AAS Style Guide

During his tenure as editor of The Astrophysical Journal (1952–1971), S. Chandrasekhar established guidelines for usage and style of common astronomical and astrophysical terms along with University of Chicago Press copyeditor Jeanne Hopkins. The AAS is reinforcing these mandatory guidelines for authors for uniformity and efficiency in the copyediting and production process.

Every accepted article is edited for grammatical correctness and clarity, as well as for the style consistency across the journals. The elements are laid out below. Be aware that, though this guide is ample, it is not comprehensive and all changes made by copyeditors may not be explained herein. An appendix with technical terms can be found at the end of this document.

  • Article titles are set in title case (i.e., all words have initial capital letter, but articles, conjunctions, and prepositions remain lowercase). Subtitles are preceded by a colon and the first word has an initial capital letter even if it is an article, conjunction, or preposition. In the titles of companion papers, the numeric designation of each companion must be formatted in uppercase Roman numerals and enclosed in periods (e.g., “Quantum Spin Dynamics. II. The Kernel of the Wheeler–DeWitt Constraint Operator”).
  • Section and subsection headings should also be written in title case.
  • In all titles and headings, the second word of a hyphenated combination does not take a capital (e.g., Post-collision Reaction). The only exceptions to this are X-Ray, Gamma-Ray, and Cosmic-Ray.
  • For en-rule combinations, both words are capitalized (e.g., Spin–Orbit Coupling).
  • If an author is not currently at an institution and prefers not to include a personal address, then affiliations such as “Planet Hunter,“ “Private Astronomer,” or “Independent Researcher” are acceptable.

Use the Unified Astronomy Thesaurus (UAT) concepts found at http://astrothesaurus.org/thesaurus/alphabetical-browse/. A minimum of one UAT concept is required; no maximum.

  • Acknowledgments should be gender neutral when addressing unknown persons.
  • Funding information should be included in the acknowledgments section.
  • For facility key words use Telescope facilities available at https://journals.aas.org/facility-keywords/. New facility key words can be added with the approval of the AAS journals’ data editors; please see the instructions at https://journals.aas.org/facility-keywords/ for proposing a new facility keyword.
  • Software listed in the acknowledgements or in \software{} should include at minimum the name of the software; corresponding reference citations are optional, however, appropriate software citations should otherwise be given in the main text and in the reference list.
  • All online-only elements (i.e., animations, MRTs, figure sets, etc.) are indicated in parentheses following the caption (notes) of the figure (table) they are associated with. This label is automatically inserted during typesetting and includes a link to the online-only element. Please see https://journals.aas.org/data-guide/ and https://journals.aas.org/graphics-guide/ for more information.
  • Online-only appendices are not accepted (e.g., extra PDFs).
  • Any non-table/figure related data (e.g., simulation or fitting or raw data) should be moved to an appropriate third-party repository and linked to the text by DOI. See https://journals.aas.org/data-guide/ for more details.
  • Define acronyms at their first occurrence in both the abstract and main text. After this, use the acronym only.
  • Do not use an acronym if the definition or phrase is used only once.
  • Definitions should be lower case, unless they contain proper nouns, e.g., “cosmic microwave background (CMB)” but “modified Newtonian dynamics (MOND).”
  • Common acronyms that are never defined: rms (root mean square), FWHM (full width at half maximum), IDL (interactive data language), IRAF (Interactive Reduction and Analysis Facility), NASA (except can be spelled out in acknowledgments), NATO, NIRSPEC, RHESSI, ROSAT, SExtractor.
  • Punctuate equations (inline and numbered) as part of the sentence they appear in. If an equation concludes a sentence, it should be followed by a period, and if it appears at the end of a clause (or acts as part of a list), it should be followed by a comma.
  • Fractional minute symbols: Right ascension and declination in text and equations are given in the form below. (Note the position of second and fractional minute symbols above the decimal point in the fractional unit.)

  • Vectors are distinguished by bold type (e.g., B); arrows over symbols are not used to denote vectors in AAS articles. Vector operations and operators (e.g., ×, ∇) are also set in bold.
  • Do not use hyphens between numbers and their units (e.g., 5 cm thick, not 5-cm thick).
  • Fractions in the main text that are not associated with a unit should be spelled out, e.g., one-third, one-ninth, etc. Fractions associated with a unit in the main text should be shilled (1/2), not stacked (½). Note that stacked fractions are preferred in Equations.
  • Footnote numbering is continued from the affiliations; thus, if there are three affiliations (numbered 1—3), the first footnote in the article will be labeled with a “4.”
  • When a footnote appears at the end of a sentence, the footnote symbol is placed outside the full stop (e.g., “period.3”).
  • Footnote symbols next to numbers or mathematical variables should be avoided, so they are not mistaken for power indices.
  • Each table must be mentioned at least once in the text, and table citations must appear in numerical order.
  • Every table should have a concise title (less than a line), which should be set in title case (like the article title and section headers). All details describing the contents of the table should appear in the Notes section following the table.
  • Each table column must have a heading (table column headings are also set in title case).
  • Tables must not include color or shading. If color/shading cannot easily be changed to an allowable font, such as bold or italic, then the table will be converted into a figure.
  • Tables should not contain empty rows, or use en dashes or em dashes to indicate that there is no data in a cell. These will be changed to ellipses (…).
  • Tables may not include vertical rules (though horizontal rules are permitted).
  • Table footnotes are denoted with lower case superscript letters, e.g., “a,” “b,” “c,” etc.
  • Each figure must be mentioned at least once in the text, and figure citations must appear in numerical order.
  • In multipart figures, the captions should distinguish each component of the figure ((a), (b), (c), etc.). If the figure has no labels, then panels should be referred to by position (top right, top left, middle, bottom, etc.). All lines (solid, dashed, dotted–dashed, dashed–dotted, etc.) and symbols (circles, squares, triangles, etc.) should be explained in the caption.
  • Note that each appendix must include at least one sentence of text. If the appendix is meant to include tables or figures, please include citations to them in the appendix text.
  • Figures, tables, and equations that appear in Appendices should be numbered independently from those in the main text (i.e., they should begin, A1, A2, A3, B1, B2, C1, C2, etc.)
  • For references with more than five authors, the last name and initials of the first three authors should be listed, followed by a comma and “et al.” For references with five authors or fewer, the last name and initials of all five authors should be listed.
  • “In press” and “submitted” articles are included in the reference list with the name of the journal they have been submitted to. Please provide the preprint link if available.
  • “In preparation” and “personal/private communication” sources are cited in-text only; year and first initial(s) with surnames must be included.
  • Journal abbreviations follow NASA ADS format. A list of common journal abbreviations is available at http://adsabs.harvard.edu/abs_doc/journals1.html.
  • If your paper has an associated DOI data set or software (e.g., Zenodo, MAST, CANFAR), it will be treated as an online-only element if it was created for the article. Otherwise, any other DOI data sets or software referenced will be cited in the text and included in the reference list.
  • Software (and Data References) should include a version number if possible.
  • If your article includes an associated Journal of Open Source Software (JOSS) DOI, please note it is required that this source be cited in the text and appear in the reference list.
  • All references must be cited in the text and all citations (in the main text and tables) must have a corresponding reference, or they will be deleted.
  • Be careful to use the correct TeX coding when inserting an in-text citation that is active in a sentence, i.e., “according to Smith et al. (2019),” to prevent the citation from being set apart from the text and disrupting the meaning of the sentence, i.e., “according to (Smith et al. 2019).”
  • Parenthetical citations are not allowed in the abstract as it is meant to stand alone from the main text and therefore citations do not link to the reference list. If the citation is integral to the sentence, then the year is not included, e.g., “according to Smith et al.”
  • Note that for general language styling the AAS follows the Chicago Manual of Style (CMOS) and MerriamWebster Dictionary.
  • For guidance on prefix hyphenation, see Section 7.89 of CMOS.
  • See the appendix for a list of compound words that are commonly set as two words when they are used as nouns but hyphenated (or closed up) as modifiers (note that this list is not comprehensive).
  • US spelling is mandatory in AAS journals. Non-US spelling will be retained only in proper nouns and names (e.g., Square Kilometre Array). For example, common UK spellings such as amongst, towards, whilst, firstly, secondly are changed to the US equivalent spellings of among, toward, while, first, second.
  • “a” vs. “an”: use according to sound of what actually appears on the page (e.g., an S/N, an H I region, an n-point configuration, but a Hermitian operator).
  • “onboard” vs. “on board” (e.g., The ROSAT onboard spectrograph; the spectrograph on board ROSAT.)
  • When units appear in the text without values, they should be spelled out, e.g., submillimeter, kiloparsec, arcsecond. (For example, “over several gigayears” not “over several Gyr,” but “for 10 Gyr”; kiloparsec scale; millimeter wavelength.)
  • Use italic text sparingly. If necessary, use italic text to emphasize a new/important term on first mention, but set the term in Roman font thereafter.
  • Quotation marks: use double quotation marks. Single quotation marks should denote a quote within quote. Note that periods and commas at the end of quotes appear within the quotation marks, but colons and semicolons appear outside of the quotation marks.
  • Numbers less than 10 (0–9) without units should be written as words (e.g., four times, six cases). An exception is where they are in a list with larger numbers, e.g., “The experiment was repeated using 4, 11, 17, and 25 iterations”), where a mixture of words and numbers must be avoided.
  • Dates are written in the following order: year, month, day; e.g., 1996 January 1.
  • Use versus in text, but vs. in figure captions.
  • Space-based craft should be set in roman, whether decommissioned or not.
  • Lists: items in a displayed, indented list should be labeled 1, 2, 3, 4; a, b, c, d; or i, ii, iii, iv (a bulleted list will be converted to one of these options in the proof). In-text lists may use any of these labels, but they will be enclosed in parentheses, e.g., (1), (2), (3); (a), (b), (c).
  • No abstract included with an erratum.
  • Affiliations must match the original published article.
  • Any figures, tables, or equations referenced will retain the numbering of the published article (e.g., if Figure 13 has been corrected, it will be referenced as Figure 13, and not renumbered as Figure 1).
  • 1D, 2D, 3D: do not require definitions, but definitions are not prohibited (if defined, only define on first appearance)
  • Abell catalog: e.g., Abell 2666 formatted as A2666 throughout the text
  • Alphanumeric designations: if one letter, close up (e.g., M31); if more than one letter, add a space after the letters (e.g., NGC 1468, NGC 6866). Note the exception of gravitational waves, beginning “GW,” which are always closed up (i.e., GW150914).
  • antennas (metal rods) vs. antennae (sensory organs on anthropods)
  • antiparticle, antimatter (no hyphen)
  • Astronomical objects (uppercase): Earth (planet), Galaxy (Milky Way), Gaussian/Gauss, Kuiper Belt, Local Group (astronomy), Mercury (planet), Moon (Earth’s), Sun
  • Astronomical objects (lowercase): earth (electrical/soil), galaxy/galaxies (general), local group (math), mercury (element), moon (not Earth’s), solar system, universal, universe
  • bandpass, bandwidth (one word)
  • baseband, baseline (one word); base length, base level (two words)
  • beamwidth (one word)
  • Big Bang (capitalized)
  • black hole (two words)
  • blackbody, graybody (one word)
  • BL Lacertae objects, also BL Lac objects (spell out in titles; do not use BL Lac or BL Lacs)
  • blueshift, grayshift, redshift; blueward, redward (one word)
  • Cerenkov (not Cherenkov)
  • Cloud: Large Magellanic Cloud, Small Magellanic Cloud (Large Cloud; Small Cloud; the Clouds)
  • database (one word); data cube, data point, data set (two words)
  • declination abbreviated as “decl.” in the text and “Decl.” in table column headings; right ascension abbreviated as “R.A.”
  • Directions: written out (southeast) or abbreviated (SE) allowed, but be consistent. Use abbreviations in tables and with numbers. Use lowercase for northern and southern hemisphere, unless referring to Earth’s Northern and Southern Hemispheres.
  • disk (not disc, unless referring to a thin, circular object such as a CD or DVD)
  • eigenfunction, eigenmode, eigenvalue, eigenvector (one word)
  • error bar(s) (two words)
  • freefall (noun, adjective)
  • globular cluster (not globulars)
  • Heliocentric Julian Date (HJD; use commas in date, e.g., 2,444,000.235)
  • Keck I and II (not Keck 1 and 2)
  • Latin phrases (a priori, in situ) are regular font, not italic
  • line width (two words)
  • Markov Chain Monte Carlo (note that “Chain” should be capitalized)
  • Maunakea (not accepted Mauna Kea)
  • Milky Way (MW): the Milky Way, not Milky Way Galaxy
  • northeast, northwest, southeast, southwest (directions should not be hyphenated; however, en dash should be included when movement is being indicated, i.e., north–south)
  • ohmic (lowercased)
  • parameterize (note spelling)
  • pointlike (one word)
  • protogalaxy (general); proto-Galaxy (Milky Way)
  • Seasons: fall, spring, summer, winter (set lowercase)
  • semimajor, semiminor (one word)
  • sigma: set using the Greek letter symbol (σ)
  • SN, AGN, PN: plural forms of SNe, AGNs, PNe may be used, but are not required
  • S/N is used for “signal-to-noise ratio”; SNR is used for “supernova remnant”
  • spacetime, spacecraft (one word)
  • starspot (one word)
  • sunlit, sunspot, sunward, sunlight, sunshine, sunbeam (lowercased; one word)
  • super star cluster (three words); supercluster (one word)
  • supergalactic, supergiant, superluminal, supermultiplet, superradiant (one word); super-Earth, super-Kamiokande (hyphenated)
  • time step (two words); timescale (one word)
  • trans-Neptunian (hyphenated)
  • wave band, wave front, wave function, wave mechanics, wave noise, wave plate, wave zone (two words); waveform, waveguide, wavelength, wavenumber, wavevector (one word)
  • website (lowercase; one word)
  • best fit (n.); best-fit (adj.)
  • broad band (n.); broadband (adj.)
  • field of view (n.); field-of-view (adj.)
  • line of sight (n.); line-of-sight (adj.)
  • main sequence (n.); main-sequence (adj.)
  • narrow band (n.); narrowband (adj.)
  • point source (n.); point-source (adj.)
  • rest frame (n.); rest-frame (adj.)
  • steady state (n.); steady-state (adj.)

The following words are always hyphenated:

  • zero-point
  • radio-loud, radio-quiet, and radio-loudness
  • metal-poor and metal-rich
  • flat-fielding
  • n-body
  • x-axis, y-axis, z-axis (hyphenated with italic letter)