The standard units in the metric system are mostly based on factors of 10. This greatly increases the usability and convenience in varying fields of study.
In imperial measurements there are 12 inches in a foot. Other than that, it is just as useful as any number - all numbers are useful in science, depending on what you want to do wit them. Also the capactity of this or the amount or the measurement of this container is 12 :D
astronomy
Imperial and metric
Nothing - they are both the same measurement. One is metric - the other is imperial.
physics and chemistry
There are many branches of science. A simple answer would be the main 3 areas: Biology, Chemistry and Physics. Any other areas of science usually stem from one of these main 3 areas. In the related links section I have included links to examples of the 3 main areas of science.
Science is the pursuit of knowledge. Learning about anything is a science. Computer Science is the science of computers and how the are controlled and also other aspects of computing, like databases, networking, programming and a lot of other subjects. Computers are also involved in all sorts of other areas of science, as people use computers to do many different things. Nowadays computers are important in most areas of science.
Scientifically speaking, metrology is the science of measurement. Unlike other scientific fields, metrology covers all levels of uncertainty in any field of science and technology.
The Imperial units of measure are a combination of British and Roman units, that have been standardized over time. Go to the attached link titled "English Units", to learn a little more about various Imperial and other measures.
physics and chemistry
This question appears to be related to what is called "outer space". With that in mind, the science of astronomy is the correct answer. With that said, however, it's important to know that astronomers often rely on the expertise of other scientists that work in the fields of physics, materials science and meteorology. These areas of expertise help astronomers in many aspects of their work including measurements.
Most countries use the metric system. The US uses the Imperial or British system.