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Comet

Helin-Roman-Alu

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117P/Helin-Roman-Alu 1

Where is it now

Distance from Sun
5.132 AU
True anomaly
183.65°
Distance from Earth
4.98 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 Helin-Roman-Alu — 5.132 AU from the Sun Helin-Roman-Alu
Seen from above the ecliptic, north up, to scale. Grid: Earth's orbit in blue. Helin-Roman-Alu is 4.98 AU from Earth today (41.4 light-minutes).

In the sky

Right ascension
07h 58m 09s
Declination
+27° 17′ 05″
Constellation
Gemini
Distance from Earth
4.97 AU
Elongation from the Sun
93.69° — well clear of the Sun

Favours the northern hemisphere; low or below the horizon from far south.

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.

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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
4.096 AU
Eccentricity
0.2538
Inclination
8.7°
Orbital period
8.29 years
Perihelion
3.056 AU
Aphelion
5.136 AU
Longitude of ascending node
58.9°
Argument of periapsis
222.69°
Epoch · J2000
2456714.5
Orbit class · JFc
Jupiter-family comet (P < 20 y)
Earth MOID · 796.3 LD
2.0462 AU
Tisserand (Jupiter)
2.967

Orbit quality

Orbit very well determined (uncertainty code 0).

Observations used
6,500
Data arc
22.14 years
First observed
30 November 2003
Last observed
18 January 2026
Residual RMS
0.73 ″
Solution · Davide Farnocchia
9 March 2026

Physical properties

Mean radius
4.50 km

Visual & observation

Absolute magnitude (H)
5.7
Total magnitude M₁ · K₁ 15
5.7

Discovery & classification

Discovered by
Helin, Eleanor, Roman, Brian and Alu, Jeff
Discovery date
2 October 1989
Discovery site
Palomar Mountain Observatory, California

Also known as 117P · 117P/1989 T2 · 1987 XXXVII · 1989w

Named

Close approaches 16 on record

When (UTC) Body Distance Lunar distances Relative speed
2029-09-30 22:24:00 Juptr 1.852 AU 720.7 LD 4.5 km/s
2057-03-10 09:40:00 Juptr 1.7818 AU 693.4 LD 4.1 km/s
2061-08-14 11:34:00 Juptr 1.6511 AU 642.6 LD 6.3 km/s
2083-12-15 03:50:00 Jupiter 0.2149 AU 83.6 LD 3.8 km/s
2083-12-15 03:50:00 Juptr 0.2149 AU 83.6 LD 3.8 km/s
2090-08-31 13:52:00 Juptr 1.2368 AU 481.3 LD 3.2 km/s
2098-08-22 02:10:00 Juptr 0.9638 AU 375.1 LD 4.9 km/s
2143-07-23 07:30:00 Juptr 1.3168 AU 512.5 LD 5.8 km/s
2150-12-22 03:41:00 Juptr 1.3248 AU 515.6 LD 3.6 km/s
2158-01-14 11:41:00 Juptr 0.8728 AU 339.7 LD 4.7 km/s

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

Sources