The moon of Jupiter – Leda (XIII) –
was discovered in 1974 by C. Kowal (an astronomer of Polish origin, the discoverer of the famous asteroid Chiron that was shown to display some
→cometary
activity!).
Leda has been known as the Queen of Sparta and the wife of Tyndareus. Zeus first saw her when she bathed in the river Eurotas. He fell in love with her and seduced her in the form of a swan. Following their union Leda brought forth eggs which produced the future Helen of Troy, Pollux (Polydeucus)
and Castor. According to other traditions Zeus fathered only the first two with Castor and also Clytemnestra being the children of her husband... The motif of a flirt with a swan was one of the favourite topics in ancient art. Even later on it was very pupular among such artists as Leonardo da Vinci and Salvatore Dali
(''Leda Atomica'').
The moon by this name is in elliptical prograde orbit (→eccentricity
e = 0.1636) with a →semimajor axis a = 11,165,000 km. At pericenter (closest to the planet) Leda is separated from the Jupiter a distance of q = 9,338,406 km. At apocenter (furthest from the planet) this moon is separated from the Jupiter a distance of Q = 12,991,594 km. In future these parameters may vary due to a large orbital distance from Jupiter and the orbital motion being disturbed by the Sun and other
factors. Perhaps it is a captured asteroid (with a diminutive mass of ~1.0940×1016 kg –
somewhat less than 1.5 mountain like Giewont
!),
and in future will possibly return to heliocentric orbit.
An in teresting feature of that moon is that being the in nermost "irregular" satellite of Jupiter (in a higly inclined elliptical orbit), it revolves in the same direction as the planet is spinning on its axis.
Due to its similarity in semimajor axis to some of the other satellites of Jupiter, it is considered to be a member of a so called
Himalia (probably the remnants of a single large body).
The orbital period is almost 2/3
earthly year, which means that the average speed of its celestial motion is only
1°29'39'' per day. When this motion was detected and compared to the changes in
Jupiter's position, this body was classified as a true planetary satellite (and not a distant celestial body with its position projected near the planet).
Other obstacle in detecting this moon earlier was its brightness of only 19.5m
(over 251 thousand times fainter than the faintest stars visible to naked eye). For comparison:
Jupiter's brightness is about –2.7m, so Leda is shining fainter by about
22.2m. The corresponding difference in brightness is
over 759 million times!
I have given some crucial data of Leda below. Table one contains the basic
information. Whereas table two gives more detailed parametrs of its orbit (calculated using the following formulae).
Translated by Karol Pankowski
|
Leda
|
|---|
| Mean distance from the planet [×103 km] |
11,165.0
|
| Mean distance from the planet [planetary R] |
156.2
|
| Orbital period [days] |
240.92
|
| Orbital eccentricity [e] |
0.1636
|
| Orbit inclination [degrees] |
27.5
|
| Mean diameter [km] |
20.0
|
| Main discoverer and year of the discovery |
C. Kowal 1974
|
| Visual magnitude [mag] |
19.5
|
| Mass [kg] |
~1.0940 × 1016
|
Orbital Parameters |
Pericenter
[q] |
Apocenter
[Q] |
| Distance from the planet [×103 km] |
9,338.4
|
12,991.6
|
| Distance from the planet [planetary R] |
130.6
|
181.7
|
| Angular size of the moon's orbit observed from the Earth* [degrees] |
0°51'03.58''
|
1°11'02.20''
|
|
| Angular diameter of the planet's disc as observed from the moon [degrees] |
0°52'38.24''
|
0°37'50.14''
|
| Brightness of the planet as observed from the moon** [mag] |
–11.8
|
–11.1
|
| Diameter of the moon's disc as observed from the planet's "surface" [degrees] |
0°00'00.45''
|
0°00'00.32''
|
| Brightness of the moon as observed from the planet's "surface"** [mag] |
10.4
|
11.1
|
|
Orbital velocity [km/sec] |
3.97
|
2.86
|
* This value is calculated for Jupiter at opposition (distance 628.8 million km = 4.2 AU)
** The given value of magnitude is not corrected for some decreasing factors (e.g. the changing phase of illumination)
|
See other related links:
Astronomy for every – Jupiter's moons
Monde
des Monats
– HIMALIAGRUPPE
Views
of the Solar System – LEDA
– Photo
Archives
Solar
System Exploration – LEDA
The
Nine Planets – LEDA
The Astronomy Workshop – Satellite Viewer
Planetary Satellite Mean Orbital Parameters
Natural Satellite Physical Parameters
 |
