Thread by @starlightgeek

I'm definitely not shocked that navigating by the stars won, given that approximately 60% of you are here because of the map thread.

All right, let's do this!

So, first of all, I want to start off by saying I actually teach a class called Navigating by the Stars at some of my medieval recreation/reenactment events. It's fairly popular and I actually teach it during the daytime. It's not really an astronomy class, but orienteering.

Why even learn how to navigate by the stars? It’s a traditional skill we’ve used for thousands of years but lost in the past 150 years as electric lights blot out the night sky. We no longer need to rely on the moon to hunt at night nor the sun to show us which direction to go.

It’s also a useful survival skill, should you ever find yourself without access to a modern compass or GPS. The stuff I'm going to talk about today is still used across the world. I've actually found it to be useful in my everyday life.

Let's start with the basics: In the Northern Hemisphere, stars generally move from east to west, rotating around Polaris (AKA the North Star). This means that *some* stars underneath Polaris will appear to move west to east.

A visual aid for why this is

So, how do you even find Polaris?

Well, there are a couple of ways. The one most folks learn is to find the bowl part of the big dipper and use the two stars on the far side as guides, which point to Polaris.

You can also use Cassiopeia to find Polaris.

Cool: The Big Dipper and Cassiopeia are more or less on opposite sides of Polaris, which means that, barring a physical block, you should be able to see at least one of them at all times.

The dippers are part of larger constellations called Ursa Major and Ursa Minor.

The long handles of the dippers looked, to the Romans, like the tails of bears.

Which tells you exactly how close Romans were able to successfully get to bears. :D

Look for Cassiopeia if you are having trouble spotting the Big Dipper. If she looks like a 3, draw a line to the left until you reach the North Star. If she looks like a Σ, draw a line to the right until you reach the North Star. M - down, W - up.

So, say you can't spot Polaris for some reason.

Look for Orions. Seen in the evenings from late autumn to early spring, it is considered a “winter” constellation. Orion’s sword always points south.

It is visible in the very early mornings during summer. If you can find Orion’s belt, the rightmost star -- Mintaka -- rises and sets closest to true east and west.

Look for Crux (the Southern Cross) when south of the equator. The bottom star in the cross (Acrux) points to the south pole. IT IS NOT A POLE STAR. It’s the closest visible, easily found constellation. It's on the NZ and Australian flags, too, so should be readily recognizable.

How to measure the sky:
An extended fist is generally 10º (about the distance the sun travels in an hour). This means each clenched finger is about 15 minutes of solar travel. Very helpful for knowing how far off sunset is! I use this ALL THE TIME.

Other methods of measurement:
- An extended little finger (when arm is fully extended) is approximately 1º.
- If you hold out your three middle fingers, they total about 5º.
- An extended pinky to extended thumb is about 25º.

So... what's the point of knowing this?

In addition to measuring solar travel and being able to tell how far apart stars are...

Polaris’ distance above the ground is your latitude. You can now use your measuring tricks to find your latitude.

This means that at the axial north pole Polaris is directly overhead. At the equator, it would be on the horizon.

In Austin, we're at about 30ºN. When I lived in London, I was at 51.5ºN. It's a noticeable difference, to say the least.

Okay, everyone feeling all right about finding Polaris and other "pointer" constellations? Good.

Time to move on to... THE MOON.

The Moon shows the same face to us as it is tidally locked to Earth. The illuminated part of the moon always faces towards where the sun is. It moves east to west across the sky. The moon rises roughly one hour later each night.

The Moon takes 27.3 days to orbit Earth. The lunar cycle (new Moon to new Moon) is 29.5 days — approximately every four weeks. A full moon rises at sunset. A new moon rises with the sun. A first quarter moon rises around noon and a third quarter moon rises around midnight.

Knowing this, you can actually tell what time of night it is based on the lunar cycle and its height above the horizon (use your measuring tricks!). I love doing this at reenactment events; it kind of freaks people out. :D

"Wait, what the hell IS a first quarter moon, anyway?" you ask. WELL, I'M GLAD YOU ASKED.

Waxing Crescent: new to first quarter
Waxing Gibbous: first quarter to full
Waning Gibbous: full to third quarter
Waning Crescent: third quarter to new

BTW, that's for the northern hemisphere. If you live south of the equator, the moon "runs" the other direction (waxing on the right side of the drawing, waning on the left side). It still rises in the east and sets in the west.

If the moon is a crescent and you’re in the Northern Hemisphere, you can draw a line between the “tips” to point you south -- just take the line to the nearest horizon. (If you are in the Southern Hemisphere, they will point you north.)

Some visual aids to explain the moon things

Okay, so. Let's talk about the sun. We all know the sun rises in the east and sets in the west. Unfortunately, this is only kind of true.

The sun only truly rises in the east and sets in the west right around the equinoxes -- March 21st and September 21st (roughly). For a month on either side of these days, you can consider their directions more or less east and west.

At winter solstice (just a few days ago for the northern hemisphere), the sun rises in the southeast and travels to the southwest. The "angle" between this and due east/west will depend on your latitude.

At summer solstice (a few days past for the southern hemisphere), the sun rises in the northeast and sets in the northwest. The angle thing applies again.

Illustrations incoming!

Consider these images of Austin's solar paths for the equinoxes -- left and right. Yellow bar indicates where the sunrise is and orange bar indicates where the sunset is.

The amber line indicates the sun's position at the time indicated (1 PM) and the amber arched line indicate's the sun's path.

But perhaps something at 30N isn't that compelling. How about Reykjavik, which is at 64N?

Check out the differences between winter sunrise/sunset (left) vs summer sunrise/sunset (right)

Compare Reykjavik (previous tweet) vs Quito, which is very nearly on the equator.

Those screenshots were taken from suncalc.net btw, which is an excellent tool for showing this sort of thing to others. :D

This is why, in the northern hemisphere, we went to build our houses facing south. Good architects will take solar position throughout the year into consideration.

I have a large window in my living room, which should be absolute hell in Texas. It's not -- b/c it faces south.

I get loads of sunlight in my living room from November through February, then nothing direct after that. I don't bake in the summer and can use solar heating to best effect in the winter. It's ideal.

Anyway, if it helps you to remember which way the sun shifts during the year, the sun heads south for the winter.

Knowing the way the sun moves and where it rises depending on the time of year can help you navigate. You have to be mindful of this sort of thing.

So, now to compasses.

A magnetized needle in a piece of cork, set to float freely in a bowl or cup of water, will point to magnetic north.

(If it appears to point south, run the needle through the magnet the other direction)

You'll need to keep electronics at least a few feet away from the needle.

Electronic devices have their own (very mild) magnetic field and can interfere with the accuracy of your proto-compass. This includes smart watches! So, be mindful when using a compass to keep it away from your electronics, lest you point yourself in the wrong direction.

Fun fact: magnetic north is actually a moving target! Good news: it's about as close to axial north as we are likely to get in our lifetimes.

Image shows path of magnetic north over time.

Let's talk about some fun ways to figure out what direction you're facing.

First up: solar drift
When the sun is high in the sky, it can be difficult to ascertain its movement. Set a stick in the ground (the longer, the better). Mark where the end of the shadow is.

15-60 minutes later, mark where the shadow’s new location ends. If you draw a line between the two, the direction of the line -- from first mark to second mark -- will point roughly east.

Helpful if you are really, really turned around and if you have the patience to wait.

While a more modern method, you can use an analog wristwatch to orient yourself. Hold the watch level and point the hour hand at the sun. South is about midway between the hour hand and the number twelve in the smaller angle.

Illustrations. You may need to remove your wristwatch to do this.

The next thing actually saved my life once, so I highly, highly recommend it as a tool for your navigational arsenal.

Taking a survey!

To take a survey, you set two sticks in the ground about a yard apart and line the tops of the sticks up so that a star is “set” on top of

the sticks. Sit still and watch. The star will begin to drift. The direction that it tracks will tell you what cardinal direction you are facing.

Take your usual idea of directions and rotate them 90 degrees to the left.
- If the star drifts to the left, you are facing north
- If the star drifts to the right, you are facing south
- If the star drifts up, you are facing east
- If the star drifts down, you are facing west

If the star drifts at an angle, you are facing a secondary direction -- southeast, northeast, northwest, or southwest.

BTW, even though the idea of north = up goes back to at least Ptolemy, but it was not really implemented in maps until the modern era. For a very, very long time, East was seen as the standard "up" in maps.

This is why we have terms like "orienteering" and "to orient oneself."

Some good reading on the whole north = up standard and how it fucks with things:

america.aljazeera.com/opinions/2014/…

So, I've put a lot of information out here in this thread. To put it to good use, I recommend you start looking up. Even if you live in a city with limited night visibility, you can still see the sun and the moon. Pay attention to what they're doing, when they come up, etc.

You don't have to be 100% attuned to what's going in the sky at all times. You can mentally note where things are, check your watch, and start piecing this stuff together. Seeing it in the real world really has an impact.

You'll find your way around a lot more easily, I bet.

Got questions? Need clarification on something? Ask here.

Otherwise, I'd like to dedicate this story about finding your way through the world using the stars to the late, great @carrieffisher, our Eternal Space Mom and Giver of No Fucks.