– a prefix M followed by a hyphen,
Naming of Astronomical Objects
Questions have been asked about the proper English spelling of names of astronomical objects, especially as regards capitalization of such names.
The IAU formally recommends that the initial letters of the names of individual astronomical objects should be printed as capitals (see the IAU Style Manual, Trans. Int. Astron. Union, volume 20B, 1989; Chapter 8, page S30 – PDF file); e.g., Earth, Sun, Moon, etc. “The Earth’s equator” and “Earth is a planet in the Solar System” are examples of correct spelling according to these rules.
It is emphasized, however, that language conventions are the responsibility of individual nations or groups of nations. While the IAU is willing to help to achieve a minimum degree of orthographic consistency as regards astronomical terms, it cannot undertake to do so for all languages, nor is it in the power of the IAU to enforce the application of any such conventions.
If a name is difficult to spell or pronounce, it may not be the best choice for use on maps and in presentations. Sometimes multi-word names are discouraged for this reason. The purpose of nomenclature is to provide simple, clear, unambiguous names for features.
Naming of Solar System Objects and Features
The IAU has been the arbiter of planetary and satellite nomenclature since its inception in 1919 (also see Resolution 13 of the Fourth United Nations Conference on the Standardization of Geographical Names, held in Geneva in 1982). The various IAU Working Groups normally handle this process, and their decisions primarily affect the professional astronomers. But from time to time the IAU takes decisions and makes recommendations on issues concerning astronomical matters affecting other sciences or the public. Such decisions and recommendations are not enforceable by any national or international law; rather they establish conventions that are meant to help our understanding of astronomical objects and processes. Hence, IAU recommendations should rest on well-established scientific facts and have a broad consensus in the community concerned.
The eight major planets in our Solar System and Earth’s satellite have official IAU names. The names of the major planets were already in common use when the IAU formed in 1919 (e.g. scientifically, in professional and amateur astronomy literature, in nautical almanacs, etc.). However, the names of the planets have been included in wording for IAU resolutions multiple times since the IAU’s founding and these names can be considered formally adopted by the IAU membership. While there are cultural names for the planets and Earth’s satellite in other languages, there are classic names for the major planets and Moon which appear in English language IAU resolutions and the IAU Style Manual (which was approved by an IAU resolution in 1988).
What follows is a partial list of instances of use of these planet names, but it is by no means exhaustive. This compilation demonstrates, however, that the names of the planets and Moon have appeared in IAU resolutions (or in wording of documents approved by IAU resolution) approved by IAU General Assemblies multiple times, and continue to be in ubiquitous use.
- 1976: The names of the then major planets (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto) and the Earth’s satellite (Moon) appear in IAU Resolution No. 10, which was approved by the XVIth General Assembly of the IAU in Grenoble, France in 1976.
- 1988: The IAU XXth General Assembly — which met in Baltimore in 1988 — approved IAU Resolution A3 on the Improvement of Publications, which recognized “the importance of identifying astronomical objects by clear and unambiguous designations” and recommended “that the authors and editors of the astronomical literature adopt the recommendations in the IAU Style Manual“. The “IAU Style Manual (1989): The Preparation of Astronomical Papers and Reports” by George A. Wilkins (President of IAU Commission 5) was published in December 1988, and reprinted as Chapter VIII (“IAU Style Book”) in the “Transactions of the International Astronomical Union Vol. XXB: Proceedings of the Twentieth General Assembly Baltimore 1988” (1990; ed. Derek McNally; Kluwer Academic Publishers; Dordrecht). The IAU Style Manual Sec. 5.25 lists the names of the “principal planets” as Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto.
- 2006: IAU Resolution B5 (Definition of a Planet in the Solar System) explicitly lists the eight planets Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. While Resolution B5 defined the category of dwarf planet, Resolution B6 explicitly lists Pluto as an example.
One also sees these planet names are used ubiquitously by modern IAU working groups (e.g. IAU Working Group for Planetary System Nomenclature, the IAU Working Group on Cartographic Coordinates and Rotational Elements in their recent report by Archinal et al. 2011 Celestial Mechanics and Dynamical Astronomy, Vol. 109, Issue 2, pp. 101-135, etc.).
So the IAU does recognize official names for the major planets (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune) and Earth’s satellite (Moon).
Planetary Features
Planetary nomenclature, like terrestrial nomenclature, is used to uniquely identify a feature on the surface of a planet or satellite so that the feature can be easily located, described, and discussed. The procedure is as follows:
- When the first images of the surface of a planet or satellite are obtained, themes for naming features are chosen and names of a few important features are proposed, usually by members of the appropriate IAU task group.
- As higher resolution images and maps become available, names for additional features may be requested by investigators mapping or describing specific surfaces or geological formations.
- At this point, anyone may suggest that a specific name be considered by a Task Group, but there is no guarantee that the name will be accepted. Please submit name requests via this form.
- Names successfully reviewed by a task group are submitted by the task group chair to the Working Group for Planetary System Nomenclature (WGPSN).
- Upon successful review by vote of the members of the WGPSN, names are considered approved as official IAU nomenclature, and can be used on maps and in publications. Approved names are immediately entered into the Gazetteer of Planetary Nomenclature, and posted on its web site. Any objections to these names based on significant substantive problems or inconsistent application of normal IAU naming convention must be forwarded in writing or email to the IAU General-Secretary within three months from the time the name was placed on the web site. The General-Secretary will make a recommendation to the WGPSN Chair as to whether or not the approved name(s) should be reconsidered. The General-Secretary, in concurrence with the IAU President, may seek the advice of external consultants.
- Approved names are also listed in the transactions of the IAU (A and B).
- The categories of the planetary features are listed here.
Teacher’s Guide
To help your students analyze these primary sources, get a graphic organizer and guides: Analysis Tool and Guides
For millennia, humans have gazed at the sky and tried to make sense of what they saw there. Many of the men and women who puzzled over the dazzling displays and movements of the stars recorded their explanations in systematic ways—that is, they created models of the cosmos.
Background
These models were small versions of large systems that astronomers could hold in their minds, and that they could then set down on paper to share with their fellow stargazers. The astronomers who created them came from many different cultures and eras, and they often used very different approaches.
However, they shared many of the same methods and practices that are used by scientists and engineers today. They made observations and identified patterns. They evaluated evidence to determine the merits of arguments, and they used their models to test theories and make predictions about other cosmic phenomena.
The models in this primary source set were found in a variety of items in the collections of the Library of Congress, and span more than five centuries- -from the pages of rare 15th-century books, to educational charts, to 20th-century magazine illustrations. Today, these models can tell us not only about the ways in which their creators understood the cosmos, but also about the times in which they lived, and the nature of discovery across centuries. Teachers and students exploring science, world history, the theory of knowledge, or even philosophy can find much to discover in these age-old illustrations.
Models as Arguments about the Natural World
These models were created by many different individuals, and their creators had a wide range of perspectives on the natural world. When each model first appeared, it offered an argument–a set of claims about the universe. For example, Copernicus’ diagram of a cosmos centered on the sun served as a powerful representation of a core part of the argument of his book. Today, a student can analyze Copernicus’ images to articulate and evaluate the claims he made, just as his fellow mathematicians and astronomers did.
When Thomas Wright published his Synopsis of the Universe in 1742, he included a diagram of the theory of tides showing the moon, the Earth, and the shifting of the tides. Wright sought to show how Newton’s universal theory of gravitation explained the relationship between the movement of the moon and the tides. Close observation and analysis of this diagram can help students today understand both Newton’s theory and how to interpret these kinds of diagrams and models.
Changing Models, Changing Ideas
Scientific knowledge is always open to revision. The changing models of the cosmos show how scientists reassess and revise scientific knowledge. Studying select primary sources in chronological order can illuminate how ideas of the structure of the universe have developed over time.
A comparison of models from different eras can reveal the gradual shift from an Earth-centered universe to a sun-centered solar system, the discovery of new planets and moons orbiting other planets, and eventually the understanding that our solar system is just one of many in our galaxy. These sources clearly show that ideas change gradually–even once new discoveries are made. Older models of the universe persisted for centuries even after new evidence contradicted them. Seemingly contradictory ideas about the cosmos still exist today.
Models and Evidence
The argument made by each model’s creator depended on evidence. A close look at a particular model can reveal a great deal about the evidence that its creator used to support his or her perspective. Many major breakthroughs were triggered by new technologies for gathering evidence–from the first telescopes, to improvements in lenses, to the rise of photography and radio telescopes. For example, for many centuries astronomers largely accepted Aristotle’s notion that the moon was a perfect sphere. However, when Galileo saw the moon through a telescope and discovered that it was actually cratered and mountainous, he argued against Aristotle’s interpretation. Galileo included drawings of the moon in his treatise Sedarius Nuncius as evidence to support his argument about the nature of the cosmos.
These models may have been intended primarily for their creators’ peers and contemporaries. Today they might seem alien in their language and their assumptions. But they speak to us across the centuries about the endless drive to discover what lies beyond the Earth and about the ways in which scientific practices have shaped our understanding of the cosmos.
Suggestions for Teachers
Invite students to select and study one model from the primary source set. Ask them to speculate on what information was available to the person who created the model and consider the following questions: What assumptions about the natural world are evident in the item? How might the item have shaped the worldview of those who encountered it? You can use this activity in world history, Earth science, or astronomy classes to enrich student understanding of the era represented.
Ask students to select and study one item from the set. If this model were the only portrayal you knew, what else would you believe to be true about the universe and Earth’s place in it? What would you need to know or do to challenge this model? Include this activity in a world history or astronomy class studying historical understandings of the cosmos.
Select or ask students to choose a few items featured in the primary source set from different eras that explain the same phenomenon, such as eclipses or the movement of celestial objects. Lead a class discussion with the following questions: Which elements are consistent across time? Which elements change over time? How does current scientific thinking explain that phenomenon? This exercise would be valuable in an Earth science or astronomy class studying the origins and evolution of the universe, a physics class studying planetary motion, or world history/world cultures courses.
Each model and depiction of the universe grapples with communicating the relative size and scale of the immense universe. Present students with an array of items and ask them to identify various ways that they communicate size and scale. Ask them to consider the difficulty of communicating the vastness of space. Select one item and ask students to identify decisions that the astronomer made about where to skew the scale. What evidence do they find to indicate whether the scale is skewed intentionally or from a lack of information? These activities meet standards for Earth science studies of scale and map-reading.
TODAY
Planets
Moons
Mercury
The swiftest planet.
Venus
Earth’s superheated twin sister.
Earth
Mars
Jupiter
King of the planets.
Saturn
Jewel of the solar system.
Uranus
The original ice giant.
Neptune
The farthest planet in our solar system.
Pluto
A small world with a big heart.
Exoplanets
Planets beyond the solar system.
Our solar system can be divided into three regions: the inner solar system, the outer solar system, and the Kuiper Belt and Oort Cloud.
The inner, rocky planets are Mercury, Venus, Earth, and Mars. These worlds also are known as terrestrial planets because they have solid surfaces. Mercury, Earth, and Mars are currently being explored by spacecraft. Two rovers are on the surface of Mars. NASA’s newest rover — Perseverance — landed on Mars on Feb. 18, 2021. Three missions are in development to return to Venus.
The outer planets are gas giants Jupiter and Saturn and ice giants Uranus and Neptune. NASA’s Juno spacecraft is on an extended mission at Jupiter and ESA’s JUICE mission is on the way. NASA also is building Europa Clipper and Dragonfly to explore moons of Jupiter and Saturn.
Beyond Neptune, a newer class of smaller worlds called dwarf planets reign, including longtime favorite Pluto. NASA’s New Horizons spacecraft visited there in 2015, and is currently exploring the Kuiper Belt beyond Pluto. Thousands more planets have been discovered beyond our solar system. Scientists call them exoplanets (exo means “from outside”).
