Starship Asterisk*

Sinan İpek wrote:No electronic device could substitue our own sight, I think. The electronic noise is disgusting. By the way, does human sight have noise also?

Have you seen the image through an integrating video camera, or a Gen 3+ image intensifier? The noise in both cases is very low, and the views markedly better than you can achieve with the eye- both technically and aesthetically (for most people).

Yes, there is noise in the human visual system. In the first place, there is the simple statistical noise that is always present on any signal, which is equal to the square root of the number of photons collected. Since the eye typically only records between 1% and 10% of the photons that reach it, this Poisson noise is a major factor. In addition, there is "instrumental" noise- falsely firing neurons. You can see this if you go into a completely dark room and allow yourself 30 minutes or so to dark adapt- funny little bright flashes in your visual field, sometimes colored.

I think, a kind of glass material can be produced such that it multiplies the number of photons.

Possibly, but it can still never be more sensitive than current real-time instruments like night vision goggles or integrating video cameras, and I see no reason that the visual result would be any better.

In a radio of 100 million light years around Local Group, we found the Virgo Cluster
the more rich in galaxies.
Second place is Fornax Cluster, less rich that Virgo Cluster

Boomer12k wrote:...

It is not enough to have just larger aperture, or magnification. It takes LONG EXPOSURE PHOTOGRAPHY to capture enough light for a good image. I don't even see the Andromeda Galaxy with my GOOD GLASSES. A bit of haze with my 10-30 power zoom binocs. I see only a bright core with my 10inch Meade. ...

...

You want to capture photons? Photography is the way to go! Otherwise you would not be enjoying these fine APODS!!!

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Boomer, I have great respect and appreciation for astrophotography and the lovely pictures here on APOD. But I'm grateful that we don't have to choose between imaging and direct observing. For me, there is something magical about seeing the actual photons that have been travelling through space for minutes or tens of millions of years, even if all I can see is a faint fuzzy patch. For public outreach, the wow factor created by a good telescopic view of the Moon, Jupiter, or the Pleiades is worth a thousand images of distant galaxies. And for the dedicated observer, the more you observe, practice your observing skills, learn about an object, and reflect on what you're seeing, the more detail you will see -- there's a unique satisfaction in that.

Anthony Barreiro wrote:For me, there is something magical about seeing the actual photons that have been travelling through space for minutes or tens of millions of years, even if all I can see is a faint fuzzy patch.

So, here's another little curiosity: you don't see the actual photons that left the object. Photons don't pass through transparent materials, but rather, are absorbed and re-emitted by a scattering process. The actual photons that hit your retina were created in your eye a few picoseconds earlier.

For public outreach, the wow factor created by a good telescopic view of the Moon, Jupiter, or the Pleiades is worth a thousand images of distant galaxies.

Possibly. But most people have little appreciation for any but the handful of super bright objects- which doesn't include any galaxies. At public outreach events, my observation is that a real-time integrated video image wows a lot more people- which is why this is becoming the standard at many observatory events.

Chris Peterson wrote:

Anthony Barreiro wrote:For me, there is something magical about seeing the actual photons that have been travelling through space for minutes or tens of millions of years, even if all I can see is a faint fuzzy patch.

So, here's another little curiosity: you don't see the actual photons that left the object. Photons don't pass through transparent materials, but rather, are absorbed and re-emitted by a scattering process. The actual photons that hit your retina were created in your eye a few picoseconds earlier.

For public outreach, the wow factor created by a good telescopic view of the Moon, Jupiter, or the Pleiades is worth a thousand images of distant galaxies.

Possibly. But most people have little appreciation for any but the handful of super bright objects- which doesn't include any galaxies. At public outreach events, my observation is that a real-time integrated video image wows a lot more people- which is why this is becoming the standard at many observatory events.

Chris, are you trying to harsh my mellow? The light I see through my little telescope is qualitatively more closely related to the object I'm observing than the light I see on a computer screen. The subjective experience is completely different. As for (nearly) real-time video, yes, it's impressive and has its place. But I hope future generations will also continue to look through telescopes. Google Earth is wonderful, but so is walking around and looking at actual trees and buildings.

Would someone please take pity on a layman's ignorance and explain how galaxies are capable of "evolving"?

The Manning Dutchfly wrote:Would someone please take pity on a layman's ignorance and explain how galaxies are capable of "evolving"?

In this context, evolve just means change. Galaxies change for various reasons: their stars age, their metallicity increases, they interact with other galaxies.

Anthony Barreiro wrote:Chris, are you trying to harsh my mellow? The light I see through my little telescope is qualitatively more closely related to the object I'm observing than the light I see on a computer screen.

Of course, I know what you mean. And my bit of physics trivia wasn't really meant to discourage. But subjective experience does vary. Personally, I never feel closer to an astronomical object than when I see it appear on my screen during an imaging session- much more so than when I see it through the eyepiece. But that doesn't mean I don't completely understand your viewpoint, as well.

Anthony: Sir. Thank you for your comment.

I agree up to a point, the simplest of pleasures are still good. Looking THROUGH a telescope is still a pleasure. But I, personally, want MORE than just a temporary WOW moment. I am not trying to impress the public with a display, although I did impress people who walked by and saw my setup with my projector! I am already suitably impressed with the night sky. I want to STUDY.
For a Wow moment, I put my setup on my projector. WOW. Jupiter the size of my car door!! Or I take my APOD and other pictures and project them as well. Man, the Hubble telescope pictures are just awesomely inspiring when they are the size of your living room wall! You no doubt have a bigger setup for your public showings. But if I had to just look through the scope, even though I could tell I was actually looking at something, I would be disappointed. Gee, it is all black and white, no color. Why do I see all these color photos then? Well, it is our eyes. That was why I got the bigger scope, I thought I would see more. Well, up to a point. It is limited. That is why in the old days the telescopes got just plain insanely HUGE.
My WOW moment was back in the early 90's. There was a PBS show on telescopes, one was using a CCD camera, at that time relatively new to me for Astronomy. Although I had used one for digitizing pictures. This college had a 24inch scope with the camera and was showing a galaxy in real time on a monitor. I WENT, WOW!!!!! It really impressed me. That was a setup I wanted. Someday, if I ever have the means....I said to myself...and I did just that. But I don't have the 24inch scope, I got what I could afford and what I could LIFT AND HANDLE! Or I would have bought the 16inch Meade.

Not to take sides, but I agree with Chris. PERSONALLY, I feel CLOSER to the object of observation through an imaging session. I feel more connected, and more satisfaction, especially since I can improve my image now. M27 for example. I feel much closer to it, and better about it than just a hazy patch. I feel more satisfied about what it is. It seems more fulfilling. It may not BE the object, it may only be a image of the object, but it is a million times better than what my eyes see in the eyepiece. UNLESS IT IS THE MOON! That is just as impressive, through my scope. (Even my Binocs.) I resolved ONE pointy mountain out on the plains one night, man I was impressed, I can see into a crater now. But I get MOON-BLIND, from just a short view, and even with a Moon filter. With a camera and my laptop, I don't get moon-blind.
If all I was ever going to see was a hazy patch. I would not do it for long. I feel so much more connected to the universe being able to take a picture and go, "Yeeeeaaaaaah, that is more like it. Look at all that STRUCTURE!" When all I saw was a red dot for Mars, I was disappointed. Now I can get a photo and see some dark surface features features. Cooooool.
It would be like ANN, seeing things only in black and white, when she has such a wonderful understanding of the color BLUE!!!! She would be lost...I think.


For Public Display Events I am sure looking though the scope is exciting to look through. I let people LOOK THROUGH my scope too when they stop by. If ever I am down that way, I will drop by and have a look myself!!!!!

On another note and topic of the general discussion aimed at no one in particular...It is something that was not mentioned.
The other reason for bigger aperture is not so much brightness as Chris pointed out to someone, but better Resolution. It is like a 10 megapixel photo, and resizing it to 640x480. You lose allot. So you get more detail, clarity, etc. with a larger aperture. My 4inch Tasco Luminova was great for the Moon. But even Jupiter was just an Equal Sign on a disk, if that. And you could forget deep sky objects. (I would like to have seen what my DSI camera could have done with that scope.)
Now I see the cloud bands. Also with Saturn. And even so, deep sky objects are still hard. Globular Clusters are probably the best since they are stars. Nebula often need filters to bring out other wavelengths of light, (I still have not SEEN The Horsehead Nebula through my scope), and I still only see a patch or wispy cloud like thing. The same for Galaxies. M51 is two hazy dots...not impressed. If it were not for the software telling me what I was looking at, I would not know. So bigger aperture, better resolution, clearer, better detail. Not that you can't get great awesome pictures with a small scope, and a good camera, and some post processing. No doubt, seen it done. Awesome pictures.

Just had to add that on.

:---[===] *

Galaxies are unimpressive visually, there's no help for it.

So we are lucky to have people who are passionate about photographing those objects that don't look so good through a telescope. Thanks for your passion and your pictures, Boomer12k! And thank you for your passion and grace, Anthony. And thank you for your willingness to share your great experience and knowledge, Chris!

Ann

Thanks to Chris, Boomer, and Ann. This has been a satisfying discussion for me. We've all been able to share our passions and aesthetic sensibilities with mutual respect and, for me at least, greater understanding. I just want to say that I am extremely grateful to you people who spend time, money, and effort creating beautiful and informative astronomical images and explaining what we see in them. I've occasionally been tempted to put my toe in the astroimaging waters, but the learning curve is so steep that I content myself with admiring the work of others. I think I make a small contribution at public star parties and other events, using my laser pointer to help people learn how to find the North Star and to understand why it stays in the same place in the sky, or pointing my mounted binoculars at the waxing quarter Moon and explaining the difference between the maria and highlands.

Ann wrote:Star clusters = often lots of blue stars (and sometimes pink nebulosity)!

Galaxy clusters = very few blue stars, but lots of yellow splotches!

But thanks for NGC 1365, Marco, and it's a nice APOD!

Ann

Ann, I'm new here so may well ask about something obvious - apologies in advance.
I followed the link to "lots of blue stars", there was a marvellous photo but nothing to say what it was of.
Can I show my newness to all this (my intro explains HOW new) and ask why star clusters have lots of blue stars and galaxy clusters don't? I think it may be something to do with blue = younger, but I am still struggling with understanding the Hertzsprung (spelling?) - Russell diagram.
Best wishes
Margarita

MargaritaMc wrote:

Ann wrote:Star clusters = often lots of blue stars (and sometimes pink nebulosity)!

Galaxy clusters = very few blue stars, but lots of yellow splotches!

But thanks for NGC 1365, Marco, and it's a nice APOD!

Ann

Ann, I'm new here so may well ask about something obvious - apologies in advance.
I followed the link to "lots of blue stars", there was a marvellous photo but nothing to say what it was of.
Can I show my newness to all this (my intro explains HOW new) and ask why star clusters have lots of blue stars and galaxy clusters don't? I think it may be something to do with blue = younger, but I am still struggling with understanding the Hertzsprung (spelling?) - Russell diagram.
Best wishes
Margarita

Welcome Margarita!

You're right, blue stars are young stars. As you've learned from the Hertzsprung-Russell diagram, for main-sequence stars, those on the main diagonal band from lower right to upper left, stars in the upper left part of the diagram are hotter, bluer, and brighter than stars that are further down and to the right. These stars are hot bright and blue because they are bigger. With greater mass pressing inward, the hydrogen in the cores of these big stars is under greater pressure and temperature than the hydrogen in the cores of smaller stars, so the hydrogen is fused into helium more quickly, producing more heat and light.

You might think that bigger stars would live longer than smaller stars because they are born with more hydrogen fuel, but they burn their hydrogen so much more quickly that they burn it all up in a relatively short time. Big hot bright blue stars like Sigma Orionis (visible in the belt of Orion, just south of the easternmost bright star of the belt) will live only a few tens of millions of years before exploding in a supernova. These big show-offs are very rare, but they can be seen from great distances because they are so bright.

Smaller cooler dimmer stars like our Sun, in the middle of the main sequence, with characteristic colors in the yellow part of the spectrum, are much more common than big hot bright blue stars. These yellow stars burn their hydrogen more slowly, so they might live about 10 billions years (a thousand times longer than the big hot bright blue stars) before running low on hydrogen, puffing up into a cool red giant, and eventually collapsing into a tiny dim white dwarf.

Our current understanding is that small, dim, red dwarf stars, at the lower right of the main sequence, are by far the most common stars in the universe. And because these red dwarf burn their hydrogen so slowly, they live essentially forever, many tens of billions of years, much longer than the universe has existed so far.

So a young open star cluster will still have some pretty bright blue stars, outshining the more numerous but less impressive yellow stars. But as the cluster ages the blue stars will die first, and their more homely yellow sisters will long outlive them. Most of the light we see from distant galaxy clusters is from these older yellow stars. But occasionally a galaxy like NGC 1365 will experience a burst of star formation, producing a new generation of hot young bright blue stars, and making for more interesting photographs.

Best wishes as you explore the cosmos!

The star cluster in my earlier post is NGC 3293, whose estimated age is ten million years. That's very young for a cluster. We can see that the cluster is rich and quite compact, and it stands out very well from the background. (Check out this image of NGC 3293 and NGC 3324, too!)

Any cluster that contains so many blue stars of relatively similar brightness is sure to be young and massive. The fact that it contains at least one bright orange star tells us that one star has used up the hydrogen in its core and expanded and cooled. The star is likely a red supergiant, for the simple reason that the blue stars in the cluster are too massive to evolve into "ordinary" red giants.
This is the Hertzsprung-Russel diagram, which shows the connection between stellar mass, brightness and temperature.

When stars are born, they start fusing hydrogen to helium in their cores. A star that is fusing hydrogen to helium in its core is a main sequence star. You can see the main sequence in the diagram - its' the diagonal line running from lower right to upper left. The farther to the left that a star is placed in the Hertzsprung-Russel diagram, the hotter and bluer the star is. The farther to the right the star is placed, the cooler and redder it is.

Stars are also brighter the higher up in the diagram they are, and fainter the farther down they are in the diagram.

When a star gets the hydrogen fusion going in its core, it will enter the Hertzsprung-Russel diagram in a position that corresponds to its mass. The more massive a main sequence star is, the brighter and bluer it is. The less mass it has, the fainter and redder it will be.

The more massive a star is, the faster it uses up the hydrogen in its core. When this happens, the star becomes a supergiant. Massive stars can turn into blue, white, yellow and red supergiants. Supergiants are typically more or less equally bright, but the red supergiants are much, much bigger and cooler than the blue supergiants. The best-known red supergiant in the sky might be Betelgeuse, and the best-known blue supergiant might be Rigel.

Stars like the Sun also use up the hydrogen in their cores eventually. When that happens, they turn into more modest red giants, not supergiants. The hydrogen in the core of the Sun will last much, much longer than the hydrogen in the cores of the really massive stars.

Stars don't remain red giants or supergiants forever. Almost all supergiant can be expected to explode as supernovae. When they explode, they typically leave an extremely, extremely compact neutron star behind. The red giants don't explode, but rather "slough off" their puffed-up atmospheres and leave a white dwarf behind. A newborn white dwarf is very hot indeed and very blue, but it isn't very bright. Soon the white dwarf will cool, becoming ever fainter, cooler and redder.

Why do star clusters typically have lots of blue stars in them, and galaxy clusters don't? A short answer is that the star clusters that are born today typically aren't very massive, even if they contain a number of massive stars. The overall gravity of the cluster is still not enough to keep the cluster together for many hundred million years. This means that most open clusters in the Milky Way are young. And any cluster that is compact and obvious is sure to have been born with stars of blue spectral class B, and they may also have been born with at least one star of even hotter and bluer spectral class O. We can also be sure that it was born with several stars of spectral class A. Even though the hottest stars will burn out quickly and other blue stars will turn red, a cluster born with stars of spectral classes B and A will be predominantly blue for at least 200 million years.

Why don't galaxy clusters have many blue stars at all? The short answer is that blue stars are born out of massive cool gas clouds, but in galaxy clusters, larger-scale galactic interaction and enormous jets from supermassive black holes keeps the gas hot and turbulent. Young blue stars simply aren't born here. Galaxy clusters typically contain enormous numbers of stars, but almost all the stars are old and therefore yellow. (And by the way, the Sun isn't yellow, but white. Yellow stars are cooler and often older than the Sun.)

Strong forces in galaxy clusters also simply "blow" the gas out of the constituent galaxies. This is galaxy NGC 4402. It is "falling" into the heart of the Virgo cluster. Can you see that its gas and dust is being "blown" upwards? As this is happening, the galaxy is losing much or most of its gas, too.

Imagine that you were going to make a loaf of bread. But when you started mixing the dough, an incredibly strong fan got going in your kitchen, blowing all the flour into a whirling white cloud. Try as you might, you would probably not be able to collect enough of the whirling flour unless you managed to turn off the fan.

In galaxy clusters, there are enormous "fans" in the shape of monster jets, blowing the gas every which way so that it isn't good for star formation.

Hope this explanation helped!

Ann

Thank you so much, Anthony and Ann! I'm thoroughly gob-smacked at how much consideration you both gave to answering my question. And, yes, both answers helped me a lot.
Ann, you wrote (about the H-R diagram) "the connection between stellar mass, brightness and temperature." In this connection, does stellar radius (which is marked on the diagram) equate to mass?
Again - a million thanks!
Margarita

ps. I've checked out NGC 3293 and NGC 3324, (as in Ann's suggestion) and saw the pink nebulosity mentioned in Ann's first post. If I'm not being too ask-ask-asking, what causes that? It is hugely pretty!
Bye the bye, am I the only person who thought that Apod of the Fornax cluster looked like a really up-market jeweller's display? With NGC 1365 being a superb brooch - the sort the Queen (I'm English!) wears on State occasions.

pps. LOVED the bread flour analogy! Really helped me to "get"it.

hang around for a few million years when Andromedae shows up at your doostep. Now that is going to be impressive

ta152h0 wrote:hang around for a few million years when Andromedae shows up at your doostep. Now that is going to be impressive

A few billion years. And I doubt it will be very impressive, unless we get some local gas cloud collisions. Up close, Andromeda would just look like an extended, spread out version of the band of the Milky Way. Indeed, by covering much of the sky, it might well be less impressive than the Milky Way, due to the overall lack of contrast.

Anthony Barreiro wrote:Thanks to Chris, Boomer, and Ann. This has been a satisfying discussion for me. We've all been able to share our passions and aesthetic sensibilities with mutual respect and, for me at least, greater understanding. I just want to say that I am extremely grateful to you people who spend time, money, and effort creating beautiful and informative astronomical images and explaining what we see in them. I've occasionally been tempted to put my toe in the astroimaging waters, but the learning curve is so steep that I content myself with admiring the work of others. I think I make a small contribution at public star parties and other events, using my laser pointer to help people learn how to find the North Star and to understand why it stays in the same place in the sky, or pointing my mounted binoculars at the waxing quarter Moon and explaining the difference between the maria and highlands.

Anthony, I TOTALLY RESPECT what you do. I think it is just awesome!!!! Connecting the Public with the stars, getting them involved, educating them about the night sky, and seeing how that influences them, IS A GREAT THING!!!!!! TOTALLY RESPECT IT!!!!! YOU'RE AWESOME. I also totally respect Chris as he is a professional at an observatory. And that was ALWAYS MY DREAM IN SCHOOL. I totally LOVE AND RESPECT ANN, for her insights and knowledge about colors, and stars, and objects, she can tell you just as much about the SCIENCE AS THE BEAUTY OF WHAT YOU ARE LOOKING AT!!!!! I find the people here at APOD are generally very good, and helpful people.

The way I got into imaging was ON THE CHEAP, with LITTLE TO NO LEARNING CURVE. I had my 10incher already. I had given away my other scopes, and when I had them I did not have a digital camera, so could not do any comparisons. But I got a small digital camera because it could do short videos. Over time I got other better cameras. But they had no LCD viewer in the back. So, this gets problematic. I had seen some fairly decent photos with just HAND HELD cameras held up to a telescope eyepiece. So, that is what I tried. Boy, is it hard with no LCD view finder on the back of the camera. It can be frustrating. BUT. I got pictures of JUPITER and the MOON!!! Deep sky objects did not work as you need longer exposures.

Go to these links to see my fledgling, (but pretty fair), efforts:
http://home.comcast.net/~swbbus/astro.htm
http://home.comcast.net/~swbbus/index.htm

These were done with a cheap SiPix Stylecam Deluxe camera. We are talking less than 50 bucks I think, maybe 30-ish. So we are not talking a 600 buck CANON here. Hand held to the eyepiece, and I thoroughly enjoyed doing it, for all the trouble it was. Since you have a mounted binocular setup, why not just try your hand held camera at one eyepiece. If it has a LCD view finder great, but even if it does not, just try different positions and angles. You might be surprised at what you get. My point is, the learning curve does not have to be that steep. Nor even EXPENSIVE.

After I determined that this was NOT THE WAY TO GO, I researched more dedicated Astrophotography cameras. They can be soooooooooo expensive, but I got a DSI 2 color camera on a Christmas special, as the new version was coming out, for 100 dollars less. About 299, or 199, I think. And with software it is REALLY FAIRLY SIMPLE!!!!! Most of it is AUTOMATIC!!! Came with a DVD done by an expert and he shows you how to set up taking a picture. It was pretty straight forward and easy. A few other programs for post processing and you saw the results earlier, and that post processing only took about another 5-10 minutes to do!!! Involved, but EASY!!!! You do not have to be a camera bug, or an expert photographer, like the experts are. Technology makes it easier for US AMATEURS. YES!!!! I AM JUST A KNOW NOTHING AMATEUR!!!!!! REALLY!!!!! I just have a healthy interest. I am no scientist. CHRIS, is a Scientist.

When we talk MARTIAL ARTS....then I am the EXPERT! 40 year Martial Arts Instructor. I do more than just the basics. We all have our little talents. But I always LOVED ASTRONOMY!!!!!!!! It is a GREAT HOBBY, and I totally respect what you do with your work for the Public.....ROCK ON!!!!!!! And give a cheap camera through your binocs a try at the Moon. I have a pair of 10-30 zoom Barska Gladiators. I mount them on the tripod, and look at things. I also have a Samsung F40 camcorder. 129 bucks on sale. It does still pictures as well as DVD quality video. With 65 power zoom, I get a picture of the moon...not even 65 power....like so below. Click on the picture for better view. That is just the camera, no scope. Not to shabby.

I think I shall ask my friend to bring over my old Jason Refractor scope. Then I can compare. Good idea!!!

CLEAR SKIES!!!!!!! Bro!

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MargaritaMc wrote:Thank you so much, Anthony and Ann! I'm thoroughly gob-smacked at how much consideration you both gave to answering my question. And, yes, both answers helped me a lot.
Ann, you wrote (about the H-R diagram) "the connection between stellar mass, brightness and temperature." In this connection, does stellar radius (which is marked on the diagram) equate to mass?
Again - a million thanks!
Margarita

ps. I've checked out NGC 3293 and NGC 3324, (as in Ann's suggestion) and saw the pink nebulosity mentioned in Ann's first post. If I'm not being too ask-ask-asking, what causes that? It is hugely pretty!
Bye the bye, am I the only person who thought that Apod of the Fornax cluster looked like a really up-market jeweller's display? With NGC 1365 being a superb brooch - the sort the Queen (I'm English!) wears on State occasions.

pps. LOVED the bread flour analogy! Really helped me to "get"it.

You're welcome, Margarita, and I'm glad the bread analogy helped!

Stellar radius does equal mass as long as the star is on the main sequence. The main sequence red dwarfs are little runts, but the massive blue main sequence O-stars are considerably larger than the Sun. Professor emeritus Jim Kaler is the expert I turn to for information about individual stars. You may check out this page, if you would like to read about a (more or less well-known) star that interests you.

One of my own favorite main sequence O-type stars is 10 Lacertae. Jim Kaler wrote about that star:

From a surface heated to a quite-amazing 32,000 Kelvin, it radiates a with a luminosity of 26,800 Suns (the majority of the light in the invisible ultraviolet), from which we derive a radius 4.7 times that of the Sun and a great mass of 16 times solar.

The best-known (and extremely puny) red dwarf is probably Proxima Centauri. Its claim to fame is that it is the closest of all stars from the Earth (with the obvious exception of the Sun). Jim Kaler wrote about Proxima Centauri:

As a mid-class M (M5.5) dwarf star, Proxima is faint indeed, to the eye 18,000 times dimmer than the Sun. From Alpha Cen proper, Proxima would appear as only fourth magnitude, about as bright as the faint stars of the Little Dipper appear to us. When infrared radiation produced by its 3040 Kelvin surface is accounted for, it is seen to be more luminous, but still only 1/600 as bright as the Sun (and 15 percent the size), the result of a mass only 12 percent solar.

But when the stars leave the main sequence, there is no longer any connection between size and mass. Check out this (large, 1.7 MB) series of pictures of the sizes of certain planets and stars.

The first picture shows the relative sizes of the inner planets of the Solar System, Mercury, Venus, the Earth and Mars. As you can see, Mars is surprisingly puny.

The second picture compares the size of the Earth with the sizes of the ice giants Uranus and Neptune and the sizes of the gas giants Jupiter and Saturn.

The third picture compares the size of Jupiter with the sizes of Wolf 359 (one of those typical tiny red dwarf stars) and with the size of the Sun and A-type main sequence star Sirius. (You shouldn't believe in that horrible orange-yellow color of the Sun in that picture. It's okay to think of the Sun as very pale yellow - although the Sun really is white - but it absolutely isn't orange.)

The fourth picture compares the size of Sirius with the sizes of Pollux, Arcturus and Aldebaran. The latter three stars are all red giants, which have given up hydrogen fusion in their cores. Pollux is the most modest of the three, the smallest, the faintest and "the least cool". Jim Kaler wrote about Pollux (which is one of the two luminous stars in the constellation Gemini):

From its distance of 34 light years, we calculate a total luminosity (incuding infrared radiation) for Pollux 46 times that of the Sun, and coupled with its temperature (4770 Kelvin), a diameter some 10 times solar, making it smaller than most of its cool giant brethren and only a quarter the dimension of Aldebaran.
...
From luminosity and temperature, the mass comes in at around 1.8 times solar.

Jim Kaler wrote about Aldebaran:

Aldebaran's surface temperature of 4010 degrees Kelvin (compared to the Sun's 5780 degree temperature) gives it a distinct orangy color not all that dissimilar to that of Mars, which commonly passes it. Allowance for infrared radiation reveals the star to have a fairly high luminosity 425 times that of the Sun, which leads to a radius of 43 times solar.
..
From the theory of stellar structure and evolution, Aldebaran carries a mass of around 1.7 times that of the Sun.

As you can see, Jim Kaler says that Pollux is probably more massive than Aldebaran, even though Aldebaran is much larger and about ten times brighter. These two stars are at different stages in their evolution as red giants. The Sun, too, will become a red giant one day, and it will certainly reach a stage in its evolution when it is brighter and larger than Pollux is now.

The fifth picture compares Aldebaran with Rigel, Antares and Betelgeuse. Jim Kaler wrote about Rigel:

At a distance of 860 light years (second Hipparcos reduction), it shines with the light of 85,000 Suns after account is taken of ultraviolet light from its 11,500 Kelvin surface. The two combine to tell of a radius swollen to 74 times that of the Sun, 0.34 Astronomical Units, nearly as big as the orbit of Mercury. Direct measure of angular diameter leads to a similar radius of 73 times solar, showing that the star's various properties are accurate. The theory of stellar structure and evolution shows that the star must carry a mass of close 18 times that of the Sun, and indicates that it has a dead helium core and is still in a swelling and cooling phase.

Jim Kaler wrote about Betelgeuse:

At a compromise distance of 570 light years, and allowing for a lot of infrared radiation and for absorption of light by circumstellar dust, the luminosity comes in at 85,000 times that of the Sun, considerably more than comes out of Antares. At the larger distance, luminosity boosts up to 105,000 Suns. From these and the temperature, we derive respective radii of 3.1 and 3.4 Astronomical Units, more than double the size of the Martian orbit.

An astronomical unit is ≈ 200 times the radius of the Sun. So if the size of Betelgeuse is more than three astronomical units, then the radius of Betelgeuse is more than 600 times the radius of the Sun.

Jim Kaler wrote about Betelgeuse:

We do not really know the star's condition at the moment, but the odds are that it is now in the process of fusing helium into carbon and oxygen in its core. From theory, its initial mass should have fallen somewhere around 18 or 19 times that of the Sun.

As you can see, the two supergiants Rigel and Betelgeuse are thought to be quite similarly bright and similarly massive, although they are at different stages of their evolution as supergiants and therefore vastly different in size and surface temperature.

The sixth picture shows some of the largest red supergiants known. Jim Kaler wrote about Mu Cephei and VV Cephei:

Mu Cep has a current estimated radius somewhere between 1200 and 1650 times that of the Sun, or 5.6 to 7.7 Astronomical Units, bigger than the orbit of Jupiter. Though VV may well top it out, the uncertainties preclude accurate assessment.
...
Radius and temperature give a luminosity that falls somewhere between 275,000 and 575,000 times that of the Sun, which in turn give masses between 25 and 40 times solar.

As for why there is pink nebulosity around blue star cluster NGC 3293, it's because there is hydrogen gas not far from the cluster, and the combined ultraviolet emission from the hot stars knocks electrons around the nucleus of a hydrogen atom (and a hydrogen atom only has one proton and one electron) into "a higher orbit". In that higher orbit, the electrons have more energy than they do in their "ground state". But soon the electrons "fall back" to their ground state again, and as they do so, they radiate their extra energy away. Most of the electrons radiate a deep red hydrogen alpha photon, but some radiate a blue-green hydrogen beta photon. The combined light is pink.

Ann

Again, many, many thanks for posting such an informative response. I am on a learning curve that is practically vertical - and this is enormously exhilarating!

The links were also most useful and I shall begin to work my way through the University of Illinois astro site. The comparative sizes link was astounding. I'm accessing the internet via my Galaxy Mini (appropriately named?) phone at present, whilst waiting for a Google Nexus to be delivered, and was impressed that it could handle that file at the same time that I had Asterisk open in another page. Viewing on such a small screen meant that I had to view the sections one at a time, which really added to the Whow! factor.
Regards
Margarita