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[vsnet-chat 241] RE: observing season of Mira (omicron Cet)

Dear Colleagues,

Taichi Kato (tkato@kusastro.kyoto-u.ac.jp) wrote in [vsnet-chat 221]:

>    The observing season of Mira (omicron Cet) from the northern hemisphere
>is over.  The latest reported observation to vsnet-obs was done by H. Itoh
>on Mar. 24.  Thanks to its brightness of the recent record, many beginner
>variable star observers enjoyed this monumental variable star.
>
>    I have been always wondering how long is the visibility of this variable
>from the southern hemisphere.  Being south, is it observable throughout the
>year?

Mira may be observed through the Solar conjunction in late April
(although
with difficulty) at far Southern latitudes (60-85 deg. S), but I beleave
there are not many variable star observers at those latitudes! From more
moderate latitudes (30-45 deg. S) it can be observed for all year long
except
a two weeks break from mid-April until the beginning of May.

The table below, calculated by undersigned, shows the observering
intervals
of Mira at various geographical latitudes. It is based on the follwing
visibility parameters: h(Sun) = -12 deg. (the Sun's maximum altitude),
h(star) = 5 deg. (Mira's minimum altitude). The table is strictly valid
for
the 1998-1999 observing season but there will be only minor
modifications
for several decades around those years. An asterisk (*) after a date
indicates that the visibility is limited by all night twilight. The
longest
Mira season (349 days) occurs at lat. 54.5 deg. S. It should be noted
that
Mira is very difficult or impossible to observe for most Northern
hemisphere observers during April, May and the first half of June.

From personal experience I have found that these visibility constraints
are reasonable for brighter astronomical objects (variables and comets).
I was
for example able to observe Mira in binoculars at March 21.79 UT, 1997
from
lat. 60 deg. N, or for nearly four days longer than given in the table.
In
order to observe Mira for as long as possible it is of course necessary
to
have a transparent atmosphere and an unobstructed view in the
appropriate
direction. In addition, it is important to correct brightness estimates
for extinction when the star is very low in the sky.

           ***** Observing season of Mira (Omicron Ceti) *****
Latitude  Observing season Interval   Latitude  Observing season
Interval
   o      Start      End        d       o       Start      End        d
S.Limit  Apr 28.0  Aug 24.7  118.8    Equator  May 15.9  Apr  9.5  328.6
 85 S    Apr 28.1  Sep  4.9* 129.8      5 N    May 18.1  Apr  8.5  325.4
 80 S    Apr 28.4  Sep 18.1* 142.7     10 N    May 20.7  Apr  7.3  321.6
 75 S    Apr 28.9  Sep 30.9* 155.0     15 N    May 23.5  Apr  6.1  317.6
 70 S    Apr 29.5  Oct 14.0* 167.5     20 N    May 26.9  Apr  4.8  312.9
 65 S    Apr 30.1  Oct 28.0* 180.9     25 N    May 30.8  Apr  3.3  307.5
         Mar 22.6  Apr  1.2    9.6     30 N    Jun  4.4  Apr  1.7  301.3
 60 S    Apr 30.9  Nov 13.6* 196.7     35 N    Jun 10.0  Mar 31.0  294.0
         Feb  1.8  Apr 14.0   71.2     40 N    Jun 16.8  Mar 29.0  285.2
 55 S    May  1.6  Dec 11.4* 223.8     45 N    Jun 25.2  Mar 26.8  274.6
         Jan  1.7* Apr 15.6  103.9     50 N    Jul  5.6  Mar 24.3  261.7
 50 S    May  2.5  Apr 15.9  348.4     55 N    Jul 18.4  Mar 21.4  246.0
 45 S    May  3.4  Apr 15.8  347.4     60 N    Aug  2.5  Mar 18.0  227.5
 40 S    May  4.4  Apr 15.5  346.1     65 N    Aug 18.7* Mar 13.9  207.2
 35 S    May  5.4  Apr 15.0  344.6     70 N    Sep  2.2* Mar  9.0  187.8
 30 S    May  6.6  Apr 14.4  342.8     75 N    Sep 15.5* Mar  2.6  168.1
 25 S    May  7.8  Apr 13.7  340.9     80 N    Sep 28.3* Feb 21.0  145.7
 20 S    May  9.1  Apr 13.0  338.9    N.Limit  Oct  5.3  Feb 10.0  127.7
 15 S    May 10.6  Apr 12.2  336.6
 10 S    May 12.2  Apr 11.4  334.2
  5 S    May 14.0  Apr 10.5  331.5
Equator  May 15.9  Apr  9.5  328.6

The Southern and Northern latitude limits are 88.0 deg. S and 82.0 deg.
N,
respectively.

Fraser Farrell <fraserf@dove.net.au> writes in [vsnet-chat 233]:

>With a Dec ~ -3, I would class Mira as equatorial, so the observing
>season would be much the same from everywhere. From here at latitude 35
>degrees-and-a-bit south, the observing season runs from May to March if
>the local horizon is flat and clear.

Although Mira is an equatorial star it can be seen for a considerably
longer part of the year at Southern latitudes, because it is located
16 deg. South of the ecliptic. The same applies for all equatorial
objects
that is South of the ecliptic, while the opposite is true for objects on
the Northern ecliptical hemisphere.

For those interested I have calculated visibility ephemerides for
several
other equatorial variables. These can be obtained via the www-address
http://vsnet.uio.no/~bgranslo/visiblty.html.

                                             With best regards,
                                             Bjoern H. Granslo.
-- 
------------------------------------------------------------------------
Bjorn H. Granslo            Telephone: +47 22 85 75 21 / +47 22 85 65 18
Postboks 1029, Blindern                     Email: bgranslo@astro.uio.no
N-0315 Oslo, Norway          WWW: http://vsnet.uio.no/~bgranslo/index.html
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