Observation by Robin Leadbeater: Comet 2025 3I (ATLAS) Spectrum

Uploaded by

Robin Leadbeater

Observer

Robin Leadbeater

Observed

2025 Nov 16 - 04:59

Uploaded

2025 Nov 21 - 10:14

Objects

Spectrum
C/2025 N1

Equipment

ALPY 200 spectrograph
ALPY 600 spectrograph
ATIK 428 ex camera
Celestron C11 SCT 280mm aperture f5.5

Exposure

16x300s, 8x300s

Location

Wigton, Cumbria, UK

Target name

C/2025 3I (ATLAS)

Title

Comet 2025 3I (ATLAS) Spectrum

About this image

Although it has come on a long journey, this interstellar comet looks typical of comets in our own solar system based on low resolution spectra in the visible region, taken at very low resolution with the faint object ALPY200 spectrograph and at higher but still low resolution with the ALPY600. (A wider slit than usual (35 compared with 23 micron) was used to increase the amount of light captured from these diffuse objects).

The graphic shows the guider image of the comet on the slit as seen in a 15 second exposure, the raw uncalibrated spectrum images and the final ALPY 600 spectrum compared with a typical solar system comet 2020 F3 (NEOWISE). The spectrum is dominated by scattered sunlight from dust, CN emission in the UV and C2 (Swan band) emission in the blue/green. (3I is too far from the sun to produce the strong sodium line emission seen in F3.

Spectra downloadable from the BAA spectroscopy database

Files associated with this observation

2025_3I_RL_THO_20251115-16.png (437.7 kB)

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Dominic Ford, Alun Halsey, Mike Harlow

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