Writing in the Sciences (in general) and Astronomy (in particular)

1. Good Writing vs. Bad Writing

1. Know your message. What are the most important things that you want your reader to come away with?
2. Know your audience. What base of knowledge do you share? What do they already know, and what is it your job to explain?
3. Present a connected argument. Does each sentence build logically on the previous one? Does each paragraph deal with a single central idea?
4. Be precise. Have you said exactly what you meant to say, or just something roughly in the ballpark?
5. Be interesting. Are you using language in a reader-friendly way?

   Good scholarly writing is difficult. Moreover, it can get more difficult the better you know your subject. The reason is that an expert's understanding of a subject is a multidimensional network of connections among many different concrete facts and abstract concepts. Writing, on the other hand, is linear. As an expert writer, it's your responsibility to create a comprehensible one-dimensional path through that network, and to lead the reader through it in a way that he or she can then begin to build his/her own network of understanding.

   The worst writing of all is unoriginal writing, and specifically plagiarized writing. Your writing must be your own creation. There is no way to sugar-coat this: There are no circumstances under which copying text from another source is acceptible. It doesn't matter if you found a writer who says things more clearly and eloquently than you'll ever be able to. Copying is wrong. Copying and making minor changes so that it doesn't obviously look like an exact copy is even more wrong. So don't do it.

   The point of this article is not to show you what the format of a scientific paper looks like. I'm assuming that you have seen and read enough papers that you are beyond that. Rather, my point is to alert you to specific writing issues that are going to come up as you write the various sections of your paper.

2. The Introduction

• Start with the big picture. Step by step, narrow the focus to arrive at your specific subject.
• At each step, give the reader specific information about what is currently known and understood, citing relevant papers (thereby giving credit to those who have contributed to this understanding).
• Also at each step, give the reader specific information about what is not understood. If there is disagreement between different researchers, explain the nature of the disagreement (with citations). Often, this provides a natural transition to the next deeper level.
• Critique the logical flow of your presentation. Does each sentence logically follow from or build on the previous one? Have you given the reader all the information he/she needs to understand it? Make sure you define terms before using them, and spell out acronyms the first time they appear.
• The last paragraph (sometimes two) of the introduction is where you finally arrive at your work. Be explicit about how your contribution adds to the work that has come before. Don't discuss your conclusions; that comes later. But if you've done your job, your reader will now be thinking that it's obvious that somebody needs to do exactly what you have done.

3. The Main Body of the Paper

   But before you start writing, work through the following key issues:

1. What is your most important result? What is the one thing that you want the reader to remember from your paper?
2. How can you best present that result? The answer is probably "graphically"---which makes the issue how to design the one perfect figure to show this one most-important thing.
3. What other supporting figures would help the reader? Remember, the goal is not for you to show everything you did, but for the reader to understand the results.

• Labeled axes, with numerical values and units;
• Error bars on any plotted data; and
• A caption, clearly explaining what is being plotted.

   Precise language is especially important here. Be careful to say exactly what you mean. If you mean "filter", don't write "color"; if you mean "luminosity", don't write "magnitude". Use the right word, not its second cousin. You need to communicate in a way that will be understandable to somebody who has not been working with you, and has not been sitting in on your meetings with your advisor/professor. Be conscious of the distinction between your private jargon and the proper vocabulary of your discipline, and remember that it's your job, not the reader's, to translate.

   And although this is not strictly a point about writing, one can't overemphasize the importance of the error analysis. Don't shirk the responsibility to do a statistically legitimate error estimate on any measured quantity. Guessing ("Oh, that's maybe good to 20 percent or so...") doesn't count. If it doesn't have an error bar, it isn't science.

4. Discussion and Interpretation

   First comes the meaning of your quantitative results themselves. You may have measured the central B-V color of M33 with unprecedented accuracy, but so what? Your measurement has meaning only to the extent that it tells us something about the natural world. This places a non-trivial burden on you to understand (in this example) what physical processes influence the optical color of a galaxy, and then to logically infer what your measurement implies about those processes. Can you rule out the presence of dust? Can you put a limit on the rate of star formation?

   This exercise in logic will probably allow (i.e., require) you to revisit the papers you cited in your introduction, and explain how your results fit in with previously published work. Be forthright about where your work agrees with or differs from others'. If there is agreement, be explicit about what that implies; it may be increased confidence in some published model, or a recognition that this particular object is unusual in an important way. If there is disagreement, try to suggest a reasonable explanation, but avoid unsupported speculation.

5. The End

6. Miscellaneous Sticky Points

• Active vs. Passive Voice. In some fields, active voice (e.g., "we observed the nebula", as opposed to "the nebula was observed") is strongly frowned upon. In astronomy, active voice is encouraged. But, of course, this doesn't rule out the use of passive voice where it is appropriate.
• Tenses. Generally, you should stick to present tense, even when you are reporting on the past work of others; e.g., "Smith and Jones (1994) show that dark matter dominates NGC8153." An exception is if you are talking about work in a historical context: "This phenomenon was first discovered by Zwicky (1930)." When describing your own observations and data reduction, you can use past tense ("the data were flat-fielded using IRAF"); but the results of that work should be described in present tense ("the flat-fielded image contains 14 resolved sources"). Remember that statements about astronomical objects should always be in present tense ("the galaxy has a strong color gradient") unless you are specifically talking about a past event or an object that no longer exists ("the supernova progenitor star was a type O supergiant").
• 1st vs. 3rd Person. In astronomy, writing in the 1st person is encouraged (e.g., "we observed M51", "we show the results in Table 2", etc.). In the case where there is only one author, opinions differ on whether one should use the "editorial we", or merely charge ahead in 1st person singular ("I"). The latter is more honest, and is becoming more common, but it can sound annoying if it is overused.

6. Additional Resources