Galaxies are inherently dynamic systems that change with time.
Because the NGST will be able to observe the first galaxies created it will be the only facility able to trace the complete evolution of galaxies from their first moments of creation to the present day. It was only in the early part of the 20th century that astronomers even recognized that the nebulous objects they often saw in the sky were in fact vast collections of stars like our own galaxy. Improvement in telescope technology allowed observers to distinguish these systems of stars from other nebulous objects such as large clouds of gas and dust or globular clusters. These intermediate structures, those smaller than the COBE fluctuations down to the size of present day galaxies have not been observed. Globular clusters of a few million stars may be the elementary particles of galaxy formation, and NGST can see them as far back as a redshift of 7.