Talk:5 Astraea

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Pronunciation

I changed the pronunciation from as-trye'-a. True, <æ> represented [aj] in Latin, but in English it regularly becomes <e> (ee or eh depending), as in encyclopædia. The mythological refs I've checked are universal in giving as-tree'-a.

Densities

A paper [Krasinsky, Icarus, Vol. 158, p. 98 (2002)] gives recent calculations for the mean densities of C, S, and M class asteroids as 1.38, 2.71, and 5.32 g/cm3. (here "C" included Tholen classes C,D,P,T,B,G, and F), while "S" included Tholen classes S,K,Q,V,R,A,E). Assuming these values (rather than the present ~2 g/cm3) is probably significantly more accurate for the mass of asteroids whose mass has not been otherwise measured, although there is still heaps of variation due to porosity, etc. Deuar 11:39, 16 November 2005 (UTC)

Dimensions

The Lopez-Gonzales reference (2005) gave diameter ratios a/b=1.35, b/c=1.5, (where the dimensions are a×b×c) from photometry. Combining these with the IRAS mean diameter of d=119.1 km using abc=d3, gives the dimensions 167×123×82 km. Deuar 18:11, 16 November 2005 (UTC)

Mass

From Table 6 of Michalak (2001), the assumed mass for 5 Astraea in his perturbation calculations is 0.015x10-10 times the mass of the sun, thus 1.9891x1030 kg x 0.015x10-10 = 3.0x1018 kg (to two significant digits). Michalak states "Asteroid masses in these models are taken from Table 6 and one should realize that they can be erroneous." One assumes Michalak's number is an educated guess, and sadly since this is apparently the only paper (up to this writing) containing any mass determination for 5 Astraea, 3.0x1018 kg is it. -- Robert.Baruch (talk) 15:06, 16 February 2010 (UTC)

I generally compare asteroids to Ceres simply because the Sun is kind of big for an asteroid comparison. :) I used 2.9E+18 simply because I have a tendency to truncate more than round-off, and even though the mass is an assumption, I wanted to come in low with the estimate. Of course any notable error in the mass of Astraea could potentially throw off calculations for the perturbing asteroid.-- Kheider (talk) 18:01, 16 February 2010 (UTC)