Forum in astronomy or astrophysics research

Archive for June, 2010

Hubble Telescope Question.

I’ve posted these same questions to the relativity newsgroup
(for good reason).
——

When the Hubble Telescope was launched into space, the images that
it returned were blurred. I think the fault was (for whatever reason)
attributed to a change in the mirror shape when it was moved into the
space environment.

My questions are;
Was the mirror fault confirmed, or only assumed?

Did the focal length of the lenses perhaps increase?
Was that ever considered as an option?

Thanks for your time.


Max Keon

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Annotated Eddington?

First of all, I’m an amateur and recently got very interested
in how stars work.  So I’m slowly working my way through
Eddington’s _Internal Constitution of the Stars_ (ICotS) in the hopes
that this will help me get a foundation before trying to
tackle more current research.

I’m somewhat familiar with white dwarf work by Chandra, in that
I know he and Eddington had a difference of opinion and Chandra
was awarded the Nobel prize for his work.

It got me wondering if someone has put together an annotated ICotS?
Or a webpage that follows certain threads from the book that have
been refuted or substantially added to?

I’d also be interested in your recommendations for a more modern
book than _ICotS_.  Hopefully one with similar lucidity, if such
a creature exists.

I just started reading this newsgroup and have to thank you guys
for these links:

http://www.arxiv.org/
http://adsabs.harvard.edu/abstract_service.html
http://sohowww.nascom.nasa.gov/

I’m excited this field has such an enormous online presence

  Joe Morris, SysAdmin and Not Insane
  Atlanta stories: http://jolomo.net

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Oliver Manuel's Iron Sun

In the summer of 2002 Oliver Manuel from University of Missouri
theorized that the sun was predominately composed of iron.  Is there a
form of "verdict" taking place on his theory yet ?

Also, he said that our sun is the iron core of a supermassive star
that went supernova.  I am having a hard time finding information on
how a star supernova’s and turns into a G2 star, can somebody point
me to an explanation of this ?

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Upcoming Occultation – Saturn & M1

On January 5-6 2003, Saturn will occult M1 as visible from my observing
location in Brisbane, Australia.

I’m wondering if this event has any scientific value, specifically in
relation to spectra etc. of Titan or even Saturn itself?  Is there anything
as far as CCD imaging that I should be trying to capture?

-
Scott Sinclair
University of Queensland
Brisbane, AUSTRALIA

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ADMINISTRIVIA: expect posting delays

Moderation will be more intermittent than usual over the Christmas/New
Year period. Please bear with us.

Martin

Martin Hardcastle             Department of Physics, University of Bristol
                                             Moderator, sci.astro.research

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Your chance to contribute to real astronomical research

This newly formed Yahoo group has three initial aims.
1) To systematically search for previously unreported double stars and
to present any discoveries made to the wider astronomical community.
2) To encourage amateur astronomers world-wide to participate in both
visual and CCD observations of known double stars – particularly those
identified as "neglected" in the Washington Double Star Catalog.
3) To share best practice in all aspects of double star observations.

Why not get involved at

http://groups.yahoo.com/group/BinaryStars

JUSTIFICATION

Sadly hunting for new double stars seems to have vanished from the
amateur astronomer’s repertoire. In the year 2000 only twelve new
systems were discovered and in 2001 this figure dropped to six. These
bare statistics create the impression that discovering a new double star
is significantly harder than discovering a supernova or a comet – which
many regard as the ultimate challenges for an amateur astronomer. Recent
work conducted by the Daventry Double Star Survey (DDSS) appears to
prove that many new double stars do exist within the range of even
modest amateur equipment.

Double stars are rarely studied in a systematic way by amateur
astronomers. This is a pity since valuable work can be still be done
when the moon is full or if you suffer from severe light pollution.
Although some well known doubles such as Albario (Beta Cygni) feature in
almost every list of celestial highlights only a tiny number of amateur
astronomers regularly measure the position angle and separation of known
double stars. The Washington Double Star Catalog (WDS), maintained by
the United States Naval Observatory, is the world’s principal database
of double and multiple star information. A significant number of the
systems listed are classed as "neglected" and hence are in urgent need
of being confirmed and ideally being re-measured. There is much scope
here for astronomers with small telescopes or even no telescope at all
to make a significant contribution.

Martin Nicholson, Daventry, UK

International Astronomical Union’s Minor Planet Centre – Observatory Code 456
http://www.gcse-ict.info/astronomy/front.htm

The Daventry Double Star Survey http://www.martin-nicholson.com/ddss/front.htm

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Re: Black hole candidates

b…@galaxy.ucr.edu (John Baez) wrote in message <news:au6bv5$r73$1@glue.ucr.edu>…
> More mathematically elegant, eh?  

> What is this solution – how does it work, exactly?

See the paper [1] which is only 4 pages long, but a news article [2]
about these gravastars mentions some reasons why experts are skeptical
about the idea of gravastars, although the article also states:

"But other astronomers are intrigued, both because black holes
themselves remain mere theory, not fact, and because gravastars might
explain strange physical observations that black holes don’t."

> Finally, you are asking the impossible if you expect astronomers
> to find "clear evidence of Hawking radiation" in typical black hole
> candidate.

I wasn’t expecting the astronomers to have detected any "clear
evidence of Hawking radiation", and this was partially my point.

> In your articles, you refer to lots of papers on the preprint arXiv.  
> I often wish you could spend more time checking the details of these
> papers before citing them.  Some of them make sense.  Others don’t.  
> Many are in the grey zone somewhere between these extremes.  It makes
> me very nervous how you sometimes lump them all together without
> distinction!  For example, when you cite Mitra’s papers along with a
> bunch of others, it makes me feel I can’t trust *any* of them.  

But you don’t have to be nervous because you are not clueless !  And
if it should turn out that loop QG is correct and that string theory
is false then perhaps up to 60-85% of the papers on hep-th could be
flawed !

I am not citing papers in some kind of official way, but just
mentioning ideas for potential discussion. You need to be both
skeptical and open-minded to be able to adapt to new ideas, and e.g.
Lubos Motl used to be quite critical of loop QG but because he is very
bright he has been able to adapt and to consider what may be an
important new finding in loop QG, i.e. Dreyer’s result.

Also, Abdus Salam would consider any idea that someone brought to him
because he was smart and confident enough to feel that he could see if
something should or must be wrong. If something were easily and
obviously wrong then he could ignore it, but otherwise he knew that he
might still learn something from a theory that turned out to be wrong.

For instance, there is a paper [3] which looks at a binary pulsar and
concludes that gravitational radiation cannot exist. I recently saw a
paper on Reissner-Nordstrom black holes which discussed the effects of
gravitational radiation back-reaction which makes me wonder if the
author of [3] has even considered the possibility of gravitational
radiation back-reaction.

I don’t know much of anything about binary pulsar systems, so even if
paper [3] is wrong I still might learn something such as where the
effect of gravitational radiation back-reaction should arise and to
what extent (assuming that people with more expertise can discuss this
for me).

[1]  http://arxiv.org/abs/gr-qc/0109035

[2]  http://www.space.com/scienceastronomy/astronomy/gravastars_020423.html

[3]  http://arxiv.org/abs/astro-ph/0211481

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A statistics question on goodness of fit estimator

In Astronomy normal technique used to find the best-fit parameters
or to test goodness of fit is chi-square technique or Maximum likelihood
estimation and fit is considered good if chi-square/dof is around 1.
However in both the above techniques there is no difference between positive
and negative excursions from the expected value.

my question is if there is any kind of function used in Astronomical
data analysis for fitting/hypothesis testing  which is
 asymmetric with respect to
positive and negative deviations from the expected value,
or which only looks for positive deviations from the expected value and
ignores any negative deviation/considers a negative deviatio a good fit.

Can someone here give what kind of    functions
 been used and their behaviour has been studied. (i.e I can know how large
thevalue of the unction should be before fit is bad) .also it would helpful
to undersand in what context they were used.
Thanks a lot

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[WWW] Saturn's ringlets explained

I have written a short web page in which I present a model in which
the formation and maintainance of the ringlets of Saturn are
explained. I have been waiting for someone else to publish such an
explanation ever since the Voyager space craft showed us those
puzzling pictures. I have wanted to see if my model was correct. Now
that we have another spacecraft on it’s way there, I feel that it
might be helpful if the operators of the craft know what to expect
there. The model can be found at
http//myweb.cableone.net/gfpmus/saturn.

George Prehmus

[Mod. note: readers are reminded that the contents of web pages are
not moderated -- mjh]

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Phobos and Deimos

IS Phobos and Deimos natural satellites of Mars?  If they are not then
is it theorized that they were nabbed by Mars gravitational pull as stray
asteroids and "turned" into satellites?

Paul

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