# Tag Info

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The AU is, by definition, exactly 149,597,870,700 m. This is based not on a distance to the sun (which varies) but on the shape of an ellipse that closely approximates the orbit of the Earth. An ellipse has two foci. In a Keplerian, two-body orbit, the combined centre of mass of the two bodies lies at the focus of the ellipse. For the Earth/sun this is only ...

20

No, there is no special name for the closest supermoon. Besides, the very name “supermoon” was coined by an astrologer, NOT an astronomer, and it is basically all just media hype. During a so-called “supermoon,” our satellite is on average 15% larger and 5% brighter than during a regular full moon. Since the previous full moon dates from a month before (the ...

9

To directly answer your question: There is no "precise" definition of the term "supermoon." Term Origin: The origin of the term is generally attributed to the astrologer Richard Nolle in 1976. As Wikipedia notes, "In practice, there is no official or even consistent definition of how near perigee the full Moon must occur to receive ...

9

You are mixing the rotation of the body around a barycenter with its moons, and the rotation of the body around its own center. For a bound rotation like Pluto and Charon both have to have the same rotation period - yet both have to be present. Thus Pluto's axis of rotation of course intersects its surface - it rotates around its own axis at exactly the same ...

5

Asteroseismology effectively measures the sound speed inside a star by finding the characteristic oscillation frequencies of a star. The sound speed depends on the composition because the pressure at a given temperature depends on the average mass of a particle in a gas. As the star gets older, it turns its hydrogen into helium, changing the composition, the ...

5

I'll just add a supplement to @planetmaker's answer. As long as a body is distinct and not connected to anything else, it will have a center of mass. If the body is roughly spherical its center of mass will be near it's middle. The body's rotational axis by definition passes through its center of mass, and is parallel to it's own angular momentum vector. If ...

4

The IAU website has this draft definition of "planet" and "plutons" page, published on 16 August 2006 in Prague. It says (emphasis mine): The world's astronomers, under the auspices of the International Astronomical Union (IAU), have concluded two years of work defining the difference between "planets" and the smaller "...

4

What was the definition of a planet before August 24, 2006? I think this deserves a bit more of an answer because it's not quite so simple. Yes, it's true that there was no formal definition of what a planet was prior to the 2006 vote, but essentially everyone knew what was and wasn't a planet, just as we know what is and isn't a star, though the boundary ...

4

I've noted before that the IAU naming critera are guidelines rather than laws of nature. If applied to Jupiter's moons the four Galilean satellites would probably be "planets" (they don't share their orbits with anything else of comparable size and are large enought to be in hydrostatic equilibrium) There is a mean-motion resonance 4:2:1 between ...

4

a) What is the definition of completeness? Completeness is the number of objects in a data set that are detected over the number that exist. In astronomy, completeness is often estimated for a particular apparent magnitude or flux density. As an example, for sources that are as bright as the Sun (-27 magnitude), we have a completeness of 1. That is, we’...

4

Milky way obviously is an English word with that literal meaning a way (path) covered in milk. So it's not exactly derived. But it is a literal translation from Latin 'via lactia' and the Greek γαλακτικός κύκλος (milky circle - galaktikos kýklos, hence the word Galaxy). It resembles our own Galaxy's appearance on the night sky as a diffuse, slightly milky ...

3

@ProfRob has already given a good answer to the question, but I wanted to add just a little more detail addressing the observational data side. As Rob already stated, the fundamental data often come (these days) from satellites like Kepler or TESS, which can measure a star's brightness with very high precision, over an uninterrupted period of many days. So ...

3

The sun's center is not the solar system center of mass and sun is not so big for this question to be important. Just compute the ratio of the quantities — you will find that the difference is negligible. There is a more important problem: the orbit of the earth is elliptical, not circular. So the distance to the sun is not constant. Just take it as ...

3

"What" is straightforward: L4 and L5 are two points on an orbit that are 60 degrees ahead and 60 degrees behind the planet, and so move as the planet orbits. If the planet is less than about 1/25 of the mass of the central object, then a combination of centrifugal and Coriolis forces will cause the L4 and L5 points to be places where a third body ...

3

$$1^{c}=57.2958^{\circ}=57.3\times3600=206265″$$ $$\Longrightarrow\theta_{\rm arcsec}=\left(\frac{d}{D}\right)\times206265$$

2

For an aircraft there are three principal axis: Pitch, roll, and yaw. I never heard the terms used in astronomy, but it does not seem to be too far-fetched in your setup, so I am confident: A roll-angle would correspond to $\theta$ of the Euler angles. PS: The drawing can be found on both wiki pages.

2

Tl;Dr: It is a matter of consideration if you want to call Kuiper belt bodies/Oort cloud bodies "asteroids" or not. Long answer: The Oort cloud defines the cosmographic boundary of the Solar System and the extent of the Sun's Hill sphere and hence it is loosely bound to the Solar System, and thus is easily affected by the gravitational pull both of ...

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It is the first one, i.e. as soon as the heavenly body can be first seen. Here a definition from http://www.ga.gov.au/scientific-topics/astronomical/astronomical-definitions Sunrise is defined as the instant in the morning under ideal meteorological conditions, with standard refraction of the Sun's rays, when the upper edge of the sun's disk is coincident ...

2

In the linked article by A. Bouchard and another by J. Daley, the words "in the journal Lunar and Planetary Science" link not to a journal article but to a poster in a K-12 education session at the 2017 Lunar and Planetary Science Conference. First author Kirby Runyon told Universe Today in 2017 that he would not submit this geophysical definition ...

2

No, as ‘coronal mass ejection’ is defined ambiguously and refers to an event that is not physically bound to some exact limit and therefore cannot have an undisputable lowest limit value, in the mathematical sense, in any parameter. For example, the Oxford dictionary states: Coronal Mass Ejection. Noun - Astronomy. An event in which a large cloud of ...

1

James K's answer, which seems cogent and self-referential enough that I'm willing to buy it without researching his points would, by the logic of his points, require it to be the center of the sun. This is mainly because the foci are mathematical points, not smeared objects in real life that have "width", so to speak, and even vary as the sun ...

1

Interesting questions! I'm not sure if I can answer your questions fully, but I'll share what I know and have found. Is the term Ellerman bombs really widely used? In the field of heliophysics, the phrase "Ellerman bomb" is more or less widely used, in the sense that various approaches to understanding the phenomenon use the term. For some ...

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Yes, very much so. The lines or circle of constant longitude always form a great arc which intersects with the poles; thus it always has the same length. A circle of constant latitude varies in circumference: the largest is at the equator while it has intermediate length at intermediate latitudes and no length anymore when you reach the pole. See e.g. that ...

1

I assume that $L$ stands for lumniosity, i.e. energy emitted per time interval, and the index is refering to the respective band: $L_{H \alpha}$ is the lumniosity of the visible spectral line in the Balmer series with $656.28 {\rm nm}$ wavelength $L_B$ might be the lumniosity for B band, i.e. for radio frequencies between $250\ldots 500 {\rm MHz}$, or for ...

1

Based on the history of the Wikipedia article for planet preceding the IAU 2006 vote, there was no formal definition. So basically, a planet was just any body from this list of nine objects.

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