, isn’t a particularly bright star in the sky.   In fact, in terms of brilliance,  you can consider it a “B-lister”.   But it’s one of the most important stars in our heavens, because it happens to be aligned the axis of the Earth’s rotation.

This means Polaris stays virtually motionless in the night sky while all the other stars appear to rotate around it.   And Polaris always points North.

(Well, not exactly, but to within 0.5 degrees, which is close enough for most of us.)

People all over the planet have recognized this for hundreds of years.    Which makes Polaris a pretty handy celestial guide to help us find our way around.

The angle Polaris makes above the horizon corresponds to your latitude.    If you were at the North Pole,  at 90 degrees north, Polaris would be directly overhead, and the stars would circle around you in a counter-clockwise manner, neither rising or setting.

The further south you went, the lower Polaris would be in the sky, until you got to the Equator at zero degrees north.   Here, Polaris would lie on the northern horizon, with the stars rising and setting from East to West.

The early explorers who first crossed the oceans knew this.  They’d measure the angle Polaris made above the horizon to figure out their latitude.    This was usually done at dawn or dusk, when both the horizon and stars would be visible a the same time.

(Unfortunately, there’s no simple way to measure longitude.   That came much later, but that’s another story…)

Constellations that are close to Polaris are always present in the night sky…they just circle around the North Celestial Pole, neither rising nor setting.   These are known as “circumpolar” constellations.   The further north you are, the higher in the sky these circumpolar constellations are.

In the Northern Hemisphere, examples of circumpolar constellations are Cassiopeia (the “W” you see in the sky) and the famous Big Dipper, which forms part of Ursa Major, the Great Bear.

(By the way, the Greek word for Bear is “Arktos”.   Hence the origin of the word “Arctic”,  referring to the part of the planet where the Great Bear is more prevalent in the sky.  And conversely, “Antarctic” refers to the opposite part of the globe in the southern Hemisphere).

As I mentioned earlier, at the Equator, Polaris would be located just on the horizon.   As you’d proceed further south, Polaris would disappear below the horizon, as would the northern constellations.   However, the South Celestial Pole would become visible and rise higher in the sky, as would the southern constellations.

One of the more famous southern constellations is the Southern Cross.   You can’t see it in Canada or the States, except perhaps glimpses of it in Florida.   But don’t feel bad.   Those who have seen it say the Big Dipper is more impressive.  And I tend to agree.

As for the South Pole, unfortunately, there isn’t really an equivalent “South Star” to guide us.  The closest star would be Sigma Octantis, but it’s quite dim and unremarkable.   It’s nowhere near as prominent as Polaris. is.

Getting back to Polaris: it’s aligned with the axis of the Earth’s rotation, or the Geographic North Pole.   Let’s not confuse this with the  North Magnetic Pole, which is where the Earths’ magnetic field intersects the Earths’ surface.

The Geographic North Pole is at 90 degrees latitude.   Right now the North Magnetic Pole is at about 82 degrees latitude (about 850 kilometers away), but its location is changes by tens of kilometers a year.

A compass will point to the North Magnetic Pole.  From where we are, thousand of miles away, a compass reading is close enough to help us find the true, geographic North. (It’s like San Francisco and LA being about the same direction from New York).

But at higher latitudes,  the compass readings will be off, and will no longer be practical for navigation.   At that point, we would need to refer to Polaris to find the “True North” (That is, we you don’t have a GPS.)

If you think, however, that we can always rely on good ol’ dependable Polaris, guess again.

The Earth’s axis of rotation, as measured against the stars, slowly changes directions, similar to a wobbly spinning top.    Though this it takes a while….the cycle takes 26,000 years to complete, and is known as the procession of the equinoxes.

What this means is that the North Pole will point to different parts of the sky over time, and it’s constantly changing.

Right now, we happen to be alive at a time when Polaris happens to be the Pole Star.

In 3000 BC, the Pole Star was Thuban (a star in the constellation of Draco).   In 14,000 years, the Pole Star will be near Vega, wich is one of the brightest stars in the sky.

And in 27800 AD, it will be Polaris again.

Just goes to show, what goes around, comes around.

Even with the North Celestial Pole.

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10 Comments on “Perfessor Friar finds his True North”

  1. Viking Thunder Says:

    So lets see, early man, like primitive really primitive man, gets to live under the sign of the dragon.

    Cool

    We, get to live under the sign of the bear. Not a dragon, but hey, Bears are cool. There all Gree, and stuff.

    The future, the distant future mind you, will live under the sign of…. the olde tyme’ harp. Lame

    u___u The hippied will rule the future!

  2. Allison Day Says:

    You rock, Friar. I always love your Perfessor Friar posts. ^_^

  3. dave1949 Says:

    Those ancients should have learned to use the gps to figure out the longitude. What morons, their vcrs probably were flashing 12 all the time.

  4. XUP Says:

    Huh? Science is so complicated. If you have to pore into the individual subtleties and intricate details to try to get what’s going on in the sky…then I dont’ think science is very good.

    Good science should be able to get its point across in a way that keeps me entertained, yetin a way that your grandomother could understand it.

  5. Friar Says:

    @VT
    Yes…it will be the Age of the Harp. Harmony and understanding. La-la-dee-dah.

    At least Polaris is omnivorous.

    @Allison
    Glad you like it. You get a Gold Star for being my prize pupil. (Though saying that will probably get Eyeteaguy all riled up!) 🙂

    @dave
    First, they’d have had to put a Global Positioning Satelite into orbit.

    I don’t think they had catapults that big, back then.

    @XUP
    Good point. If you’re not following, I probably didn’t write this very well.

    Perhaps celestial mechanics would better be explained by a 19th-century romance novelist.

  6. Julie Says:

    Friar, this is the first time anything about the cosmos was explained so clearly that I understood. Gives a whole new meaning to “what goes around comes around.” Love that playfulness!

  7. Friar's Mom Says:

    @Perfessor,

    One of your commenters stated that your info was clearly understood; while another commented that science is so complicated.

    Personally, I think some of us are scientifically inclined; while others tend towards the arts and philosophy. Some of us are multi-faceted and are open to a variety of knowledge.

  8. Friar Says:

    @Julie
    Gee…thanks! Based on the luke-warm response I got…I was wondering if this was just a poorly-written post. I’m glad to hear at least a few people like it.

    @Friar’s Mom
    At this point, with mixed reviews, I have no idea whether this is a good post, or not.

    But like I said, it’s gotten a luke-warm response.

    I don’t think technical or scientific posts are that popular. What people seem to want to read these days are “Tips”. Tips on how to be happy. Tips on how to organize your life. Tips on how to achieve your dreams…etc…

    Maybe I should start writing more of those… 🙂

  9. Allison Day Says:

    Frair – It was an excellently-written post. I loved it. (But you already knew that.)

    Regarding people wanting “Tips”… everyone wants a quick fix. Nobody wants to have to think, or to have to do any work… they just want life handed to them on a silver platter.

    (Heck, I’m pretty sure no one at all reads my coding posts, so you’re actually doing pretty well, compared to me. 😉 )

  10. Friar Says:

    @Allison

    I know a little bit about coding (not very much). But I think your posts are extremely well-written!


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