AK, S. 1991. The sunspot observations made in 1990. Istanbul University, Faculty of Science, Journal of Astronomy and Physics , vol.56 , 21-48.

AK, S., (1991). The sunspot observations made in 1990. Istanbul University, Faculty of Science, Journal of Astronomy and Physics , vol.56, 21-48.

AK, Serap. "The sunspot observations made in 1990," Istanbul University, Faculty of Science, Journal of Astronomy and Physics , vol.56, 21-48, 1991

AK, Serap. "The sunspot observations made in 1990." Istanbul University, Faculty of Science, Journal of Astronomy and Physics , vol.56, pp.21-48, 1991

AK, S. (1991) . "The sunspot observations made in 1990." Istanbul University, Faculty of Science, Journal of Astronomy and Physics , vol.56, pp.21-48.

@article{article, author={Serap AK}, title={The sunspot observations made in 1990}, journal={Istanbul University, Faculty of Science, Journal of Astronomy and Physics}, year=1991, pages={21-48} }