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61 votes

Do our sun and moon have names?

What is a name? A name is a word, that is reasonably unique, that is used to identify a person or thing. When a child is born there is no word that identifies it, and so its parents have to choose a &...
James K's user avatar
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56 votes

Is the Big Bang a theory or a model?

Back in the good old days, we used words like theory, model, hypothesis, law and so on, and their meanings arose from how the words were used, and dictionaries organised these senses - just like other ...
James K's user avatar
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44 votes
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Is lithium considered a metal in astronomy?

The latter. To astronomers, a metal is any element that is not hydrogen or helium, because these elements together constitute most of the elements in the Universe, by far. This means that, in many ...
pela's user avatar
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42 votes
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Hydrogen burning vs Hydrogen fusing

In stellar astrophysics, "burning" means nuclear fusion, not chemical combustion. So a star burns hydrogen to helium. (Incidentally, normal chemical burning of hydrogen in air produces water)...
PM 2Ring's user avatar
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33 votes
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Is there a word for an object orbiting a brown dwarf?

In the question IAU 2018 Exoplanet definition the IAU's definition of an exoplanet is given which includes objects around brown dwarfs. So the answer to your question is that a planetary-mass object ...
sno's user avatar
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30 votes
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What's the reason that we have a different number of days each month?

You make a great point. The reason behind the discrepancy between the dates is due to a complicated history behind it. The calendar is based on the calendar created by ancient Romans, which is based ...
Max0815's user avatar
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28 votes

Do our sun and moon have names?

Of course the Sun and the Moon have names. The names of those objects in English are "the Sun" and "the Moon". Note the use of a definite article ("the") and the ...
David Hammen's user avatar
  • 34.1k
23 votes

Do our sun and moon have names?

It is named 'Sol' and the moon was named 'Luna'. Hence the term Lunar explorer and 'Solar' System.. Other cultures have used different names for our Sun and Moon (for thousands of years) - So actually ...
Ryan's user avatar
  • 255
23 votes

Milky Way vs Milky Way Galaxy

I think that distinction is wrong, or at least not commonly accepted. We live in a disk-shaped galaxy, which is interchangeably called "the Milky Way", "the Milky Way Galaxy", or &...
pela's user avatar
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23 votes
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Milky Way vs Milky Way Galaxy

Milky Way vs Milky Way Galaxy I recommend recognizing and honoring the distinction! The two words being interchangeable is a narrow view that only one well versed in Astronomy can have, and doesn't ...
uhoh's user avatar
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23 votes

Is the Big Bang a theory or a model?

My understanding is that the "big bang" (which I am taking to be a synonym for $\Lambda$CDM cosmology) is a model. It sets out a (relatively) simple framework, starting from a set of ...
ProfRob's user avatar
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22 votes
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So, what exactly is an 'ultra-cool' dwarf star?

Breaking the phrase down: Dwarf star - a term I will never understand - is used to describe relatively small, dim stars. Unfortunately, this encompasses most main-sequence stars, which are indeed ...
HDE 226868's user avatar
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21 votes
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What (the heck) is a Super Worm Equinox Moon?

All those adjectives being smooshed together signify an uncommon event. That's why you've never seen them together like that before. All 3 conditions have to hold true: It's a supermoon, which means ...
Octopus's user avatar
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18 votes
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What is the name of meteoroids which hit Moon, Mars, or pretty much anything that isn’t the Earth?

Oxford English Dictionary is an authoritative source, but it's aimed at the general public. I think no astronomer will frown upon you when you're using the terms meteoroid and meteorite to describe a ...
Glorfindel's user avatar
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16 votes

What (the heck) is a Super Worm Equinox Moon?

All the monthly Full Moons are named e.g. list at timeanddate.com, of which "Harvest Moon" is the one people are probably most familiar with. So the March Full Moon is indeed the "Worm Moon" although ...
astrosnapper's user avatar
  • 8,357
16 votes

What are "non-Keplerian" orbits? What are some familiar examples in our solar system, and can some still be closed?

What exactly are "non-Keplerian" orbits? Strictly speaking, no orbits are in perfect accordance with Kepler’s laws. Kepler’s laws aren’t really “laws” in terms of physical laws, but are ...
Connor Garcia's user avatar
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16 votes
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"Periapsis" or "Periastron"?

No. These words are English, not Greek. "Periapsis" means the point on the orbit when the two bodies are at their closest. It doesn't matter if this good Greek or bad Greek, it is correct ...
James K's user avatar
  • 123k
16 votes

14,000 square degrees

The whole sphere has approximately 41,253 square degrees of solid angle. $$4\pi\left(\frac{180}{\pi}\right)^{2}\approx 41,253$$ so for a hemisphere there should be half this number or about 20,627 ...
GrapefruitIsAwesome's user avatar
15 votes

What are "non-Keplerian" orbits? What are some familiar examples in our solar system, and can some still be closed?

What exactly are "non-Keplerian" orbits? Orbits that don't follow Kepler's laws. Strictly speaking, all orbits are non-Keplerian. In practice, one can model some orbits as basically ...
David Hammen's user avatar
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14 votes

What is the name of meteoroids which hit Moon, Mars, or pretty much anything that isn’t the Earth?

Wikipedia's entry for Heat Shield Rock says: Heat Shield Rock is a basketball-sized iron-nickel meteorite found on Mars by the Mars rover Opportunity in January 2005. The meteorite was formally ...
uhoh's user avatar
  • 30.6k
13 votes
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Usage of $\sim$, $\approx$, $\simeq$, and $\cong$ in observational astronomy?

$\simeq$ and $\approx$ both mean "approximately equal to". I don't think $\cong$ is used so often, but if I read it, I would interpret is as the same as the two others. $\sim$ in principle means "of ...
pela's user avatar
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13 votes
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What's the meaning of virial in Astronomy, and in particular the expression "a virialized cluster of galaxies"?

A slightly modified version of the virial theorem that you cite states that for a system of N bodyes (galaxies in a cluster) autogravotating $${1 \over 2} \ddot I = 2K + V$$ Where $K$ is the total ...
Prallax's user avatar
  • 4,431
12 votes
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What do the words "p-type" and "s-type" mean?

"Satellite type" and "Planet type". The terms seem to have been coined by Rudolf Dvorak in 1982 paper "Planetenbahnen in Doppelsternsystemen" Due to the fact that ...
James K's user avatar
  • 123k
12 votes
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What is the mnemonic reason behind b being galactic latitude? (in the Galactic Coordinates frame)

Länge und Breite are the German words for longitude and latitude. Thus 'b' seems like a natural choice for latitude and 'l' for longitude. A century ago when traditional choice of variable names were ...
planetmaker's user avatar
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11 votes
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Do astronomers generally agree that the distinction between comets and asteroids is not so clear?

If we're going to get technical, Asteroids are not really an official name anymore. In 2006, when the IAU redefined what a planet was (and thus demoted Pluto), they also decided to more formally ...
zephyr's user avatar
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11 votes
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Do astronomers have an established, systematic way for saying what does or doesn't orbit what? (e.g. "Mars orbits Earth")

It is possible that there is nothing "official", there is just the technical use of language. For example Phil Plait notes that He incorrectly used the word "orbit" for the motion of the Hayabusa ...
James K's user avatar
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11 votes
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Is REDSHIFT one word or two?

It’s a single word. Used to be double, but quickly became single. https://en.wiktionary.org/wiki/redshift https://en.wikipedia.org/wiki/Redshift https://www.merriam-webster.com/dictionary/redshift ...
Pierre Paquette's user avatar
10 votes
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At what point are orbital resonances no longer "ordered" but "chaotic?"

Consider a child on a stationary swing. The fastest way to get them going is to push once every time they swing (a 1:1 resonance). If you push 581 times for every 137 swings, the pushes will mostly ...
Connor Garcia's user avatar
  • 16.3k
9 votes

What's the name for [the other kind of planet] in a binary star system?

I don't know about names for the planets, specifically, but the orbits are called S-type and P-type: S-type: The planet orbits around one star, and the host star has a binary companion (i.e., "the ...
J. O'Brien Antognini's user avatar
9 votes
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Sorting out Julian Day, Julian Date, Julian Day number, Julian Day Calendar, and Julian Day Table

The Julian Date (JD) is the real number of days since 12:00 UT, January 1, 4713 BCE (proleptic Julian calendar). The Julian Day Number (JDN) is floor(JD), the nearest integer ≤ JD. The Modified Julian ...
Mike G's user avatar
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