Talk:Deimos (moon)

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Contents 1 Ice? 2 pronunciation 3 Orbital evolution 4 Density discrepancy 5 Appearance of Mars from Deimos

[edit] Ice?

So, what kind ice does Deimos have, with a surface temperature of "~313 K" (a very hot summer day where I live)? Gene Nygaard 19:45, 5 Jan 2005 (UTC)

The ice mentioned is inside Deimos. Because of its low albedo (0.07), a steadily illuminated Deimos surface would reach equilibrium at ~313 K. With rotation and shadowing, one would expect the average temperature to be somewhat lower. The interior could contain a lot of ice, protected by the insulating dark crust. Just a guess. Do we have any actual surface temperature measurements quoted anywhere?

Urhixidur 03:45, 2005 Jan 6 (UTC)

[edit] pronunciation

The article had DAY-mus. This is an attempt at the classical Greek pronunciation; the English equivalent is DYE-mus or perhaps DEE-mus. Most refs, including Geyley's 1893 (1911, 1939) Classic Myths in English Literature and in Art and Zimmerman's 1964 Dictionary of Classical Mythology have the former; a few, such as Tripp's Meridian Handbook of Classical Mythology have the latter.

The Greek is the same as in dinosaur (just substitute N for M), if that helps you decide on a pronunciation. (Deinothere has the same vowel spelling in English as Deimos as well; it's also pronounced DYE-.) —kwami 07:44, 7 Apr 2005 (UTC)

Added the Greek spelling, which will provide the DAY-mus pronunciation to anyone who wants to be 'authentic'. --kwami 01:11, 11 Apr 2005 (UTC)

Anyone know of an adjectival form? I can't find anything. I assume something like Deimian would be acceptable, but don't know if anything else is in use. kwami 2005 June 30 06:22 (UTC)

It is related to dinosaur; it is not the same. But the first syllable should pronounced the same way. Septentrionalis PMAnderson 17:06, 3 June 2007 (UTC)

[edit] Orbital evolution

Anybody know of good info on the orbital evolution of Deimos? Since it's higher than synchronous orbit, it is moving outward, and I believe it will eventually escape; but I haven't found any good refs for the time scale required. --Reuben 21:05, 4 April 2007 (UTC)

[edit] Density discrepancy

The current listed density (2.2 g/cm³) (unreferenced) differs significantly from these 2 NASA data pages:

• NASA JPL: 1.471 g/cm³
• NASA NSSDC 1750 kg/m³ (= 1.750 g/cm³)

Therefore, I decide to change it to the JPL value (that page is better referenced), and adding a reference to that page. Regards, --Dna-Dennis (talk) 21:33, 29 January 2008 (UTC)

[edit] Appearance of Mars from Deimos

The figures comparing the appearance of mars from Deimos to that of the full moon from earth are calculable from almanac data. The apparent radius of mars is given by arcsin ( R_mars / R_orbit ), giving 0.145 radians or 8.3 degrees . 90/8.3 = 10.8 gives the "one-eleventh" figure cited as the fraction of the width of the celestial hemisphere (i.e. 180 degrees ) taken up by the martian apparent diameter.

The apparent radius of the moon from the earth varies, and brackets the value of 0.00457 radians required to give the "1,000 times larger" comparison for mars' appearance from Deimos.

The intensity of lunar and martian sunlight also vary, and the minimum and maximum ratios bracket the value of 2.5 required to justify the "400 times brighter" comparison, assuming equal albedos. The albedo of the full moon approaches that of mars, but may be somewhat less, so a figure as high as "500 times" is perhaps justifiable, although the question is probably moot for a comparison of this type.--L mammel (talk) 01:30, 16 April 2008 (UTC)

Please correct me if I'm wrong but I'm seeing a contradiction in your explanation of the "one-eleventh" figure. Dividing 90/8.3 should yield the fraction Mars takes up of one half of the sky. 180/8.3 (21.6) would be the entire celestial hemisphere, because just as you say, it is 180 degrees across. 63.116.54.200 (talk) 17:04, 16 April 2008 (UTC)

Note that 8.3 degrees is the apparent radius of mars, and 90/radius = 180/diameter . I guess I kind of snuck that one in, but it's there!--L mammel (talk) 22:17, 16 April 2008 (UTC)