Themisto (moon)

Themisto
	Rediscovery images of Themisto taken by the UH88 telescope in November 2000
Discovery
Discovered by	Charles T. Kowal (1975); Elizabeth P. Roemer (1975); Scott S. Sheppard (2000); David C. Jewitt (2000); Yanga R. Fernández (2000); Eugene A. Magnier (2000)
Discovery site	Palomar Observatory; Mauna Kea Observatory (rediscovery)
Discovery date	30 September 1975; 21 November 2000 (rediscovery)
Designations
Designation	Jupiter XVIII
Pronunciation	/θəˈmɪstoʊ/
Named after	Θεμιστώ Themistō
Alternative names	S/2000 J 1; S/1975 J 1
Adjectives	Themistoan /θɛməˈstoʊ.ən/ Themistoian /θɛməˈstoʊ.iən/
Orbital characteristics
	Epoch 23 March 2018 (JD 2458200.5)
Observation arc	42.54 yr (15,536 days)
Semi-major axis	0.0494401 AU (7,396,130 km)
Eccentricity	0.2522112
Orbital period (sidereal)	+129.95 d
Mean anomaly	2.39396°
Mean motion	2° 46m 13.369s / day
Inclination	45.28121° (to ecliptic)
Longitude of ascending node	192.64162°
Argument of perihelion	241.25168°
Satellite of	Jupiter
Group	(own group)
Physical characteristics
Mean diameter	9 km; 16.4 km
Albedo	0.04 (assumed)
Apparent magnitude	21.0
Absolute magnitude (H)	12.9; 13.06±0.34 (V)

Themisto /θəˈmɪstoʊ/, also known as Jupiter XVIII, is a small prograde irregular satellite of Jupiter. It was discovered in 1975, subsequently lost, and rediscovered in 2000.

^ Cite error: The named reference IAUC2845 was invoked but never defined (see the help page).
^ Cite error: The named reference IAUC7525 was invoked but never defined (see the help page).
^ Cf. 'Themista' in Noah Webster (1884). A Practical Dictionary of the English Language.
^ 'Themis[t]oan' in James Hall (2015). Moons of the Solar System. p. 82.
^ ^a ^b Cite error: The named reference MPC110499 was invoked but never defined (see the help page).
^ ^a ^b Cite error: The named reference SheppardMoons was invoked but never defined (see the help page).
^ ^a ^b Cite error: The named reference EmelyanovEtAl2022 was invoked but never defined (see the help page).

Discovery^[1]^[2]
Rediscovery images of Themisto taken by the UH88 telescope in November 2000
Discovered by	Charles T. Kowal (1975) Elizabeth P. Roemer (1975) Scott S. Sheppard (2000) David C. Jewitt (2000) Yanga R. Fernández (2000) Eugene A. Magnier (2000)
Discovery site	Palomar Observatory Mauna Kea Observatory (rediscovery)
Discovery date	30 September 1975 21 November 2000 (rediscovery)
Designations
Designation	Jupiter XVIII
Pronunciation	/θəˈmɪstoʊ/^[3]
Named after	Θεμιστώ Themistō
Alternative names	S/2000 J 1 S/1975 J 1
Adjectives	Themistoan /θɛməˈstoʊ.ən/^[4] Themistoian /θɛməˈstoʊ.iən/
Orbital characteristics^[5]
Epoch 23 March 2018 (JD 2458200.5)
Observation arc	42.54 yr (15,536 days)
Semi-major axis	0.0494401 AU (7,396,130 km)
Eccentricity	0.2522112
Orbital period (sidereal)	+129.95 d
Mean anomaly	2.39396°
Mean motion	2° 46^m 13.369^s / day
Inclination	45.28121° (to ecliptic)
Longitude of ascending node	192.64162°
Argument of perihelion	241.25168°
Satellite of	Jupiter
Group	(own group)
Physical characteristics
Mean diameter	9 km^[6] 16.4 km^[7]
Albedo	0.04 (assumed)
Apparent magnitude	21.0^[6]
Absolute magnitude (H)	12.9^[5] 13.06±0.34 (V)^[7]