Questions tagged [classification]

Questions regarding grouping objects together based on one or more shared property.

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1answer
627 views

Why are type 1b and type 1c supernovae called type 1 rather than type 2; if they result from large exploding stars, rather than accreting dwarfs?

What similarities do types Ib and Ic supernovae have in common with type 1a? Are their spectra or their magnitudes more similar to accreting white dwarfs than the other supermassive, main sequence, ...
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110 views

Is the transition between ice giants and Jupiter-like gas giants somewhat fluid?

The ice giants Uranus and Neptune are often being distinguished from Saturn and Jupiter who consist mostly of hydrogen and helium, while the ice giants have more of heavier elements than hydrogen and ...
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68 views

How many Kuiper Belt objects have moons? How do we know this?

On 2012 in the New Horizons' The PI's Perspective Alan Stern wrote The Kuiper Belt at 20: Paradigm Changes in Our Knowledge of the Solar System (more also archived) which includes: Most of the known ...
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1answer
249 views

Dataset for machine learning MK stellar classification

I would like to create program for automatic Morgan-Keenan stellar classification using machine learning. For that, I need dataset of stars with known absolute magnitude, temperature and luminosity ...
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1answer
74 views

Does "spectral type" and "stellar classification" refer to the same thing?

Should the tags stellar-classification and spectral-type be merged? has been asked in meta two weeks ago. It requires some careful consideration but so far no response has been forthcoming, so I'm ...
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Are falling evaporating bodies (FEBs) and exocomets the same thing? How does one know they're falling and evaporating?

Looking for a (short) list of comets with heliocentric escape velocity I stumbled upon Wikipedia's exocoments which like exoplanets, are bound to other stars. I should have been looking for "...
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1answer
94 views

Are there ways to determine a star's spectral type without the spectrum itself?

Because of the lack of available data online, I am trying to find other ways to determine an exoplanet's host star's spectral type.
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57 views

Where do stellar classes names come from?

Under Morgan-Keenan classification stellar classes are called O, B, A, F, G, K, M, but what is the logic behind these letters? I can't see any pattern and I doubt they have just been chosen randomly. ...
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720 views

Up to 384 minor planets (including Pluto) qualify as planets?

In 2006, the International Astronomical Union redefined the definition of planet in order to exclude Pluto, Eris, and several other objects whose category was disputed. This new definition of a planet ...
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1answer
213 views

What does Sa and Sab mean for spiral galaxies?

I have learned that the notation to classify spiral galaxies in the De Vaucouleurs system goes like "SA for spirals without bar, SB for spirals with bar and SAB for intermediate spirals". But in some ...
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1answer
187 views

Why have brown dwarf classes been dubbed L, T and Y?

The classes used to categorize stars (O, B, A, F, G, K, M) are in a bizarre order for historical reasons. Stars were labeled based on the spectral lines that were visible, then the categories were put ...
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51 views

How are Y-dwarf spectral subtypes defined?

It is often stated that the spectral subtype indicates the relative position between spectral types, e.g. G5 being halfway from the start of spectral type G to the beginning of spectral type F. Given ...
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Grammar of stellar classification

How to write G2V correctly (I mean space)? I saw in articles $ G\,2\,V$ and $G2\,V$, on the internet webside it is usually $ G2V$.
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Can Jupiter's nightside be classified as spectral type Y?

As far as I am aware, the latest spectral types that have been assigned are around Y2, for objects like WISE 0855-0714 that have temperatures around 250 K or so. I've also seen several directly-imaged ...
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3answers
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Sun's Stellar Class at Birth?

The Sun currently has a stellar class of G2V. However, since its birth, the Sun has brightened significantly. What would the Sun's class have been when it was born ~4.6 gyr ago?
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Is the point of this paper to say that Pluto's status as a planet should have been handled scientifically, rather than by a vote?

The abstract of a paper currently in-press in Icarus: The Reclassification of Asteroids from Planets to Non-Planets (Metzger et al. 2018, https://doi.org/10.1016/j.icarus.2018.08.026) says: It is ...
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Classification and discovery of stars

How do astronomers find the difference between a 'Cephid Variable Star' and distinct normal stars with opaque objects blocking it's light, like stars with planets revolving around them while both ...
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588 views

Currently proposed ways to distinguish between a really big planet and a really small star

The Next Big Future article Rogue Exoplanet 12.7 times bigger than Jupiter is 20 light years away Astronomers using the National Science Foundation’s Karl G. Jansky Very Large Array (VLA) have made ...
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Musk's Roadster is now Russell's Teapot?

Space Exploration Stack Exchange were not very fond of this question and closed it, so I think it might fit better here. Summary: Assuming no foreknowledge of its existence, can Elon Musk's Tesla ...
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1answer
84 views

What abbreviations, letters, or symbols do we use to denote highly degenerate stars?

We have OBAFGKM to denote the strength of hydrogen lines. Apparently we added S, N, C, and the W classes when we learned of new kinds of stars. We use T, L, and Y to denote brown dwarfs. The D ...
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278 views

How are the numerical stellar subclassifications determined?

From Wikipedia: The spectral classes O through M, as well as other more specialized classes discussed later, are subdivided by Arabic numerals (0–9), where 0 denotes the hottest stars of a given ...
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270 views

Is there an alternative (potentially easier to understand) Euler diagram of the new solar system body classification?

note: This question is asking for a representation of the astronomical classification scheme now used for solar system bodies as established (presumably) by the Working Group for Planetary System ...
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How accurate and complete is the Hubble sequence diagram?

The Hubble sequence sorts and characterizes or classifies galaxies by their shape. It was suggested by Edwin Hubble back in 1926. One drawback, or criticism, of this scheme is that Hubble had a ...
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Where did the grand design spiral galaxy designation come from?

What is the history behind the name that we gave to that class of galaxies?
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361 views

Is there a strict chronological order that determines the shape of galaxies?

Assuming no collision happens, do all elliptical galaxies eventually become spiral? Also, when a galaxy becomes spiral or barred spiral, can it switch between these shapes or is it set forever?
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Is Ceres in the inner solar system or outer solar system?

Do we consider the dwarf planet Ceres to be in the inner solar system or outer solar system (or possibly neither / in between). It is located within the asteroid belt, but is the asteroid belt part ...
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1answer
2k views

Planets classification by density

In our Solar system, the density of major planets varies from 0.7 g/cm3 (Saturn) to 5.5 g/cm3 (Earth). For exoplanets, the density varies from very low (0.03 g/cm3 for Kepler-51x) to very high (77.7 ...
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Betelgeuse and sun classification

In this video, between 4 and 6 minutes, the lecturer describes M type stars as being less massive, smaller, and redder than G type stars. He then gives Betelgeuse as an example of an M type star and ...
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Why does spectral class and U-V colour correlate slightly differently for main sequence, giant and supergiant stars?

In this diagram the $x$-axis is spectral type for stars and the $y$-axis is B-V colour. Taking Series 1 as the Main Sequence, Series 2 as Giants and Series 3 as Super-giants. Why the spectral class ...
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Why does the Hertzsprung–Russell diagram's x-axis go from large temperatures to lower?

In my textbook, the H–R diagram’s y-axis is $\log(L/L_{\odot})$ and values are higher as we go higher on the scale, but the x-axis is $\log(T_\text{eff})$ and gets smaller as we proceed to the right. ...
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Synthesising types of galaxies using various stellar spectra

I have asked this on Physics Stack Exchange but Astronomy is probably more appropriate. I have been given the task of synthesising an elliptical galaxy, a starburst galaxy and a spiral galaxy (...
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1answer
665 views

Star class according to initial mass

Studying the stars classes for my homework (school) i learned that stars are classified by the spectral types (Harvard) and luminosity class (MKK) .. So the sun is a star class ...
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Is Pluto still a dwarf planet?

Recent news seem to suggest that astronomers are arguing about whether Pluto should become a planet again. However, I cannot find an official source for this. Is this actually true?
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Classification of a Comet

Google's definition of a comet is: a celestial object consisting of a nucleus of ice and dust and, when near the sun, a ‘tail’ of gas and dust particles pointing away from the sun. This doesn'...
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1answer
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Our galaxy, the Milky Way, forms part of a galaxy group called The Local Group. What are the parameters that dictate what a galaxy group is?

Are there different classifications or just the one? How does our galaxy group compare with others?
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What is the origin of the OBAFGKM classification system?

Once a body has been identified as a star it is classified into a subsection of either O,B,A,F,G,K or M (I think there are also 3 more letters recently added) What is the origin of this ...
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2answers
1k views

What physical features determine if a planet is a major, minor or dwarf planet?

Like many, when I was growing up, we always were taught, hence always learned that there were 9 planets. However, recently, decisions were made and all of a sudden there were 8 major planets and a ...