Re: precession of mercury

On Dec 25, 3:09 pm, hw@..(Dr. Henri Wilson) wrote:
On Thu, 25 Dec 2008 04:22:32 -0800 (PST), Jerry
<Cephalobus_alie...@xxxxxxxxxxx> wrote:
On Dec 24, 3:24 pm, hw@..(Dr. Henri Wilson) wrote:

The whole process could be simplified if the thing was sent into a circular
orbit in the ecliptic plane. However as long as the axis of precession of the
axis of rotation is perpendicular to that plane, a small tilt in the orbit
plane wont cause much of a problem or error.

A worthless suggestion inconsistent with your earlier posts
(you are obviously trying to make it fit the nominal Hipparcos
orbit) and quite clueless.

It should be obvious that what I said is correct. Placing it an ecliptic orbit
would allow for much simpler analysis and greater accuracy.

False. A satellite in ecliptic orbit around the Sun at one of
Earth's stable Lagrangian points will still observe aberration.
Stars at the Ecliptic poles will apparently move around in
circles, stars on the ecliptic will move back in forth in
straight lines, and stars at intermediate declinations will
apparently move in ellipses.

A satellite in ecliptic orbit around the Earth will see
superimposed on the yearly stellar aberration ellipse of 20.5"
semimajor axis smaller ellipses whose period will correspond to
the satellite's orbital period about the Earth, and whose semi-
major axes will depend on the satellite's orbital velocity.

So there is no benefit at all to an ecliptic orbit.

What would have been of great benefit to Hipparcos was if the
satellite had been successfully inserted into its nominal orbit.
High above the Earth, it would have experienced eclipses only
around equinox time, its slower, more uniform speed would have
necessitated simpler aberration corrections, and it would not
have experienced as much radiation damage through repeated
passages through the Van Allen belts.

An ecliptic orbit, by the way, would have made eclipses a year-
round affair.

An equatorial or
other orbit requires additional and very complcated corrections.
The Hipparcos telescope was meant to be sent into an ecliptic orbit.

Nope. It was meant to be sent into a geostationary orbit.

Obvoiusly neither you nor Paul can get it into your head that aberration can be
virtually eliminated from parallax measurements if the telescope used does not
rotate around its own axis.

Not only inconsistent with the immediately preceding paragraph,
but utterly false and clueless. In the preceding paragraph, you
propose a telescope whose "axis of precession of the axis of
rotation is perpendicular to [the ecliptic] plane" while here
you propose a telescope that does not rotate, period.

Try thinking occasionally Crank.
As long as it is in the same orientation when specific stars are in view, that
constitutes 'NOT ROTATING'.

That's called making use of guide stars, an old technique.

The scanning procedure is clearly quite ingenious and the same stars are viewed
a number of times during the year. They are identified by the direction in
which the telescope is pointing at the time. It is has the same angular
position at the time, aberration effects are avoided.

You haven't the foggiest idea what you propose, do you? It keeps
changing from post to post, and even within this single post, it
changes...

I have to explain it in more basic terms so you can understand what I said.
Aberration CAN EFFECTIVELY BE ELIMINATED.

As I have tried to explain to you, the guide star technique has
distinct limitations as regards the needs of high precision
imaging and high precision astrometry. A suitable guide star
cannot always be found in the immediate vicinity of an object
to be imaged. A mere 1 minute of arc separation between guide
star and target object would result in an approximately 1 mas
tracking discrepancy for the HST. Try working it out.

No...I doubt you can. OK. Figure 7 km/s orbital velocity for HST
works out to about 5" semimajor axis for the aberration ellipse.
At 90 degrees normal to the HST orbital plane, the aberration
takes on a circular pattern, so the semiminor axis is 5". In
the plane of the HST orbit, the semiminor axis is zero. Divide
5" by 5400 minutes of arc in a right angle, equals on average
1 mas stellar aberration discrepancy per minute of arc difference
in declination between guide star and target.

Did you follow? A similar type of estimate can be made for
differences in right ascension between guide star and target.

Do you understand now why your proposal is worthless as regards
the needs of high precision astrometry and high precision
imaging?

Jerry
.

Relevant Pages

  • Re: precession of mercury
    ... orbit in the ecliptic plane. ... However as long as the axis of precession of the ... Well, if the telescope does not spin on its own axis, the whole field of view ... Thus, relative star movement ...
    (sci.physics.relativity)
  • Re: precession of mercury
    ... orbit in the ecliptic plane. ... However as long as the axis of precession of the ... Thus, relative star movement ...
    (sci.physics.relativity)
  • Re: precession of mercury
    ... orbit in the ecliptic plane. ... However as long as the axis of precession of the ... an Earth orbit in the ecliptic plane". ... Thus, relative star movement ...
    (sci.physics.relativity)
  • earths orbit about sun
    ... I underdstand the earth's orbit is elliptical, ... sun is at one of the focal points. ... I also know that the earth's axis ... same plane, but they are not actually in the same plane. ...
    (sci.astro)
  • Re: Eotvos.
    ... It is pointing elsewhere. ... >>> No difference between this and a gyroscope. ... If the orbit is circular it will not precess. ... >>of its axis as a direct result of space being curved. ...
    (sci.physics.relativity)
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