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Comet

Hartley

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100P/Hartley 1

Where is it now

Distance from Sun
4.495 AU
True anomaly
207.24°
Distance from Earth
3.887 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 Hartley — 4.495 AU from the Sun Hartley
Seen from above the ecliptic, north up, to scale. Grid: Earth's orbit in blue. Hartley is 3.887 AU from Earth today (32.3 light-minutes).

In the sky

Right ascension
04h 48m 59s
Declination
+36° 39′ 21″
Constellation
Perseus
Distance from Earth
3.88 AU
Elongation from the Sun
122.47° — 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.

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
3.428 AU
Eccentricity
0.4138
Inclination
25.58°
Orbital period
6.35 years
Perihelion
2.01 AU
Aphelion
4.847 AU
Longitude of ascending node
37.76°
Argument of periapsis
181.87°
Epoch · J2000
2457114.5
Orbit class · JFc
Jupiter-family comet (P < 20 y)
Earth MOID · 390.3 LD
1.0029 AU
Tisserand (Jupiter)
2.851

Orbit quality

Orbit very well determined (uncertainty code 0).

Observations used
644
Data arc
37.17 years
First observed
13 June 1985
Last observed
15 August 2022
Residual RMS
0.7 ″
Solution · Otto Matic
31 July 2025

Visual & observation

Absolute magnitude (H)
9.9
Total magnitude M₁ · K₁ 23.5
9.9

Discovery & classification

Discovered by
Hartley, Malcolm
Discovery date
13 June 1985
Discovery site
U. K. Schmidt Telescope Unit

Also known as 100P · 100P/1985 L1 · 100P/1991 E1 · 1985 VII · 1985f · 1991 VII · 1991j

Named

Close approaches 15 on record

When (UTC) Body Distance Lunar distances Relative speed
2083-02-10 16:13:00 Juptr 0.6372 AU 248.0 LD 6.7 km/s
2094-12-04 21:59:00 Jupiter 0.4716 AU 183.5 LD 6.6 km/s
2094-12-04 21:59:00 Juptr 0.4716 AU 183.5 LD 6.6 km/s
2106-12-03 19:46:00 Juptr 1.6012 AU 623.1 LD 9.1 km/s
2166-01-30 13:58:00 Juptr 1.8553 AU 722.0 LD 10.8 km/s
2177-10-12 05:20:00 Jupiter 0.4423 AU 172.1 LD 7.1 km/s
2177-10-12 05:20:00 Juptr 0.4423 AU 172.1 LD 7.1 km/s
2189-08-20 07:28:00 Juptr 0.767 AU 298.5 LD 7.8 km/s

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

Sources