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

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5
votes
1answer
64 views

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 ...
1
vote
1answer
31 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 ...
1
vote
2answers
60 views

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 ...
1
vote
0answers
58 views

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 ...
6
votes
2answers
154 views

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. ...
12
votes
6answers
2k views

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?
3
votes
1answer
655 views

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 ...
2
votes
0answers
41 views

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 ...
1
vote
1answer
109 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 ...
14
votes
2answers
528 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 ...
6
votes
1answer
1k views

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 ...