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Comet Near-Earth

Swift-Tuttle

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109P/Swift-Tuttle

Where is it now

Distance from Sun
42.985 AU
True anomaly
173.06°
Distance from Earth
43.609 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.

Sun Earth — 0.998 AU from the Sun Earth Swift-Tuttle — 42.985 AU from the Sun Swift-Tuttle
Seen from above the ecliptic, north up, to scale. Grid: Earth's orbit in blue. Swift-Tuttle is 43.609 AU from Earth today (6.0 light-hours).

In the sky

Right ascension
09h 43m 55s
Declination
-18° 42′ 34″
Constellation
Hydra
Distance from Earth
43.6 AU
Elongation from the Sun
51.16° — near the Sun — look low at dusk or dawn

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
26.092 AU
Eccentricity
0.9632
Inclination
113.45°
Orbital period
133.3 years
Perihelion
0.96 AU
Aphelion
51.225 AU
Longitude of ascending node
139.38°
Argument of periapsis
152.98°
Epoch · J2000
2450000.5
Orbit class · HTC
Halley-type comet
Earth MOID · 0.3 LD
0.0009 AU
Tisserand (Jupiter)
-0.28

Orbit quality

Orbit very well determined (uncertainty code 0).

Observations used
652
Data arc
257.7 years
First observed
8 July 1737
Last observed
29 March 1995
Residual RMS
1.2 ″
Solution · M.S.W. Keesey
9 October 2001

Physical properties

Mean radius
13 km

Visual & observation

Absolute magnitude (H)
4.5
Total magnitude M₁ · K₁ 15
4.5

Discovery & classification

Discovered by
Swift, Lewis
Discovery date
16 July 1862
Discovery site
Marathon, New York

Also known as 109P · -68 · 109P/-68 Q1 · 109P/1737 N1 · 109P/1862 O1 · 109P/188 O1 · 109P/1992 S2 · 1737 II

Near-Earth Object Named

Close approaches 3 on record

Flyby geometry
Ecliptic flyby of Swift-Tuttle at 2126-08-05 15:50 UTC Top-down view of the ecliptic, Earth at the centre, for the 2126-08-05 15:50 UTC close approach of Swift-Tuttle. Catalogue miss distance 59.7 LD · 2.29 × 10⁷ km. The curve is the geocentric path from 2126-08-02 to 2126-08-08, 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 approximate: a two-body Kepler propagation of the catalogue orbital elements, not a numerical integration. The Moon’s position is approximate. The inset is a heliocentric view and is approximate. approximate Sun 59.7 LD · 2.29 × 10⁷ km 2126-08-05 15:50 UTC Earth Moon Heliocentric, approximate

Top-down view of the ecliptic, Earth at the centre, for the 2126-08-05 15:50 UTC close approach of Swift-Tuttle. Catalogue miss distance 59.7 LD · 2.29 × 10⁷ km. The curve is the geocentric path from 2126-08-02 to 2126-08-08, 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 approximate: a two-body Kepler propagation of the catalogue orbital elements, not a numerical integration. The Moon’s position is approximate. The inset is a heliocentric view and is approximate.

When (UTC) Body Distance Lunar distances Relative speed
2124-02-26 00:27:00 Satrn 1.3456 AU 523.7 LD 18.3 km/s
2126-08-05 15:50:00 Earth 0.1534 AU 59.7 LD 58.3 km/s

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

Sources