Ages back Plato said confidently, 'Beauty lies in the eyes of the beholder', and it seems true.
Beauty is permanent and perfect in itself. What lies in the lap of nature is beyond the thresholds of beauty still, man has created his own concepts of defining and measuring beauty. These concepts sometimes fail to define the beautiful object correctly. What all one can say is that beauty is non-definable.
'A thing of beauty is joy forever' sings John Keats and feels happy for he has said everything about beauty. It may be a moment's paradise but it lasts longer. But the thing of beauty for one person need not be beautiful for another person.
Who can say what is beautiful for me, except I? The beholder is an individual with his/her individual senses of perception, caught in a particular moment of enjoying beauty. The object of beauty at present moment may bring pleasure and joy to some viewers, not to all and also the next moment it may not remain the object of beauty.
Extreme is the case where the same object may not remain beautiful for all the viewers at the same time.
Generations change along with their concepts of beauty, the same heroine in the same phase of popularity is liked by the audience from different angles of her beauty. Thus nobody can define beauty except the beholder.
It can be said that the social mood and the collective mind to a certain extent define the line of beauty as it can be seen in the beauty contests where judges from different spheres of life and age groups are included in the panel. This is done to increase the chances of correct judgment. But can beauty be judged?
Let it be left for the beholder to behold and the beheld to feel the joy of being beautiful.