A Challenge with a Question

Being a navigator and a pilot, I tend to watch the skies during both the day and nighttime hours.

My challenge is to determine what direction true north is in relation to your own position when you watch the sun rise or set. Mark the true direction of the sun as it rises or sets, as the case may be.

You might want to think about what hemisphere that you are in.

You might also find it interesting marking the bearing of the moonrise and moonset.

I will apparently be the first to admit that I don't have a clue as to how to find true anything from where the sun/moon rises/sets. My GPS will tell me all of that and more, but I suspect that would be considered to be cheating. I can do pretty well at finding north from other means though...

In fact, in order to find the really true north, you have to consider also the date and time of observation, your geographical location, your altitude, altitude of the horizon line, the temperature in your place and temperature gradient in atmosphere along the direction line to the Sun, the same for air pressure, and for air humidity. Everything else is just a basic math i.o.w. the answer depends on precision (or task) you are going to achieve from such an observation. Otherwise the answer is as simple as pointing to the right looking at sunset, and to the left at sunrise

Hey OBG,

You can hang out with me if needed. I have been told more than once that I am the south end of a north bound horse. You'll quickly learn which way north and south are from that stand point.

I do this pretty much in the night time since I do a lot of amateur astronomy. I the daylight hours, (when not sleeping) I usually am familiar enough with the area I am visiting to know which way north is. Though a compass and GPS do come in handy from time to time.

Still, it's a very useful tip.

Stargazer

I'm with OBG. I have no clue how to get anything more than a rough guess from rising and setting suns and moons.

But then I'm rarely far from a compass and/or a GPS.

If you have a clear view of the horizon and can see both sunrise and sunset, a line between those two positions is East-West, 90 deg offset is North (point your right arm at sunrise and your left arm at sunset and you should be looking at North).

If you are in the Northern hemisphere, the sun is on the South side unless you are really near the equator in mid-summer.

Is that what you mean or is this a trick question?

"...Otherwise the answer is as simple as pointing to the right looking at sunset, and to the left at sunrise..."

That works for me!!!

"...Hey OBG, You can hang out with me if needed..."

Considering where you live, we might take you up on that offer some day!!!

Is it just me or wouldn't that require you to say put from sunrise to sunset before going anywhere? That wouldn't be practical as you'd only be able to get your bearings once a day...and only if you'd been sitting put all day.

My experience with the bush is that you can't properly see sunrise and sunset anyhow. The bush can be so thick at times you're lucky to see much sun at all.

wildman800,

It seems to me like you are asking for how to take and calculate an amplitude. With an amplitude you observe and take a bearing of the sun as it rises or sets, then you calculate what the true bearing of the sun is based on it's declination and your latititude.

See pp. 284-286: http://www.irbs.com/bowditch/pdf/chapt17.pdf

Note that that time to take the bearing with the sun is when the lower limb of the sun is about 2/3 of the sun's diameter above the visible horizon.

You might also be able to take an azimuth at that time. But IIRC, and I have not taken on since the late 80s, an amplitude is easier to figure out.

Also, IIRC, amplitudes are very accurate and because the bearing of the sun chages little as it approaches and is on the horizon.

Not to sound rude, but you've all missed the point of the question.

I know how to take an amplitude and find my location via celestial navigation. I've done both for many, many years of open ocean sailing. I know how to find true north during the day or night (nighttime is easier).

The solution mentioned to find north by placing the sun or the moon to your right or left would send you off in the wrong direction, based on my recent observations. Will your observations match mine???

Just try figuring out where true north is and then look to the sun or moon and see if either lines up to a east-sou'east or west-sou'west direction from you, providing that you are in the northern hemisphere, like I am.

By the way, moonset has been a little after midnight in the central daylight savings time zone.

If I'm not getting the question, then I'll admit I'm lost.

If one can observe the sun on the horizon, and you whether it is setting or rising, then you should be able to get rough estimate of north (or any direction) based on simply figuring that it is rising or setting in the east or west. As the Sun approaches a solstice, or as latittude increases, these estimates will become less correct. Right now the sun is nearer the solsitce, so it is probably not at least 20 degrees off of direct east or west when observed at sunrise or sunset.

But if you are not quizzing about an amplitude or about the thinking that north will be to the left when one looks at sunrise, then I don't get the question. What are you asking about? You're making me curious. Teach me something.

Hmm. I see the sunset every evening. Why would it be west-sou'west? It must be west-nor'west during summer. Or you mean "direction from you (me)"? Not from north? Maybe it's about time to replace your compass? It looks like its arrow have reversed magnetic polarity.

On the same note, what direction is shown by the shortest shadow a local noon when using the stick and shadow method of direction finding.

Wouldn't that depend on both the observers latitude and the sun's declination?

Hi Wildman800,

The azimuth direction where the ecliptic (green line in the picture below) bisects the horizon will depend on the latitude of the observer and time of year. True north will just be the angle you look up from a prepared table added to the azimuth direction.

Example;



Date 10th June 2008
Latitude 58° 28' N
Sunset 22:17
Azimuth direction to sunset 320° 35' degrees
Angle between Sunset and true north = 39° 25' degrees

Am Fear Liath Mor, I think that that's pretty much an amplitude.

Being that far North, shouldn't the sun be setting to the west-sou'west???? It sure looks to me like you are seeing a sunset in the northwest while in the northern hemisphere.

By the way, I've been observing a nor'east sunrise and a nor'west sunset (the same is true for moonset) for the last few months. I've been making these observations between the 30N to 41N Latitudes.

It seems to me that the declination is much higher than it should be.

It doesn't matter much if the sun rises north of east and sets north of west. If you put a stick in the ground vertically and trace the shadow of the tip of the stick, it will form a straight East-West line. A perpendicular line to teh trace will be True North-South. You'll find Polaris on one end, that's North

The sunrise at this time of year in these parts is 04:04 AM with the sunset at 22:17 PM so it really doesn't get dark during the night. Go above 67 degrees latitude and there is no sunset or sunrise so north is just where the sun is at its lowest in the night time sky.



Midnight sun at Nordkapp, Norway. (The Sun is indicating where north is)

No, it wouldn't depend on either. The shortest shadow from a steady vertical stick points directly to the true north (in northern hemisphere) no matter what. Just remove the "local noon" wording and don't be confused with magnetic north term.

IIRC, in the lower northern latitudes in summer (about this time of year), the sun will cast a southerly shadow. . .

Nice image!
By the way the stick and shadow will work there as good as near the equator. But also at midnight too (longest shadow points to south).

You're right, Russ. At some extreme latitude it will be hard to work with. But still the shortest shadow will point to the north. Except that you're watching the shadow from the flag on the North Pole.

If you're standing at the North Pole, which direction are you facing???

South!

Actually, I was at the other extreme. The lower northern latitudes would be near the equator and as the sun gets higher in the sky for us further north, it passes north of folks nearer the equator and causes a southerly shadow. The Tropic of Cancer (23° 26' 22" north of the Equator) is the northern limit in this hemisphere.

Ops! Me bad. Missed the word "lower" Sure, you are absolutely right.

I don't think so. In summer, then sun should set in the northwest for the entire northern hemisphere, and in the southwest in all of winter. It only sets near the true west close to the equinox.

Not always.

If you are near the Equator, and the sun is near the solstice, then the sun is going to possibly cast a shadow toward the south, even though you are in the northern hemisphere.

For example, today the sun has a declination of about 23.1 degrees North. If you were at a latitude of ten degrees north, then the sun would cast a shadow to the south at noon or local apparent north. As the sun was nearer setting or rising, the direction of the shadow would change toward the eat or west, but it would never be north during the day.

Alternatively, if you are in very high latitudes near the solstice, the days during which the sun never sets, then near midnight, the sun will also cast a shadow toward the south.

As a scienturvival (don't use that one in scrabble) project, I was gonna stay up late to see exactly where the moon set, then get up early to see where the sun rose, then try to figure out how to fine true north. But I failed...

you have to find true north first and then observed what bearing the sun or moon rose/set.

I think you'll find the rising/settings are more north than what it should be.

As we approach the Summer Solstice the sun should rise and set further north. Am I missing something?

I don't think so.

We tend to think the sun sets toward the equator. So when we are further north of the sun, we think it should set toward the southwest. If you looked at the spherical trigonometry invovled, you'd see that it's more a factor of the sun's declination, i.e. when the sun is in the North, it sets closer to Northwest. As the sun and the observer both get further north, then the differences get larger.

Holy crap… the only thing this thread has taught me is to make sure I have a compass in every kit.

"...you have to find true north first and then observed what bearing the sun or moon rose/set..."

Silly me, I thought from your original challenge that we were supposed to find north from where the sun rises and sets. Now you say to find true north first. I am sooo confused. Again. But I am glad I didn't get up at oh dark thirty...

"...My challenge is to determine what direction true north is in relation to your own position when you watch the sun rise or set. Mark the true direction of the sun as it rises or sets, as the case may be..."

Hi OldBaldGuy,





Here are some quick sunset bearings for today for some US city Locations. You can use a protractor - line up the 0 degree mark with the setting sun.

Example - Los Angeles sunset is 299 degrees azimuth, so to get true North just read 61 degrees on the protractor.

Los Angeles 61 degrees
Houston 63 degrees
New York 58.5 degrees (all ready set)
Chicago 57.5 degrees (all ready set)
San Francisco 60 degrees
Seatle 54.5 degrees

Thanks. I'm not sure you can see the sunset from L.A. (and possibly some of those other cities) though, thanks to the smog...

We get some nice sunsets in this part of the world!!

Vincent Thomas Bridge that ain't...

I like this one of the Tay Railway Bridge opened in 1881. Kind of reminds me of the river Nile at Luxor Egypt but without the Felluca sailing boats.

You are obviously more bridge knowledgeable than I am. I only know the Vincent Thomas 'cuz I patrolled over it for two years, and took the first surviving jumper to the looney bin...

IMHO, no matter what is the relation between sunset and the true north, but this topic have the most beautiful images to support (or...whatever) the point on a subject. Thanks to Am_Fear_Liath_Mor!

"...the most beautiful images..."

Indeed you to. I could rival you with some pics of a sunset from the Pearl Islands, in the Gulf of Panama, back when there was on one living on the islands but a few natives, but my ex has probably burnt those pics up years ago...

I can imagine. If only you could publish them on internet back then, they could survive any local/personal TEOTWAKI.

Heck, I still don't know how to publish pics on the internet today! Gotta give it a try one of these days I guess...

Try photobucket.com - very intuitive and free (requires registration). It's also very easy to insert images from photobucket to the forum.

I kindasorta have an account there, just haven't taken the time and effort to learn how to use it. One of these days...