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  • Rapt in Awe

    My Journey through the Astronomical Year

    Think of this as a "companion text" to this, the main web site. Not required reading, butI hope you'll find it interesting and helpful.

Step 2 – Finding Polaris: Our First Guidepost Star

Quick Guide

  1. Find north
  2. Find your approximate latitude – the North Star is the same height above the horizon as your latitude.
  3. About one hour after nightfall, look north as high as your latitude.
  4. The North Star – Polaris – is the bright, isolated star you see. There is no star as bright as it within about 15-degrees – half again the distance covered by your fist when held at arm’s length.

Our journey through the astronomical year begins with knowing where we are and where we’re headed and fortunately for northern hemisphere observers we have a constant guidepost amidst a constantly changing skyscape – Polaris, the North Star. So the first task is to find it.One of the stars in this video is Polaris – can you guess which one?

Yep, as Shakespeare had Julius Caesar point out, it’s the steady one, right in the center of the screen. (”But I am constant as the Northern Star, of whose true fixed and resting quality there is no fellow in the firmament.”) Of course we’ve speeded up time in the video – you’re seeing a whole day of apparent movement in less than a minute! But I suspect people in Shakespeare’s time were much more in tune with the night sky. They knew what Caesar meant because they had watched the stars. They will appear to move – it’s us doing the moving, of course – far enough in an hour for any careful observer to notice the change.

But while we may find it difficult to pick out the constant one just by glancing up there, once we’ve found it we can be certain it’s going to be in the same place all night, every night, while everything else is always on the move. So here’s a more detailed guide to locating our constant companion. Once you know it, you’ll find yourself checking it every time you go out at night – and yep, there it is, right where you left it!

Clue 1: Find north

A GPS system can tell you this precisely. A compass can point to magnetic north which should be close enough to what you want – just don’t take it as an absolute guide.   Or if you know that the Sun first appears at daybreak in the east and it vanishes at nightfall in the west, then you are well on your way. Just  face east, and north is to your left – face west and north is to your right. At noon the sun is due south – north is the other way.  Any of these are approximations. Your true guide to north is going to be the North Star. But, of course, you have to find it first!

Clue 2: Find your approximate latitude – the North Star is the same height above the horizon as your latitude.

All we need is a round number in degrees. The site linked above will give your latitude as something like:

Latitude, Longitude: (41.630773, -71.08854)

All you need at this point is the first number without the stuff after the decimal point. In my example it is 41. (If you’re in the southern  hemisphere this site puts a minus sign in front of your latitude and you can’t see the North Star.) There are, of course, many others way to find this out. This is the quickest, easiest one I’ve found.

This number also indicates how high the north star is above your northern horizon.

About one hour after nightfall, look north as high as your latitude.

Why one hour? Again, not an absolute, but if you go out during twilight the brightest stars will emerge first and the North Star will be among the first to appear in the northern sky, though not the only one and it is NOT the brightest star in our sky – just one of the brightest.  (It actually ranks 48th on the list of brightest stars. Seeing it in twilight like this is simply less confusing.)

Next problem – how do we look “as high as our latitude?”  Again, there are a number of ways. You could actually measure the angle using a protractor with maybe a ruler to sight along – but that’s too involved for most people. Can you estimate? Sure! Just point your arm straight out at the horizon. That’s zero degrees. Point it straight up. That’s 90 degrees. Point it half way up. That’s 45 degrees. One third of the way up? That’s 30 degrees. Experiment with this method for a minute or less and you should get the hang of it. Will you be able to point to something real specific like 41 degrees? Of course not. But I bet you can get within about 5 degrees just by rough estimate and that will be close enough.

A second method frequently recommended is to use your fist as a measuring device. The idea is that your fist – no matter what your size – when held at arm’s length, covers 10 degrees of sky. My experience is that this doesn’t work for everyone and I’m not sure why, but I think the problem comes when they use just one fist to try to estimate a large number of degrees, such as 40. There are several simple solutions.

First, when you are measuring more than 10 degrees, stack one fist on top of the other – trying to do large measurements, such as 30 degrees or more with a single fist is, I believe, one of the causes of inaccuracies. So go fist over fist over fist.

Second, don’t wear gloves, it will throw things off.

Jacob's Staff or Cross Staff was a Medieval instrument used for detrmining the altitude of the North Star.

Jacob’s Staff or Cross Staff was a Medieval instrument used for determining the altitude of the North Star.

Third, make a “star stick” –  or maybe we should call it a degree stick.  Any stick about two or three feet long will do. A wooden dowel would be fine, but no need to get fancy. Measure the width of your fist across the knuckles, including your thumb as folded tight into a fist. (Mine comes in at 4-inches.) Now put pieces of masking tape – or white tape if you have it, every four inches – or whatever – on your stick .  Try to cover 40 degrees this way – 60 would be better.  Now you take a measurement by holding the stick out at arm’s length – great in the winter time because you can wear gloves. Does it work? mine does. At least it puts me in the right ball park. It is not as sophisticated as the ancient navigation instrument, the cross staff, but in a rough way is the same idea.

So either by using a stick, your fist, or just raising your arm for a rough estimate,  you should be able to make a reasonable guess at how high to look for the North Star from your location.

The North Star – Polaris – is the bright, isolated star you see. There is no star as bright as it within about 15-degrees – half again the distance covered by your fist when held at arm’s length.

Think you’ve found it? The first way to confirm that you have the right star is to see if there’s another star, as bright, or almost as bright, nearby. There shouldn’t be. But it’s fairly easy to mistake Kochab as Polaris. Kochab is just as bright and some 16 degrees away – about a fist and a half. But Kochab has a bright companion just three degrees away – not as bright as it, but pretty bright.  Take a look at this chart which includes just the brighter stars.

Notice Polaris is isolated, while Kochab has a nearby companion that is almost as bright. (adapted from Starry Nights Pro software)

Notice Polaris is isolated, while Kochab has a nearby companion that is almost as bright. Click image to enlarge. (Adapted from Starry Nights Pro software)

If you hold your closed fist out at arm’s length so that what you think is Polaris is just peeking around one end or the other of your fist, then your fist should not cover up any other bright stars. Polaris is that isolated.

There are some other common guides used to quickly find it, but I must stress that these work best at the higher latitudes. What we’ve shown so far is good for 40 degrees north. Remember that each degree you go farther north puts everything higher in the sky. Go to the North Pole, brave explorers, and Polaris will be directly overhead. Go south to the equator and Polaris will be on the horizon – invisible. And, of course, south of the equator it’s a who different ball game. Folks there see many of the same stars we do, but  they also see ones we never see and they don’t see Polaris, or any similar star, marking the south celestial pole. So as you look at these guides keep two things firmly in mind.

1. Your latitude determines how high Polaris will be.

2. As you saw from the movie, the stars all circle it in the course of 24 hours. This also means that they will appear at different places on different dates. The patterns remain the same. The Big Dipper always looks like the Big Dipper. But sometimes it’s right side up and sometimes upside down. Early on a January evening you’ll find Kolchab beneath Polaris. In the summer it will be above it – by the same distance.

The most common guide for finding the North Star – Polaris – are the “Pointer Stars” of the Big Dipper. The Dipper itself is probably best known seven stars in our sky. Look at the chart below to see how this can be used to find Polaris.  BUT . . . keep in mind, there are times of year – December and January in particular – where this may be two low in your sky – or hidden entirely – to be of use.  So here’s how it looks in January at 41 degrees north latitude.

A line through the Big Dipper's "pointer stars" show us Polaris.

A line through the Big Dipper’s “pointer stars” show us Polaris. (Click image to enlarge.)

Where I usually observe, the pointer stars are hidden in some trees at this time of year. But another good guide post is the “M” of Cassiopeia. It too is distinctive, bright, and easy to recognize. And when the Big dipper is low in the sky, it is high. It doesn’t contain pointer stars, but it’s still serves as a pretty good guide when looking for Polaris.

The "M" of Cassiopeia helps when the Big Dipper is too low to see - or see well.

The “M” of Cassiopeia – it looks like a “W” when it climbing up the sky – helps when the Big Dipper is too low to see – or see well. Click image to enlarge.

Now that you have these patterns in mind, you might want to take another look at the movie to see how they change in relation to Polaris.

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2 Responses

  1. […] Step 3 – Finding Polaris: Our First Guidepost Star […]

  2. […] Step 2 – Finding Polaris: Our First Guidepost Star […]

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