In 1899, five years after establishing the first Bulgarian astronomical observatory in Sofia,Marin Bachevarov started regular sunspot observations with his students with the foremostcontemporary telescope in Bulgaria - a 6-inch refractor ^[1] .

In the mid-XXth century Angel Bonov lays the foundation of solar physics in Bulgaria with hisstudies on the 22- ^[2] , 44- ^[3] and 176-year ^[4] cycles of solar activity and the first heliophysicscourse, led in Sofia University. Other scientist, like Marin Kalinkov and Donka Raikova, alsogive their contribution in solar research in the newly established Astronomical Departmentin the Institute of Physics of Bulgarian Academy of Sciences in 1952. In 1977 VladimirDermendzhiev becomes the first to get a PhD in heliophysics in Bulgaria after defending athesis “Study on the height, heliographic distribution and activity cycles of solarprominences”. In 1985 he established Solar Physics Department and marks the beginning ofregular and extensive research on Sun and solar activity in our country.

In the early 1990s, a solar tower with 8-m Carl Zeiss dome, built in the NationalAstronomical Observatory (NAO) Rozhen, marks the first steps of observational heliophysicsin Bulgaria. It was equipped with 13-cm refractor to explore solar photosphere (left panel onthe image below). The initiator and head of the project was Vladimir Dermendzhiev. Afteralmost 15 years of usage, in 2005 the 13-cm telescope in the solar tower of NAO is replacedby 15-cm coronagraph (right panel on the image below). Supplied with Hα filter, its mainpurpose is dedicated to observations of solar prominences.

Meanwhile, for less than 40 years the path of lunar shadow passes through Bulgarian landstwice – in 1961 and in 1999, and solar physicist use the opportunity to organize total solareclipse observations. On 15 February 1961 despite the unfavourable weather conditionsMarin Kalinkov makes one of the first successful attempts in Europe to observe the eclipseaboard plane in order to extend the totality (left panel on the image below) ^[5] . Theexpedition, held 38 years later (on 11 August 1999) in northwestern part of the countryincluded more participants and scientific experiments under the supervision of NationalCouncil for Coordination of Observational Programmes (headed by D. Mishev) ^[6] . Theobservations were successful covering topics from spectral and white-light observations ofthe corona (right panel on the image below) to geomagnetic and seismological research.This two events establish the Bulgarian total solar eclipse observations. In the years after itoutgrows in organization of Bulgarian solar eclipse observational expeditions abroad withthe eclipses in 2006 ^[7] , 2009 ^[8] , 2017 ^[9] and 2019 ^[10] .

In 2019 a project for construction of new solar telescope in NAO Rozhen started. It iscurrently in its final phase and the telescope is expected to receive its first light in 2022.

Sources:

[1] N. Petrov, D. Kjurkchieva, Ts. Tsvetkov (2018) Astronomical and AstrophysicalTransactions 30 (4) 441-452.
[2] A.D. Bonov (1975) On the Relation between the 11-Year Cycles Which Constitute the 22-Year- Cycle of Solar Activity. Astrophysical Investigations 1 5.
[3] A.D. Bonov (1977) On the 44-year cycle of solar activity. Byulletin Solnechnye DannyeAkademie Nauk SSSR 1977 66-70.
[4] A.D. Bonov (1973) Characteristic Features of Secular and Supersecular Cycles of SolarActivity. A 180-Year Cycle. In: Solar Activity and Related Interplanetary and TerrestrialPhenomena. Proceedings of First European Astronomical Meeting, Athens, Greece, 4-9September 1972.
[5] V.N. Dermendzhiev, D. Mishev, K. Koleva (1999) “Solar eclipses”. Prof. Marin DrinovAcademic Publishing House
[6] V.N. Dermendjiev, D. Mishev (1999) Final Status of Preparation of the ObservationalProgramme for 1999 Total Solar Eclipse in Bulgaria. In: Third Advances in Solar PhysicsEuroconference: Magnetic Fields and Oscillations, ASP Conference Series 184 344-347.
[7] J. Kokotanekova, N. Petrov, P. Duchlev (2007) Observations of the total solar eclipse on22 July 2009 in China. Bulg. J. Phys. vol. 34 s2 224-231.
[8] N. Petrov, P. Duchlev, K. Koleva (2010) Observations of the total solar eclipse on 22 July2009 in China. Bulgarian Astronomical Journal 14 102.
[9] Ts. Tsvetkov (2020) Bulgarian Astronomical Journal 33 117.
[10] Ts. Tsvetkov, N. Petrov, R. Miteva, E. Ivanov, V. Popov (2019) Research on Ac-tive Solar Processes During 2019 July 2 Total Solar Eclipse. Proc. of the Eleventh Workshop“Solar Influences on the Magnetosphere, Ionosphere and Atmosphere”, Primorsko, Bulgaria,3-7 June 2019.

More information:

- Ts. Tsvetkov, N. Petrov (2021) Development of Solar Observations in Bulgaria: New30-cm Chromospheric Telescope. Bulg. J. Phys. vol. 47 55-61.
- Ts. Tsvetkov, N. Petrov (2020) New 30-cm Solar Telescope at National AstronomicalObservatory Rozhen. Proc. of the Twelfth Workshop “Solar Influences on the Magnetosphere, Ionosphere and Atmosphere”, September, 2020.