"STELLAR TWINS" IN THE SLOAN DIGITAL SKY SURVEY

"STELLAR TWINS" IN THE SLOAN DIGITAL SKY SURVEY

A total of 216 pairs of stars within 30 arc seconds of each other and
having all five listed magnitudes within 0.03 magnitudes of their
partner values have been identified from the 215 million objects
listed in the Sloan Digital Sky Survey.

Sample results are included on the web site - plus a link to results
for all 216 pairs.

http://www.martin-nicholson.info/1/3cd.htm


Martin Nicholson, Daventry, England.
http://www.martin-nicholson.info/1/1a.htm

Visit the Astronomical Hall of Shame at http://www.geocities.com/queen5658/

"ukastronomy" wrote in message
...
: "STELLAR TWINS" IN THE SLOAN DIGITAL SKY SURVEY
:
: A total of 216 pairs of stars within 30 arc seconds of each other

What is this strange fascination with pairs of stars on approximately
the same line of sight all about?
London is close to New York when seen from Luxembourg, they are
within 30 arc seconds of each other on the same great circle. Maybe
they are twins. What is it you are trying to say?

On Nov 30, 12:01 am, ukastronomy
wrote:
"STELLAR TWINS" IN THE SLOAN DIGITAL SKY SURVEY

A total of 216 pairs of stars within 30 arc seconds of each other and
having all five listed magnitudes within 0.03 magnitudes of their
partner values .....

Well, I like double stars as much as the next guy, especially twins
like Mesarthim, but why would you go to all this trouble for these
sparticular tars, most of which have magnitutes between 16 and 20?

And, what's with the decimal RA & DEC values? Converting RA
238.4083822 to a more conventional RA of 15H etc. etc. may not be
hard, but who needs it?

\Paul

On Fri, 30 Nov 2007 14:23:53 -0800 (PST), palsing
wrote:

And, what's with the decimal RA & DEC values? Converting RA
238.4083822 to a more conventional RA of 15H etc. etc. may not be
hard, but who needs it?

More convenient for some, but not all. Some areas of astronomy (e.g.
meteoritics) have converted almost completely to expressing RA in
degrees, rather than hours. And I'm increasingly seeing that convention
adopted in professional circles, with papers sticking to decimal
degrees. That is, both hour notation and sexagesimal notation seem to be
falling out of favor. And that really does make good sense, given that
using degrees uniformly is simpler and less subject to confusion.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

More convenient for some, but not all. Some areas of astronomy (e.g.
meteoritics) have converted almost completely to expressing RA in
degrees, rather than hours. And I'm increasingly seeing that convention
adopted in professional circles, with papers sticking to decimal
degrees. That is, both hour notation and sexagesimal notation seem to be
falling out of favor. And that really does make good sense, given that
using degrees uniformly is simpler and less subject to confusion.

_________________________________________________

Chris L Peterson
Cloudbait Observatoryhttp://www.cloudbait.com

*********************

Hi Chris,

Well, in the Professional ranks, you are probably correct, and I can
see how it makes perfect sense. Of course, it was stated that
converting to the metric system made good sense, too, except that the
man-on-the-street soundly rejected the idea and has no idea how many
mm's are in an inch. Most of the time, he doesn't need to know, and I
don't think that anyone is going to force him to learn.

In my strictly amateur astronomy world, however, all of my reference
materials, my many star charts, my various charting software, the
setting circles on many telescopes (and I could go on-and-on), are all
showing me hours/minutes/seconds for RA, and I'll bet that yours do,
too.

I, for one, would be unhappy to see such a change carried throughout
the hobby, the transition period would be brutal and lengthy.

Besides that, in some way, there is something very romantic about hour
angles and such, something very *historical*, that helps to connect us
to ancient amateurs, a common thread that newbies must adopt and
understand before they can become one of *us*... ;)

\Paul A

On Fri, 30 Nov 2007 15:44:25 -0800 (PST), palsing
wrote:

Well, in the Professional ranks, you are probably correct, and I can
see how it makes perfect sense. Of course, it was stated that
converting to the metric system made good sense, too, except that the
man-on-the-street soundly rejected the idea and has no idea how many
mm's are in an inch. Most of the time, he doesn't need to know, and I
don't think that anyone is going to force him to learn.

In my strictly amateur astronomy world, however, all of my reference
materials, my many star charts, my various charting software, the
setting circles on many telescopes (and I could go on-and-on), are all
showing me hours/minutes/seconds for RA, and I'll bet that yours do,
too.

And I expect it will be a long time before there's much pressure to make
any changes, either in printed charts or in setting circles. Unlike
converting from English to metric, of course, there's really nothing new
to learn. I think we are all pretty comfortable with degrees. So it
mostly does just come down to reference materials.

I do increasingly expect my software tools (such as charting and
planning apps) to work in the units of my choice- hours or degrees, and
the format of my choice- decimal or sexagesimal. There's really no
reason for software to do otherwise. There are times and places where
any of these are the units of choice.

Keep in mind, Martin is working with data extracted from professional
catalogs, many of which use degrees for RA. This includes the Sloan
Digital Sky Survey. It is perfectly reasonable for him to use the native
units, rather than converting them.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

Chris is 100% correct here - I extracted the data from Sloan and kept
it in the format they used. It never crossed my mind to convert it
into another format.

However if somebody wants to do so it is simple enough to do using a
spreadsheet.

Martin Nicholson, Daventry, England.
http://www.martin-nicholson.info/1/1a.htm

Visit the Astronomical Hall of Shame at http://www.geocities.com/queen5658/



Keep in mind, Martin is working with data extracted from professional
catalogs, many of which use degrees for RA. This includes the Sloan
Digital Sky Survey. It is perfectly reasonable for him to use the native
units, rather than converting them.

_________________________________________________

Chris L Peterson
Cloudbait Observatoryhttp://www.cloudbait.com

Hi Paul

True binaries, as opposed to line-of-sight double stars, are important
in astrophysics for a number of reasons - not least since orbital
studies allows the mass of the stars to be determined.

http://www.martin-nicholson.info/1/2c.htm

On 30 Nov, 22:23, palsing wrote:
Well, I like double stars as much as the next guy, especially twins
like Mesarthim, but why would you go to all this trouble for these
sparticular tars, most of which have magnitutes between 16 and 20?

"ukastronomy" wrote in message
...
: Hi Paul
:
: True binaries, as opposed to line-of-sight double stars, are important
: in astrophysics for a number of reasons - not least since orbital
: studies allows the mass of the stars to be determined.
:
Here's a true binary, the rest are fake binaries.
http://antwrp.gsfc.nasa.gov/apod/ap070416.html

Chris L Peterson wrote:
On Fri, 30 Nov 2007 14:23:53 -0800 (PST), palsing
wrote:

And, what's with the decimal RA & DEC values? Converting RA
238.4083822 to a more conventional RA of 15H etc. etc. may not be
hard, but who needs it?

More convenient for some, but not all. Some areas of astronomy (e.g.
meteoritics) have converted almost completely to expressing RA in
degrees, rather than hours. And I'm increasingly seeing that convention
adopted in professional circles, with papers sticking to decimal
degrees. That is, both hour notation and sexagesimal notation seem to be
falling out of favor. And that really does make good sense, given that
using degrees uniformly is simpler and less subject to confusion.

As I have said before, I completely disagree with the supposed utility
of degrees and with your conclusions about the trend in professional
astronomy. While it might be argued that hours of R.A. are not
necessary, there are very few (if any) reasons why degrees would be any
more useful. Very few, if any, astronomers do spherical trigonometry on
their calculators and it is trivial to do unit conversions on the more
sophisticated math applications. The funniest part of this argument is
that the people who insist on using degrees would typically be the last
ones to doing these calculations! And of course computers use radians
internally anyhow.

There has always been a tendency toward non-standard coordinate units in
certain areas of professional astronomy, such as radio astronomy, and
the involvement of large physics institutions in recent years is another
force (in general physicists are too arrogant to bother with quaint
astronomical standards), but I see very little evidence for your
assertion in general. Not among "real" astronomers, that is. ;-)

I have no problem with decimals, although there are many examples where
sexagesimal notation is much more useful to the humans reading the
coordinates. If only machines are to read them, then radians would make
more sense than degrees.

Whether you will admit it or not, the standard unit for R.A. in
astronomy is hours and has been for a long time. I will personally
continue to use hours because this unit relates to the sky in a more
useful way than degrees. A computer may not care, but humans do. That
has not changed, even if some humans who study the Universe no longer
have a connection with the sky. I personally feel this should be
considered something of a pity rather than celebrated as "progress."

Not to restart the argument--I just feel that it should be pointed out
that your views do not necessarily reflect those of other astronomers.

Greg

--
Greg Crinklaw
Astronomical Software Developer
Cloudcroft, New Mexico, USA (33N, 106W, 2700m)

SkyTools: http://www.skyhound.com/cs.html
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