Match the words at the left to the correct blanks in the sentences at right. Use each choice only once.

1. A camera is an example of an instrument used for ________.

2. ________ refers to telescopic observations in which we separate an object's light so we can measure its intensity at different ________.

3. If we want to confirm that a star's brightness alternately dims and brightens, we need ________ observations of the ________.

4. The familiar twinkling of the stars is caused by ________, which also blurs telescopic ________.

5. Human civilization is responsible for what astronomers call ________.