B Why does the Andromeda galaxy appear so tiny from our perspective?

[DaveC426913]

No, that isn't correct. Not even Jupiter or Venus are large enough to see (close though),

??

I assume you mean see "as a disc".

Venus can be seen when in crescent phase by the naked eye.

 

[davenn]

And it gets fairly dark, suburban .

This is a sky dark enough to see all of Ursa Minor, but none of the Milky Way haze.

there you go ... If you can't see the glow of the Milky Way, you are not going to see ( naked eye)
the fuzz of Andromeda

Suburbia is not the place for faint object observations. I have to travel an hour from home to get
far enough out of the city lights to see the elongated fuzz of AndromedaDave

 

[sophiecentaur]

Sorry, I meant not large enough to resolve disks with the naked eye.

Rayleigh criterion can be a bit pessimistic for some aspect of an object. The 3dB point is a bit arbitrary but easy to apply - that's in its favour.

 

[Dnj23]

there you go ... If you can't see the glow of the Milky Way, you are not going to see ( naked eye)
the fuzz of Andromeda

Suburbia is not the place for faint object observations. I have to travel an hour from home to get
far enough out of the city lights to see the elongated fuzz of AndromedaDave

Ok, thanks. This and other replies make sense. I never realized just how star photography can be so deceiving.

Also, you guys have amazing eyesight...Seeing Venus in phases?

Chinese historian of astronomy, Xi Zezong, has claimed that a "small reddish star" observed near Jupiter in 362 BCE by Chinese astronomer Gan De may have been Ganymede, predating Galileo's discovery by around two millennia.

https://en.wikipedia.org/wiki/Galilean_moons
Also interesting

 

[Zeke137]

So, here's another picture which shows the Andromeda galaxy as it would appear to the naked eye in a not very dark sky - it's the fuzzy blob at the center of the red ellipse. The full extent of the outer regions of Andromeda are outlined in red, and Andromeda's dwarf satellite galaxies M110 and M32 are pointed out. The moon is also shown in the correct size on the sky as comparison to the extent of Andromeda:

Hope this helps in visualizing the sizes and appearances on the sky.

 

[Dnj23]

So, here's another picture which shows the Andromeda galaxy as it would appear to the naked eye in a not very dark sky - it's the fuzzy blob at the center of the red ellipse. The full extent of the outer regions of Andromeda are outlined in red, and Andromeda's dwarf satellite galaxies M110 and M32 are pointed out. The moon is also shown in the correct size on the sky as comparison to the extent of Andromeda:

View attachment 251160

Hope this helps in visualizing the sizes and appearances on the sky.

No way dude.

 

[Zeke137]

No way dude.

Ummm, in what way "no way", dude?

 

[Dnj23]

Ok. Where does your picture fall in this top 10?

https://earthnworld.com/top-10-brightest-objects-in-space-that-you-can-see-with-your-naked-eye

 

[Zeke137]

OK, so here's another image, this time from NASA's Astronomy Picture Of The Day site, which overlays an image of the Moon on an image of the Andromeda Galaxy as recorded by a decent telescope, so the galaxy appears much brighter and wider than when seen with the naked eye.:

https://apod.nasa.gov/apod/image/0612/m31abtpmoon_c720.jpg
Note the positions of the two dwarf satellite galaxies M110 and M32...

 

[Zeke137]

Ok. Where does your picture fall in this top 10?

Ask a question that illuminates or adds to the discussion, and you'll get a sensible answer.

 

[snorkack]

So what does the eyepiece of a proper 150x20 scope have to be like? TeleVue offers eyepieces with 100 and 110 degree field of view. Eye does have more than 110 , but peripheral vision is limited resolution. What does te focal length need to be?

 

[phyzguy]

Ok. Where does your picture fall in this top 10?

I don't understand your question. First, do you understand that the moon in the image @Zeke137 posted is there to give you a sense of scale, not brightness? The actual moon would be far, far brighter. Having said that, everything in his image is much dimmer than your "top 10" list.

 

[sophiecentaur]

Also, you guys have amazing eyesight...Seeing Venus in phases?

I think, as with distinguishing between a star and a planet, a 'half Venus' looks different and someone with experience can interpret what's actually going on from a very poor image.
No Elves on PF mate.

 

[Dnj23]

I don't understand your question. First, do you understand that the moon in the image @Zeke137 posted is there to give you a sense of scale, not brightness? The actual moon would be far, far brighter. Having said that, everything in his image is much dimmer than your "top 10" list.

Oh really?

"So, here's another picture which shows the Andromeda galaxy as it would appear to the naked eye in a not very dark sky "

 

[Dnj23]

I think, as with distinguishing between a star and a planet, a 'half Venus' looks different and someone with experience can interpret what's actually going on from a very poor image.
No Elves on PF mate.

Ok.

You can detect differences in light, but you can't actually see the phases.

 

[Dnj23]

What else can you guys see? Neptune white briefs of clouds?

 

[russ_watters]

So, here's another picture which shows the Andromeda galaxy as it would appear to the naked eye in a not very dark sky...

View attachment 251160

Hope this helps in visualizing the sizes and appearances on the sky.

Ummm, in what way "no way", dude?

The way that is worded, it sounds like you are saying that in a not very dark sky you should see Andromeda looking like that. I agree with the "no way". Perhaps in an exceptionally dark sky you might.

 

[Zeke137]

it sounds like you are saying that in a not very dark sky you should see Andromeda looking like that

Well, actually I'm not saying it as such. The background photo comes from Flickr - https://live.staticflickr.com/7016/6467038861_01b1efebf9_b.jpg - so maybe we should all take this up with the person who took the photograph. I do note that neither the image of the tree nor the stars appear to be smeared, so I'd assume this was basically a snapshot of a scene as he/she had seen it.

My own personal experience, however, has always been that Andromeda is a naked eye object only on very dark nights.

Let's just say that the image I posted above shows rather well the relative sizes of Andromeda and the Moon on the sky, and has a nice tree in the foreground as a further aid to visualizing relative sizes. And that the central portion of Andromeda as viewed with the naked eye is just about the size on the sky as portrayed in the picture.

 

[Dnj23]

The way that is worded, it sounds like you are saying that in a not very dark sky you should see Andromeda looking like that. I agree with the "no way". Perhaps in an exceptionally dark sky you might.

Andromeda would be synonymous with the Moon, Venus, Jupiter, Sirius, etc.

 

[Zeke137]

Andromeda would be synonymous with the Moon, Venus, Jupiter, Sirius, etc.

Nice list of point-like or disk objects with no indistinct or fuzzy regions extending well beyond them.

Comparing apples with smoke will get us nowhere.

 

[russ_watters]

Andromeda would be synonymous with the Moon, Venus, Jupiter, Sirius, etc.

Synonomous in what way?

 

[Dnj23]

Synonomous in what way?

In terms of significant brightness to make it noticeable.

 

[Dnj23]

I'm done with this thread.

 

[pinball1970]

I'm done with this thread.

It's your thread! You've had some great stuff/images/explanations!

 

[Zeke137]

I think it might be helpful at this stage to point out how telescopes actually make the beautiful bright images of deep-sky objects like the Andromeda Galaxy, or the Orion Nebula, or the Crab Nebula, to name but a few:

These objects are pretty faint (they're a long way away), so the amount of light received by a telescope from such an object in anyone instant is simply not sufficient to capture a decent image. The same goes for the naked eye, which can only see the brightest parts (relatively speaking) of such objects and hence why it's so difficult to see them with the naked eye.

Even looking through a large telescope with the naked eye, the objects still appear pretty faint. I myself have vivid memories of viewing Halley's Comet on several occasions over a period of few weeks back in 1986 through a 1-meter Cassegrain reflector and being disappointed at how very faint it appeared through the eyepiece.

So, a quick snapshot of such an object as taken by a telescope, or even by a simple camera pointed at the sky, will only register a faint image of the object, and almost none of the fine filigree detail and colors as seen in pictures like those above would appear in the snapshot. It usually takes at least a few minutes, and as much as several hours of the telescope being pointed at the object, and following it precisely as it moves across the sky, in order to gather enough light in the photographic plate or CCD sensor to arrive at the splendid and colourful images we are lucky to see these days.

Let's imagine that we have at our disposal a particular telescope, which will take six minutes to capture enough light to produce a good image of the Andromeda Galaxy. The sensor would register something very like each of the following images at the end of each 1-minute interval during the exposure:

after 1 minute

after 2 minutes

after 3 minutes

after 4 minutes

after 5 minutes

at the end of the full exposure​

It's only after the full period of the exposure (six minutes in our example here) that the full extent of the galaxy is visible. It takes that long for our telescope to gather enough light to be able to discern the finest details of the galaxy at its' furthest extents.

Again, I hope this helps to explain why images taken by powerful telescopes of extended objects in the sky like galaxies and nebulae look nothing like how they would appear to the naked eye.

(Image: By Adam Evans - M31, the Andromeda Galaxy (now with h-alpha)Uploaded by NotFromUtrecht, CC BY 2.0, https://commons.wikimedia.org/w/index.php?curid=12654493)

 

[pinball1970]

I think it might be helpful at this stage to point out how telescopes actually make the beautiful bright images of deep-sky objects like the Andromeda Galaxy, or the Orion Nebula, or the Crab Nebula, to name but a few:

View attachment 251165​

These objects are pretty faint (they're a long way away), so the amount of light received by a telescope from such an object in anyone instant is simply not sufficient to capture a decent image. The same goes for the naked eye, which can only see the brightest parts (relatively speaking) of such objects and hence why it's so difficult to see them with the naked eye.

Even looking through a large telescope with the naked eye, the objects still appear pretty faint. I myself have vivid memories of viewing Halley's Comet on several occasions over a period of few weeks back in 1986 through a 1-meter Cassegrain reflector and being disappointed at how very faint it appeared through the eyepiece.

So, a quick snapshot of such an object as taken by a telescope, or even by a simple camera pointed at the sky, will only register a faint image of the object, and almost none of the fine filigree detail and colors as seen in pictures like those above would appear in the snapshot. It usually takes at least a few minutes, and as much as several hours of the telescope being pointed at the object, and following it precisely as it moves across the sky, in order to gather enough light in the photographic plate or CCD sensor to arrive at the splendid and clourful images we are lucky to see these days.

Let's imagine that we have at our disposal a particular telescope, which will take six minutes to capture enough light to produce a good image of the Andromeda Galaxy. The sensor would register something very like each of the following images at the end of each 1-minute interval during the exposure:

View attachment 251167
after 1 minute

View attachment 251168
after 2 minutes

View attachment 251169
after 3 minutes

View attachment 251170
after 4 minutes

View attachment 251171
after 5 minutes

View attachment 251172
at the end of the full six-minute exposure​

It's only after the full period of the exposure (six minutes in our example here) that the full extent of the galaxy is visible. It takes that long for our telescope to gather enough light to be able to discern the finest details of the galaxy.

Again, I hope this helps to explain why images of extended objects in the sky like galaxies and nebulae look nothing like how they would appear to the naked eye.

Amazing set of images.

 

[Zeke137]

I'm done with this thread.

Too many facts and too little fake news for your taste?

 

[Dnj23]

Let's just say that the image I posted above shows rather well the relative sizes of Andromeda and the Moon on the sky, and has a nice tree in the foreground as a further aid to visualizing relative sizes. And that the central portion of Andromeda as viewed with the naked eye is just about the size on the sky as portrayed in the picture.

Let's just say.

 

[Zeke137]

Let's just say.

You started this thread, and people came into try and help out. Plenty of people here, some of whom are practising scientists, and others who have university degrees in relevant scientific areas, have tried to help you out here.

But it would appear that you are not at all prepared to accept the help that you have been given. That's OK, that's your call, but I'm wondering why on Earth you bothered to ask the question "Where am I going wrong with this?" in the first place, and why you've persisted in rejecting help.

Well, you'll get no more help from me. Good luck with your obstinately dismissive attitude.

 

[Dnj23]

I don't understand your question. First, do you understand that the moon in the image @Zeke137 posted is there to give you a sense of scale, not brightness? The actual moon would be far, far brighter. Having said that, everything in his image is much dimmer than your "top 10" list.

I don't understand your response.

"So, here's another picture which shows the Andromeda galaxy as it would appear to the naked eye in a not very dark sky -"

 

[Dnj23]

You started this thread, and people came into try and help out. Plenty of people here, some of whom are practising scientists, and others who have university degrees in relevant scientific areas, have tried to help you out here.

But it would appear that you are not at all prepared to accept the help that you have been given. That's OK, that's your call, but I'm wondering why on Earth you bothered to ask the question "Where am I going wrong with this?" in the first place, and why you've persisted in rejecting help.

Well, you'll get no more help from me. Good luck with your obstinately dismissive attitude.

If anyone had a nice tree in the foreground near sunset, they aren't looking at anything what I'm mentioning.

 

[fresh_42]

If anyone had a nice tree in the foreground near sunset, they aren't looking at anything what I'm mentioning.

Before we end up with the birds and the bees, and since the question has been answered in all detail, it's time to close the discussion.

Thank you for participating.