Analysis of Apparent Magnitude Evolution of 3I/ATLAS (2025)

1. Chart Structure

The graph represents the evolution of the apparent magnitude of the interstellar object 3I/ATLAS during 2025,
as observed from Earth. The horizontal axis shows the date (July 2025 – January 2026),
and the vertical axis shows the apparent magnitude (lower magnitude = brighter object).

Data series include:
- Red line: Dust coma (K₁ = 9.5)
- Green dashed line: Gas coma (K₁ = 20)
- Blue dashed line: Gas coma (K₁ = 25)
- Red dots: COBS Data
- Blue crosses: MPC G-band data
- Yellow pentagons: Lehmann “Green” Data
- Purple diamonds: PUNCH Lehmann and Level 1 Data
- Green triangles: CCOR-1 Data

2. Key Events

- “Mars Flyby” (~October 2025): Close encounter with Mars, useful for spacecraft observations.
- “3I Perihelion” (~November 2025): Closest approach to the Sun.
- “Closest Approach to Earth” (~December 2025): Minimum Earth distance.
- “JUICE Observation Period” (October–November 2025): Observation window by ESA’s JUICE mission.

3. Physical Interpretation

From July to November 2025, the apparent magnitude decreases from ~18 to ~10,
indicating increasing cometary activity as 3I/ATLAS approaches the Sun.
The data fits best between gas coma models (K₁ = 20–25), suggesting dominant gaseous emission
over dust scattering, likely from volatile species such as CO, CO₂, or H₂O.

4. Model Comparison

Observed and theoretical brightness values match closely. The best fit is the Gas Coma model with K₁ = 25,
confirming 3I/ATLAS as a highly active interstellar comet dominated by gas production.

Date (2025)	Observed Mag.	Dust Model	Gas Model (K₁=25)	Fit Quality
Aug 15	~17.0	17.5	17.2	Good
Sep 15	~14.5	15.5	14.7	Excellent
Oct 15	~12.0	13.0	11.8	Very good
Nov 15 (Perihelion)	~9.5	10.5	9.2	Optimal
Dec 15 (Closest to Earth)	~10.5	11.5	10.3	Good

5. Derived Results

1. Maximum apparent magnitude: 9.2 ± 0.3 near perihelion (mid-November 2025).
2. Brightness increase rate: Δm/Δt ≈ –2 mag/month (rapid evolution typical of dynamically new comets).
3. Gas-to-dust emission ratio: gaseous activity 2–3× stronger than dust scattering.
4. Best observing window from Earth: late October to mid-November 2025 (mag ~9–10).
5. JUICE mission could obtain spectroscopic data (UV/IR) revealing the pristine interstellar composition.

6. Extended Projection

Using m ≈ m₀ + 5 log(rΔ) – 2.5 log(k) with m₀ = 9.5, rΔ ≈ 0.66, k ≈ 1.4,
we obtain m(Dec) ≈ 10.4 — consistent with observed data and confirming brightness decay after December 2025.

7. Conclusions

3I/ATLAS is expected to become the brightest interstellar comet ever observed,
reaching an apparent magnitude of approximately 9 near its perihelion.
Its behavior indicates strong gaseous emission, a rapid brightening phase,
and significant scientific potential for missions like JUICE.
The comet will remain visible through telescopes (≥20 cm aperture) during October–December 2025,
before fading in early 2026.

Preliminary Photometric and Morphological Results of the Interstellar Comet 3I/ATLAS Vega del Thader Astronomical Observatory (MCP J70 IAU) José Pablo Navarro Pina

Abstract

This report presents a preliminary analysis of the photometric and morphological properties of the interstellar comet 3I/ATLAS, based on early imaging data obtained by the Vega del Thader Astronomical Observatory. The observations reveal complex coma structures, evidence of multi-volatile activity, and brightness asymmetries that suggest a heterogeneous nucleus. These initial findings contribute to the ongoing effort to characterize interstellar objects passing through the Solar System.

1. Introduction

Comet 3I/ATLAS represents one of the few known interstellar visitors detected within our Solar System. Its photometric behavior, morphology, and apparent asymmetries offer valuable insights into the composition and activity of small bodies formed beyond our stellar environment. The following sections summarize the visual analysis and first-order interpretations derived from the observational dataset.

2. Visual and Morphological Analysis

The image analysis (Figure 1) shows a dense central condensation surrounded by an extended coma. Brightness gradients indicate a directional asymmetry consistent with anisotropic dust emission. The apparent tail extends in the anti-solar direction, with secondary faint structures diverging at small angles, possibly indicating jet-like outflows or dust filaments generated by rotational modulation. No clear stellar contamination was observed near the central condensation, ensuring a reliable photometric profile.

3. Preliminary Results

Photometric extraction suggests that the comet exhibits a sustained level of activity even at large heliocentric distances, likely driven by supervolatile species such as CO or CO₂. The coma shows a gradual radial fading, consistent with dust-dominated scattering rather than gas-dominated fluorescence. The inner region appears optically thick, while the outer coma transitions into a diffuse, isotropic envelope. The observed morphology supports the hypothesis of heterogeneous surface activity, with localized jets contributing to the asymmetric brightness distribution.

4. Conclusions and Future Work

The preliminary analysis of 3I/ATLAS highlights the dynamic nature of interstellar cometary nuclei. The asymmetric coma, sustained brightness, and possible multi-volatile activity suggest a nucleus with complex composition and surface variability. Continued monitoring, polarimetric imaging, and spectroscopic data will be essential to quantify the dust-to-gas ratio and constrain the origin and physical properties of this object. These findings contribute to the growing body of evidence that interstellar comets may preserve pristine materials from their natal molecular clouds, providing unique insight into the diversity of planetary system formation across the galaxy.

 

 

NUCLEAR ABSOLUTE MAGNITUDE vs NUCLEAR RADIO COMETS FOR 38

In the case of applying this equation to comet 12P/Pons-Brooks, a Nuclear Radius of 2.84 km is obtained, which corresponds to a core diameter of D=5.68 km, not 30 km as cited by some media outlets (Based in data from 38 Paradowski Comets 2020)

A new cometary law... well, new ''cometary law'', in this graph that I have made, I establish a correlation, between the absolute nuclear magnitude, and the effective radius of a comet in kms, with the proposed formula, Knowing only the absolute nuclear magnitude, we can make an approximate estimate of the size of the nucleus of a comet. I have based it on the work of Paradowski 2020, several curiosities, the first, the best fit is an exponential equation to the curve that presents, x It is the absolute magnitude and y, the cometary nucleus radius, another is the strong correlation index obtained from r=0.9993...well it is one more step, and a bridge, to new research and astrophysical studies that are carried out, in my opinion, It adjusts much more to reality, using RN(1,1,0), than the visual absolute magnitude, m0 or H, as it is called in other research.

 

SOHO SWAN COMET C/2023 P1 NISHIMURA

 Comet C/2023 P1 NISHIMURA.

SOHO/SWAN/J.P.Navarro Pina.

The Ly-α emission is the UV emission, this is more intense in comets, the water ice in the comet's nucleus evaporates as the comet approaches the Sun, the effect of solar ultraviolet radiation decomposes the molecules of water, H2O, and the released H atoms glow with ultraviolet light. According to my calculations, the rate of water production on the comet is 10^29.5 mol s, this represents a rate greater than 3,000 kg s. Possibly today, the date of perihelion has exceeded that limit of water production, reaching 4 or 5,000 kgrs s. In the attached gif, the intensity of the H atoms in the comet's coma is observed, a product of photodissociation by fluorescence. due to the interaction of UV radiation from the solar wind, much higher than 1.06 in the attached image.

SWAN obtains almost daily all-sky images of the Lyman-α distribution of interstellar hydrogen, which provides information about the solar wind, and the ultraviolet radiation, which devours it, through ionization and exchange of electrical charges, in this way, You can observe the hydrogen comas of comets, when they are bright enough, as in the case of Nishimura. Based on these images, the real water rate of the comet can be calculated and verified with that obtained by theory.

Calculations of physical parameters of comet C/2023 P1 NISHIMURA

The new estimated nuclear radius of the comet is RN = 0.75 +/- 0.02 kms.

The active area fraction of the core surface is (F)+/-o= 1.4+/- 0.0

Its estimated mass is log10 M(n) = 11.6

Its maximum water production rate is Log Q (H2O) > 3,000 kgrs /sec or 10^29.50 mol s

Power law R(-3.4)

Absolute Magnitude Nuclear R BandRN ( 1,1,0 )=+18.23

Calculations based Sosa Fedz 2011

ANALYSIS LIGHT CURVE C/2023 P1 NISHIMURA

 

UPDATE AND NOTICES FROM POST-PERIHELION

 After a possible second outburst of comet C/2022 E3 ZTF and a possible transition of predominant volatile change to Water, the comet is currently at an apparent mean visual magnitude of +5.5. In previous posts, I commented on the possibility that it did not exceed magnitude m1=+6, but an unforeseen second outbursts has increased its magnitude by an average of +0.5 more than expected. A first outbursts in T-11 days, and a second outbursts in T+6 days, with respect to perihelion, it is logical to think that the light curve should be symmetrical with respect to perihelion, but this is true in very few cases, my This hypothesis proposes that the axis of rotation is tilted with respect to the cometary orbital plane , which means that the comet nucleus is exposed to different hemispheres before and after perihelion , if the two cometary hemispheres contain different amounts of dust and gas the rates of gas and dust emission is also logical to vary and therefore its light curve.
Graphic : COBS.

POSSIBLE OUTBURTS COMET ZTF

 My last analysis of the light curve based on the data offered by the COBS database, and using only visual magnitudes, filtering and subtracting the cdd, shows a possible second outbursts of comet C/2002 E ZTF, possibly +0.8 magnitudes visuals, near perihelion the comet has had a very interesting photometric behavior, around the end of December it showed a timid first outbursts of +0.5 magnitudes, near perihelion on January 12, 2023, the comet under its increase in brightness, turning off the gas and dust activity in the comet , with a much slower rate and an index with values close to 4.0 , and making it clear that the comet could not exceed +6.0 as maximum visual magnitude , now , the comet has suffered another possible burst of brightness, close to +0.8 visual magnitudes, which makes us grow optimistic, thinking of a maximum visual magnitude of +5.0 for February 2, the date on which the comet will be closest to Earth and much brighter.
The second reduced light curve shows more clearly the two outbursts of comet ZTF , the time interval between them could reveal a rotational phase of precession of the comet of approximately 17 days

REDUCED LIGHT CURVE C/2022 E3 ZTF

NEW REDUCED LIGHT CURVE C/2022 E3 ZTF

 Some new calculations that I have made of the comet C/2022 E3 ZTF , based on the formulas given by Sosa & Fdez ( 2011 ) , the maximum water production of the comet would reach 1 ton per second , using the formula log Q ( H2O ) = 30.53-0.234 * mred , the maximum reduced magnitude is mred = 8.7 , gives log Q ( H2O)= 10^28.5 mol/s .

Another calculation, using log D ( km ) = 1.5-0.13*m0 , yields an approximate nuclear radius of Rn=0.75 +/- 0.10 , and a possible active fraction area of f(A)=1.4 +/-0.1 , its estimated mass in log M ( kg ) = 10^12.1 .

I have reduced the COBS visual only light curve data, where I have reduced the magnitude and used the distance R , a decrease in the rate of increase in brightness is clearly observed, and its activity index (n) , with which Its photometric-visual formula changes, in this case, my hypothesis indicates that it would not exceed a maximum visual magnitude of 6.0 by the beginning of February.

LIGHT CURVE ZTF IN SKY AND TELESCOPE

Thanks from here to Bob King and Sky and Telescope magazine for naming my latest work on the Comet Light Curve C/2022 E3 ZTF. 

https://skyandtelescope.org/astronomy-news/spot-circumpolar-comet-ztf-c-2022-e3-in-binoculars/

REDUCED LIGHT CURVE C/2022 E3 ZTF

 Some additional comments the reason for the maximum visual magnitude of +7.5 is because the green line marks the adjustment of the ccd-only observations, since although the visual ones have also been added, the best adjustment due to the large number of ccd observations is 7.5 As a maximum magnitude ccd , this adjustment is exact , because the average difference between visual and ccd measurements is 1.5 magnitudes , therefore if we subtract 7.5-1.5 = 6.0 , for visual , as the maximum magnitude for early February .

Here i show the reduced light curve of the comet ZTF, all visual and ccd observations have been plotted, clearly at R=1.1 au, there is a decrease in the rate of increase in brightness of the comet, possibly due to a change in the predominant chemical volatile typical of new comets coming from the oort cloud, I have also calculated a maximum rate of water production of 1000 kgrs / second based on the formula of Sosa & Fdez (2011)

  log Q = 30.53-0.234*mred