APOD: The Double Cluster in Perseus (2021 Oct 08)

[APOD Robot]

The Double Cluster in Perseus

Explanation: This pretty starfield spans about three full moons (1.5 degrees) across the heroic northern constellation of Perseus. It holds the famous pair of open star clusters, h and Chi Persei. Also cataloged as NGC 869 (top) and NGC 884, both clusters are about 7,000 light-years away and contain stars much younger and hotter than the Sun. Separated by only a few hundred light-years, the clusters are both 13 million years young based on the ages of their individual stars, evidence that they were likely a product of the same star-forming region. Always a rewarding sight in binoculars, the Double Cluster is even visible to the unaided eye from dark locations. But a shroud of guitar strings was used to produced diffraction spikes on the colorful stars imaged in this vibrant telescopic view.

<< Previous APOD

This Day in APOD

Next APOD >>

[Ann]

Ah, the Double Cluster in Perseus!

The Double Cluster in Perseus. Photo: Jack Groves.

The Couble Cluster in Perseus. Photo: Roth Ritter.

---

Me being me, I prefer Roth Ritter's image at right, because the bright B-type stars in NGC 869 (at top in Jack Groves' image, at right in Roth Ritter's image) and NGC 884 look bluish in his picture. And these stars really are bluish, but admittedly they are reddened by 7,500 light-years of dust. So it's not wrong to show them as all white as Jack Groves has done, but it's not wrong to show them as bluish, either.

The Double Cluster is a unique pair of clusters in the Milky Way, as far as I know. There is no other known example in our galaxy of two really giant young clusters that are so similar in mass, so perfectly similar in age and so close together in space. NGC 869 and NGC 884 are both 12.8 million years old, according to Wikipedia.That means that they are really young, but not young enough to be babies or toddlers, and they have lost their O-type stars. (So you may think of them as a pair of really strapping 12-year-old twin boys or twin girls, why not?)

Click to view full size image

You have to wonder what forces conspired to create two such amazingly rich and massive clusters in such close proximity, all in one go!

Anyway. Can't keep this from you.

---

Cassiopeia wide field. Image: Tom Wildoner.

Look at the picture at left. Can you guess what it is? It looks a little bit like the "W" in Cassiopeia, doesn't it? We can see a number of individual bright stars in a vaguely W-shaped configuration, and something that looks like a background cluster is visible at right. It is not too unlike Cassiopeia. By the way, don't miss the Double Cluster at lower left in Tom Wildoner's image at right.

Okay. What you are seeing in the picture at left is the Double Cluster in infrared. The individual bright stars are the red supergiants scattered around NGC 884. The seeming little "cluster" at right is NGC 869, which does not contain any red supergiants.

This is what the Double Cluster will look like when the James Webb telescope is looking at it!!!

Ann

[Whiskybreath]

I find diffraction spikes quite distracting - especially when artificially introduced! However, in the frame of an exceedingly distant object (ie Hubble's renditions of galaxy groups) the appearance of one or two gives a measure of the scale of the piece.

[orin stepanek]

I like this view: they could almost be one cluster except for the thin
lane between them!
The stars being hotter and younger than the sun; do they be size
comparable to old Sol?

[Ann]

Click to view full size image

I like this view: they could almost be one cluster except for the thin
lane between them!
The stars being hotter and younger than the sun; do they be size
comparable to old Sol?

The bright stars of the Double Cluster are much larger and more massive than the Sun.

ThoughtCo wrote:

While red supergiants are the largest stars, each with a radius between 200 and 800 times the radius of our Sun, blue supergiants are decidedly smaller. Most are less than 25 solar radii. However, they have been found, in many cases, to be some of the most massive in the universe. (It's worth knowing that being massive isn't always the same as being large. Some of the most massive objects in the universe—black holes—are very, very small.) Blue supergiants also have very fast, thin stellar winds blowing away into space.

But because NGC 869 and NGC 884 are such rich clusters, we can be sure that there are (or will be!!!) stars in them that are comparable to the Sun in mass. The solar-mass stars of NGC 869 and NGC 884 may be smaller than the Sun, because they are very young - maybe possibly maybe they have not been fully born yet, or got their hydrogen fusion going, since they - or rather, since their very massive siblings - are only some 13 million years old. That's not a lot, in view of the fact that the Sun is about 5 billion years old!

Ann

[johnnydeep]

The Double Cluster in Perseus

Explanation: This pretty starfield spans about three full moons (1.5 degrees) across the heroic northern constellation of Perseus. It holds the famous pair of open star clusters, h and Chi Persei. Also cataloged as NGC 869 (top) and NGC 884, both clusters are about 7,000 light-years away and contain stars much younger and hotter than the Sun. Separated by only a few hundred light-years, the clusters are both 13 million years young based on the ages of their individual stars, evidence that they were likely a product of the same star-forming region. Always a rewarding sight in binoculars, the Double Cluster is even visible to the unaided eye from dark locations. But a shroud of guitar strings was used to produced diffraction spikes on the colorful stars imaged in this vibrant telescopic view.

But a shroud of guitar strings was used to produced diffraction spikes on the colorful stars imaged in this vibrant telescopic view.

I have to ask, huh? The photographer's (Jack Groves) Instagram blurb about the photo reveals this:

Twinkle twinkle little star! This is the Double Cluster in Perseus. The two together are classified as Caldwell 14 and separately as NGC 884 and 869.

They are surprisingly large and bright and can be viewed faintly from my Bortle 7/8 backyard with the right conditions. I love how they fill the frame up with this camera and telescope combination. I used my homemade diffraction spike cover on my refractor to produce fake-but-real diffraction spikes and I think it really makes these clusters look great! This was just a quick 2 hours of shooting under a 100% full moon using 2 minute exposures. It is also probably the quickest and lightest edit I have ever done - just a DBE, noise reduction and a masked stretch! No color saturation at all.

I have to ask why introduce unnecessary diffraction spikes (which, since this photo was taken on a refractor, would not otherwise exist)? Purely for aesthetic reasons? (And I'm still looking for where they are said to be produced by guitar strings...)

[johnnydeep]

Click to view full size image

I like this view: they could almost be one cluster except for the thin
lane between them!
The stars being hotter and younger than the sun; do they be size
comparable to old Sol?

Wait. What are the two subject clusters in that pic? I see two clearly separated groupings of stars, fairly far apart. Unless only one of those is actually the pair shown in this APOD.

[alter-ego]

Click to view full size image

I like this view: they could almost be one cluster except for the thin
lane between them!
The stars being hotter and younger than the sun; do they be size
comparable to old Sol?

Wait. What are the two subject clusters in that pic? I see two clearly separated groupings of stars, fairly far apart. Unless only one of those is actually the pair shown in this APOD.

If I understand your question, the two main clusters in Orin's image are the same ones in the APOD. Rotate the APOD image CCW by ~120° and the clusters will be oriented the same way.

[Bird_Man]

Johnnydeep, “(And I'm still looking for where they are said to be produced by guitar strings...)”. If you look two photos down in the photographer’s Instagram, he explains using the guitar strings and shows a photo of his setup.

[johnnydeep]

Click to view full size image

I like this view: they could almost be one cluster except for the thin
lane between them!
The stars being hotter and younger than the sun; do they be size
comparable to old Sol?

Wait. What are the two subject clusters in that pic? I see two clearly separated groupings of stars, fairly far apart. Unless only one of those is actually the pair shown in this APOD.

If I understand your question, the two main clusters in Orin's image are the same ones in the APOD. Rotate the APOD image CCW by ~120° and the clusters will be oriented the same way.

Thanks. I never would have figured that out. But doing just as you said plus some resizing all the stars match up! My confusion stemmed from Orin's statement that they looked like one cluster in the wide field night scape with the walkway, when they certainly look very distinct to me!

Double Cluster - Two Views

[johnnydeep]

Johnnydeep, “(And I'm still looking for where they are said to be produced by guitar strings...)”. If you look two photos down in the photographer’s Instagram, he explains using the guitar strings and shows a photo of his setup.

Thanks. Of course, the photo with the telescope! And only two wires were needed - I was expecting something way more elaborate. From https://www.instagram.com/p/CUD-KlbMxIY/

astrojackmn I’ve always liked diffraction spikes on stars but since I have refractor telescopes they aren’t present in my images.

I decided to try and put together something to use with my FLT91 that would produce ‘natural’ diffraction spikes. I used a guitar string and some cardboard from a case of beer! Swipe right to see a quick 15 minutes on the star Mirach (with NGC404 to the top left of it). I’m impressed how it turned out!

[farlightteam]

Una preciosidad, si señor