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The (very) Little Cub


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This is a bit of an experiment. The discussion that followed my posting of an image a few days ago, brought a very faint target to my attention (thanks @AKB ) . Galaxy ngc 3359 has a small and very faint companion, called the Little Cub (yes, that's the name it actually has in the catalogues).

The Little Cub is a blue compact galaxy, also described as an Extremely Metal-poor Star-forming Galaxy (EMPG) in the constellation Ursa Major (Great Bear, hence the name Little Cub).

To quote from the original paper reporting the discovery:

"[...] making the Little Cub one of the lowest-metallicity star-forming galaxies currently known in the local universe. The Little Cub appears to be a companion of the spiral galaxy NGC 3359 and shows evidence of gas stripping. We may therefore be witnessing the quenching of a near-pristine galaxy as it makes its first passage about a Milky Way–like galaxy."


Little Cub has a gravitational interaction with ngc 3359 and is slowly being devoured by this Milky Way class galaxy. Little Cub has a surprisingly low ratio of Metallic atoms (atomic number larger than 2), meaning that it consists mainly of Hydrogen and Helium, the first two elements that formed in the young Universe. These properties make Little Cub an interesting research subject. But it is a difficult little rascal to image.

Here's my one night attempt (4 hours Luminance and 4 hours RGB) at catching this dwarf galaxy.


Do you see it? No it's not the Big'un at the left, nor any of the small spirals. This image (inverted L) zooms in on it.


Like I said, a difficult little rascal. According to a Swedish expert, the small star inside the circle (lower half) is a magnitude 21.9 red star, and objects down to magnitude 23 can be resolved.

Capture data:

  • Telescope/Camera: SkyWatcher 190MN and ZWO ASI294MM with Optolong LRGB filters
  • 80 x 3 min L frames at 0 gain, 4 hours
  • 20 x 4 min RGB frames per channel, 4 hours

When the moon is out of the way, I plan to add more LRGB and a few hours of Ha.

Edited by wimvb
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Progress is slow on this project. (I'm blaming the moon, because we've had enough clear nights since I posted the first version.)

I'm slowly starting to add Ha (65 subs here, 90 more this night hopefully). But what I really need is more colour and a lot more Luminance. Hopefully we'll have clear nights two weeks from now.

This is at 11 hrs and 50 mins total integration time.


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Hello Wim,

Interesting story and nice to see you chasing after such an off the beaten path object.

If your weather is a bit like mine here in NL, clear skies are abundant in spring, so there is hope to get a "finished"image soon. (It is a race with the increasingly shorter nights, though).




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Dank je wel, @Annehouw.

It’s a bit like in the Netherlands with clear skies and also dry air. But nights get shorter a lot faster up here and from end April we won’t have astro darkness until late August. I should have enough time to finish this project as well two other projects I’m working on.

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On 16/03/2022 at 10:34, ollypenrice said:

Nice project!


Thanks, Olly. Normally I wouldn’t even notice such a faint fuzz. But there is some very interesting physics related to this type of galaxies. That makes this an image with a story.

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