The following discussion about how to find the true north took place in the Moon-Net reflector. I found the subject so interesting that I decided to put together all the messages in this page.
On 9-Feb-1999 JR1EDE wrote:
Hello folks,
As the subject says, my friend needs how to find true north in daytime for his rover
system.
He knows the method of using a telescope etc but he needs more accurate and faster way.
This is necessary to aim the target within 1 to 2 degree for his 24GHz or above contact.
He says he uses a GPS but it fails in the range of hundred meters and still further needs
the true north for aiming.
This is not a matter for eme but think it's good place to ask.
Hope your good understand, thanks.
On 10-Feb-1999 K9EK wrote:
One way to find true North, outside during the day: Put a fairly tall,
thin pole in the ground, vertically, on a flat area. In the morning, mark the end of the
stick's shadow on the ground. In the late afternoon, mark the end of the shadow again. A
line through those two points is East-West, so, a line at right angles to the line is
North-South.
On 10-Feb-1999 WB4APR wrote:
Seems like you would have to do this at preciesly the same time before
and after local-apparent-noon for this to work?
On 10-Feb-1999 ON7RB wrote:
Hi, here's my frank's (or euro's) worth on this matter:
No it is not true north, even if you keep precisely the same time before and after noon
(the true noon = culmination of the sun)
There is a difference between the length of a sun-day and a star-day 23h56m4.091s. As the
sun is moving along the ecliptica, the sun-day is not always 24h, in fact 24h is an
average over a whole year. If you calculate the mid-day time for your longitude, you will
find the culmination of the sun to be somewhere between 15 minutes fast (early November)
or slow (early April); it will be exact 4 days only (April 16, June 15, September 2 and
December 26).
I have not figured out in how far the simple pole-shadow method would be influenced by
this time equalization phenomenon.
My idea: point a telescope to Polaris and you've got true north for the next century or
so.
On 10-Feb-1999 W8MQW wrote:
I seem to remember working this out once --- the shadow scribes
a perfect E-W line. It is a question of geometry, not of time. I'm rechecking it now
On 11-Feb-1999 K9EK wrote:
Doesn't have to be exactly either side of noon. If you plotted a LOT
of points all day long, they all would lie on the same line; east-west.
On 11-Feb-1999 PE1OGF wrote:
Why not doing it much easier.. If you have Instant-track you can find
out at what (local) time exactly the sun is at 180deg for true south. In this case you
don't have to calculate.
On 11-Feb-1999 K7RR wrote:
John, that is EXACTLY how I determine local apparent noon! With
some effort using Instantrack one can narrow down the time window to less that a minute.
It takes some patience, but the results are confirmed using IT and normal
navigational methods.
(Note: I'm not showing any E-Mail
address here in order to avoid them from being collected by SpamBots. You can
possibly find the E-Mail addresses of the above OM at QRZ.COM.)
This discussion is still not closed. If you have any opinions or additional
related information you would like to be published here, just send
me an E-Mail
Read
other Moon-Net discussions
Home page
Site map
Radio Sherlock search engine
Terms of service
Privacy
Cookies