Comet C/2017 T3 (ATLAS) will make its closest approach to the Sun on 19 July, at a distance of 0.82 AU.
From Cambridge on the day of perihelion it will not be observable – it will reach its highest point in the sky during daytime and will be 25° below the horizon at dawn.
The events that comprise the 2018 apparition of C/2017 T3 (ATLAS) are as follows:
| Date | Event |
| 19 Jul 2018 | Comet C/2017 T3 (ATLAS) passes perihelion |
The table below lists the times when C/2017 T3 (ATLAS) will be visible from Cambridge day-by-day through its apparition:
| Date | Constellation | Comet visibility |
| 28 Jun 2018 | Orion | Not observable |
| 30 Jun 2018 | Orion | Not observable |
| 02 Jul 2018 | Orion | Not observable |
| 04 Jul 2018 | Orion | Not observable |
| 06 Jul 2018 | Orion | Not observable |
| 08 Jul 2018 | Orion | Not observable |
| 10 Jul 2018 | Orion | Not observable |
| 12 Jul 2018 | Orion | Not observable |
| 14 Jul 2018 | Monoceros | Not observable |
| 16 Jul 2018 | Monoceros | Not observable |
| 18 Jul 2018 | Monoceros | Not observable |
| 20 Jul 2018 | Monoceros | Not observable |
| 22 Jul 2018 | Canis Major | Not observable |
| 24 Jul 2018 | Canis Major | Not observable |
| 26 Jul 2018 | Puppis | Not observable |
| 28 Jul 2018 | Puppis | Not observable |
| 30 Jul 2018 | Puppis | Not observable |
| 01 Aug 2018 | Puppis | Not observable |
| 03 Aug 2018 | Puppis | Not observable |
| 05 Aug 2018 | Pyxis | Not observable |
| 07 Aug 2018 | Pyxis | Not observable |
A more detailed table of C/2017 T3 (ATLAS)'s position on each night is available here. A diagram of the orbit of C/2017 T3 (ATLAS) is available here.
Finder chart
The chart below shows the path of C/2017 T3 (ATLAS) over the course of its apparition, as calculated from the orbital elements published by the Minor Planet Center (MPC). It is available for download, either on dark background, in PNG, PDF or SVG formats, or on a light background, in PNG, PDF or SVG formats. It was produced using StarCharter.
Comet brightnesses
Comets are intrinsically highly unpredictable objects, since their brightness depends on the scattering of sunlight from dust particles in the comet's coma and tail. This dust is continually streaming away from the comet's nucleus, and its density at any particular time is governed by the rate of sublimation of the ice in the comet's nucleus, as it is heated by the Sun's rays. It also depends on the amount of dust that is mixed in with that ice. This is very difficult to predict in advance, and can be highly variable even between successive apparitions of the same comet.
In consequence, while the future positions of comets are usually known with a high degree of confidence, their future brightnesses are not. For most comets, we do not publish any magnitude estimates at all. For the few comets where we do make estimates, we generally prefer the BAA's magnitude parameters to those published by the Minor Planet Center, since they are typically updated more often.
No estimate for the brightness of comet C/2017 T3 (ATLAS) is currently available.
The comet's position at perihelion will be:
| Object | Right Ascension | Declination | Constellation | Magnitude |
| Comet C/2017 T3 (ATLAS) | 06h44m10s | 9°27'S | Monoceros | 8.6 |
The coordinates are given in J2000.0.
The sky on 19 Jul 2018
| The sky on 19 July 2018 | ||||||||||||||||||||||||||||||||||
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53% 6 days old |
All times shown in EDT.
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Source
This event was automatically generated on the basis of orbital elements published by the Minor Planet Center (MPC) , and is updated whenever new elements become available. It was last updated on 23 Feb 2025.
Image credit
© Andy Roberts 1997. Pictured comet is C/1995 O1 Hale-Bopp.