An Etymological Dictionary of Astronomy and Astrophysics
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The incompatibility between → Galilean relativity and Mawxell's theory of → electromagnetism. Maxwell demonstrated that electrical and magnetic fields propagate as waves in space. The propagation speed of these waves in a vacuum is given by the expression c = (ε₀.μ₀)^-0.5, where ε₀ is the electric → permittivity and μ₀ is the magnetic → permeability, both → physical constants. Maxwell noticed that this value corresponds exactly to the → speed of light in vacuum. This implies, however, that the speed of light must also be a universal constant, just as are the electrical and the magnetic field constants! The problem is that → Maxwell's equations do not relate this velocity to an absolute background and specify no → reference frame against which it is measured. If we accept that the principle of relativity not only applies to mechanics, then it must also be true that Maxwell's equations apply in any → inertial frame, with the same values for the universal constants. Therefore, the speed of light should be independent of the movement of its source. This, however, contradicts the vector addition of velocities, which is a verified principle within → Newtonian mechanics. Einstein was bold enough to conclude that the principle of Newtonian relativity and Maxwell's theory of electromagnetism are incompatible! In other words, the → Galilean transformation and the → Newtonian relativity principle based on this transformation were wrong. There exists, therefore, a new relativity principle, → Einsteinian relativity, for both mechanics and electrodynamics that is based on the → Lorentz transformation.

→ Newton; → Maxwell; → incompatibility.

A method for finding roots of a → polynomial that makes explicit use of the → derivative of the function. It uses → iteration to continually improve the accuracy of the estimated root. If f(x) has a → simple root near x_n then a closer estimate to the root is x_n + 1 where x_n + 1 = x_n - f(x_n)/f'(x_n). The iteration begins with an initial estimate of the root, x₀, and continues to find x₁, x₂, . . . until a suitably accurate estimate of the position of the root is obtained. Also called → Newton's method.

→ Newton found the method in 1671, but it was not actually published until 1736; Joseph Raphson (1648-1715), English mathematician, independently published the method in 1690.

Of or pertaining to Sir Isaac Newton or to his theories or discoveries.

Newtonian, from → Newton + -ian a suffix forming adjectives.

A particular solution of the → general relativity when the → gravitational mass is small. The → space-time is then approximated to the → Minkowski's and this leads to → Newtonian mechanics.

→ Newtonian; → approximation.

Same as the → gravitational constant.

→ Newtonian; → constant; → gravitation.

The use of → Newtonian mechanics to derive homogeneous and isotropic solutions of → Einstein's field equations, which represent models of expanding Universe. The Newtonian cosmology deviates from the prediction of → general relativity in the general case of anisotropic and inhomogeneous models.

→ Newtonian; → cosmology.

Any → fluid with a constant → viscosity at a given temperature regardless of the rate of → shear.

→ Newtonian; → fluid.

The focus obtained by diverting the converging light beam of a reflecting telescope to the side of the tube.

→ Newtonian; → focus.

The limit attained by → general relativity when velocities are very smaller than the → speed of light or gravitational fields are weak. This limit corresponds to the transition between general relativity and the → Newtonian mechanics. See also → Newtonian approximation.

→ Newtonian; → limit.

A system of mechanics based on → Newton's law of gravitation and its derivatives. Same as → classical mechanics.

→ Newtonian; → mechanics.

A potential in a field of force obeying the inverse-square law such as → gravitational potential.

→ Newtonian; → potential.

The Newton's equations of motion, if they hold in any → reference frame, they are valid also in any other reference frame moving with uniform velocity relative to the first.

→ Newtonian; → principle; → relativity.

The laws of physics are unchanged under → Galilean transformation. This implies that no mechanical experiment can detect any intrinsic diff between two → inertial frames. Same as → Galilean relativity.

→ Newton; → relativity.

A telescope with a concave paraboloidal objective mirror and a small plane mirror that reflects rays from the primary mirror laterally outside the tube where the image is viewed with an eyepiece.

→ Newtonian; → telescope.

Immediately following in time, order, place, and so on.

M.E., from O.E. next, nehst, niehsta, nyhsta "nearest, closest," superlative of neah "nigh" + superlative suffix. Cognate with Du. naast "next," O.H.G. nahisto "neighbor," Ger. nächst "next."

Podâ, literally "placed after," from *upada-, from *upa- "near, next, after," + *dâ- "to place, put," → thesis; cf. Baluci pôši "the day after tomorrow," from pô- contraction of *upa- + *aušah- "dawn," + → aurora, + suffix -i; cf. also Baluci godâ (from *uidâ-?) "then, next;" Bašâgardi, Baluci randâ "next, then."

A → Seyfert galaxy, which is the central, dominant member of the large and relatively nearby → Perseus cluster of galaxies. A powerful source of X-rays and radio emission, NGC 1275 accretes matter (→ accretion) as intercluster material falls into it, ultimately feeding a → supermassive black hole (SMBH) at the galaxy's core. NGC 1275, hosts a narrow-line radio source, Perseus A (3C 84), which interacts with the intracluster gas through its jets and bipolar outflows.

NGC, → New General Catalogue.

A prominent → star cluster, and the ionizing core of giant → H II region → N66 in the → Small Magellanic Cloud galaxy. NGC 346 hosts the largest sample of young, → massive stars in the whole SMC, containing 33 → O-type stars among which 11 are of type O6.5 or earlier. This is young massive star cluster with an estimated age of about 3 million years.

346, a serial number in the → New General Catalogue.

The most massive and luminous visible → starburst region in the Galaxy. This is our local → giant H II region lying at a distance of about 6-7 kpc in the → Carina arm (→ right ascension = 11h, → declination = -61°). Its central starburst cluster hosts the largest known concentration of extremely young, mostly unevolved → high-mass stars in the Galaxy. With an age of only 1-2 Myr for its most massive stars, NGC 3603 is one of the youngest starburst clusters known. It has about 40 known → O stars and → W-R stars, producing a → Lyman continuum flux of 10⁵¹ s^-1, about 100 times the ionizing power of the Orion → Trapezium cluster. The OB stars contribute to more than 2000 → solar masses to the cluster mass. With a bolometric luminosity over 10⁷→ solar luminosities, NGC 3603 has about 10% of the luminosity of → 30 Doradus and looks in many respects very similar to its core, → R136. A total mass of 7,000 solar masses is measured in the inner 1 pc from the cluster center, whereas the → low-mass stars extend out to at least 5 pc. The mass segregated core of the cluster, with 10⁵ solar masses per pc³, displays the highest local stellar density outside the Galactic Center region. The spectral analysis of the W-R like massive component in the cluster core (→ HD 97950) suggests a → metallicity close or equal to solar (See, e.g., Melena et al. 2008, AJ 135, 878, and references therein).

3603, a serial number in the → New General Catalogue.

A → binary star lying in the core of the Galactic → giant H II region  → NGC 3603. NGC 3603-A1 is double-eclipsing → Wolf-Rayet binary of type → WN6ha with an orbital period of 3.77 days. Their masses have been derived to be M1 = (116 ± 31) Msun for the primary and M2 = (89 ± 16) Msun for the secondary component of A1. The primary in A1 is the most massive star weighed so far (Schnurr et al., 2008, MNRAS 389, L38).

→ NGC 3603.

A galaxy discovered in 1784 by William Herschel that happens to lie nearly along the line of sight to the star → Beta Andromedae. More specifically, it lies at an angular separation of seven arc-minutes. For this reason it is known also as → Mirach's Ghost. NGC 404 is in fact a → dwarf galaxy lying at a distance of about 10 million → light-years (3.07 ± 0.37 Mpc). NGC 404 harbors a low-luminosity → active galactic nucleus powered by the lowest-mass (< 150,000 Msun) central → massive black hole (Nyland et al., 2017, ApJ 845, 50).

NGC, → New General Catalogue.