Interstellar comet 3I/ATLAS (C/2025 N1; hereafter 3I) has been extensively monitored since 2025 November 29 using the imaging capabilities of the Two-Meter Twin Telescope (TTT) and the Transient Survey Telescope (TST) both located at the Observatorio del Teide (IAC, Tenerife, Spain). We confirm the detection of a sunward-oriented tail-like feature in deep TST imaging of 3I. The structure appears as a narrow elongation extending sunward from the central condensation of the coma, with a projected length that increases as the Sun-observer-target angle increases (see linked figure). On 2025 December 19 (perigee), the projected length of the feature is approximately 450000 km. A detailed geometric analysis based on images obtained at different epochs (2025 November 29 and December 19), together with the absence of a fan-shaped structure in the Laplacian-filtered images, indicates that this feature is best explained as a geometric projection of the curved dust tail, rather than as a physically sunward-directed outflow. The measured position angles (PA) of the dust tail are 287.4 +/- 0.5 deg on November 29 and 285.4 +/- 0.5 deg on December 19 (red lines in linked figure). The observed change in the dust-tail PA, 2 +/- 1 deg, is consistent with the corresponding change in the projected velocity-vector PA (from 289.94 deg to 288.63 deg, a difference of 1.3 deg), supporting a geometric interpretation of the observed sunward feature. This feature is compatible with older, large grains confined near the orbital plane in a simple synchrone/syndyne analysis. A faint ion tail is also detected on the December 19 image (yellow line in linked figure). The measured PA angle of ion tail 293.8 +/- 0.5 deg is coincident with the anti-solar PA direction 292.38 deg (yellow arrows in linked figure). Projection-induced sunward tails are well known in solar system comets, but this detection demonstrates that interstellar comets can exhibit comparable dust-tail geometries when observed under favorable viewing conditions. Continued monitoring of 3I/ATLAS as the phase angle evolves will help to further constrain the dust dynamics and grain properties of this object. We encourage additional imaging and modeling efforts to better constrain the dust size distribution and emission history responsible for the observed morphology. The linked figure presents the unprocessed images (right panels) and the corresponding Laplacian-filtered images (left panels) of 3I. The observation date (YYYY-MM-DD), start and end times (UTC), number of sidereal-tracking exposures, and total integration time are indicated above each panel. The projected velocity vector (red arrow) and the antisolar direction (yellow arrow) are shown, together with the image scale and orientation. Red crosshairs mark the comet optocenter. The position angles of the dust and ion tails are indicated by thin red and yellow lines, respectively. Isophotal contours of the original unfiltered image are overplotted on the filtered frame using ten logarithmically spaced levels between the 80th and 95th percentiles of the pixel-intensity distribution. The TST, a 1 m telescope, is equipped with FERVOR-L, a 14304 x 10748 Sony IMX411 BSI sCMOS detector providing a pixel scale of 0.60 arcsec per pixel and a field of view of 2.4 x 1.8 degrees. For the study of fine coma and tail structures, observations were also obtained with TTT3, a 2 m f/6 Ritchey-Chretien telescope currently in its commissioning phase. TTT and TST are operated by Light Bridges in Tenerife, Canary Islands (Spain). The observation time rights (DTO) used for this research were consumed in the PEI -PLANETIX25-. This research used storage and computing capacity in ASTRO POCs EDGE computing center at Tenerife under the form of Indefeasible Computer Rights (ICR).

Image of the interstellar object 3I/ATLAS (top left panel) from a 0.25-meter telescope in Calabria, Italy, taken on December 15, 2025 at 1:58 UTC with 1.38 arcseconds per pixel — corresponding to 3,850 kilometers at the source distance. The other three panels show a brightness map at different wavelength bands centered on 0.658 [R], 0.53 (Green) and 0.445 (Blue) micrometers, using a Larson-Sekanina gradient filter. Their field of view spans 1.6 by 0.7 million kilometers and shows a prominent tightly-collimated anti-tail jet from 3I/ATLAS in the sunward direction, towards the bottom left corner. (Image credit: Toni Scarmato)

Image of the interstellar object 3I/ATLAS (top left panel) from a 0.25-meter telescope in Calabria, Italy, taken on December 15, 2025 at 1:58 UTC with 1.38 arcseconds per pixel — corresponding to 3,850 kilometers at the source distance. The other three panels show a brightness map at different wavelength bands centered on 0.658 [R], 0.53 (Green) and 0.445 (Blue) micrometers, using a Larson-Sekanina gradient filter. Their field of view spans 1.6 by 0.7 million kilometers and shows a prominent tightly-collimated anti-tail jet from 3I/ATLAS in the sunward direction, towards the bottom left corner. (Image credit: Toni Scarmato)

The top panel shows an image of 3I/ATLAS, taken on December 15, 2025 at 02:28:12 UTC on a 0.25-meter telescope in Calabria, Italy. The bottom panel includes the brightness map from a Larson-Sekanina rotational gradient filter on a fraction of the entire field of view, spanning 0.86 by 0.39 million kilometers and featuring an anti-tail going out to half a million kilometers from 3I/ATLAS in the sunward direction towards the lower left. (Image credit: Toni Scarmato).

You can get live location of comet 3I ATLAS from this website.

Figure 1 shows optical magnitudes for 3I/ATLAS from a variety of sources. Comet coma magnitude estimates are highly sensitive to aperture and color, as their diffuse edges mean wider fields of view collect more light, increasing flux and lowering magnitude. Additionally, gas comas have strong spectral emissions, which can bias magnitudes depending on the pass-band. We initially focused on G band as a proxy for the pass-bands of spacecraft telescope cameras. At present the Minor Planet Center Database (MPCD) contains 3989 entries for 3I/ATLAS in 14 different spectral bands, with 48.8% of these entries being in the broad (400 to 1000 nm) G band displayed in Figure 1. In early September, 2025, it became clear that 3I/ATLAS had developed a gas coma, with a characteristic green color from C2 emissions. Since July 2nd, coauthor Thomas Lehmann has acquired a long series of green-filtered optical images and magnitudes, shown on Figure 1 as green squares, in order to obtain visual equivalent magnitudes using a green filter or the green color channel to emphasize gas coma light over dust. The imaging reduction pipeline was also  intended to detect gas coma light to a larger angular extent than typical imaging. These data match the MPCD G band measurements well up until early September, and then clearly show a faster magnitude drift rate. The Comet Observation Database (COBS), maintained by Crni Vrh Observatory and open to amateur contributions, records coma and tail sizes. For 3I/ATLAS, data points with coma diameter >1’ (red dots in Figure 1) match the trend of the Lehmann Green Filter magnitudes well with a bias of +0.5 magnitudes. 

Figure 1 The concentrated, but diffuse appearance of 3I/ATLAS two weeks after its perihelion. a) A 6.5 minutes stacked image at 0.3 arcsec/pix. obtained from TJO telescope and MEIA2 camera on Nov. 13.216, 2025 (JD: 2460992.71), b) A 9º LarsonSekanina filtered image rotated in the false nucleus (red cross) reveals several spirallike jets surrounding the body. In both images, South is top, and West right. 

We report the detection of CN, C3, and C2 gas emission features in the pre-perihelion visible spectrum of interstellar comet 3I/ATLAS taken with the Gemini South 8.1-m telescope at Cerro Pachon (observatory code I11, program GS-2025B-DD-102/PI: Bolin). We used the Gemini Multi-Object Spectrograph (GMOS) to observe 3I/ATLAS on 2025 September 14 23:54 UTC (see attached spectrum and g- and r-band images). The spectrum shows clear detections of CN, C3, and C2 gas emission features at 388 nm, 402 nm, and 517 nm, respectively. Additional CN and C2 gas emission features are seen at 421 nm and 474 nm, as seen in panel A of the attached image. Panel B shows g and r images of the comet, where its detection is divided by the azimuthal average. The enhanced images show evidence of a dust fan ~15 arcsec long, pointing in the anti-solar (southeast) direction, more extended than the compact appearance seen in the initial imaging (Bolin et al. 2025, MNRAS:L, 542, 1, pp. L139-L143). The appearance of the dust fans and morphology is comparable to the features seen in other images of the comet taken before perihelion (Ivanova et al. 2025, ATel #17372, Jewit & Luu, ApJL, 994, 1, id.L3, 13 pp.) and after perihelion (Jewitt & Luu 2025, ATel #17490). This study is based on observations obtained at the international Gemini Observatory, a program of NSF's NOIRLab, which is managed by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation on behalf of the Gemini Observatory partnership. 

Images from the Nordic Optical Telescope on UT 2025 November 11 show that 3I/ATLAS continues as an active, single body, with no evidence for breakup following the recent perihelion passage. Asymmetries in the coma project to position angles 106+/-10 degrees and 301+/-1 degrees. The former is close to the projected orbit (110 degrees) and sunward direction (115 degrees), suggesting that it is the sunward fan observed on the inbound leg of the orbit and consisting of large and slowly launched particles projected sunward by dayside sublimation (c.f. 2025 Ap. J. Letters, 994 L3). The latter is close to the projected antisolar direction (295 degrees) on this date, identifying it as a normal dust tail. Plasma structures evident in recent wide field pictures taken by others are not evident in our data presumably because we used an R filter to isolate the dust, so excluding most gaseous emission lines. The heliocentric, geocentric distances and phase angle on UT 2025 November 11 were 1.43 au, 2.16 au and 22 degrees, respectively. Linked images show 3I/ATLAS with North to the top, East to the left, and a region approximately 0.5 million km wide. The projected antisolar direction (-S) and negative heliocentric velocity vector (-V) are marked. The diffuse object to the upper left of 3I is a galaxy. Other discrete objects are stars. The images are 1) linear stretch 2) contoured 3) color contoured 4) spatially filtered within a 0.13 million km radius region by subtracting the median signal in concentric annuli centered on the brightest pixel. The faint diagonal line from upper left to lower right is an "Elon".