Why was it difficult for astronomers to develop a clear ...

[Jramos095]

Why was it difficult for astronomers to develop a clear understanding of the Milky Way until the last few decades?
 
  What will be an ideal response?

Question 2

Define and distinguish among the terms speed, velocity, and acceleration.
 
  What will be an ideal response?

[bimper21]

Answer to Question 1

Interstellar dust obscures most of the light from the galactic center and blocks light from many parts of the disk. Until modern telescopes were able to look at other parts of the electromagnetic spectrum, the galaxy could not be studied and understood in detail.

Answer to Question 2

Speed is the pace at which an object moves through a distance (regardless of direction).Velocity is the pace at which an object moves through a distance, including a specific direction. Acceleration is the rate at which an object's velocity changes. The distinguishing feature between speed and velocity is that speed does not include a direction, whereas velocity specifies a direction.