Mars' Motion

Hi All....

When viewing Mars through my 8" dob, i've noticed a strange motion as it
drifts through my FOV: i let it drift in from the right and it moves to the
left, then straight down where it hangs for a few seconds, then continues
toward the left again, like a zig-zag motion. I've never noticed this with
other objects. Whats up with Mars' motion?? or is sumthin' up with my
scope??

Thanx

Cheers
D.

I can assure you it is NOT Mars doing this. Either your scope is moving,
or there's soemthing odd about your optics or perhaps you are
experienceing gross atmospheric refraction variations. Does it do it
consistently every time? If so, that probably rules out the atmosphere
since it is somewhat random.

Bryan

Dave O'Neill/Bea Benian wrote:
Hi All....

When viewing Mars through my 8" dob, i've noticed a strange motion as it
drifts through my FOV: i let it drift in from the right and it moves to the
left, then straight down where it hangs for a few seconds, then continues
toward the left again, like a zig-zag motion. I've never noticed this with
other objects. Whats up with Mars' motion?? or is sumthin' up with my
scope??

Thanx

Cheers
D.

"Dave O'Neill/Bea Benian" wrote in message ...
Hi All....

When viewing Mars through my 8" dob, i've noticed a strange motion as it
drifts through my FOV: i let it drift in from the right and it moves to the
left, then straight down where it hangs for a few seconds, then continues
toward the left again, like a zig-zag motion. I've never noticed this with
other objects. Whats up with Mars' motion?? or is sumthin' up with my
scope??


Is it followed by a blue fuzzy thing or a black squishy thing with a
piece of wood in it?

When viewing Mars through my 8" dob, i've noticed a strange motion as it
drifts through my FOV: i let it drift in from the right and it moves to
the
left, then straight down where it hangs for a few seconds, then continues
toward the left again, like a zig-zag motion. I've never noticed this
with
other objects. Whats up with Mars' motion?? or is sumthin' up with my
scope??

Thanx


LOL

Quite obviously, and almost without even saying...its the scope, not Mars.
Check your balance point...sounds like at low altitudes, you're losing
the balance point slightly.....sounds like slightly mirror heavy.
That "straight down" motion is your scope moving very slightly.
You also appear to have irregularly smooth (or rough) altitude bearings,
and/or teflon pieces installed. You've probably never noticed this
before because with 'other' objects, you were at a much higher
altitude...just a guess on my part.
FWIW
Tom W.



Tom A. wrote:
When viewing Mars through my 8" dob, i've noticed a strange motion as it
drifts through my FOV: i let it drift in from the right and it moves to

the

left, then straight down where it hangs for a few seconds, then continues
toward the left again, like a zig-zag motion. I've never noticed this

with

other objects. Whats up with Mars' motion?? or is sumthin' up with my
scope??

Thanx



LOL

Any motion that you see in anything in the sky tht you observe is not
"their" motion, but the earth's rotation, or the movement of your scope, or
both.

Neal

"Dave O'Neill/Bea Benian" wrote in message
.. .
Hi All....

When viewing Mars through my 8" dob, i've noticed a strange motion as it
drifts through my FOV: i let it drift in from the right and it moves to
the
left, then straight down where it hangs for a few seconds, then continues
toward the left again, like a zig-zag motion. I've never noticed this
with
other objects. Whats up with Mars' motion?? or is sumthin' up with my
scope??

Thanx

Cheers
D.

Neal Matthis wrote:

Any motion that you see in anything in the sky tht you observe is not
"their" motion, but the earth's rotation, or the movement of your scope, or
both.

The motion of Mars that makes it necessary to occasionally re-center it
in the eyepiece these days is due to the difference between the Earth's
and Mars' orbital motion. It's in retrograde motion now and appears to
be moving to the west. IOW, it's orbital motion, not the Earth's
rotation. Same with the Moon and Sun.

This has nothing to do with the OP's problem, though, unless there is
something new going on with the planets!

Mike Simmons

You're saying that when I look at Mars and turn off my clock drive, Mars's
movement out of my field of view is because of it's orbital movement
relative to Earth, and not simply Earth's rotation? If that is the case,
how does my telescope track Mars perfectly for hours using the same
corrective movement it uses to track stars and galaxies? How does my scope
track the motion of stars, which is no doubt due to Earth's rotation, then
when I point it to a planet it magically tracks that planet's orbital
movement?

Neal

"Mike Simmons" wrote in message
...
Neal Matthis wrote:

Any motion that you see in anything in the sky tht you observe is not
"their" motion, but the earth's rotation, or the movement of your scope,
or
both.

The motion of Mars that makes it necessary to occasionally re-center it
in the eyepiece these days is due to the difference between the Earth's
and Mars' orbital motion. It's in retrograde motion now and appears to
be moving to the west. IOW, it's orbital motion, not the Earth's
rotation. Same with the Moon and Sun.

This has nothing to do with the OP's problem, though, unless there is
something new going on with the planets!

Mike Simmons

Is it really that little apparent motion? I have seen it drifting well
across the field of view of a few different telescopes. I've generally
been using higher power than you, though, with fields of view no greater
than 11 arcminutes and usually more like 6 or 7 (and in one case only
about 2 arcminutes). It still doesn't seem that it should be a problem
with observations over an hour or two, though. I know these scopes
track well enough. Perhaps it's differences in atmospheric refraction
with changes in altitude (with Mars always at more than two air masses
from here) that causes the apparent drift (or a combination of the two).

Regardless, this wasn't meant as a reply to the original poster, who
describes motion of Mars that can't be due to anything but the
telescope. Mars definitely shouldn't be exhibiting "zig-zag motion"! I
was responding to the claim that only the Earth's rotation and the
telescope's motion can cause Mars to appear to move. The numbers you
give indicate my explanation can't be all there is to what I've seen;
differential atmospheric refraction is the only other explanation I can
think of.

Mike Simmons

David Knisely wrote:

Hi there. You posted:

Take a telescope that tracks the stars perfectly and then put Mars in
the center of the field and you'll see it move out of the field over a
period of a few minutes to several minutes WHILE THE CLOCK DRIVE IS
WORKING. Mars has an apparent motion across the sky IN ADDITION to the
rotation of the Earth that is compensated for by the telescope's clock
drive.

Well Mike, while Mars does appear to move slowly with respect to the
background stars, the motion is much to small to cause the object to drift out
of a high-power field in only a few minutes (unless the clock drive was
malfunctioning). In fact, right now (Sept. 16th), its motion is roughly 21.2
arc seconds per hour, which is comparable to the planet's current angular
diameter. At that rate, using my 4.9mm Speers-Waler in my ten inch (288x,
18.73' arc TFOV), it would take 26.5 *hours* for Mars to move from the center
of the field to its edge (an angular distance of 9.37 arc minutes). Clearly,
if Mars is drifting out of the gentelmen's field in only a few minutes, the
clock drive or the polar alignment is at fault. Clear skies to you.
--
David W. Knisely
Prairie Astronomy Club: http://www.prairieastronomyclub.org
Hyde Memorial Observatory: http://www.hydeobservatory.info/

**********************************************
* Attend the 10th Annual NEBRASKA STAR PARTY *
* July 27-Aug. 1st, 2003, Merritt Reservoir *
* http://www.NebraskaStarParty.org *
**********************************************

Hi again. You posted:

Is it really that little apparent motion?

Yes, it is. Many decent star-charting programs like MEGASTAR can give you the
magnitude of that motion. It can be somewhat higher (1.3 to 1.6 arc minutes
per hour) a month or two prior to or after Mars exits the retrograde loop, but
it is still small enough that it would be hard to notice in a short period of
time (certainly a lot more than a few minutes).

I have seen it drifting well
across the field of view of a few different telescopes.

Then they clearly have clock drive or polar alignment issues (surprisingly, in
my experience with other people's instruments, the latter is often nearly as
much of a problem as the drive rate).

I've generally
been using higher power than you, though, with fields of view no greater
than 11 arcminutes and usually more like 6 or 7 (and in one case only
about 2 arcminutes).

The power I cited was merely an example, as I often start my observing at that
level and go up from there. This apparition, I have tended to use from 288x
to 588x on Mars (I have gone as high as 720x). With the 4.9-7.9mm
Speers-Waler set at 6mm focal length plus the 2.5x Powermate (588x), that
field *radius* at that power is about 4.5 arc-minutes. Even with my old 6mm
Brandon Orthoscopic and the 2.5x Powermate, it still gives me 2.3' arc field
radius, so even at a 1.6' arc per hour rate, it still would take over 86
minutes of time to move from the center to the edge of a driven field.

Clear skies to you.
--
David W. Knisely
Prairie Astronomy Club: http://www.prairieastronomyclub.org
Hyde Memorial Observatory: http://www.hydeobservatory.info/

**********************************************
* Attend the 10th Annual NEBRASKA STAR PARTY *
* July 27-Aug. 1st, 2003, Merritt Reservoir *
* http://www.NebraskaStarParty.org *
**********************************************