Transcript: In science we deal with two fundamentally different types of errors. Random errors are usually associated with limitations in the measuring apparatus. A random error can displace a measurement either to the high or low side of the true value. Random errors are fundamental in science and in astronomy, and their theory was put in place by Carl Friedrich Gauss. Random errors can even apply when we count things. Although you may be able to count the number members in your family completely accurately, in astronomy we’re not able to count with complete precision. So we estimate the number of stars in a galaxy or the number of galaxies in the universe, and the count has an error attached to it. The second type of error is called the systematic error. A systematic error does not displace equally to the high or low side of the true value. It represents either a failure in our understanding of how to make a measurement or a flaw in the measuring equipment itself. For example, if you used a ruler to measure the width of a table and that ruler was either miscalibrated in the way it was a applied the scale when it was manufactured or the ruler had its scale applied at a different temperature from the temperature you are making the measurement, then all of your measurements of distance would be off in one direction. That’s called a systematic error. It is one of the most dangerous and tricky things in astronomy or in any science to track down systematic errors.