to do on a Moonlight Night
and Observing Proxima Centauri - (V 645 Centauri)
With a magnitude of 10.7, Proxima Centauri can be glimpsed
even on a bright Moon lit night using a reasonable pair of
binoculars or a small telescope. This faint star is exceptional
for one reason, it is the nearest star to the Solar System.
At about 4.3 light years, Proxima Centauri is marginally closer
than the easily identifiable and bright star Alpha Centauri.
In space, both stars are separated by about one sixth of a
light year. The question as to whether Proxima Centauri is
gravitationally linked to the famous double star system of
Alpha Centauri is not yet fully resolved.
after being interested in astronomy for several years did
I get around to looking for Proxima Centauri. When I did however,
I found it more difficult than I had thought owing to the
problem of accessing a detailed enough star chart that clearly
and unambiguously showed the exact position of the star. I
tried several different charts but even so, trying to find
Proxima Centauri proved to be much harder than I had anticipated.
To make matters worse, I was unsure whether I had actually
observed Proxima Centauri or just some other nearby look-alike
reddish/orange star. I could not claim a positive sighting.
This uncertainty was compounded by the star's faint magnitude
and its location in a relatively rich star field. For other
observers, the two charts supplied with this article should
remove any of that uncertainty.
is a well known variable flare star and has been described
by Robert Burnham in his Celestial Handbook as possibly one
of the most active stars known of its type. Flare stars are
usually dim red dwarfs which for some reason, increase and
decrease their brightness over a matter of minutes. These
changes in brightness appear to occur at random sometimes
hours, days or months between each event. It is currently
believed that such changes in brightness are caused by flares
on the star's surface similar to the solar flares that the
Sun produces from time to time.
to the Sun, red dwarfs are relatively dim objects so when
a major surface flare occurs, these flares add substantially
to the overall brightness level of the star. With much brighter
stars, a surface flares contribution to the luminosity of
a star is usually lost amid the star's overall brilliance.
As Proxima Centauri is intrinsically around 13,000 times less
luminescent than the Sun, any increase in brightness over
a short period can often be readily observed.
to Burnham*, Proxima Centauri has a diameter around 64,000
kilometres or about five times the size of the earth, hence
it is a very small star when compared to the Sun. Its a bit
like comparing a pea with a large rock melon. To put this
into some context, it must be remembered that the Sun itself
is considered a dwarf star on the stellar scale.
The two charts shown here differ in both their scale and limiting
stellar magnitudes. Chart
A (21K) shows Alpha and Beta Centauri (pointers to the
Southern Cross) and Alpha Circinus. The latter is a bright
naked eye star about four degrees from Alpha Centauri in the
direction of the South Celestial Pole. Also, Alpha Circinus
forms an easily identifiable right angle triangle with the
other two stars. The cut off magnitude of Chart A is close
to 10. Note the asterism shaped like a broken cross marked
on the chart. Chart
B (17K) is a more detailed map of the immediate region
of Proxima Centauri with a limiting magnitude of about 12.
It should provide enough background stars for the observer
to zero in on Proxima Centauri.
locate Proxima Centauri, I suggest that you first find the
cross shaped asterism using Chart A. This should not be too
difficult. Now with the help of Chart B, in the direction
of Alpha Circinus look for a reddish/orange star about half
a degree from the asterism (the diameter of the Moon). Depending
on the instrument you are using, Proxima Centauri and the
asterism might be in the same field of view. If not, you will
need to move your instrument a small amount in a direction
towards Alpha Circinus.
* (Editor's note) Burnham refers to the three volume work
of Robert Burnham Jr published c1978. The three volumes examine
the objects (notable features, double stars and deep-sky)
in each constellation in great detail. Burnham also included
information about specific objects (white dwarfs, nova etc.).
It is a well prepared work. Even though it is now somewhat
dated it is still a useful work for any astronomer.
ABOUT THE AUTHOR
Doug Brown has been an ASWA member for 17 years, originally
attracted to the Society after attending a public viewing
night in 1983. He built his own 20 cm Newtonian, which he
has since converted for photographic use, as a prototype of
a larger scope he still intends to build. Doug most enjoys
photographing some of the lesser known objects and abides
by the motto that "unphotographed photons are wasted photons".
He has yet to succumb to the temptations offered by CCDs,
automatic guiders and imaging software.
Doug remains a valuable member of the Society, having served
on Council, and actively participates in viewing nights, Astro-Camps,
etc. He is of the strong view that the future of ASWA will
remain bright as long as the membership stays focussed on
the real reason for ASWA's existence. To him it is providing
an opportunity for like-minded people to come together to
develop and share their love of astronomy.