Review: fchart for Linux (DSO charting)

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Review: fchart for Linux by Michiel Brentjens
An invaluable deep sky navigation aid

by Margo Schulter
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Recently I was involved in a discussion on Usenet with the noted deep
sky observer and author Tony Flanders, who remarked that starhopping
with a wide-angle eyepiece having a field of view around 2 degrees was
indeed possible, but would require top-quality star charts. Not long
after this discussion, I found myself in another situation calling for
fine-detail charts: trying to identify an object I had come upon in
casual "surfing" around Sagittarius with my new Sky-Watcher 20cm f/6
Dobsonian.

Happily, some months ago, I had already downloaded a fine and free
solution for both types of situations: fchart by Michiel Brentjens, a
text-based software program for Linux that can produce detailed finder
charts for thousands of deep sky objects in the Messier and NGC/IC
catalogues as well as a nice selection of many others included in a
database of the Saguaro Astronomy Club. Additionally, it's possible to
specify any arbitrary location as the center for a chart by giving the
coordinates of right ascension and declination.

http://www.astro.rug.nl/~brentjen/fchart.html

Especially for those of us who are accustomed to command-line Linux,
the user interface is natural, efficient, and friendly. Finder charts
are output as Encapsulated PostScript (.eps) files which can be viewed
on screen using Ghostscript and the zgv graphics viewer, for example,
or printed on various printers either directly (if the printer has
built-in PostScript support) or through an interpreter such as
Ghostscript. There's also an option to produce these charts in the
popular PDF format, which is the default format for platforms other
than posix ones (Unix-related systems including Linux).

The fchart program nicely complements _Taki's 8.5 Magnitude Star
Atlas_ http://www.asahi-net.or.jp/~zs3t-tk/atlas_85/atlas_85.htm by
Taki Toshimi, another fine resource for astronomy freely and
generously made available on the Web. While Taki's atlas is great for
surveying a general area and routine star hopping with a finder scope
or binoculars, fchart gives the more detailed views that can be
invaluable for finding and confirming one's arrival at a known object,
or for identifying a serendipitously spotted object.


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Installation and setup
----------------------

For those of us accustomed to installing GNU and related Linux
software, the procedure for getting fchart up and running is for the
most part familiar, but with a couple of interesting twists.

First, the program uses the python language; so while developed in
Linux, which is what I use, it might also run on other platforms which
support python. As the README file explains, fchart requires the
numarray library of the Space Telescope Science Institute, happily
easy to download and install. Once this library is in place, there's a
default installation script ready to go, and pleasantly designed for
those of us less well versed on the intricacies of python so that
files will be installed in appropriate directories for finding by the
program when needed.

Secondly, to place stars in those finder charts for deep sky objects
(DSO's), the program uses the excellent Tycho 2 database. While one
option is to get the Tycho 2 catalogue and build a binary file from
it, I chose the alternative of simply downloading this binary file,
available on the fchart site. This binary is about 29M, and took me
about 90 minutes to download at 5.6K using wget -- but is well worth
the time, since it provides the basis for really comprehensive
charts. The default is to map stars to a limiting magnitude of 13.8,
close as it happens to cited limits for a 20cm (or 8") reflector.

An obvious but amusing caution is to be sure that tyc2.bin has
actually been downloaded in full. When I got fchart last year, I used
a Web browser for this download, assumed that I had the complete file,
tried the program, and got curious error messages on lots of Messier
and NGC/IC objects, although others generated eps charts as expected,
and very nice ones. Only this month did I follow through and contact
Michiel Brentjens, the author, to inquire about what might be
happening. He very gracefully suggested, among other things, that I
check the length of tyc2.bin. Then I saw that this file was 9M instead
of the expected 29M, and used wget to download it again and verify
success. This quickly resolved my problems.

In keeping with the traditional philosophy of the Unix operating
system and its variants such as Linux, fchart does one basic thing and
does it well: producing an eps (or pdf) chart of a specified DSO, or
optionally a number of DSO's specified in a single command line, or
all of the Messier objects. The Unix philosophy also invites the user
to combine programs to fit a given situation or computing style. Thus
I found it easy to write a couple of Linux shell scripts to handle the
process of generating a DSO chart with fchart in eps format, producing
a displayable bitmap graphic with Ghostscript, and displaying that
graphic with zgv.


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Some flexible options
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One attraction of fchart is that you can keep things simple and get
the benefit of very reasonable defaults. For example, you could simply
enter:

fchart m31

and get a nice chart, m31.eps, with a 7-degree field of view (FOV),
typical for 7X50 binoculars and some finder scopes. The chart also
includes M32 and M110, with a default of mapping DSO's to a limiting
magnitude of 12.5. The right ascension and declination coordinates for
M31 also conveniently appear at the upper left of the chart, together
with a guide to scale showing a distance of 2 degrees.

At times we might want to customize the FOV for a chart. For example,
recently I used fchart to help identify a beautiful object I had seen
and sketched in Sagittarius using my 20cm f/6 Dob with a 25mm Super
Plossl at 48X. To see how M25, one of my possible guesses, might look
centered in this eyepiece's field of approximately 1 degree 5', I
could enter:

fchart m25 -f 1.083

This time the little guide rule at the upper left to show scale
indicates a distance of 10' rather than 2 degrees, a neat feature.

With a telescope such as a Newtonian reflector, a useful trick after
generating a chart is to rotate it 180 degrees to match the telescope
image or a sketch of it. Using zgv to view a bitmap of the eps chart
generated by a program such as Ghostscript, this can be quickly
accomplished by hitting the "r" key twice (rotating 90 degrees each
time), or by hitting "f" and then "m" (for "flip" and "mirror").
Turning a printed chart upside down serves the same purpose.

Other options, for example, let you set limiting magnitudes for stars
and DSO's, respectively with -s and -d; specify an output directory
other than the current one; select paper width (in millimeters) and
output format (eps or pdf); choose English or Dutch as the language
appearing on a chart ("en" or "nl"); or place a cross with an optional
label or caption in a chart at any specified coordinates (for example,
to show the location of a supernova within a galaxy).


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Customized charts for starhops or sweeps
----------------------------------------

The option to draw a chart for specified arbitrary coordinates rather
than a named DSO could be helpful for starhops or sweeps using an
eyepiece which on a given telescope has an FOV around 2 degrees, for
example. Suppose we want to sweep from M24 to M25. Since these two
objects have declinations within a degree of each other, respectively
-18deg29' and -19deg6', we're doing essentially a right ascension
sweep.

Starting at M24, we could generate a series of charts as follows,
moving 4 minutes of right ascension (one degree) and 10' of
declination between charts, so that they overlap and provide a guide
for the whole sweep:

fchart m24 -f 2
fchart "18:20:54,18:39:00,Hop1" -f 2
fchart "18:24:54,18:49:00,Hop2" -f 2
fchart "18:28:54,18:59:00,Hop3" -f 2

As this example shows, to make a customized chart we specify the right
ascension, declination, and some caption for the chart, delineated by
commas, opening and closing with ASCII double quotes. Generating and
then viewing or printing each chart reveals that the goal of our
sweep, M25, appears near the eastern border of our "Hop3" chart. For
these customized charts, the chosen caption determines the name of the
output file: thus Hop1.eps, Hop2.eps, and Hop3.eps.

With objects like M24 and M25 which are about 3-5 degrees apart, a
different approach would be to generate a single chart with a field of
view just large enough to include both objects. Such a chart covers
more territory than a single eyepiece field of around 2 degrees, but
may provide enough detail to guide the starhop or sweep with only one
page of output required.

In this approach we seek to place the center about midway between the
two objects in terms of both right ascension and declination, and a
bit of trial and error helps in getting the best coordinates for this
center. On a system which can display eps (or pdf) files on screen,
this is easy. With M24 and M25, I reached this solution:

fchart "18:24:54,-18:35:00,"SweepM24-M25" -f 4.0

which includes the eastern portion of M24 and all of M25.

To evaluate these strategies in practice, I'll need to try them for
some actual starhops; and more experienced observations might have
interesting comments on which strategy is best, and when. A nice
feature in making such detailed maps is that limiting magnitudes for
DSO's and stars, which can affect perceptions of star patterns or
asterisms, can be adjusted to fit a given instrument or light
pollution level, etc.


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A "random" test: Baade 1 or PK 171-125.1
----------------------------------------

While reading a Web commentary by Stephen R. Waldee, whose engaging
essays on deep-sky observing and related topics offer some fascinating
ideas as to practice and philosophy alike, I encountered a brief
discussion of an object known as Baade 1, a small and faint planetary
nebula given in the Saguaro Astronomy Club (SAC) database used for
fchart as having a diameter of 38" and a magnitude of 13.9.

In sharing with us a problematic attempt at finding and sketching this
elusive object for visual as opposed to photographic observing, Steve
emphasizes the need for star atlases or the like with narrower fields
showing fainter stars. Could fchart help with Baade 1?

To find out, I started by pulling up the SAC database file, sac.txt,
on the 'most' text browser, and searching for Baade 1. Happily I found
it as a name synonymous with PK 171-25.1, so that I could ask for a
chart under the latter name. To generate the chart for this faint
object, I would specify a limiting magnitude for DSO's of 15 rather
than the default 12.5, and a field of view of 2.05 degrees, which
happens to be the field for my 30mm Garrett Optical 2" eyepiece.

fchart pk171-25.1 -d 15 -f 2.05

Baade 1 illustrates a helpful caution concerning object names other
than those of the Messier and NGC/IC catalogues: sometimes in the
sac.txt database, a name doesn't get an entry of its own (where it
appears at the beginning of a row), but rather appears as a synonym
for another object name, here pk171-25.1., which fchart can find.
As we'll in the next section, searching for a desired object name in
sac.txt, and taking note if its main entry is under a different name,
can be a good strategy for avoiding or solving problems.


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A couple of possible upgrade ideas
----------------------------------

Just as it as proverbial that all nontrivial programs have bugs, so it
seems that these programs are likely to inspire a review to propose at
least one or two extra features, however practical or otherwise to
implement. Therefore I might mention a couple of ideas.

First, I might welcome an option to label brighter stars with their
Bayer letters or Flamsteed numbers, although it might be very fairly
pointed out that fchart is meant to supplement rather than replace
usual star charts or atlases which provide this information. Keeping
the database demands of the program simpler, and the charts more
uncluttered, could both be strong arguments for leaving things as they
are.

Secondly, recognizing that the database of DSO catalogues even for a
quite comprehensive program like fchart must necessarily be partial, I
have encountered one situation where an additional cross-reference
would seem a logical choice, although I was able to produce a chart
for the desired object by using another name for it.

Having produced charts for some of the Palomar globular clusters
(numbered Palomar 1-15), I looked at fchart's Saguaro Astronomy Club
catalogue file sac.txt, and noted that all of these globulars were
listed under their Palomar numbers -- except for Palomar 7. When I
tried

fchart Pal7

the result, not so surprisingly, was a message that the object could
not be found.

However, I quickly determined that Pal7 is also known as IC 1276, an
identity listed in the entry for IC 1276 in sac.txt, so that

fchart IC1276

produced a chart of the desired object without any problem.

Here it would seem to me that the best approach would be to treat
Palomar 7 (IC 1276) like Palomar 9 (also NGC 6717), which can be
specified by either name and is identified by both on a chart.
However, as my experience with Palomar 7 shows, the problem of
incomplete cross-referencing of names can at least sometimes easily be
solved by requesting the desired object under another name -- and such
situations might be almost inevitable for a program with as large and
useful a database as fchart.

My experience with Pal 7 nicely prepared me for the exercise of
charting Baade 1 (PK 171-25.1), as related in the previous section.
More generally, browsing through the databases with a utility like
'most' can be lots of fun; but it's sometimes essential to find out
whether a desired object is included and, if so, under which name(s)
it can be found by fchart.


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Summing up: A great program!
----------------------------

From an amateur astronomer's point of view, I find fchart invaluable
for the detailed charts it draws both of DSO's and of their
surrounding star patterns or asterisms. It also can be fun simply to
choose a random NGC number, for example, and see what's there. A big
bonus that comes with the program is a set of ASCII text databases for
the Revised NGC/IC project and the Saguaro Astronomy Club. The NGC and
IC files (revngc.txt, revic.txt) format very nicely for some enjoyable
browsing with 'most' or 'links'; while the SAC file (sac.txt) has some
delimiting characters like double quotes, but is still quite
human-readable.

The author also makes available on his Web page collections of charts
ready for downloading: one of all the Messier objects, in eps format;
and another with 800 of the 2500 or so objects discovered and
catalogued by William and Caroline Herschel, in pdf format (the
"Herschel 400" and "Herschel 2" sets).

From another perspective, fchart is a fine example of a Linux program
especially apt for those of us who often use a text-based environment
to generate and view graphics. However, I hope that people running in
graphical environments (Linux or otherwise) also try and enjoy this
program, which illustrates the impressive quality and utility possible
with open source software, as well as the dedication and generosity of
those who make it available.

Most appreciatively,

Margo Schulter

In sci.astro.amateur Margo Schulter wrote:
Sometimes, go scatter a destruction! Many excellent orange prisoners will
outside tear the silences. While ads largely disclose cults, the
workforces often admit relative to the imperial scenes. I was
[snip]

Please let me confirm that this was _not_ posted by me, not so unsurprisingly.

Normally I would ignore such messages, but wonder if a disclaimer of a post
using my name and e-mail might sometimes be in order, and if so, when.

Best,

Margo Schulter

"Margo Schulter" wrote in
message ...
In sci.astro.amateur Margo Schulter
wrote:
Sometimes, go scatter a destruction! Many excellent
orange prisoners will
outside tear the silences. While ads largely disclose
cults, the
workforces often admit relative to the imperial scenes.
I was
[snip]

Please let me confirm that this was _not_ posted by me,
not so unsurprisingly.

Normally I would ignore such messages, but wonder if a
disclaimer of a post
using my name and e-mail might sometimes be in order, and
if so, when.


Basically, there's nothing you can do. Everone with any
experience on USENET has encountered hipcrime-like trash at
one time or another. Nobody with any sense believes the
posts are from you.

A little background: some script punkie has been attacking
sci.crypt (and half of USENET) with by flooding them with
sporged (=spam+forged:
see http://en.wikipedia.org/wiki/Sporge )
messages for about 3 months. In addition he has cleverly
enlisted the aid of people such as yourself to carry his
dirty underwear by cross-posting to other groups and/or
using the "followups to" features of USENET to get others to
unwittingly help him flood sci.crypt with useless, off-topic
messages.

In sci.astro.amateur John E. Hadstate wrote:

A little background: some script punkie has been attacking
sci.crypt (and half of USENET) with by flooding them with
sporged (=spam+forged:
see http://en.wikipedia.org/wiki/Sporge )
messages for about 3 months. In addition he has cleverly
enlisted the aid of people such as yourself to carry his
dirty underwear by cross-posting to other groups and/or
using the "followups to" features of USENET to get others to
unwittingly help him flood sci.crypt with useless, off-topic
messages.

Thank you for this helpful reminder, with my situation as an
object lesson about how an unfamiliar disruption tactic (to me,
that is!) can cause a user to react in less than optimal
fashion.

What happened is that I accessed sci.astro.amateur after a break
of maybe about a week, and it happened that this thread was the
first to come up on tin. Although I've been on Usenet for over
ten years, the "sporge" tactic was a form of spam I hadn't seen
before, or at least didn't recall. However, there had been some
other vicious things going on of a more personalized nature,
so I took this as maybe specific to me or a few others, and
thought it might be helpful to clarify that I wasn't the author.

Then after looking through the next few hundred posts, the nature
of the situation became clearer, to say the least rueful grin.

If I can serve as an object lesson of how an unfamiliar situation
can cause a user who normally avoids responding to spam to do the
less than optimal thing, and provide a bit of humor, then maybe
this experience can help others and Usenet.

Best, with many thanks,

Margo Schulter

Thank you for this helpful reminder, with
my situation as an object lesson about
how an unfamiliar disruption tactic (to
me, that is!) can cause a user to react in
less than optimal fashion.

http://img.villagephotos.com/p/2005-...0-picture.jpeg
Marty