Instruments used in astronomical investigations are

The blue colour of sky is due to :

The defect of vision which cannot be corrected by using spectacles is :

The least distance of distinct vision for a young adult with normal vision is about :

The size of the pupil of the eye is adjusted by :

The splitting up of white light in to seven colours on passing through a glass prism is called 

The human eye forms the image of an object at its :

Who discovered by his experiments with glass prisms that white light consists of seven colours?

The red colour of the sun at the time of sunrise and sunset is because :

A young man has to hold a book at arm's length to be able to read it clearly.The defect of vision is :