Comet C/2023 A3 (Tsuchinshan-ATLAS) began its evening apparition during the second week of October 2024. During the period when the comet was at its brightest, observers were still able to spot it despite fighting the light of the waxing Moon. On October 20th, observatory director Billy Teets acquired this 30-second exposure of the comet as it appeared just above Dyer Observatory. To prevent the comet and stars from creating streaks due to the rotation of Earth, the camera was mounted atop a telescope tripod that tracked the motion of the stars. Credit: Billy Teets
Comet C/2023 A3 (Tsuchinshan-ATLAS) put on quite an evening show for us starting the second week of October. The comet, which some billed as possibly being a “comet of the century” due to its anticipated brightness, came in between the Earth and the Sun on October 9th. A few days later, it had moved far enough from the Sun in our sky to become visible at dusk shortly after the Sun disappeared below the horizon. Binoculars provided a much better view, even allowing the long dust tail to be visible in moderate light pollution. As sunlight caused ice to sublimate from the frozen nucleus, a hazy atmosphere, known as the coma, formed around the nucleus. Radiation pressure and solar wind pushed away the freshly released material to create the dramatic dust tail. We often picture the tail as trailing behind the comet, much like a dust cloud kicked up as you speed down a dry country road; however, that is not often the case, especially as the comet makes its way back toward the outer solar system. In fact, the tail can mostly lead the nucleus at this point.
As Comet Tsuchinshan-ATLAS receded from the Sun, an anti-tail began to show. This image, taken on October 15th from Antioch, TN, shows the long dust tail stretching to the upper left of the frame from the bright coma. Extending in the opposite direction toward the treetops at lower right is a faint, needle-like anti-tail composed of more massive dust particles. The fuzzy star just to the right of the bright coma is the globular cluster M5. Credit: Billy Teets
It was around October 14th that comet Tsuchinshan-ATLAS sprouted an “anti-tail.” This tail points toward the Sun and is composed of more massive dust particles left behind in the comet’s orbit. Their greater mass makes them much less susceptible to the effects of solar wind and radiation pressure, which helps to keep the particles from spreading out. This also makes the anti-tail more easily observed when Earth passes through the orbital plane just as we did on October 14. The space-based Solar and Heliospheric Observatory (SOHO), which has been monitoring the Sun 24/7 for nearly three decades and has discovered over 5,000 comets as they come in toward the Sun, also observed a grand view of the comet and its anti-tail, especially as it passed through the comet’s orbital plane with us.
As comet Tsuchinshan-ATLAS moved between the Earth and Sun in early October, the Solar and Heliospheric Observatory (SOHO) observed the passage. In these two images from SOHO’s LASCO C3 camera, the comet’s immense dust tail shines brightly from scattered sunlight. The central blue disk is an “occulter disk” in the camera, which blocks the bright Sun to allow the faint solar corona and other objects in the image to show, and the dark line extending from it to the lower left of the each image is a support arm holding it in place. The white circle within the blue disk indicates the size of the Sun. The small spike on the tip of the comet in the left image is an artifact from the camera resulting from the comet’s brightness and is not the anti-tail. Credit: ESA/NASA/SOHOOn October 14, 2024, Earth and the Sun-orbiting SOHO spacecraft passed through the orbital plane of Comet Tsuchinshan-ATLAS. In this view from SOHO’s LASCO C3 camera, the diagonal line extending down from the upper left is dust left behind after the comet passed through a few days prior (the comet is well outside the frame to the upper left). The dust is relatively well confined to the orbital plane of the comet, and as we passed through this plane to observe it edge-on, the dust trail appeared to narrow. This needle-like appearance is what we observed as the comet’s anti-tail. Credit: ESA/NASA/SOHO
Comet Tsuchinshan-Atlas came into the inner solar system on highly eccentric elliptical orbit (the path’s shape resembled an extremely stretched rubber band). After feeling planetary gravitational effects, its orbit has changed a bit and is now slightly hyperbolic. As a result, it may never return to the inner solar system.
Comet Tsuchinshan-ATLAS became bright enough during mid-October to be seen in bright moonlight and provided an easy target for cameras of all types. Dyer Observatory’s all-sky camera, which is mounted atop the observatory and images the sky 24/7, caught the comet (arrowed) for about a week as dusk faded. Credit: Dyer Observatory
