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Discussion in 'International Current News & Events' started by lexsurivor, Jan 7, 2011.
I dont like this... That and the birds dying sounds like a great way to start off the new year
Flags raised for sure....
Hi, Guys...I read on another site an ATC employee said this happens all the time...things shift..they just close the lane, painters come in and paint new letters and numbers..
Think compasses. Say something were to happen unrelated to the pole moving, and you want to go some where due north. Instead you end up walking NNW the whole time. Not a good situation.
The magnetic north "pole" is always moving. MN is a result of the earth's core spinning. It spins somewhat independantly from the outer "shell" much like spinning a glass of water. The water never quite catches up so if you tilt the glass while spinning it the water takes a second to react and also tilt. Tilt the glass back the other way and the water once again has to play "catch up." Since the earth is constantly tilting back and forth the magnetic core is also playing catch up. It the earth didn't tilt over the seasons the magnetic core would eventually get caught up and be aligned with true north. That's why magnetic north changes over time.
Incidentally, topographic maps should have a date beside the listing for magnetic declination. If it's over a couple of years old get the correct number from the website below.
Here's a website to go to for up-to-date info on magnetic declination. NOAA's Geophysical Data Center - Geomagnetic Data
Put in your location and let it tell you what your magnetic declination is.
Living on an airport I can tell you that this is nothing new; runway designations change over time because the magnetic poles slowly drift on the Earth's surface and the magnetic bearing will change. Depending on the airport location and how much drift takes place, it may be necessary over time to change the runway designation. As runways are designated with headings rounded to the nearest 10 degrees, this will affect some runways more than others. For example, if the magnetic heading of a runway is 233 degrees, it would be designated Runway 23. If the magnetic heading changed downwards by 5 degrees to 228, the Runway would still be Runway 23. If on the other hand the original magnetic heading was 226 (Runway 23), and the heading decreased by only 2 degrees to 224, the runway should become Runway 22. Because the drift itself is quite slow, runway designation changes are uncommon, and not welcomed, as they require an accompanying change in aeronautical charts and descriptive documents. When runway designations do change, especially at major airports, it is often changed overnight as taxiway signs need to be changed and the huge numbers at each end of the runway need to be repainted to the new runway designators. In July 2009 for example, London Stansted Airport in the United Kingdom changed its runway designations from 05/23 to 04/22 overnight.
Just a note for consideration. Here in Tampa FL, they recently shut down the runway at the manin airport, to paint new numbers on the concrete. Magnetic ****. Not that rare of an event apparently.
Alright, I'm a little confused now. My compass and their map differ by about 10° :confused:
According to the website your magnetic declination should be approximately 9 degrees, 11 minutes west of true north. (I used Pittsburg, PA for the zip code.) That means the compass needle is off by almost ten degrees from true north. (Ours is almost 15 degrees. ) In other words magnetic north is actually located west of true north when measured from PA.
That means when you take a compass reading you need to subtract ten degrees to get the reading for true north. If your magnetic declination was 10 East you'd have to add ten degrees to your compass reading.
Wikipedea has a fair article on understanding MD at
Magnetic declination - Wikipedia, the free encyclopedia
The big thing to remember is that MD changes over time so if you make a cache and use a compass to mark the location then try to find it again in ten years you may not be able to because your compass is not pointing in the exact same direction. If the distances are short it may not matter but here I may take bearings off mountain peaks 20 or more miles away. A five degree error at those distances makes a big difference.
Looks like I need some more "edge-ih-kay-shun"
I thought the earth always had the same tilt. And when it moves around the sun the hemisperes get more or less sunlight. Because the northern hemisphere is angled towards or away from the sun depending on where it is in its orbit.
In general it does. The magnetic pole however moves around.
This may help visualize it.
Geomagnetism - Long Term Movement of the North Magnetic PoleIntroduction
Good point Lex: I kind of set up the problem here by oversimplifying my explanation. The earth's tilt does change somewhat over time albeit, very slowly. See Axial tilt - Wikipedia, the free encyclopedia. It's a phenomenon the serious stargazers (astronomers) have to take into account when doing their calculations. I'm also working off knowledge gained from a book that's now almost 40 years old so there may be new or revised theories now.
Declination as measured at the earth's surface can also change due to underlying geographic phenomena. That's why, if you look at a map showing the lines of magnetic declination across the earth's surface they have waves and dips in them.
Just food for though here...can you imagine how confounding this subject was centuries ago when MD was first discovered? One of the early pioneers in the field tried to determine MD by measuring the differences at various places on the earth. His data didn't make sense and he eventually concluded that there were at least two magnetic north poles/south poles. We take so much of our knowledge for granted and seldom realize the brilliance of past scientist and their work in bringing us to where we are today.