There we measure shadows, and we search among ghostly errors of measurement for landmarks that are scarcely more substantial.

At the last dim horizon, we search among ghostly errors of observations for landmarks that are scarcely more substantial. The search will continue. The urge is older than history. It is not satisfied and it will not be oppressed.

A scientist naturally and inevitably ... mulls over the data and guesses at a solution. He proceeds to testing of the guess by new data-predicting the consequences of the guess and then dispassionately inquiring whether or not the predictions are verified.

The history of astronomy is a history of receding horizons.

The great spirals, with their enormous radial velocities and insensible proper motions, apparently lie outside our Solar system.

I knew that even if I were second or third rate, it was astronomy that mattered.

Not until the empirical resources are exhausted, need we pass on to the dreamy realms of speculation.