I recently spent 20 minutes filming the wrong spot of the sky. I knew that some Starlink satellites were due to flare due West of me, so I got out my Theodolite app and pointed it West (270°) to see what I should be looking at.
That was great, because it was a gap in the trees. So I zoomed in with my long lens, and nothing showed up.
The problem was the compass in my iPhone was wrong, in fact it was off by about 13 degrees. Now 13° is the difference between true north and magnetic north here in Sacramento, but my phone was set to use true north, so it was simply wrong.
So if you wanted to point your camera exactly due West, how would you do it?
You could use this method, or the phone's compass app, if you first check to see if the phone's compass is correct. To do that, first, take off any watch you are wearing (they are usually magnetic), and then open a map app, like Google Maps, align the phone with the sides of your house or a road, and then tap the arrow that makes the display rotate to face the same direction as you. It should alight up and down with your phone:
Personally, I'd still not trust it. I've had it good at one point, and then 15 minutes later, it was 10° off.
A better approach is to use some fixed object. Find the spot you are going to stand on in Google Maps, then look due west. To do this, switch to the Satellite layer, and hold Shift and drag the mouse to rotate. You can get it approximate by looking at the compass:
You can click on the arrows to rotate though 0,90,180,270 degrees. But to get a precise number you can edit the URL, which will say something like:
https://www.google.com/maps/place/Sacramento,+CA/@38.5652333,-121.4115042,1080a,35y,270h/
Change the "270h" to the heading you want (e.g. 240h for 240°)
You can then pick something that's directly above your position on the screen, typically a distinctive house or object, and aim for that. Example:
Here I'm standing on the roof of a parking structure, I want to point due West, so I make sure it's 270h in the URL, center my position, and see that there's a small hut in the tennis center. Now I know that's exactly due West, I can just point my camera above that.
I find this using ground reference to be the most accurate way of aligning things, assuming there's something there you can use.
You can also use a regular old-fashioned compass if there's no other way. First you need to convert the heading from true to magnetic. There's a good explanation of how to do that here:
For Sacramento, it's 13° East, so Magnetic = true - 13, so magnetic West 270-13 = 257°. So set your compass arrow to 257, turn it so the needle reads north, and you'll be pointing due West. You can then (sometimes) find an object in that direction and use that as a reference to point your camera.
There are other techniques. You can use the sun (or rather, shadows), or stars. But they are a bit trickier and time-dependent.
That was great, because it was a gap in the trees. So I zoomed in with my long lens, and nothing showed up.
The problem was the compass in my iPhone was wrong, in fact it was off by about 13 degrees. Now 13° is the difference between true north and magnetic north here in Sacramento, but my phone was set to use true north, so it was simply wrong.
So if you wanted to point your camera exactly due West, how would you do it?
You could use this method, or the phone's compass app, if you first check to see if the phone's compass is correct. To do that, first, take off any watch you are wearing (they are usually magnetic), and then open a map app, like Google Maps, align the phone with the sides of your house or a road, and then tap the arrow that makes the display rotate to face the same direction as you. It should alight up and down with your phone:
Personally, I'd still not trust it. I've had it good at one point, and then 15 minutes later, it was 10° off.
A better approach is to use some fixed object. Find the spot you are going to stand on in Google Maps, then look due west. To do this, switch to the Satellite layer, and hold Shift and drag the mouse to rotate. You can get it approximate by looking at the compass:
You can click on the arrows to rotate though 0,90,180,270 degrees. But to get a precise number you can edit the URL, which will say something like:
https://www.google.com/maps/place/Sacramento,+CA/@38.5652333,-121.4115042,1080a,35y,270h/
Change the "270h" to the heading you want (e.g. 240h for 240°)
You can then pick something that's directly above your position on the screen, typically a distinctive house or object, and aim for that. Example:
Here I'm standing on the roof of a parking structure, I want to point due West, so I make sure it's 270h in the URL, center my position, and see that there's a small hut in the tennis center. Now I know that's exactly due West, I can just point my camera above that.
I find this using ground reference to be the most accurate way of aligning things, assuming there's something there you can use.
You can also use a regular old-fashioned compass if there's no other way. First you need to convert the heading from true to magnetic. There's a good explanation of how to do that here:
Article: The magnetic reference for Earth is north regardless of whether you are traveling north or south. Magnetic declination, or declination, is the difference between the true north reading from the map and the magnetic north reading from a compass. When a compass is used in combination with a map, a correction must be made to allow for declination.
In North America, magnetic declination varies from 30 degrees East in Alaska to 20 degrees West in Labrador, Maine. The degrees of declination for an area are usually located on the bottom margin of the map near the north arrow, or they can be located using a declination chart.
The method for correcting for declination is as follows:
1. For Easterly Declination, subtract the declination from the true reading to obtain the magnetic reading. Magnetic = true - easterly declination
2. For Westerly Declination, add the declination to the true reading to obtain the magnetic reading. Magnetic = true + westerly declination
An easy way to remember whether to add or subtract is "West is best and East is least." So for West declination, add to the true reading (West is best, and therefore a larger number) and for East declination subtract from the true reading (East is least, and therefore a smaller number).
For Sacramento, it's 13° East, so Magnetic = true - 13, so magnetic West 270-13 = 257°. So set your compass arrow to 257, turn it so the needle reads north, and you'll be pointing due West. You can then (sometimes) find an object in that direction and use that as a reference to point your camera.
There are other techniques. You can use the sun (or rather, shadows), or stars. But they are a bit trickier and time-dependent.
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