astronomy

Newcomb's Tables of the Sun

Newcomb's Tables of the Sun is a astronomy topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Newcomb's Tables of the Sun rather than just read about it. In short: Newcomb's Tables of the Sun (full title Tables of the Motion of the Earth on its Axis and Around the Sun) is a work by the American astronomer and mathematician Simon Newcomb, published in volume VI of the serial publication Astronomical Papers Prepared for the Use of the American Ephemeris and Nautical Almanac. The work contains Newcomb's mathematical development of the position of the Earth in the Solar System, wh…

Key takeaways

Newcomb's Tables of the Sun belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Newcomb's Tables of the Sun to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Newcomb's Tables of the Sun from memory before moving on to harder problems.

Reference excerpt

Newcomb's Tables of the Sun (full title Tables of the Motion of the Earth on its Axis and Around the Sun) is a work by the American astronomer and mathematician Simon Newcomb, published in volume VI of the serial publication Astronomical Papers Prepared for the Use of the American Ephemeris and Nautical Almanac. The work contains Newcomb's mathematical development of the position of the Earth in the Solar System, which is constructed from classical celestial mechanics as well as centuries of astronomical measurements. The bulk of the work, however, is a collection of tabulated precomputed values that provide the position of the sun at any point in time. Newcomb's Tables were the basis for practically all ephemerides of the Sun published from 1900 through 1983, including the annual almanacs of the U.S. Naval Observatory and the Royal Greenwich Observatory. The physical tables themselves were used by the ephemerides from 1900 to 1959, computerized versions were used from 1960 to 1980, and evaluations of the Newcomb's theories were used from 1981 to 1983. The tables are seldom used now; since the Astronomical Almanac for 1984 they have been superseded by more accurate numerically-integrated ephemerides developed at the Jet Propulsion Laboratory, based on much more accurate observations than were available to Newcomb. Also, the tables did not account for the effects of general relativity which was unknown at the time. Nevertheless, his tabulated values remain accurate to within a few seconds of arc to this day. He developed similar formulas and tables for the planets Mercury, Venus, Mars, Uranus and Neptune; those of the inner planets have proved to be the most accurate.

Expressions Certain expressions have been cited in a number of other works over a long period, and are listed below. Newcomb assigns the symbol T to the time since "1900, Jan. 0, Greenwich Mean noon", measured in Julian centuries of 36,525 days.

Sun's geometric mean longitude The Sun's geometric mean longitude, freed from aberration is given as

L = 279° 41' 48.04" + 129 602 768.13" T + 1.089" T2 Authors citing this expression include Borkowski (p. 12) and the Nautical Almanac Offices of the United Kingdom and United States (p. 98).

Fictitious mean Sun Newcomb gives the Right ascension of the fictitious mean Sun, affected by aberration (which is used in finding mean solar time) as

τ = 18h 38m 45.836s + 8640184.542s T + 0.0929s T2 Authors citing this expression include McCarthy & Seidelmann (p. 13) and the Nautical Almanac Offices of the United Kingdom and United States (p. 73).

Discontinuance By 1970 the astronomical community recognized the need for improved ephemerides, which are used to prepare national almanacs. The changes required were

a new fundamental catalog of stars to replace FK4 the use of improved values of astronomical constants that had been discovered a better definition and practical realization of ephemeris time which would take advantage of atomic time a new epoch to replace 1950.0 It was decided to introduce as many changes as possible at one time in a consistent system, and the new system would go into effect for the 1984 edition of the ephemerides. "The majority of the resolutions were prepared and adopted by the General Assembly of the IAU at the 1976 and 1979 meetings." The new fundamental ephemeris was prepared by the Jet Propulsion Laboratory and named DE200/LE200. It uses numerical integration.

Notes

References

Works cited Borkowski, K. M. "The Tropical Year and Solar Calendar". Journal of the Royal Astronomical Society of Canada 85 no. 3 (1990): 121–130. McCarthy, D. D. & Seidelmann, P. K. TIME from Earth Rotation to Atomic Physics. (Weinheim: Wiley-VCH, 2009). [U.S.] Nautical Almanac Office and HM Nautical Almanac Office. "The Improved IAU System", a supplement bound with The Astronomical Almanac for the Year 1984. (Washington and London: U.S. Government Printing Office and Her Majesty's Stationery Office, 1983). Nautical Almanac Offices of the United Kingdom and United States of America. Explanatory Supplement to the Ephemeris. (London: Her Majesty's Stationery Office, 1961). Newcomb, Simon. Tables of the Four Inner Planets, 2nd ed. (Washington: Bureau of Equipment, Navy Dept., 1898).

Worked examples

Example 1 — a first encounter with Newcomb's Tables of the Sun

Start with the simplest possible case. Write down what Newcomb's Tables of the Sun claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In astronomy, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Newcomb's Tables of the Sun before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Newcomb's Tables of the Sun ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Newcomb's Tables of the Sun

In research: Newcomb's Tables of the Sun appears in astronomy research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Newcomb's Tables of the Sun in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Newcomb's Tables of the Sun is common in secondary-school and first-year university syllabi. It links to neighbouring topics Astronomy books, so understanding it makes those chapters shorter.
In everyday life: Look for Newcomb's Tables of the Sun outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Newcomb's Tables of the Sun in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Newcomb's Tables of the Sun means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Newcomb's Tables of the Sun out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Newcomb's Tables of the Sun in simple terms?

Why does Newcomb's Tables of the Sun matter?

Because it connects several astronomy ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Newcomb's Tables of the Sun?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Newcomb's Tables of the Sun.