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Asteroid Near-Earth

Poseidon

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4341 Poseidon (1987 KF)

Where is it now

Distance from Sun
1.281 AU
True anomaly
250.17°
Distance from Earth
0.377 AU
As of
11 October 2026

Two-body Kepler propagation — accurate to ~0.1% for major planets over decades, less so for highly-perturbed bodies. Use JPL Horizons for high precision.

Orbit of Mercury Orbit of Venus Orbit of Mars Sun Earth — 0.998 AU from the Sun Earth Poseidon — 1.281 AU from the Sun Poseidon
Seen from above the ecliptic, north up, to scale. Grid: Earth's orbit in blue. Poseidon is 0.377 AU from Earth today (3.1 light-minutes).

In the sky

Right ascension
01h 13m 22s
Declination
-41° 29′ 43″
Constellation
Phoenix
Distance from Earth
0.37 AU
Elongation from the Sun
131° — well clear of the Sun

Favours the southern hemisphere; low or below the horizon from far north.

From your location

See how high it is right now, whether it is up after civil twilight, and when it rises and sets where you are.

How do I find my coordinates?

Google Maps on a computer

  1. Right-click the spot where you'll be observing.
  2. The first line of the menu is the coordinates, e.g. 51.50722, -0.12758 — click it and they're copied.
  3. Paste them above.

Google Maps on a phone

  1. Press and hold the spot to drop a pin.
  2. The coordinates appear in the search bar (or on the pin's card) — tap to copy, then paste above.

A full Google Maps link works too, but the short maps.app.goo.gl share links don't carry coordinates — copy the numbers instead. We round to about a kilometre; that's all the sky calculation needs.

Know your what3words address? Paste it, e.g. ///filled.count.soap. This is optional — the three words are sent to what3words to convert them, and we don't store the address or the result.

Your location stays in your browser and is sent only for this calculation. Using a what3words address is optional; if you do, the three words go to what3words to be converted and we don't record them. Set a location first, then you can save an email alert for this object. See our privacy policy.

Two-body approximation, good to about a degree for the planets — enough to find the constellation and know whether it is up.

Orbital elements

Semi-major axis
1.834 AU
Eccentricity
0.6801
Inclination
11.84°
Orbital period
2.48 years
Perihelion
0.587 AU
Aphelion
3.082 AU
Longitude of ascending node
108.02°
Argument of periapsis
15.84°
Epoch · J2000
2461200.5
Orbit class · APO
Apollo
Earth MOID · 75.6 LD
0.1942 AU
Tisserand (Jupiter)
3.689

Orbit quality

Orbit very well determined (uncertainty code 0).

Observations used
1,068
Data arc
39.36 years
First observed
29 May 1987
Last observed
8 October 2026
Residual RMS
0.52 ″
Solution · Otto Matic
9 October 2026

Physical properties

Mean radius
1.59 km
Rotation period
6.26 hours

Visual & observation

Geometric albedo
0.054
Absolute magnitude (H)
16.07
Spectral type (SMASS)
O

Discovery & classification

Discovered by
Shoemaker, C. S.
Discovery date
29 May 1987
Discovery site
Palomar

Also known as 4341 · 1987 KF

Apollo Near-Earth Object Named

Close approaches 22 on record

Flyby geometry
Ecliptic flyby of Poseidon at 2118-11-05 19:02 UTC Top-down view of the ecliptic, Earth at the centre, for the 2118-11-05 19:02 UTC close approach of Poseidon. Catalogue miss distance 76.2 LD · 2.93 × 10⁷ km. The curve is the geocentric path from 2118-11-02 to 2118-11-08, with a mark at UTC midnights and an arrow for the direction of motion. The circle is the Moon’s mean orbit; the Moon is plotted at closest approach. A ray shows the Sun’s direction. The labelled distance is the full separation. The drawn radius is the part that lies in the ecliptic plane. At closest approach the object is south of the ecliptic. The path is a geocentric ecliptic ephemeris from JPL Horizons. The inset is a heliocentric view and is approximate. Sun 76.2 LD · 2.93 × 10⁷ km 2118-11-05 19:02 UTC Earth Moon Heliocentric, approximate

Top-down view of the ecliptic, Earth at the centre, for the 2118-11-05 19:02 UTC close approach of Poseidon. Catalogue miss distance 76.2 LD · 2.93 × 10⁷ km. The curve is the geocentric path from 2118-11-02 to 2118-11-08, with a mark at UTC midnights and an arrow for the direction of motion. The circle is the Moon’s mean orbit; the Moon is plotted at closest approach. A ray shows the Sun’s direction. The labelled distance is the full separation. The drawn radius is the part that lies in the ecliptic plane. At closest approach the object is south of the ecliptic. The path is a geocentric ecliptic ephemeris from JPL Horizons. The inset is a heliocentric view and is approximate.

JPL Horizons

When (UTC) Body Distance Lunar distances Relative speed
2026-12-25 00:46:00 Venus 0.1318 AU 51.3 LD 16.5 km/s
2029-07-05 13:52:00 Venus 0.0982 AU 38.2 LD 17.1 km/s
2084-02-04 23:56:00 Venus 0.0849 AU 33.0 LD 18.3 km/s
2086-08-15 12:40:00 Venus 0.1255 AU 48.8 LD 16.3 km/s
2089-02-25 04:26:00 Venus 0.1174 AU 45.7 LD 16 km/s
2091-09-01 12:44:00 Venus 0.111 AU 43.2 LD 20.3 km/s
2118-11-05 19:02:00 Earth 0.1959 AU 76.2 LD 18.7 km/s
2143-10-04 14:31:00 Venus 0.1092 AU 42.5 LD 21.2 km/s
2146-04-10 01:28:00 Venus 0.1076 AU 41.9 LD 16 km/s
2148-10-21 02:46:00 Venus 0.1275 AU 49.6 LD 16.2 km/s

Next ten from today. 1 lunar distance = 384,400 km. Source: JPL close-approach data.

Sources