# Tag Info

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Yes, Pluto is still a dwarf planet. According to the IAU website, it still fits the criteria for a dwarf planet, fails to meet the criteria for a planet, and still carries the "dwarf planet" label, whatever its future status may be. I'm sorry I can't provide a longer or more detailed answer, but this is really a yes-or-no question.

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Planets For a body to be classified as a planet it must have a few physical characteristics: Mass It must have enough mass to have a strong enough gravity to overcome electrostatic forces to bring it to a state of hydrostatic equilibrium. Hydrostatic equilibrium is important because early in a planets life it is nearly entirely fluid, crust and all ...

9

A galaxy group is a set of galaxies that are close together and gravitationally bound, i.e. barring outside influences they will stay together indefinitely. That means a galaxy that is in the space occupied by the group but "passing through" it at a high velocity would not be considered part of the group. The upper limit for calling it a group is roughly 50,...

9

That actual IAU Resolution B5 adopted at the IAU General Assembly in 2006 states: (1) A planet is a celestial body that: (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit. The ...

8

Spectral type is determined by (and is an indicator of) photospheric temperature and surface gravity. The classification of G2V applies to a star with a photospheric temperature of about 5800K and a surface gravity of about 100-1000 m/s$^{2}$. The Sun's temperature and gravity have not changed greatly since it first appeared on the "zero age main sequence" -...

8

The Wikipedia article on stellar classification has the full list of letters: Class Surface Temperature Notes O > 33,000 K B 10,000 - 33,000 K A 7500 - 10,000 K F 6000 - 7500 K G 5200 - 6000 K K 3700 - 5200 K M 2000 - 3700 K L 1300 - 2000 K L T and Y are those new letters T 700 - 1300 K Y < 700 K History This Cornell doc explains much of ...

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In 2006 the Internaional Astronomical Union (IAU) (that's a download link, 85KB) came to the resolution that a planet is: a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood ...

7

The original Hertzsprung-Russell diagrams constructed by Henry Russell and Eijnar Hertzsprung consisted of absolute magnitude on the y-axis and a spectral type or an indicator of spectral type on the x-axis. Below you can see an original HR diagram produced by Russell in 1913. When the diagrams were constructed, it was not at all clear what the sequence of ...

7

Originally, what was plotted was luminosity against colour, and by colour I mean the wavelength of the peak intensity. Short wavelengths on the left, and long on the right, as you would expect. Now since stars emit (nearly) black body radiation, there is a close relationship between colour and temperature. I suspect that the reason that the x axis isn't ...

6

There is no 1:1 mapping between density and composition/structure. You have to look at detailed planetary models. For example, some hot Jupiters are extremely dense ($\geq 10$ g/cm$^3$) but they are undoubtedly gas giants. The origins of this diversity are the source of much speculation and theory, but are certainly within the realms of known physics. An ...

6

Part of the problem here is semantics. The meaning of "planet" was really poorly defined prior to 2006 (and some argue that it still is). In the early 2000's, this started to become an issue. You can blame Mike Brown. In January 2005, Mike Brown's team at CalTech in Pasadena, California, discovered an object we now know as Eris (they nicknamed it Xena ...

5

The dividing line between star and brown dwarf is the mass at which hydrogen fusion via the pp-chain occurs at its core. A brown dwarf below this mass limit will never reach a sustainable equilibrium due to this reaction and will continue to cool as it gets older. A star will reach the long-lived main sequence. The dividing line between planet and brown ...

5

Inner. The entire asteroid belt is in the Inner Solar System (now). The definition of "Inner" vs. "Outer" is non-arbitrary, based on the current "frost line", approx. 5 a.u. radius. https://en.wikipedia.org/wiki/Frost_line_%28astrophysics%29 https://en.wikipedia.org/wiki/Solar_System#Inner_Solar_System

5

The classification of stars using spectral class is a very useful classification when considering the properties of (the atmosphere of) a star at that moment. If you consider the different stages in human development (embryo, fetus, infant, toddler, etc...), for instance, here one person also continuously changes its class. So it is not strange/uncommon/...

4

The term can be traced back to the theoretical work of C.C.Lin in explaining the spirals as due to density waves in galactic discs. A paper from 1970 discusses the "Existence of 'Grand Design'". Note the use of "scare quotes", suggesting that the term was new and would not be widely recognised by his readers. Chia-Chiao Lin was an important Chinese/...

4

Cepheid variable stars and exoplanets transiting stars have very different light curves (the relation between brightness and time). Exoplanet light curve from NASA: Cepheid variable light curve from astronomynotes.com: Also, as Rory Allsop points out, the scale of the change in brightness is very different. Cepheid variables can be seen at great distances,...

4

Neutron stars and black holes do not have assigned spectral types since they do not have a measurable optical/IR spectrum - which is the basis for assigning a spectral type. There are many classifications for systems containing black holes and neutron stars. They are not related to the letter-based spectral types of "normal" stars or white dwarfs, but more ...

4

To respond to the question as is: yes the paper is trying to point out that the concensus was not scientific. However, this claim is not true at all. In order to understand how classifications within the solar system are made, one can look at the history of the planets. The short answer is, the demotion of a planet is a result of much scientific consensus ...

4

Capitalization is critical here. (As is knowing which classification system is being used.) The traditional spiral stages (going back to Hubble) are Sa - Sb - Sc; this was a sequence from more centrally concentrated (more dominant central "bulge") + smoother disk + more tightly wrapped spiral arms (Sa) to less centrally concentrated (smaller or even ...

3

If they wanted to make this paper about Pluto, why would they not just discuss Pluto? You may be right that the comment about voting could be linked to the Pluto debate, but I don't see any reason why they would need to conceal their intentions. I think it is more likely that they are actually researching and discussing asteroids, and they have linked their ...

3

Like in each of the other cases you mention, when dividing really big planets from really small stars you're drawing a bright line across a continuous range of objects. Whenever you do that, you're going to get legitimate and reasonable disagreement, because different people with different purposes will see a different place to draw the (ultimately ...

3

Small objects in space are hard to detect and characterise. Compare the tesla with another small solar system body: 2015TC25, It is currently about 0.3AU (3/10 of the distance from Earth to the sun) and it has a magnitude of about 30. That is perhaps detectable if you know exactly where to look. It would not be "discoverable" at this distance, with current ...

3

Galaxies evolve from spiral to elliptical. The spirals are formed by patterns of new star formation in the disk surrounding the bulge, which contains mostly old stars. As galaxies run out of hydrogen gas clouds, which is the raw material from which stars are formed, then no new stars form, and with no new star formation, the complex structures of the arms ...

3

If you take a look at the Hertzsprung-Russell Diagram that helps us to classify stars (c) Wikimedia commons (while this one uses data gathered from the Hipparcos satellice, roughly 100.000 stars) we see, that there are 2 main types of red stars: Giants and M-dwarves. The latter are stars on the main sqeuence (they have stable hydrogen-burning in their ...

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The color index of the star can give you that information. I can look it up for you if I know which exoplanet you're interested in, or you can find it in the NASA Exoplanet Database here.

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"Moons" is a misnomer here, the majority of Kuiper Belt Objects (KBOs) with companions are binaries. Now there are several populations in the Kuiper Belt, characterized by their eccentricities and inclinations. The cold classicals are hereby the most important ones, having mostly circular, low inclination orbits and a high binarity fraction of ...

2

You've answered your own question there, the difference between the two is that asteroids are rock whereas comets are made up of ice and dust. An asteroid doesn't heat up when it gets close to the Sun and doesn't produce a tail. Comets can orbit the Sun or any star in a long elliptical (Comet West) or short elliptical (Comet Encke 3.3 Years) period whereas ...

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