Great book. I recently read it and thought it was excellent, and I've recommended it to others. I did, however, notice one thing that I feel compelled to correct.

In the Hubble Shoots the Moon section of the Hubble Space Telescope Misconceptions chapter, it is stated that the Moon moves too rapidly for Hubble to track. It is also stated that the Moon observations that Hubble did in 1999 were accomplished by "ambushing" the Moon i.e. using a fixed telescope pointing at just the right time to snap a short exposure as the Moon was passing through the field of view. Both of these statements are incorrect.

The Moon does not move too quickly for Hubble to track, and it was tracking during the 1999 observations. (I was heavily involved in implementing those and other Hubble observations of the Moon.) While it is true that Hubble's ability to track the Moon is limited, the issue is not that the Moon moves too quickly. The issue is that Hubble can track a moving target only in a straight line and only at a constant rate. On the short time scale of an individual Hubble observation, a constant rate linear track works well for almost all bodies in the solar system. However, the apparent motion of the Moon as seen from Hubble varies significantly in both rate and direction - even on a very short time scale. When Hubble tracks the Moon, it is trying to match a constant rate to the Moon's varying rate while at the same time trying to match a straight line to the Moon's curved path.

The result is that some smearing of the observation is inevitable. However, by tracking the Moon as best as Hubble can, the smear will, in most cases, be less than what would result from even a very short exposure using the "ambush" observing strategy.

For more details about Hubble's capabilities for observing the Moon, take a look at this User Information Report which was written to inform astronomers who may be considering lunar observations using Hubble.

Tony Roman
Space Telescope Science Institute