What could astronomers better estimate once they knew what nebulae really were？A．The diame

According to the passage, what do people often think about astronomers？A．They spend most o

What is the lecture mainly about？A．How astronomers found the correct interpretation for a

According to the professor, what did a 1920s telescope allow astronomers to dc for the fir

What did eighteenth－century astronomers have in common with astronomers today？A．They could

What do astronomers use photographic plate for？A．Decreasing the time it takes to photograp

What is the one reason astronomers make long time exposures？A．To spend less time at their