APOD: Galaxies and a Comet (2023 Oct 20)

[APOD Robot]

Galaxies and a Comet

Explanation: Galaxies abound in this sharp telescopic image recorded on October 12 in dark skies over June Lake, California. The celestial scene spans nearly 2 degrees within the boundaries of the well-trained northern constellation Canes Venatici. Prominent at the upper left 23.5 million light-years distant is big, beautiful spiral galaxy NGC 4258, known to some as Messier 106. Eye-catching edge-on spiral NGC 4217 is above and right of center about 60 million light-years away. Just passing through the pretty field of view is comet C/2023 H2 Lemmon, discovered last April in image data from the Mount Lemmon Survey. Here the comet sports more of a lime green coma though, along with a faint, narrow ion tail stretching toward the top of the frame. This visitor to the inner Solar System is presently less than 7 light-minutes away and still difficult to spot with binoculars, but it's growing brighter. Comet C/2023 H2 Lemmon will reach perihelion, its closest point to the Sun, on October 29 and perigee, its closest to our fair planet, on November 10 as it transitions from morning to evening northern skies.

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[Ann]

Galaxies and a Comet. Image Credit & Copyright: Dan Bartlett

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Well, nice! It's always interesting to see comets in the company of deep-sky objects. Some absolutely lovely images were taken when Comet C/2014 Q2 Lovejoy passed near the Pleiades (and the Hyades, and the California Nebula). A gorgeous picture was taken by Leonardo Orazi:

Cyan-green comet with a blue tail, C/2014 Q2 Lovejoy passing near yellow-orange Aldebaran in the Hyades, blue Pleiades and red California Nebula. Credit and copyright: Leonardo Orazi.

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Compared with the sizzling colors of the deep-sky objects in Leonardo Orazi's image, the background galaxies in today's APOD look bland. And indeed, the most famous picture of galaxy M106 is so much more colorful than what we can see in today's APOD:

M106 in visible and infrared light. Credit: NASA, ESA, the Hubble Heritage Team (STScI/AURA), and R. Gendler (for the Hubble Heritage Team). Acknowledgment: J. GaBany

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Wow, sizzling!!! But the colors here are either mapped (the infrared data) or very saturated. The appearance of M106 in today's APOD is not wrong, but the colors are very unsaturated. However, other objects in the APOD are nicely colored, for example blue B-type star HD 106420, orange K-type star SAO 44089 and yellowish late G-type star HD 106556 (which is whiter in color than I just suggested):

The star colors here look good. So we have very good reasons to believe that NGC 4217 (at left in the picture) is dominated by stars like yellow HD 106556 and orange SAO 44089.


And of course it's really funny that a green comet is called C/2023 H2 Lemmon! It doesn't look much like a lemon. But frankly it doesn't look much like a lime either, but more like a green traffic light:

A green traffic light.

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A lime.

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Neither a lemon nor a lime, but a green traffic light! That's what almost all comets are. And the light is always green when comets are moving along their own orbital "roads" in the solar system.

Unless, of course, their orbital roads cause the comets to hit an obstacle. Such as the Sun.

Click to play embedded YouTube video.

Ouch! There should have been a red light for that comet! Instead, there was blinding white light, incredible heat and incineration.

Ann

[Roy]

A green electric traffic light indeed. Any chance analysis of the spectrum will show us the contents? The “dirty snowball” theory is pretty well disproven by flybys and impacts. It would also be interesting to see a graph of size versus solar distance of the coma.

[Chris Peterson]

A green electric traffic light indeed. Any chance analysis of the spectrum will show us the contents? The “dirty snowball” theory is pretty well disproven by flybys and impacts. It would also be interesting to see a graph of size versus solar distance of the coma.

The "dirty snowball theory" is fully supported by all of our observational evidence, including flybys and impacts. No idea where you're getting that!

The green comas are well understood, the product of emissions from C₂ (mainly) and CN₂ (secondarily). Spectroscopically (mostly outside the visible spectrum) we see other outgassed components: mostly water (90% or more of the gaseous coma), CO₂, ammonia, methane and other hydrocarbons.

Because the ratio of rock to volatiles varies widely between different comets, so too does the activity as they warm, and therefore the size of the coma with distance to the Sun.

[orin stepanek]

Neat; I love the photo! The comet C2023 H2 is a good fit with Ngc
4253!

[johnnydeep]

"Here the comet sports more of a lime green coma though,"

Ok, what is the "though" in that sentence comparing the "lime green coma" to?

[johnnydeep]

I love that image of M106 that Ann posted above, and reproduced below. It looks like it has 4 arms, three more reddish and one more blueish!

M106 in visible and infrared light. Credit: NASA, ESA, the Hubble Heritage Team (STScI/AURA), and R. Gendler (for the Hubble Heritage Team). Acknowledgment: J. GaBany

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[Ann]

"Here the comet sports more of a lime green coma though,"

Ok, what is the "though" in that sentence comparing the "lime green coma" to?

It may have something to do with the fact that the comet is called C/2023 H2 Lemmon (Lemmon)? So the comet is not a lemon but a lime?

Ann

[Roy]

A green electric traffic light indeed. Any chance analysis of the spectrum will show us the contents? The “dirty snowball” theory is pretty well disproven by flybys and impacts. It would also be interesting to see a graph of size versus solar distance of the coma.

The "dirty snowball theory" is fully supported by all of our observational evidence, including flybys and impacts. No idea where you're getting that!

The green comas are well understood, the product of emissions from C₂ (mainly) and CN₂ (secondarily). Spectroscopically (mostly outside the visible spectrum) we see other outgassed components: mostly water (90% or more of the gaseous coma), CO₂, ammonia, methane and other hydrocarbons.

Because the ratio of rock to volatiles varies widely between different comets, so too does the activity as they warm, and therefore the size of the coma with distance to the Sun.

Rosetta & Comet C-G, Shoemaker-Levy 9 impacting Jupiter. Pieces of the latter does not mean that the comet broke up. Could have been a gaggle of chunks traveling together like C-G’s two lobes. The latter comet’s organic compounds are not satisfactorily explained.

[Chris Peterson]

A green electric traffic light indeed. Any chance analysis of the spectrum will show us the contents? The “dirty snowball” theory is pretty well disproven by flybys and impacts. It would also be interesting to see a graph of size versus solar distance of the coma.

The "dirty snowball theory" is fully supported by all of our observational evidence, including flybys and impacts. No idea where you're getting that!

The green comas are well understood, the product of emissions from C₂ (mainly) and CN₂ (secondarily). Spectroscopically (mostly outside the visible spectrum) we see other outgassed components: mostly water (90% or more of the gaseous coma), CO₂, ammonia, methane and other hydrocarbons.

Because the ratio of rock to volatiles varies widely between different comets, so too does the activity as they warm, and therefore the size of the coma with distance to the Sun.

Rosetta & Comet C-G, Shoemaker-Levy 9 impacting Jupiter. Pieces of the latter does not mean that the comet broke up. Could have been a gaggle of chunks traveling together like C-G’s two lobes. The latter comet’s organic compounds are not satisfactorily explained.

No idea what you're talking about.

[Ann]

I love that image of M106 that Ann posted above, and reproduced below. It looks like it has 4 arms, three more reddish and one more blueish!

M106 in visible and infrared light. Credit: NASA, ESA, the Hubble Heritage Team (STScI/AURA), and R. Gendler (for the Hubble Heritage Team). Acknowledgment: J. GaBany

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M106 does have four arms, but one set of arms is "anomalous". (Or is that six arms, where two sets of arms are anomalous?)

Composite image of NGC 4258 features X-rays from Chandra (blue), radio waves from the VLA (purple), optical data from Hubble (yellow and blue), and infrared with Spitzer (red). NGC 4258 is well known to astronomers for having 'anomalous' arms that are not aligned with the plane of the galaxy, but rather intersect with it. Researchers are trying to understand how the giant black hole in the center of NGC 4258 is affecting the rest of the galaxy.

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The way I understand it, the strange arms are made of gas, not stars, and their formation and creation has something to do with conditions in the center of M106.

Yeah, I know. Very illuminating.

Ann

[Christian G.]

I love that image of M106 that Ann posted above, and reproduced below. It looks like it has 4 arms, three more reddish and one more blueish!

M106 does have four arms, but one set of arms is "anomalous". (Or is that six arms, where two sets of arms are anomalous?)

The way I understand it, the strange arms are made of gas, not stars, and their formation and creation has something to do with conditions in the center of M106.

Yeah, I know. Very illuminating.

Ann

I've read the following two comments of yours Ann several times and they ARE very illuminating! viewtopic.php?p=312327&hilit=m106#p312327
(I also love that image of M106, even have a big laminated poster of it at home)

[johnnydeep]

"Here the comet sports more of a lime green coma though,"

Ok, what is the "though" in that sentence comparing the "lime green coma" to?

It may have something to do with the fact that the comet is called C/2023 H2 Lemmon (Lemmon)? So the comet is not a lemon but a lime?

Ann

Yes, that's the answer of course. Sadly, the witty reference was lost on silly me.

[johnnydeep]

I love that image of M106 that Ann posted above, and reproduced below. It looks like it has 4 arms, three more reddish and one more blueish!

M106 does have four arms, but one set of arms is "anomalous". (Or is that six arms, where two sets of arms are anomalous?)

The way I understand it, the strange arms are made of gas, not stars, and their formation and creation has something to do with conditions in the center of M106.

Yeah, I know. Very illuminating.

Ann

I've read the following two comments of yours Ann several times and they ARE very illuminating! viewtopic.php?p=312327&hilit=m106#p312327
(I also love that image of M106, even have a big laminated poster of it at home)

Which one, the "four arm" or the "six arm" version?

[Christian G.]

M106 does have four arms, but one set of arms is "anomalous". (Or is that six arms, where two sets of arms are anomalous?)

The way I understand it, the strange arms are made of gas, not stars, and their formation and creation has something to do with conditions in the center of M106.

Yeah, I know. Very illuminating.

Ann

I've read the following two comments of yours Ann several times and they ARE very illuminating! viewtopic.php?p=312327&hilit=m106#p312327
(I also love that image of M106, even have a big laminated poster of it at home)

Which one, the "four arm" or the "six arm" version?

The one from your post above.

[johnnydeep]

I've read the following two comments of yours Ann several times and they ARE very illuminating! viewtopic.php?p=312327&hilit=m106#p312327
(I also love that image of M106, even have a big laminated poster of it at home)

Which one, the "four arm" or the "six arm" version?

The one from your post above.

Ah, the one first posted by Ann. There are various size jpegs and a cool zoomable version at https://esahubble.org/images/ann1301a/

[Ann]

M106 does have four arms, but one set of arms is "anomalous". (Or is that six arms, where two sets of arms are anomalous?)

The way I understand it, the strange arms are made of gas, not stars, and their formation and creation has something to do with conditions in the center of M106.

Yeah, I know. Very illuminating.

Ann

I've read the following two comments of yours Ann several times and they ARE very illuminating! viewtopic.php?p=312327&hilit=m106#p312327
(I also love that image of M106, even have a big laminated poster of it at home)

Which one, the "four arm" or the "six arm" version?

Maybe the six arm version?

Ann

[johnnydeep]

I've read the following two comments of yours Ann several times and they ARE very illuminating! viewtopic.php?p=312327&hilit=m106#p312327
(I also love that image of M106, even have a big laminated poster of it at home)

Which one, the "four arm" or the "six arm" version?

Maybe the six arm version?

6 arms in M106 Chandra Hubble Spitzer.png

Ann

Well, now I'm not sure. Above, he said the one from my post when replying to me, which would have been the one with four arms. But frankly, both images are quite poster worthy!