What is Modern Art?

Yesterday H, N and I went to London and boy was it busy. I don't think I will go in the Summer holidays again. The queues at the Natural History Museum were horrendous and inside it was packed and extremely hot! N's favourite thing was the girobot Tyranosaurus Rex, which was very realistic. It was huge and only three quarters of the size of a fully grown adult.

Later we went to The Tate Modern. I think N enjoyed this. My favourite room in the Tate Modern is the one with the massive paintings by Mark Rothko. I love this room, the paintings are so huge and the perspective in them seems to change as you look at them. N really liked the work of Roy Lichtenstein.

We had planned to go to the Saatchi Gallery as well but that will have to wait for another time. N asked me the difference between the two galleries. The Saatchi is much smaller, it is a more old fashioned building, but the main difference is that the work is more contemporary (modern). That made me think - is there a difference between contemporary and modern? And when does the work in the Tate Modern cease being modern? After all a lot of the work in The Tate Modern is now quite old (Picasso, Ernst, Monet, etc). At some point this will surely cease to be classified as "Modern Art".

I would consider the work in the Saatchi gallery to be more "Modern", it is certainly more up to date. The dictionary defines modern as :
Of or relating to recent times or the present: modern history.
a) Characteristic or expressive of recent times or the present; b) contemporary or up-to-date: a modern lifestyle; a modern way of thinking.

If you are using this definition then quite a bit of the art at T.M. is not modern any longer. However another definition defines modern art as a general term, used for most of the artistic production from the late 19th century until approximately the 1970s. Modern art refers to a new approach to art where it was no longer important to literally represent a subject through painting or sculpture - so if you use this definition of modern art then the Tate is about right.

But hang on a minute, The Tate is also showing art that is more recent than the 70s - confused - I am. Maybe it is time someone redfined what modern art actually is - is it simply art made since the mid ninteenth century, when the arrival of cameras changed the function of art and also the way artists painted, or is it up to date art, stuff that has been made recently and is in tune with recent times?