Tom tells Greta that his father, an astronomer, is planning a scientific experiment to study another galaxy. Using a powerful telescope, Tom's father will record data of shifts in light patterns and track their different sources every 30 seconds. He will later study the data. Greta says that this is not an experiment. Which of these reasons supports Greta's statement?
It is not performed in a lab.
There are too many variables.
It does not have a control group.
It uses only theoretical predictions.