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Comet

West-Hartley

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123P/West-Hartley

Where is it now

Distance from Sun
2.157 AU
True anomaly
17.45°
Distance from Earth
2.962 AU
As of
22 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 — 0.995 AU from the Sun Earth West-Hartley — 2.157 AU from the Sun West-Hartley
Seen from above the ecliptic, north up, to scale. Grid: Earth's orbit in blue. West-Hartley is 2.962 AU from Earth today (24.6 light-minutes).

In the sky

Right ascension
12h 19m 36s
Declination
+08° 18′ 24″
Constellation
Virgo
Distance from Earth
2.96 AU
Elongation from the Sun
30.1° — near the Sun — look low at dusk or dawn

Visible from both hemispheres.

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
3.86 AU
Eccentricity
0.4491
Inclination
15.36°
Orbital period
7.58 years
Perihelion
2.126 AU
Aphelion
5.594 AU
Longitude of ascending node
46.5°
Argument of periapsis
102.98°
Epoch · J2000
2457781.5
Orbit class · JFc
Jupiter-family comet (P < 20 y)
Earth MOID · 466.0 LD
1.1974 AU
Tisserand (Jupiter)
2.832

Orbit quality

Orbit very well determined (uncertainty code 0).

Observations used
3,590
Data arc
16.08 years
First observed
12 September 2010
Last observed
12 October 2026
Residual RMS
0.7 ″
Solution · Shantanu Naidu
14 October 2026

Physical properties

Rotation period
3.7 hours

Visual & observation

Absolute magnitude (H)
8.2
Total magnitude M₁ · K₁ 18.5
8.2

Discovery & classification

Discovered by
West, Richard M.
Discovery date
11 May 1989
Discovery site
European Southern Observatory

Also known as 123P · 123P/1989 E3 · 123P/1995 S2 · 1988 XVI · 1989k

Named

Close approaches 10 on record

When (UTC) Body Distance Lunar distances Relative speed
2044-04-07 05:33:00 Juptr 1.2341 AU 480.3 LD 5.6 km/s
2068-07-26 11:03:00 Juptr 1.3835 AU 538.4 LD 4.3 km/s
2092-05-09 08:07:00 Juptr 1.3965 AU 543.5 LD 4.3 km/s
2115-03-31 10:37:00 Juptr 1.2898 AU 502.0 LD 4.8 km/s
2139-02-09 04:19:00 Juptr 1.7807 AU 693.0 LD 9 km/s
2200-09-27 21:07:00 Jupiter 0.3965 AU 154.3 LD 6.8 km/s
2200-09-27 21:07:00 Juptr 0.3965 AU 154.3 LD 6.8 km/s

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

Sources