# Tag Info

59

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 "name". Similarly when a new astronomical object, such as an asteroid, is discovered, it has no word that identifies it and so it is assigned first a ...

44

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 circumstances all other elements can be neglected, at least to first order. By mass, H and He account for some 74% and 24% in the present-day Universe, ...

29

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 on one Moon cycle. One lunar cycle is 29.53 days. www.universetoday.com/20620/lunar-year/ which does not evenly divide into the 365.25 days of ...

26

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 capitalization of the names themselves to indicate a proper name. The Sun and the Moon have many names, at least one name for each for almost every language ever spoken....

22

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 dwarfs compared to large giants and supergiants. Ultra-cool, as called2voyage already discussed, means that the star has an effective temperatures of less than ...

22

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 the full moon coincides with the moons perigee or nearest approach. That can make it appear up to 30% brighter than one at apogee (farthest away). These happen ...

22

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 they have multiple names each. Most people refer to them simply as "The Sun" & "The Moon".

18

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 small body impacting another body in the solar system. As an example, Wikipedia doesn't impose the limitation that it must hit Earth: A meteorite is a solid ...

17

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 English. Apsis actually derives from "arch" and indicates the two points where the orbital curve is most "arched": ie the points of greatest ...

16

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 rarely referred to as such. The extra hyperbole ("Super", "Blood" etc) seems to be a recent (within the last few years) media phenomenon for unknown reasons...

16

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 Keplerian, but with perturbations. Sun synchronous satellites are one example of orbits that are close to Keplerian, but not quite so. The Earth's equatorial bulge ...

14

By definition, the capitalized word Universe denotes everything there is, so even if we one day discovered we're just a part of a Multiverse, all the parallel universes of it would still be parts of the Universe as a whole, where Multiverse would just describe its nature. Or, if some yet undiscovered regions of it would defy our current understanding of its ...

14

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 named Meridiani Planum meteorite by the Meteoritical Society in October, 2005 (meteorites are always named after the place where they were found) The Meteorical ...

14

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 instead trends that Kepler noticed and calculated using astronomical observations of the planets. Kepler’s laws are very accurate for planetary orbits since he ...

11

$\simeq$ 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 the order of", i.e. correct to within an order of magnitude. However, astronomers tend to be rather slobby sometimes (we call all elements except H and He for "...

11

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 probe, which does not orbit the asteroid Ryugu. But hovers over the surface. So what does Phil mean when he talks about orbiting? I summarize the meaning thus: ...

10

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 define other terms to identify objects in our solar system. You can see a diagram of all the official terms and how they relate below. Notice the important factor ...

9

"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 quasiperiodic orbits exist around stable orbits 3 different types of possible planetary orbits are found: S-types (satellite type orbit around one primary), P-types (...

8

It is far from empirically known that the universe is finite in size. The observable universe is certainly of finite size, but that is just a product of the constraints of our observation. We don't know for sure whether the universe is finite or infinite, bounded or unbounded. [Source] What we do know is that right now the universe looks very flat as far as ...

8

'Radial direction' typically means from the center, moving outwards. Typically, these kinds of studies will break a galaxy up into several annuli, or rings, and examine the star formation activity within each ring. (Imagine drawing a series of concentric circles, each one a little bigger than the last.) Then, if the star formation rate or star formation ...

8

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 other kind" in the XKCD comic) P-type: The planet orbits around both stars of the binary

8

According to Spectroscopic Properties of Ultra-cool Dwarfs and Brown Dwarf by J.D. Kirkpatrick, the working definition of ultra-cool dwarf is: dwarfs having classifications of M7 or later. That is referring to the stellar classification system which categorizes stars by their spectral characteristics. Class M stars have a surface temperature less than ...

8

A supermoon is when the full moon occurs at the time when the moon is at its closest point to us in its elliptical orbit. This means that the moon is slightly bigger (honestly, you wouldn't notice it unless you made careful comparisons) and a chunk brighter than normal full moons. Except that supermoons happen three or four times every year, so, actually, ...

8

No. (I'll note that this usage is arguably erroneous, since the nominal meaning of "intrastellar" is "within or inside a star".) First, I personally have never heard anyone use that term in my twenty-five-odd years as an astronomer. Second, a full-text search of the astronomical literature on the NASA Astrophysics Data System turns up a grand total of 51 ...

8

Yes, Near Earth Objects (NEOs) include asteroids (Near Earth Asteroids (NEAs)) and a few percent of comets (Near Earth Comets (NECs)). As shown by the Update to Determine the Feasibility of Enhancing the Search and Characterization of NEOs (NEO SDT Report) in Section 2.3, the risk from Near Earth Comets is about 1% that of asteroids. So "NEO" tends to be ...

8

The fringing pattern is caused by thin-film interference within the CCD. The signal received in a pixel will be proportional to the light falling on it, multiplied by a sensitivity, but then some extra signal is added or subtracted which depends on how much of the incoming light is at particular wavelengths that are affected by the interference (i.e. the ...

7

Since a full moon happens once every 29 days (and that's not exact, but close enough), the longest period of time where you can have 11 full moons but not 12 is 11 x 29 + 28, or 347 days, so in a normal year, it's not possible. There are slight variations in the time between full moons but not nearly enough to make up the extra 18 days needed. So you'd ...

7

As pointed out in the comments, some do prefer to use different terms for quakes on other bodies, and you can see here that "marsquake" does have scholarly usage. That said, there is also scholarly usage for "earthquake" in this context. If you think about it, this makes sense given that one definition of "earth" is "the substance of the land surface", i.e. ...

7

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 Date (MJD) is JD - 2400000.5, or the real number of days since 1858-11-17 0:00 UT. The IAU officially approves either JD or MJD as long it's clear which ...

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