stupid thing I did + polar aligning
Lotus
Is my face red. My little scope (etx90) would'nt track anymore, tried new
batteries, polar aligned 3 times, got out my compass, yada, yada. Something
about overlooking the obvious, the n/s switch was moved to southern
hemisphere, and I live in NY! Had tape over it, guess it didn't work. What
do you all do?
Trying to polar align for the sun in preparation for the Christmas eclipse,
using a compass, I forget, does the compass show magnetic north or true
north?
Thanks
Barbara
Reece Watkins
time back about putting the Sun into the Autostar database by faking it as
an asteroid in the same orbit as Earth. That way you can alt-az align the
scope before dawn and "sleep scope", waking it up after the eclipse starts.
Of course, make sure you have a full-aperture solar filter!
Clear skies,
Reece Watkins
"Lotus" <ewys...@worldspy.net> wrote in message
news:91tbmf$5gkv2$1...@ID-41705.news.dfncis.de...
Pietro
by the Sun at mid-day to get a good reading of North.
On December 25th the equation of time is zero -- meaning that sundials only
need to be corrected for longitude to match watch time. For each degree of
longitude you are away from the time zone meridian -- 75-deg West for NY --
multiply by 4 to get minutes. East of the meridian you subtract and west
you add these minutes to noon. Because NY spans from 74 to 80-degrees west,
your noon will happen from 4-minutes before (Vermont border) to 12-minutes
after (Lake Erie/PA border) watch noon. At that time all the shadows point
to true north.
If you do this experiment the day before the eclipse the shadow will be
30-seconds slow.
--
-- Pietro
http://www.Pietro.org
*Astronomy Alerts & News, Celestron, Computing, Mathcad & More*
Celestron 5" SCT: http://www.pietro.org/Astro_C5/c5_&_nexstar.htm
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"Lotus" <ewys...@worldspy.net> wrote in message
news:91tbmf$5gkv2$1...@ID-41705.news.dfncis.de...
Sidney Lee
>about overlooking the obvious, the n/s switch was moved to southern
>hemisphere, and I live in NY! Had tape over it, guess it didn't work. What
Been there, done that ;-) Took me about an hour to twig to the problem ;-)
I have no idea why Meade (in my case) chooses to place the switch right by
the power switch. I seriously doubt the base of customers who switch
hemispheres frequently demands such a "convenient" placement for instant
access. I'm pretty sure I could easily cope with having it hidden behind an
access panel or somesuch ;-)
>Trying to polar align for the sun in preparation for the Christmas eclipse,
>using a compass, I forget, does the compass show magnetic north or true
>north?
The needle on the compass points to the magnetic pole. You need to discover
the magnetic offset or declination for your location. It is readily
available from the local aiport or you can get it by going to the following
web site and entering your local latitude and longitude.
http://www.geolab.nrcan.gc.ca/geomag/e_cgrf.html
As a "reality check" you should know the following:
If you live in the western US or Canada your compass points east of the
geographic north while if you are along the East coast your compass points
west of geographic north. As you move closer to a line running through
Minnesota, Iowa, Oklahoma the offset gets very nearly zero and it increases
in size as you move east/west of that "line". For a given longitude the
offset gets larger in magnitude the further north you go. For example I
live in Calgary, Alberta, Canada and the current offset here is about 17.5
degrees east meaning the compass points 17.5 degrees east of true
geographic north.
Del Johnson
to do is note the direction of Polaris at night referencing a distant
terrestial object. Then in the daytime use the terrestial reference
when setting up the scope.
Del Johnson
In article <91tbmf$5gkv2$1...@ID-41705.news.dfncis.de>,
Sent via Deja.com
http://www.deja.com/
Frank Hollis
wrote:
>Compass shows magnetic north. There was a message on the Weasner site some
>time back about putting the Sun into the Autostar database by faking it as
>an asteroid in the same orbit as Earth. That way you can alt-az align the
>scope before dawn and "sleep scope", waking it up after the eclipse starts.
>Of course, make sure you have a full-aperture solar filter!
And somebody had the, even better, suggestion of tracking the Moon!
__
Frank J Hollis - fr...@chem.u-net.com http://www.chem.u-net.com/
These opinions have not been passed by 3 committes, 7 subcommittees
and 2 working parties. So they can't be the opinions of my employer
Michael A. Covington
eclipse,
> using a compass, I forget, does the compass show magnetic north or true
> north?
Compasses show magnetic north. How could they do anything else?
newsb...@my-deja.com
Barbara,
ALL magnetic compasses have variations. You can buy two identical
units from the same manufacturer and they won't point exactly in
the same direction. Depending on the quality of the manufacturer
and the unit, the variations can, well, vary. A good marine
compass will be the most precise. Not to sound like a gear snob,
but don't rely on anything you get at the -Marts. Find an outdoor
sports store, such as Erewhon and buy an orienteering compass.
Expect to pay around $15. Much less, you're buying junk.
Much more, you're paying for more than you need.
It gets better- the Earth's magnetic field shifts with respect
to True North over time, and the amount of difference varies from
locale to locale. You need to know what your local declination is.
The best way to do this is to check with a local airport. Aviators
need to know this for navigation purposes. Subtract positive
declinations from 360 or add negative declinations to 0 degrees to
find out what magnetic heading is True North.
My question is this: how are you going to do an Autostar
alignment without any stars in the sky? I'm planning to use an
Autostar telescope to view the eclipse too, and I have no
idea how I can accomplish this. I was planning to just point
it by hand and use the paddle to keep the Sun in the eyepiece
(it's pretty darn big, and I've never had a problem doing that
before). If you have a better way, I'd love to hear it.
::NB::
Lotus
no autostar. I'm sure someone else will jump in...
Barbara
HAVRILIAK
>north?
flabbergasted
and do the alignment, accept the alignment, and loosen the clutches to
move the 'scope to the sun. I find it's easy to do if you remove the
eyepiece and use the "shadow" method to get close then look down the
eyepiece holder and look for the light to get you home.
There's also a method on Mike Weasner's site to allow GOTO for the Sun
which will often get you pretty darn close but I usually have to
manually move the 'scope a bit to get it spot on. Once you're there it
tracks pretty well- Solar tracking rate seems close enough to Sidereal
for me.
Please don't forget to cap the finderscope! Not only will the
concentated sunlight burn the crosshairs but I'm sure it would burn
skin given the tight quarters and heaven forbid someone accidentally
look into the focussed light cone.
Clear sky and Happy Hollidays!
Bill
On Thu, 21 Dec 2000 22:05:48 -0500, "Lotus" <ewys...@worldspy.net>
wrote:
Reece Watkins
Reece
"Frank Hollis" <che...@ntlworld.com> wrote in message
news:k3m44tkicjsuppp8h...@4ax.com...
JFL
are in AltAz or Polar mode, it should always be tracking.
Do a good leveling alignment and go through the two star alignment if you
want, but don't look for the stars--just hit enter. You have to manually slew
to the sun anyway.
Cover your finder, unless you have a solar filter on its objective lens.
Aim at sun using the shadow cast on the ground, then look through scope, with
solar filter installed, to center. The ETX will track fairly well.
If you want to, you can maybe try using Venus as a single alignment star?
You'll be able to see it in your finder and your ETX (without solar filters
installed, of course). Be sure the time and location are very accurate.
Bill Nelson
: Trying to polar align for the sun in preparation for the Christmas
: eclipse,
: using a compass, I forget, does the compass show magnetic north or
: true
: north?
: Thanks
:
: Barbara
The compass shows magnetic north. You have to add or subtract your
deviation(?) to get an approximation of true North. A compass is not
good enough.
--
Bill Nelson (bi...@peak.org)
Larry Doering
"Declination" is the difference between the direction of the
magnetic north pole and the true north pole at a given point
on the earth. It's caused by the fact that the magnetic north
pole is not in the same location as the geographic north pole.
The magnetic north pole also wanders around with time, so
declination at a given location will change over a period of
years. The north magnetic pole is currently near Hudson's
Bay in northern Canada, so magnetic declination in North
America is close to zero in the center of the continent,
about 10-20 degrees west on the east coast, and about 10-20
degrees east on the west coast.
"Deviation" is the difference between the direction the compass
is indicating and the magnetic north pole. Deviation is caused by
magnetic fields (such as from a car body or electric motor) in
the vicinity of the compass that are strong enough to pull its
needle away from magnetic north.
Compasses in boats and aircraft often have a correction card that
lists the deviation at different headings -- this is determined
by orienting the vehicle with respect to the known direction of
magnetic north and measuring the difference between the compass
reading and the actual magnetic heading, usually with engine(s)
running and all electronic equipment turned on.
A reasonably accurate compass and knowledge of the magnetic
declination at your location will easily let you find true
north to within a degree or two. That's about as good as you
can get by pointing a telescope's polar axis at Polaris, since
Polaris is about 0.7 degrees away from the current celestial
north pole.
ljd