It's difficult to solve this hexagonal puzzle.

Mr. Rokkaku is my best friend.

When light enters water, the angle of refraction changes.

The pheasant-tailed jacana, known as 'the ballerina of the water' for its beautiful appearance.

The calculation of the spherical angle is a part of geometry.

He was playing the guitar at the street corner.

He was always envious of others' success, saying that the grass is always greener on the other side.

A white dwarf is a celestial body that a giant star becomes at the end of its life.

A brown dwarf is a celestial body that has a size between a star and a planet.

Red dwarfs are the most common type of star in the universe.