Translation of "Observarlos" in English

Empecé a observarlos con detenimiento.

I started looking at them really carefully.

Sabía muy bien que, además de los grandes planetas como la Tierra, Júpiter, Marte, Venus, que hemos nombrado, hay cientos de otros que a veces son tan pequeños que es muy difícil observarlos a través del telescopio.

I knew very well that in addition to the great planets - such as the Earth, Jupiter, Mars, Venus - to which we have given names, there are also hundreds of others, some of which are so small that one has a hard time seeing them through the telescope.