[bug #65255] MR: Clarify that arcsectandist is in physical kpc; other copyedits

[Boud Roukema]

URL:
  <https://savannah.gnu.org/bugs/?65255>

                 Summary: MR: Clarify that arcsectandist is in physical kpc;
other copyedits
                   Group: GNU Astronomy Utilities
               Submitter: boud
               Submitted: Sun 04 Feb 2024 05:14:32 PM UTC
                Category: CosmicCalculator
                Severity: 2 - Minor
              Item Group: Documentation
                  Status: None
                 Privacy: Public
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any


    _______________________________________________________

Follow-up Comments:


-------------------------------------------------------
Date: Sun 04 Feb 2024 05:14:32 PM UTC By: Boud Roukema <boud>
Merge request for:

https://codeberg.org/boud/gnuastro/commit/3ea51a28b6b15d27a1b63db61d98e9e3f03eca42

Description:

Prior to this commit, the command line --help and 'info'
documentation for the '--arcsectandist' option did not state
whether the tangential distance was calculated in comoving
or physical distance units.

While it is natural to expect physical units for such a small
angle, someone might guess that multiplying by 3600 gives the
tangential distance for an arc subtending one degree. However, at
one degree, the comoving separation for redshifts from 1 to 10
is about 100 Mpc give or take 50% or so, i.e. this is the cosmic
web scale, where comoving units usually make more sense than
physical units.

To avoid people not being sure what the intended unit is,
this commit adds the word "physical" to clarify that these
are the units of "ordinary" physics as opposed to comoving FLRW
distance units.

Some other copyediting is also done in this commit, including a
comment for the proper distance that it is in comoving units (by
definition). For distances such as the angular diameter distance
or the luminosity distance, it would be meaningless to describe
the units as either physical or comoving, since these do not
represent point-A-to-point-B distances in the sense of the FLRW
model.

Disclaimer: I have not checked the volume calculation.








    _______________________________________________________

Reply to this item at:

  <https://savannah.gnu.org/bugs/?65255>

_______________________________________________
Message sent via Savannah
https://savannah.gnu.org/