HDTenEightyP/NetNews huggingface dataset:
From: lip@s1.gov (Loren I. Petrich)
Subject: Re: Size of Second-Order GR Effects in Binary Pulsars
Organization: LLNL
Date: Tue, 22 Dec 1992 19:29:34 GMT

In article <1992Dec22.005303.2974@lynx.dac.northeastern.edu> mkagalen@lynx.dac.northeastern.edu (michael kagalenko) writes:
>In article <1992Dec21.211409.22248@s1.gov> lip@s1.gov (Loren I. Petrich) writes:
>>In article <BzKK19.37I@well.sf.ca.us> metares@well.sf.ca.us (Tom Van Flandern) writes:
>>>lip@s1.gov (Loren I. Petrich) writes:

>The post of Ms. Petrich indicates the lack of understanding, how 
>phenomenology works. She uses the following scheme ;
>1st  order of magnitude:  Newtonian 
>2nd  order of magnitude:  GR
>Therefore, she divides parameters into "Newtonian" and "Non-Newtonian"
>In fact, this  "perturbational" approach ought not to be used in
>discussion of principal structure of GR.

	I find it a bit difficult to understand this statement.

	Post-Newtonian theory is a standard way of expressing the
weak-field limit of alternative theories of gravity. If the
post-Newtonian formulation is just plain wrong, then given the reason(s)
for supposing it to be wrong.

... (assuming the truth of GR's
>>: post-Newtonian approximation), ...
>                  ^^^^^^^^^^^^^
>This is the point. We aren't discussing perturbational method.

	_Every_ test of GR that has offered serious precision that I
have _ever_ seen has involved phenomena in relatively weak
gravitational fields, so that is why perturbation theory is
reasonable. The only known strong-field objects are neutron stars and
black holes, and the former suffers from uncertainties in the equation
of state for highly compressed nuclear matter, while the latter
features problems of interpreting the effects of accretion flows. So
the strongest effects precisely observed to date involve binary
pulsars, where the interesting effects occur in the space between the
pairs of objects.

>>>     Sorry, that's not so.  You get different values for these parameters
>>>from the observations depending on whether or not radiation is included in
>>>the theoretical model.

>>	That is just plain wrong. See above.

>Don't be so ignorant; you aren't the sole proprietor of truth.

	To paraphrase our Vice President, ill-rel-e-vant.

	After today, I'll probably be off the net until Jan. 4 or so.

-- 
/Loren Petrich, the Master Blaster
/lip@s1.gov
Newsgroups: sci.astro
From: dsc@gemini.tmc.edu (Doug S. Caprette Bldg. 28 W191 x3892)
Subject: Re: binocular question
Organization: NASA GSFC CDP VLBI
Distribution: sci
Date: Tue, 29 Dec 1992 17:45:24 GMT

In article <199228.4258.20565@dosgate> "michael daly" <michael.daly@canrem.com> writes:
>
>IMHO, the 7 millimeter guideline is a crock.  Few older people have 7 mm
>or larger pupils when fully dilated.  If the eyepiece exit pupil is
>exactly the same size as the eye's pupil, _any_ lateral motion of the
>binoculars will result in some of the light falling on the iris.  This
>will result in dimming of the image.  I've experienced this often and
>it's really annoying.  A smaller exit pupil will allow some lateral
>motion without the light loss.  Personally I wouldn't recommend anything
>larger that a 5 mm exit pupil (i.e. nothing lower powered than 10x50,
>16x80 etc.).
>

An absolute prohibition on using telescope/eyepiece combinations (as opposed
to buying binoculars) with exit pupils larger than some arbitrary value is
also a crock of another kind.   Large exit pupils are associated with combin-
ations of eyepiece and scope that yield low power.  It is often well worth 
whiile to trade away some of the effective aperture of the scope in exchange
for the wider field of view at low power.  

The dumbell surrounded by Milky Way, M31 and its two major companions, or
the entire sword of Orion in one field of view are dramatic enough to justify
such a combination.  

I agree, however, that one should not push the limit when buying binoculars.
Newsgroups: sci.astro
From: rkornilo@nyx.cs.du.edu (Ryan Korniloff)
Subject: Re: astro gifs
Organization: University of Denver, Dept. of Math & Comp. Sci.
Date: Wed, 30 Dec 92 04:04:55 GMT

>Path: mnemosyne.cs.du.edu!uunet!gatech!darwin.sura.net!spool.mu.edu!hri.com!ukma!netnews.louisville.edu!ulkyvx.louisville.edu!jsmill01
>From: jsmill01@ulkyvx.louisville.edu
>Newsgroups: sci.astro
>Subject: Re: astro gifs
>Message-ID: <1992Dec29.170338.1@ulkyvx.louisville.edu>
>Date: 29 Dec 92 21:03:38 GMT
>References: <1992Dec27.235433.4877@engr.LaTech.edu> <725507498snz@chrism.demon.co.uk> <1992Dec29.173618.24896@aio.jsc.nasa.gov>
>Sender: news@netnews.louisville.edu (Netnews)
>Organization: University of Louisville
>Lines: 28
>Nntp-Posting-Host: ulkyvx02.louisville.edu
>
>In article <1992Dec29.173618.24896@aio.jsc.nasa.gov>,  (Carl Soderland) writes:
>> In article <725507498snz@chrism.demon.co.uk>, chris@chrism.demon.co.uk (Chris Marriott) writes:
>>> 
>>> > i would like to know whether there is an anonymous ftp site for astro gifs.
>>> > can anybody help?
>>> 
>>> Try "ames.arc.nasa.gov".  Look in directory "/pub/SPACE/GIFS".
>>> 
>> 
>> The node mentioned contains alot of GIF formatted files, but how do I look at
>> one of these.  Can anyone provide a source for the necessary imaging software?
>> 
>> Thanks for your help.
>==============================================================================
>You don't mention a machine to run it on, but a good program is 
>available in the same archive.  Ron Baalke's program is in 
>pub/SPACE/SOFTWARE or pub/SPACE/PROGRAMS (I haven't been in there in a 
>while to look, and am not sure if the particular directories are all 
>caps, all small or mixed case). It's called Imdisp**, where the *'s 
>indicate latest version.  I've used it on my 8086 to decent viewing, 
>and all I've got is EGA.  On a 386 or 486 with VGA it's bound to be 
>much better.
>
>Regards
>
>Scott Miller, Program Coordinator
>Rauch Memorial Planetarium
>University of Louisville

Yes, the directory the software is in is /pub/SPACE/SOFTWARE. The Imdisp
(Image Display) program supplied is for the MSDOS based systems.
The lastest version is "imdisp79.zip" You will need the pkunzip program to
decompress it, which I beleieve is on the same directory.
Once you are done installing the program, put the GIF images in the same
directory until you learn how to use the promgram (a quick-start method),
the program can be a little confusing to use sometimes. Then, when you want
to view a GIF type in the commands "file 'gif image'" <return> Then type
the command "display" or "dis" for short. This will display the image on
the screen. To do more complicated image monipulation, you will have to
read, most preferably print, the documentation file. It's a really nice
program after you figure out what to do.


        -- Ryan Korniloff
        -- rkornilo@nyx.cs.du.edu
From: jhouser@vax.cns.muskingum.edu
Newsgroups: sci.astro
Subject: PLEADIES   (7 sisters)
Date: 25 Dec 92 02:19:32 GMT
Organization: Muskingum College



          i was observing tonight (24/25) looking t  at the 7 sisters
 and with the naked eye i was so surprised to to see all 7 of them

then i looked through the 7x50 binoculars and saw a compact open cluster
i saw a beutifu:l  cluster  ..   i justv thought you should know.
Newsgroups: sci.astro
From: begley@l14h13.jsc.nasa.gov
Subject: Re: Galileo's Atmospheric Probe Passes Health Checks
Organization: Lockheed Engineering and Sciences
Distribution: usa
Date: Wed, 23 Dec 1992 19:01:35 GMT

>In <1992Dec15.170442.1866@elroy.jpl.nasa.gov> baalke@kelvin.jpl.nasa.gov (Ron
Baalke) writes:
>
>>New York in 90 seconds.  Deceleration to about Mach 1 -- the speed
>>of sound -- will take just a few minutes, causing a buildup of heat
>>so intense it will be like flying through a nuclear explosion.
>

   What might the speed of sound be in the upper Jovian atmosphere?


Newsgroups: sci.astro
From: oler@rho.uleth.ca (Cary Oler)
Subject: Daily Solar Geophysical Data Broadcast for 28 December
Organization: University of Lethbridge
Date: 29 Dec 92 10:13:41 GMT

!!BEGIN!! (1.0) S.T.D. Solar Geophysical Data Broadcast for DAY 363, 12/28/92
10.7 FLUX=127.2  90-AVG=139        SSN=112      BKI=2032 5454  BAI=022
BGND-XRAY=B2.3     FLU1=7.3E+05  FLU10=1.0E+04  PKI=2032 5555  PAI=029
  BOU-DEV=015,004,026,015,104,062,083,054   DEV-AVG=045 NT     SWF=00:000
 XRAY-MAX= C2.3   @ 0651UT    XRAY-MIN= B2.1   @ 0351UT   XRAY-AVG= B3.3
NEUTN-MAX= +002%  @ 0820UT   NEUTN-MIN= -003%  @ 2040UT  NEUTN-AVG= -0.5%
  PCA-MAX= +0.1DB @ 2355UT     PCA-MIN= -0.4DB @ 1055UT    PCA-AVG= +0.0DB
BOUTF-MAX=55418NT @ 2354UT   BOUTF-MIN=55357NT @ 1754UT  BOUTF-AVG=55401NT
GOES7-MAX=P:+139NT@ 1843UT   GOES7-MIN=N:-037NT@ 1259UT  G7-AVG=+072,+022,+009
GOES6-MAX=P:+163NT@ 1845UT   GOES6-MIN=N:-027NT@ 2226UT  G6-AVG=+091,-003,+029
 FLUXFCST=STD:130,130,125;SESC:130,130,125 BAI/PAI-FCST=010,010,010/015,010,010
    KFCST=2224 3111 1112 3111  27DAY-AP=015,009   27DAY-KP=3344 3322 3333 2221
 WARNINGS=
   ALERTS=
!!END-DATA!!
From: higgins@fnala.fnal.gov (Bill Higgins-- Beam Jockey)
Newsgroups: sci.astro
Subject: Terry's disclaimer (was Re: Universal time)
Date: 21 Dec 92 15:41:32 -0600
Organization: Fermilab Grossforschungenseinrichtungen
NNTP-Posting-Host: fnala.fnal.gov

In article <1992Dec20.201348.14726@newstand.syr.edu>, tmc@barnyard.syr.edu (Terry R. McConnell) writes:
[interesting idea deleted]
>  
> This is probably either well-known or won't work. 
 
Terry, this is the greatest all-purpose disclaimer I've seen in a long
time.

"Do you know the asteroids, Mr.Kemp?...    Bill Higgins
Hundreds of thousands of them.  All        
wandering around the Sun in strange        Fermilab
orbits.  Some never named, never
charted.  The orphans of the Solar         higgins@fnal.fnal.gov
System, Mr. Kemp."
                                           higgins@fnal.bitnet
"And you want to become a father."
  --*Moon Zero Two*                        SPAN/Hepnet: 43011::HIGGINS
From: steinly@topaz.ucsc.edu (Steinn Sigurdsson)
Newsgroups: sci.astro
Subject: Re: The Hole Story
Date: 22 Dec 92 18:43:45 GMT
Organization: Lick Observatory/UCO
NNTP-Posting-Host: topaz.ucsc.edu
In-reply-to: Leigh Palmer's message of Tue, 22 Dec 1992 01:16:38 GMT

In article <1992Dec22.011638.21749@sfu.ca> Leigh Palmer <palmer@sfu.ca> writes:

   In article <STEINLY.92Dec20193619@topaz.ucsc.edu> Steinn Sigurdsson, 
   steinly@topaz.ucsc.edu writes:

   >I suppose I should read the paper, but there are exact solution of
   >plane gravitational waves for GR. They're literal solution of the
   >Einstein equation.

   That's interesting. Are gravitational plane waves susceptible to 
   (linear) Fourier decomposition? Do they comprise a spanning set for 
   all gravitational wave solutions? If they are not superposable, how 
   would one generate a gravitational plane wave?

Gravitational waves are not in general superposable because they
couple to each other - they carry stress-energy. All the exact
solutions I know of are ones with special symmetry in vacua, although
I only have a passing familiarity with the subject.

   Do you consider the evidence for the observation of generation of 
   gravitational waves to be sufficiently compelling that you would 
   *expect* Yu's contention (which I have not read either) to be flawed 
   in some way?

I hesitate to comment out of fairness, I have not read the paper,
we don't have Ast Sci (?) in the reading room and I haven't made it to
the library. In some sense it has to be wrong, because an exact "wave"
solution for the Einstein equations does exist. From the description
it sounds like the issue is one most consider resolved, namely that
locally the energy-momentum flux of a g-wave can be transformed
away, I believe Feynman was actually the one to note and resolve this
particular issue, although someone else might have preceded him.

   Please do not take offense at these questions. The reason I ask them 
   in what may seem to be a confrontational manner is that I am more 
   interested in the scientific process operating here than in the 
   science itself. I respect your devotion to scholarship, and I'm 
   trying to see what goes on "under the hood".

 ;-)  Well, I haven't looked seriously at any real GR problems for
a year or two now, so I'm mostly going from what I remember from
the top of my head. I got involved mostly because I contradicted Tom
once on the "retarded" position of the Sun (and I should have known
better), and I do have some familiarity with the binary pulsar work...

*  Steinn Sigurdsson   			Lick Observatory      	*
*  steinly@lick.ucsc.edu		"standard disclaimer"  	*
*  The laws of gravity are very,very strict			*
*  And you're just bending them for your own benefit - B.B. 1988*
Newsgroups: sci.astro
From: jmcvey@boi.hp.com ( John McVey         x3638 )
Subject: Looking for achromat
Date: Wed, 30 Dec 1992 17:03:45 GMT
Organization: Hewlett-Packard / Boise, Idaho
X-Newsreader: Tin 1.1scd1 PL4

I am looking for a 60mm to 80mm achromat in the 300mm to 350mm focal
length range for a home project.  No cell is required.

Please state condition and price.

Thanks in advance,

John McVey
jmcvey@hpbslq.boi.hp.com
208-323-3638 work (day)
208-376-6164 home (eve)
Newsgroups: sci.astro
From: oler@rho.uleth.ca (Cary Oler)
Subject: Daily Solar Geophysical Data Broadcast for 01 January
Organization: University of Lethbridge
Date:  3 Jan 93 09:21:04 GMT

!!BEGIN!! (1.0) S.T.D. Solar Geophysical Data Broadcast for DAY 001, 01/01/93
10.7 FLUX=122.3  90-AVG=140        SSN=075      BKI=2331 2122  BAI=008
BGND-XRAY=B3.4     FLU1=1.4E+06  FLU10=1.1E+04  PKI=2332 2222  PAI=008
  BOU-DEV=012,023,022,009,015,009,010,019   DEV-AVG=014 NT     SWF=00:000
 XRAY-MAX= C4.2   @ 1343UT    XRAY-MIN= B2.7   @ 2139UT   XRAY-AVG= B4.6
NEUTN-MAX= +001%  @ 1200UT   NEUTN-MIN= -003%  @ 2210UT  NEUTN-AVG= -0.6%
  PCA-MAX= +0.1DB @ 0625UT     PCA-MIN= -0.4DB @ 0920UT    PCA-AVG= -0.0DB
BOUTF-MAX=55424NT @ 0331UT   BOUTF-MIN=55399NT @ 1846UT  BOUTF-AVG=55414NT
GOES7-MAX=P:+136NT@ 1859UT   GOES7-MIN=E:-003NT@ 0641UT  G7-AVG=+091,+020,+013
GOES6-MAX=P:+157NT@ 1859UT   GOES6-MIN=E:-018NT@ 0349UT  G6-AVG=+109,-007,+029
 FLUXFCST=STD:120,120,120;SESC:120,120,120 BAI/PAI-FCST=010,010,010/010,010,010
    KFCST=2224 4222 2224 4222  27DAY-AP=011,008   27DAY-KP=2333 3222 3332 1211
 WARNINGS=*SWF
   ALERTS=
!!END-DATA!!
Newsgroups: sci.astro
From: pausch@saaf.se (Paul Schlyter)
Subject: Re: binocular question
Organization: SAAF, Svensk Amat|rAstronomisk F|rening
Distribution: sci
Date: Tue, 29 Dec 92 22:40:35 GMT

In article <1992Dec29.160250.4981@macc.wisc.edu> bunner@vms.macc.wisc.edu (Dana A. Bunner) writes:
>In article <199228.4258.20565@dosgate>, "michael daly" <michael.daly@canrem.com> writes...
>
>What I was trying to point out that if your eyes do indeed have 7mm
>dark light pupils, resulting in pupil surface area of 38.48 sq mm of
>surface area, and you illuminated them with a 3.125mm image, or 7.67
>sq mm, then you are using just 19.9% of your eye's pupil surface area.
>Of course none of the incoming image is being wasted.  Your eyes would
>be capable of processing far more light than you are providing to them.

On the other hand, if the exit pupil is considerably smaller than the
size of your eye's pupil, then light creating the image on your eye's
retina will pass only the central parts of your eye's lens.  This will
improve the sharpness of the perceived image, since your eye's lens
is not very well corrected for lens aberration at its edges.


>I agree with your comments about not necessarily needing 7mm exit pupils.
>If someone had just 5.5mm pupils then the surface area of the pupil drops
>from 38.48 sq mm to just 23.76 sq mm.  This would also be true if your
>primary viewing area is not dark.  Light from nearby street lights might
>result in your pupils not expanding to their maximum size.  At this point
>one has a dilemma.  It's nice to have those 50mm objectives for light
>gathering, yet it is difficult to hold binoculars above 7X steady (for 
>many people).  

There's an easy way out of this dilemma:  put the binoculars on a tripod!

If you insist of not using a tripod, and if you therefore don't want to
use a larger magnification than 7X, and if your eye's pupil never gets much
larger than say 5 mm, then you should get a pair of 7x35 binoculars instead
of a pair of 7x50 !  The 7x35 is significantly lighter, and thus easier to
hold steady, which means you'll probably end up seeing more with the 7x35 
than with the 7x50.




-- 
---
Paul Schlyter, Swedish Amateur Astronomer's Society (SAAF)
Nybrogatan 75 A, 6 tr,  S-114 40 Stockholm,  Sweden
InterNet:  pausch@saaf.se
From: yamada@yscvax.ysc.go.jp (Yoshiro Yamada)
Newsgroups: sci.astro
Subject: A Compact Disc for Solar Observing
Keywords: solar observing
Date: 25 Dec 92 07:59:21 GMT
Organization: Yokohama Science Center, Yokohama, JAPAN


I enjoyed the partial solar eclipse of December 24 morning through a music
Compact Disc! I read this idea in the Monthly News on Astronomy and Space
Science (in Japanese) published by Nishiharima Astronomical Observatory, Japan.

-- 
-*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*---
Yoshiro Yamada                            | tel    : +81-45-832-1166
Astronomy Section                         | fax    : +81-45-832-1161
      Yokohama Science Center             | e-mail : yamada@ysc.go.jp
From: wats@scicom.AlphaCDC.COM (Bruce Watson)
Newsgroups: sci.astro
Subject: 1993
Keywords: new year
Date: 1 Jan 93 00:08:48 GMT
Organization: Alpha Science Computer Network, Denver, Co.


? = HELP
National Institute of Standards and Technology
Telephone Time Service
      .                 D  L D
 MJD  YR MO DA HH MM SS ST S UT1 msADV         <OTM>
48987 92-12-31 23:59:57 00 0 +.1 045.0 UTC(NIST) *
48987 92-12-31 23:59:58 00 0 +.1 045.0 UTC(NIST) *
48987 92-12-31 23:59:59 00 0 +.1 045.0 UTC(NIST) *
48988 93-01-01 00:00:00 00 0 +.1 045.0 UTC(NIST) *
48988 93-01-01 00:00:01 00 0 +.1 045.0 UTC(NIST) *
48988 93-01-01 00:00:02 00 0 +.1 045.0 UTC(NIST)


Happy New Year
-- 
Bruce Watson (wats@scicom) Bulletin 629-49 Item 6700 Extract 75,131
Newsgroups: sci.astro
From: DPierce@world.std.com (Richard D Pierce)
Subject: Re: STS-1 DISASTER/COVERUP
Organization: The World Public Access UNIX, Brookline, MA
Date: Tue, 22 Dec 1992 23:34:41 GMT

GAWD! We've seen enough of this crap without having to endure another copy
of the same.

However, the salient point the Dr. Beter's proponent here would try to
have us believe is that the Goverment Bolsheviks are deeply commited to
keeping what he claims as the truth silent. 

If that is true, then why is it so easy for him to publish his drivel. Can
we not consider that his own coverup conspiracy theory can be used against
him? If this is the truth, then the goevrnment will try it's damndest to
cover it up. But thousands upon thousands have seen it, and there has been
no attempt by anyone to cover it up (drown it in laughter, yes, but
supress it or censor it, no). So if the government is hell-bent on
covering up the truth (and I believe there are many REAL issues they do
this on, not this bunk), and they haven't made any attempt to cover this
uip, then maybe, by your own argument, this isn't the truth, but is, in
fact, nothing more than a fairy tail (and not a very good one at that).

So, Dr Beter, this is either the truth, in which case we would never have
read it, or it's not the truth, and the government could care less.


-- 
|                Dick Pierce                |
|    Loudspeaker and Software Consulting    |
| 17 Sartelle Street   Pepperell, MA  01463 |
|       (508) 433-9183 (Voice and FAX)      |
Newsgroups: sci.astro,sci.space
From: henry@zoo.toronto.edu (Henry Spencer)
Subject: Re: Giotto Sample Return ?
Date: Thu, 24 Dec 1992 00:01:22 GMT
Organization: U of Toronto Zoology

In article <1992Dec23.194709.4135@bnlux1.bnl.gov> wagener@gown.das.bnl.gov (Richard Wagener) writes:
>... Its [Giotto's] orbit brings it to within 210000 km of Earth on
>July 1, 1999.  Although the spacecraft still has some fuel left, ESA
>has no plans for more Giotto missions. - Stephen Cole
>
>Is there enough fuel to change the orbit for a closer encounter
>with Earth?  Could it be aerobrake'd into a stable orbit from which it
>could be captured and returned by the shuttle?

Giotto couldn't safely do more than the most minimal aerobraking; it's
not built for it.  It could do a very small aerobraking maneuver, as was
done by Hiten and as the Magellan team hopes to do, but it wouldn't be
enough to accomplish much.  (The Magellan aerobraking will -- if done --
be able to lower Magellan's orbit quite a bit, but only because Magellan
will fly an aerobraking maneuver every hour or two for *months*.  Giotto
only gets one pass.)

There is undoubtedly enough fuel to target for a closer Earth encounter,
if you start early.  It doesn't take much to make that big a difference
when it accumulates over a period of years.  Problem is, there probably
isn't enough to fly a useful third mission, e.g. another comet encounter.
There certainly isn't enough to make any kind of Earth orbit.

A secondary problem is that it's not clear ESA will still be able to talk
to Giotto in 1999.  Maintaining such a capability (while facilities get
modernized for other purposes) costs money, and it may not be thought
worth the trouble.

>Would the returned probe contain scientifically useful cometary
>samples?

The encounter velocities were rather high, especially at Halley, but some
useful science could undoubtedly be done, if the thing could be retrieved
easily.
-- 
"God willing... we shall return."       | Henry Spencer @ U of Toronto Zoology
       -Gene Cernan, the Moon, Dec 1972 |  henry@zoo.toronto.edu  utzoo!henry
Newsgroups: sci.astro
From: mje@pookie.pass.wayne.edu (Michael J. Edelman)
Subject: 8" Coulter still available
Reply-To: mje@pookie.pass.wayne.edu
Organization: Wayne State University
Distribution: mi
Date: Tue, 22 Dec 1992 16:19:57 GMT

I'm still oferring my 8" Coulter for sale or swap. It's like new, and has 
a Telrad finder and Lumicon lenscap added. $300, pickup in the metro Detroit
area only. Hey, only two shopping days left! From Coulter it would take you
two months to get this scope. 

I'm also interested in trades, part or whole. Maybe a pair of 11x80s, or an RFT
refractor around 3", or...?

  mike edelman  mje@pookie.pass.wayne.edu  1-313-577-0742


Newsgroups: sci.astro
From: chaloux@mandolin.mitre.org (Dave Chaloux)
Subject: Re: Buying an Amateur Telescope
Keywords: Telescope
Reply-To: chaloux@mandolin.mitre.org (Dave Chaloux)
Organization: The MITRE Corporation, McLean, Va
Date: Mon, 21 Dec 1992 22:43:04 GMT

Nick Kotzamanis writes:

>I have read the FAQ's but it did not address the
>advantages/disadvantages of reflector vis refractor?

Ah: Nothing like picking a nice noncontroversial topic.

Advantages for the reflector are:

1) They are much cheaper per unit of aperture. A Premium quality 7"
refractor can cost as much or more than a premium quality 20" reflector.

2) The are inherently free of color defects.

Advantages of the refractor are:

1) The unobstructed design means that more of the light gets pumped into the
central airy disk instead of into the diffraction rings.

2) Good apochromatic refractors keep color defects below what you eye can
detect so they are not at a disadvantage.

3) They don't need all the messy collimation by the user to get good images.
A newtonian reflector can have a bewildering amount of things that need to
be adjusted to get optimum performance. Most people can't or won't adjust
them all so they do not get the performance with the reflector it is
theorectically capable of. I use three different tools on my reflector to keep
it collimated.

4) They often have a nice flat field which is nice for photography.

In general, people who like deepsky (galaxies, nebula, star clusters, etc.)
often go with reflectors. People who like the moon and planets often go with
refractors. Good reflectors properly collimated can go very well on planets.

They both have their place. I own a large reflector. I plan on eventually
acquiring a good apochromatic refractor.