I applied for some observing time, together with my professor and our Canadian
colleague, for a new distance measuring programme. We tried for a couple of
times in 1997 but both applications failed probably because of the large
amount of dark nights (no moon) we were applying. At first we applied for 10
nights and later for 7 nights. The number of nights diminished because a new,
much more sensitive, CCD camera was installed to NOT. Anyway, we did not get
any time on the second attempt either, so prof. Valtonen asked whether those
lucky ones in Tuorla who got time would be willing to take a few exposures for
us on their observing time or let me go make their observations and a few of
my own at the same time. Several colleagues accepted his proposal and one,
M.Sc. Harri Pietilä let me go make two sets of his
observations with a promise of a couple of hours for my own project as well.
My intention is to measure the distance of a nearby spiral galaxy IC 342
with Cepheid observations. Simply put the Cepheids are variable stars
whose physical behaviour is well understood. The relation of a Cepheid's
period of variability to its luminosity reveals us its distance quite
accurately. When a sufficient number of Cepheids is observed in a galaxy, the
distance to that galaxy can be calculated. Cepheids are the most accurate
extragalactic distance indicator known to man. Within the Local Group of
galaxies the error is at most only 10%. Unfortunately Cepheids can be observed
only in the closest few hundred galaxies even with the best telescopes, so
distances to millions more distant galaxies must be acquired with more
uncertain methods.
"My own" galaxy IC 342 is, according to these more uncertain methods, at a
distance of 1800-3400 kiloparsecs (about 6-11 million light years) from us--
just beyond our Local Group of galaxies. This distance is supposed to
be acquired with an accuracy of tens, rather than hundreds, of kiloparsecs
using Cepheids. So far observations have been made during three months in the
beginning of 1998.
IC 342 (alias: UGC 02847)
Galaxy classification: .SXT6..
Location:
-equatorial co-ordinates (epoch 2000.0)
R.A. = 03h 46m 50s, Dec. = +68d 05m 45s
-galactic co-ordinates
l = 138.2 deg, b = 10.6 deg
-supergalactic co-ordinates
SGL = 10.6 deg, SGB = 0.4 deg
Distance: 1800 - 3400 kpc
Radial velocity: 34 +- 4 km/s
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