Title Page

Contents

Lunar and Martian Craters Related to One of the Basic Problems in Astronautics
N. Bonev (in Russian, Summary in English)

On the Relation between the 11-Year Cycles Which Constitute the 22-Year Cycle of Solar Activity
A. D. Bonov (in Russian, Summary in English)

On the Distribution of High Protuberances
A. Bonov, V. Dermendžiev (in Russian, Summary in English)

Solar Activity Around the Periods of Minima of the 11-Year Cycles
A. D. Bonov (in Russian, Summary in English)

Intrinsic U–B Colours of Cepheid Variables
N. S. Nikolov, G. R. Ivanov (in Russian, Summary in English)

The Behaviour of Ap Stars on the Two-colour (U–B, B–V) Diagram
R. Radkov (in Russian, Summary in English)

On a Little Investigated Variable of the Type U Geminorum
M. Popova, Z. Kraičeva (in Russian, Summary in English)

An Investigation of Variable Stars of the Type RR Lyrae: TW Herculis
M. Popova, Z. Kraičeva (in Russian, Summary in English)

Photometric Particularities of the Peculiar Variable Star KR Aurigae
M. Popova (in Russian, Summary in English)

Mass Spectrum Changes of M 67 with the Distance from the Center of the Cluster
M. Popova (in Russian, Summary in English)

A Correlation Approach to the Problem of Existence of Clusters of Galaxies of Second and Third Order. The Two-Dimensional Case
M. Kalinkov (in Russian, Summary in English)

Second Order Clusters of Galaxies. I. Analysis of ED Clusters of Galaxies
M. Kalinkov, N. Janeva (in Russian, Summary in English)