Talk:243 Ida

Binary Asteroid?
Should this be called a binary asteroid? The link defines a binary asteroid as one where the two objects orbit their common center of gravity, presumably this designation is the same as that for binary planets, when that center of gravity exists outside the body of the largest object (as is supposedly the case with Pluto and Charon.) If this is the case, then Ida and Dactyl would not be a binary asteroid as Dactyle is very small and the center of gravity in the Ida/Dactyle system is almost certainly within the body of Ida. In fact, references to Ida/Dactyl in other wikipedia articles list it as the first asteroid found to have a moon, rather than a binary asteroid - and in those articles about Ida, the link to asteroids with moons goes to a page describing those rather than to the binary asteroid description page.

I am not changing this because I personally do not know if in fact the center of gravity is within the body of Ida or not, but if someone else does and it indeed is, then this should be changed. Jafafa Hots 04:52, 18 January 2006 (UTC)


 * It doesn't matter if the satellite is small or comparable to the size of the parent body; all asteroids consisting of two objects are binary asteroids. Similarly, asteroid 87 Sylvia is considered a triple asteroid although its satellites are tiny compared to the parent body.--Jyril 15:42, 18 January 2006 (UTC)

where is this asteroid located in the solar system? —Preceding unsigned comment added by 68.36.202.128 (talk) 16:57, 3 May 2008 (UTC)

Apparent magnitude?
The infobox lacks this, although there is a number of absolute magnitude which is unreferenced. Pomona17 (talk) 15:58, 5 August 2008 (UTC)
 * The apparent magnitude will vary as the Earth moves closer and further away Modest Genius talk 01:51, 8 March 2009 (UTC)
 * Many asteroid articles contain a range of maximum to minimum magnitudes. The article used to contain this before Wronkiew and I started overhauling it, but it was not referenced so I left it out for now. It seems to be correct but I'm still hoping to find a reliable source. Reyk  YO!  02:11, 8 March 2009 (UTC)
 * I am the author of that information. (I waited for the massive edits to calm down before jumping in.  The article looks great.)  The APmag range is 13.44 to 15.90 from 1950 to 2100.  You can generate this data using JPL Horizons.


 * 1. Set the Time Span to 1950-01-01 to 2100-01-01.
 * 2. Go to Table Settings and deselect 1, 20, 23, and 24 to clear the output screen of clutter. Click "Use Selected Settings"
 * 3. Click Generate and wait 30 seconds.
 * 4. Text search (Ctrl-F) 13.44 (brightest and min value) and 15.90 (dimmest and max value). I added this info to the article on 9 October 2008. -- Kheider (talk) 10:47, 8 March 2009 (UTC)

20 times smaller?
What is meant when it is stated that Dactyl is 20 times smaller than Ida. The diameter is significantly less than one twentieth. Is is referring to mass? Maybe this should be stated.

N.B. if Dactyl is a twentieth of the mass then is a lot denser than Ida. Yaris678 (talk) 11:57, 29 July 2009 (UTC)
 * No the diameter is ~1/20th. You need to compare the average diameters.  Ida has an average diameter (geometric mean) of only ~27km, which is about 20x greater than 1.4km -- Kheider (talk) 14:46, 29 July 2009 (UTC)
 * The article states that "Ida has an average diameter of 31.4 km ". I would also say that 1.4km it not "a little more than a kilometer", is is significantly more.  Maybe the issue here is that the 1/20 statement is based on the geometric mean and the other statements are based on something else.  If this is the case then perhaps it should be made consistent.  Yaris678 (talk) 17:46, 29 July 2009 (UTC)
 * You may be over thinking this. Ida has a geometric mean diameter of 26.9km (3rd root of "53.6x24.0x15.2"). The article simply lists the diameter as 31.4.  There is more than one way of averaging a set of numbers. Besides these numbers are probably a "best fit ellipsoid".  Either way, 26.9/1.4=19.2 and 31.4/1.4=22.4.  Both numbers are adequate to state in the lede that "Dactyl is about 20 times smaller than Ida, at a little more than a kilometer in diameter".  The lede should not go into excessive details/complications. -- Kheider (talk) 18:09, 29 July 2009 (UTC)
 * If the calculation were 31.4/1.4 I would say that 20 would be a reasonable approximation. However, 1.4 is not  "a little more than a kilometer", it is 40% more!  Perhaps that is where the problem lies in the article.  If it instead said the diameter of Dactyl was "approximately 1.4 kilometers" I would have no problem.  Yaris678 (talk) 07:45, 30 July 2009 (UTC)
 * I see you have made a change along the above lines. I am happy with the new words.  Yaris678 (talk) 11:37, 31 July 2009 (UTC)

Orbital speed error?
In the article, the average orbital speed is said to be 0.2036°/s, and in the body of the article, the orbital period is listed as 4.84 years. My back-of-the-envelope reckoning makes me thing that the average orbital speed should be 0.2036°/d, however I'm no astrophysicist, so I don't want to make the change without someone else verifying my math. Croquesaveur (talk) 21:15, 29 July 2009 (UTC)

http://news.yahoo.com/nphotos/Most-Emailed-Photos/ss/1756;_ylt=AvenoyFpnnWAM2gDdnYbmB3mWMcF#photoViewer=/091230/photos_sc_afp/d1f1bf032c1d3093992fbdd542a7001a —Preceding unsigned comment added by 69.76.233.12 (talk) 21:35, 5 January 2010 (UTC)

Catena
According Wanglesa some Dactyl craters in catena have been caused by debris from Ida, but this does not seem to be the case, then these catenae might be find in other points of the solar system, and therefore we can not attribute a common origin or similar. A possible explanation of catenae my be a meteor shower, which seem to have a common point of origin in heaven because its continu parallel trajectories. Coronellian (talk) 15:54, 20 June 2010 (UTC)

Average orbital speed 	0.2036°/d ??
Why º/d ? In any other planet/moon/asteroid article, the average orbital speed is specified in km/s, why this one doesn't? — Preceding unsigned comment added by 81.184.198.58 (talk) 23:44, 6 September 2015 (UTC)

External links modified
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still considered a 'moon'?
I haven't tried to dig into the astronomy of Dactyl, but it would seem to me that instead of 'moon' this fractisimal object would be part of a joint-system mono identifier? Or is 'moon' just the off-hand way it is referred to. It's a spec of dust in comparison. :-) 50.111.29.1 (talk) 00:39, 28 August 2022 (UTC)

Baseball
33 feet per second is only 22.5 miles per hour. That is only 1/4 the speed of a baseball pitch (21% of Bob Feller). So the word "thrown" should probably be changed to "tossed". agb 143.43.158.178 (talk) 16:17, 24 October 2023 (UTC)


 * An untrained adult female can throw at speeds ranging from 30 to 45 mph. So the expression "a slowly thrown baseball" is fine. -- Kheider (talk) 16:56, 24 October 2023 (UTC)