TOTAL SOLAR ECLIPSE FINLAND (HELSINKI-JOENSUU) 22.7.1990
Visiting Ursa
The observatory of Ursa Astronomical Association will be open to visitors daily from noon to 3
p.m. from Monday the 16th to Friday the 27th of July, except on Saturday and Sonday. If you
would lik to visit the observatory at some other time please contact our office. The observatory,
with its two solar telescopes and a spectroscope, is in the southern part of Helsinki on the highest
point of Kaivopuisto park. The total solar eclipse will not be visible from our observatory, but it can
be observed from the southern shore of Kaivopuisto Park, just a couple of hundred meters from
the observatory.
The office and the library of Ursa are less than half a kilometer due west from the observatory,
the address being Laivanvarustajankatu 3. The office will be open daily from 9 a.m. to 3 p.m. on
weekdays. Around the date of the eclipse there will be an information service available to all
visitors with questions regarding the total solar eclipse.
Science during the eclipse
Even though the importance of total solar eclipses in the research of the Sun has dimished, they
are still useful for other kinds of scientific research.
A total solar eclipse offers an opportunity to test the possible existence of a well known Majoranaeffect. When the Moon comes exactly between the Earth and the Sun during totatlity, there
should be a slight change in the observed gravity. Around the date of the eclipse the Finnish
Geodetic Institute will make measurements in Ilomantsi with an extremely accurate absolute
gravimeter (falling body instrument). The Earth tides will be measured in Metsähovi Space
Geodetic Station in Kirkkonummi with a LaCosta-Romberg recording gravimeter and an Askania
borehole tiltmeter and in Tytyri mine in Lohja with very long water tubes with lenghts of 60 and
177 metres. A French expedition led by Dr. Guy Berthault will come to Finland and try to measure
the same Majorana-effect in Ilomantsi with a torsion pendulum. The low altitude of the Sun during
the totality will create extraordinary favorable circumstances for these experiments because of the
strong horizontal influence.
Vaisala Oy will be making the same kind of measurements as were made 45 years ago during
the previous total solar eclipse in Finland. During totality it is possible to determine the radiation
correction of the radiosondes developed by Vaisala Oy. The sondes will be sent to an altitude of
several tens of kilometers from Joensuu and Vantaa before, during and after the total solar
eclipse. The measurements to be made by the Finnish Meteorological Institute with similar
radiosondes at the same time from their stations in Jokioinen and Luonetjärvi will also be used in
the analysis of the measurements made by Vaisala Oy. Unfortunately the low altitude of the Sun
limits the measurements only to small and less important angles of elevation.
Radius of the Sun and the reactions of nature
Ursa has organized a Solrad 90 (Solar radius) experiment together wiht MAOL, the Association of
Teachers of Mathematics, Physics and Chemistry. The idea of the experiment is to determine the
radius of the Sun with a minimum of equipment, that is with a filter and a stopwatch. School
children and amateur astronomers will make observations on the borders of the zone of totality
whether the eclipse is total or not and elsewhere on the zone of the duration of the totality in
different places. Knowing the distance of the Moon and the Sun and the radius of the Moon these
observations can be used to calculate the radius of the Sun.
With BMOL, Association of Biology and Geography Teachers, Ursa has organized experiments to
observe how nature reacts to the eclipse. With the aid of scientists of the Helsinki University four
different species have been chosen to be observed: a dog, a wagtail, ant and trefoil. The choice
has been keeping in mind that the species should be easy for the school children to recognize
and as common as possible in the whole country since these observations can be made also
outside the zone of totality.
Both the Solrad and the nature experiments will be accompanied by observations of the
meteorological conditions, i.e. temperature, wind speed and direction, and cloudiness.
The instructions for making all these observations have been gathered in a leaflet which also
contains a blank form for recording the observations. After the eclipse the forms will be collected
by Ursa for an analysis. The results of the experiments will be published in the magazines of the
abovementioned associations and of Ursa.
Eclipse events in Joensuu
Joensuu is prepared to welcome all the thousands of guests coming to experience this great
phenomenon of nature. There is still some room in hotels and accommadation is also arranged in
homes and farms in the Joensuu area.
Around the date of the eclipse the city of Joensuu will be decorated with yellow banderols and the
marketplace will be a center of all kinds of activities. On Saturday the 21st of July at 2 p.m. there
will be a lecture about solar eclipses in the Carelia Hall at the University of Joensuu. The lecture
will be given by Dr. Tapio Markkanen and it will be in Finnish and in English. Later on the Sun will
be celebrated in a big feast at the Festival Stage and the eclipse will be awaited with dance and
bonfires on Ilosaari, an island in the Pielisjoki river crossing the center of the city.
In the main library of Joensuu there will be an exhibition from the 2nd to the 29th of July
commemorating the life and achievements of professor and academician Yrjö Välsälä. From the
20th to the 23rd of July cards and letters sent from Joensuu will be stamped with a special eclipse
stamp.
On Saturday the 21st of July at 1 p.m. Joensuu Tourist Information will organize a press
conference in the Mustonen Hall by their office at the address Koskikatu 1. Joensuu Tourist
Information is preparing a map of the Joensuu area with the best and most easily accessible
observing sites marked on it. Early on Sunday morning Joensuu will arrange bus tours to some of
those sites. The charge for these tours will be FIM 50 per person and the registrations should be
made to Joensuu Tourist Information. In case of cloudy weather the eclipse can be seen as a
replay on Sunday afternoon at 3 p.m. in the Carelia Hall on a video taped from a Finnair DC-9plane.
For more information about the events in Joensuu please contact:
Ms. Marjut Cadia, Joensuu Tourist Information,
Koskikatu 1, SF-80100 Joensuu, Finland
telephone 358-73-201 609