Comets C/2022 E3 (ZTF) and C/2022 U2 (ATLAS)

Comet C/2022 E3 (ZTF) could be observed between February 6 and 8, 2023. In the night between February 6 and 7 there was a conjunction with another comet, C/2022 U2 (ATLAS), almost at the same time when ZTF crossed the galactic plane.

In all pictures and videos on this site comets and stars are aligned and processed separately, also see the image processing details.

Index

Click on the previews to jump to larger images, videos and descriptions.

Feb 08, 2023. ZTF. Feb 08, 2023. ZTF near SH2-230. Feb 08, 2023. ZTF near SH2-230. Wide field. Feb 07, 2023. ZTF. Feb 07, 2023. ZTF and ATLAS. Feb 06, 2023. ZTF and ATLAS. Feb 06, 2023. Closest approach between ZTF and ATLAS. Feb 06, 2023. ZTF at galactic plane and almost in conjunction with ATLAS.

Feb 08: Comet C/2022 E3 (ZTF) near SH2-230

On February 8 comet C/2022 E3 (ZTF) was close to the large nebula complex SH2-230 in constellation Auriga. The comet was observed between 17:25 and 20:00 UTC in a mostly dark sky (astronomical dawn: 17:59, moon rise: 18:59 UTC).

Comet C/2022 E3 (ZTF) on Feb 08, 2023 — Click on the image or use the buttons to start a video.
The picture shows the positions of the comet and the stars at 18:40 UTC. The video spans the period from 17:35 UTC to 19:50 UTC. Please note how the ion tail changes over time.
Color information where obtained using SDSS I', R', B' filters (mapped to red, green and blue) using instruments 1-3 (see data section). Instrument 4 was used for the high resolution luminance data. The coma of the comet appear blue because its turquoise light (created by photodissociation of dicarbon, see [1]) is only captured by the B' filter.
The field of view is 2.3° × 1.5° and the pixel scale is 5.5 arcsec/pixel. Due to the volatility of the ion tail, the comet was integrated over a period of about 25min (in the image an each video frame).

Comet C/2022 E3 (ZTF) near SH2-230 on Feb 08, 2023 — Click on the image or use the buttons to start a video.
The picture shows the positions of the comet and stars at 18:10 UTC. The video spans the period from 17:35 UTC to 19:50 UTC. Please note how the ion tail changes over time.
This false color image is composed from SDSS I', R', B' data (mapped to red, green and blue) of instruments 1-3 (see data section) and H-alpha, taken from another data set and mapped to red to orange.

The field of view is 6.3° × 4.2° and the pixel scale is 15 arcsec/pixel. Due to the volatility of the ion tail, the comet was integrated over a period of about 45min (in the image an each video frame).

Wide field view of Comet C/2022 E3 (ZTF) near SH2-230 on Feb 08, 2023 — Click on the image to see the image in full resolution using a Javascript viewer.
The pictures shows the positions of the comet and stars at 18:40 UTC. Most of bright emission nebulae in the left half of the image belong to the nebula complex SH2-230. (In the Javascript viewer object annotation can be enabled using key '3' or via menu.) The end of the ion tail is outshined be the bright emission nebulae and also cropped at the field of view boundaries of the cameras used to capture the comet.
This false color image is composed from SDSS I', R', B' data (mapped to red, green and blue) of instruments 1-3 (see data section) and H-alpha, taken from another data set and mapped to red to bright orange.

The field of view is 12° × 8° and the pixel scale is 10 arcsec/pixel at full resolution (in the JavaScript viewer). Integration time for the comet is 45min.

Feb 07: Comet C/2022 E3 (ZTF)

A short time window between sunset and moonrise was used to capture comet C/2022 E3 (ZTF). Comet C/2022 U2 (ATLAS) is also visible in the wide field view.

Comet C/2022 E3 (ZTF) on Feb 07, 2023. FOV: 2.3°x1.6° — The picture shows Comet C/2022 E3 (ZTF) at 17:48 UTC. Due to the volatility of the ion tail, only exposures of a dark period of about 25min between sunset and moonrise where used.
Color information where obtained using SDSS I', R', B' filters (mapped to red, green and blue) using instruments 1-3 (see data section). Instrument 4 was used for the high resolution luminance data. The comas of both comets appear blue because its turquoise light (created by photodissociation of dicarbon, see [1]) is only captured by the B' filter.
The field of view is 2.3° × 1.6° and the pixel scale is 5.5 arcsec/pixel.

Comet C/2022 E3 (ZTF) and Comet C/2022 U2 (ATLAS) on Feb 07, 2023. FOV: 5.2°x3.8° — The picture shows Comet C/2022 E3 (ZTF) at 17:48 UTC. The blue object at the end of the dust tail is Comet C/2022 U2 (ATLAS). Due to the volatility of the ion tail, only exposures of a dark period of about 40min between sunset and moonrise where used.
This false color image is composed from SDSS I', R', B' data (mapped to red, green and blue) of instruments 1-3 (see data section). The field of view is 5.2° × 3.8° and the pixel scale is 12.5 arcsec/pixel.

Feb 06: Comets C/2022 E3 (ZTF) and C/2022 U2 (ATLAS) near the galactic plane

On Feb 06 there was a close apparent approach between comets C/2022 E3 (ZTF) and C/2022 U2 (ATLAS). In that night ZTF also crossed the galactic plane. That unusual event was observed between 17:10 and 00:40 UTC.

The images where captured one day after full moon and therefore suffer from low signal to noise ratio (due to the photon noise from the bright background). The bright background also caused other artifacts which could not be removed completely, see the documentation of artifacts.

Comets C/2022 E3 (ZTF) and C/2022 U2 (ATLAS) on Feb 06, 2023 — Click on the image or use the buttons to start a video.
The larger comet is C/2022 E3 (ZTF), the smaller one is C/2022 U2 (ATLAS). The picture shows the positions of the comets and stars at 18:40 UTC. The video spans the period from 17:30 UTC to 00:30 UTC. Please note how the ion tail changes over time.
Comet ZTF was only integrated over period of 30 min due to the volatility of the ion tail (see the videos). Comet ATLAS and the stars where integrated over the whole observation period of about 7.5h
Color information where obtained using SDSS I', R', B' filters (mapped to red, green and blue) using instruments 1-3 (see data section). Instrument 4 was used for the high resolution luminance data. The comas of both comets appear blue because its turquoise light (created by photodissociation of dicarbon, see [1]) is only captured by the B' filter.
The field of view is 2.1° × 1.5° and the pixel scale is 5 arcsec/pixel.

Comet C/2022 E3 (ZTF) at the galactic plane and almost in conjunction with and comet C/2022 U2 (ATLAS) — Click on the image to see the image in full resolution using a Javascript viewer.
The pictures shows the positions of the comets and stars at 22:53:45 UTC, the moment at which ZTF was on the galactic plane. 54 minutes later both comets where in conjunction (in right ascension). That region is rich of emission nebulae which are also shown in the image.
This false color image is composed from SDSS I', R', B' data (mapped to red, green and blue) of instruments 1-3 (see data section) and H-alpha, taken from another data set and mapped to red to bright orange.

The field of view is 9.2° × 7.2° and the pixel scale is 10 arcsec/pixel at full resolution (in the JavaScript viewer). Integration times are 60min for comet ZTF and 7.5h for the stars and comet ATLAS.

Instrument and image

The comet was simultaneously captured with 5 instruments.

Instruments 1-3:	D=100mm, f=300mm photo lens. SDSS I', R' and B' filter. R' filter combined with 400nm to 650nm band pass filter in oder to block H-alpha. Camera sensor: IMX455 (36mm × 24mm) Used for the wide field images and the color information of the comet in the small field images
Instrument 4:	D=200mm, f=850mmm Newton telescope 400nm to 700nm band pass filter Camera sensor: IMX455 (36mm × 24mm) Used for the luminance information of the comet in the small field images
Instrument 5:	D=200mm, f=850mmm Newton telescope Camera sensor: 36mm × 24mm sensor with RGB color filter array Used for the stars in the small field images. Not used for the comet because sensitivity of instruments 1 to 3 is higher.
H-alpha data:	From this source
Location:	Pulsnitz, Germany
Orientation:	North is up

Image processing

All image processing steps are deterministic. The software which was used can be downloaded here.

Darkfield and flatfield correction, calibration using stars
Background image:
1. Stacking with alignment to stars and dropping of outliers (in that case moving objects)
2. Star subtraction
3. Removing the comet residuals by masking and interpolation of the masked region
4. Add previously subtracted stars
Comet images:
1. Stacking with alignment to the comet and subtraction of the stars and the background
2. Background estimation by masking the comet (plus a wide border) and interpolation of the masked region
3. Low-pass filtering that estimated background and subtracting it from the stacked result
4. Denoising
Shifting the components to the position at the given time and color composition
Dynamic range compression
Tonal correction

Artifacts

The images on this page suffer more or less from a bright background, especially the images captured on Feb 06, one day after full moon. This caused certain artifacts that could not be removed in a save (without altering the image information) and deterministic way.

For a correct evaluation of the images shown above, these artifacts are documented hereinafter.

Inaccuracy of the flatfield correction due to bending of the optics. With a dark background the effect is negligible. In the images from Feb 06 this effect is probably responsible for the green and blue spot in the dust tail of ZTF.
Moon light which illuminated the dew caps / telescope tube. Due to internal reflections this becomes visible in the image. Optical leaks have a similar effect. This kind of artifacts could be strongly reduced by the background correction as described in the previous section. But some of the fluctuations in the ion tail may be caused by this
Color information are heavily denoised at costs of accuracy
Internal reflections of bright stars which appear as small spots mainly in the NIR channel (probably because the lens is not optimized for that wavelength)

References

Jasmin Borsovszky & Klaas Nauta & Jun Jiang & Christopher S. Hansen & Laura K. McKemmish & Robert W. Field & John F. Stanton & Scott H. Kable & Timothy W. Schmidt. (2021). "Photodissociation of dicarbon: How nature breaks an unusual multiple bond". Proc Natl Acad Sci USA. 118 (52) e2113315118. Monthly Notices of the Royal Astronomical Society. stad027.

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