# How would I measure the angle of a certain street from true north?

1. Jun 15, 2011

### Ironside

As the title says, I want to measure the angle of a street from true north so I can know what time of the year the sun will align with it.

2. Jun 15, 2011

### DaveC426913

Google maps always worked for me. It will show you precisely what angle your street is from True North. That's how I built my garden (a giant compass rose - aligned to magnetic North).

3. Jun 16, 2011

### Ironside

I can't seem to find that function. Mind helping me out?

4. Jun 16, 2011

### turbo

If you get a current topographical map of your region, it will show you just how much magnetic north deviates from true north. You can use this value to determine the correction necessary to determine the true alignment of the street in question. It's a pretty simple problem once you know the local variance between magnetic and true north.

5. Jun 16, 2011

### DaveC426913

Sorry, not a Google function. Just plain ol geometry on a map. I did it with PhotoShop.

You want to know the orientation of your street referenced to True North. Google Maps are aligned to True North. How far your street varies (in degrees) from vertical on the map is the angle your street is from True North in reality.

When I did this, I got the best Google map available of my lot, screengrabbed the image, and pulled it into Photoshop. Ensuring I had the 'Info' window open, I drew a Line element vertically over my street. Then I used the Rotate tool to rotate the line until it was aligned with my street. The Info window tells me what angle I just rotated my line through.

So, I had to rotate my vertical line 16 degrees counterclockwise until it matched up with my street. That tells me my street is aligned 16 degrees west of north.

(From there, I calculated Magnetic North for my location and applied the correction to make my garden, but you don't need to do that step)

#### Attached Files:

• ###### Photoshop.jpg
File size:
62.3 KB
Views:
360
Last edited: Jun 16, 2011
6. Jun 16, 2011

### Ironside

Ahh ok, cause i've been calculating them manually so far based on the latitudes and longitudes, I hoped google maps had that whole function set up lol. What you guys suggested will definitely save some time though. Thanks!

7. Jun 16, 2011

### DaveC426913

He doesn't need to deal with mag north at all. That's my thing.

He's looking for True North. Which, if he has a topo map in-hand, is, in a word, simple.

8. Jun 16, 2011

### Staff: Mentor

You could also record the time the sun is aligned with your street, multiply by 15 and subtract/add your angular distance from the center of your time zone.

You could also drive down the street and read it off a gps.

9. Jun 17, 2011

### Ironside

One more question I gotta ask you guys, I had posted another thread relating to a phenomenon called Manhattanhenge where the sun aligns with the streets in Manhattan twice a year where it gets a nice view during sunset.

http://en.wikipedia.org/wiki/Manhattanhenge

I've been asking these questions in this thread because I wanna do something similar and find the dates when the sun will align with the streets I'm working with based on the angle of the streets deviating from true north. However, I've calculated the angles and that's great, but now how would I calculate the dates in which the sun would align with the streets so it gets that nice view?

I notice how the streets of Manhattan are 29 degrees off of true east-west, and that's why the sun aligns with them on May 28th and July 11th because of their offset.

How would I be able to find the date for example, on a street that is offset from true east-west at 8 degrees? or 42 degrees, or whatever?

10. Jun 17, 2011

### turbo

OK, this is a bit more complicated because the locations of sunsets are a function of your latitude. You'll want to figure out where your street is pointed, and consult a planetarium program to see when sunset will occur in that section of the horizon. You'd have better opportunities at high latitudes, since sunsets can be long, horizon-grazing events up here vs in southern locations.