The Official Astronomy Thread

[mercurial]

I had my first look at the Orion nebula last night, but it was nothing like the stuff I see on the web I'm so disappointed. All I could see was a cloud. The filters helped a bit but I was expecting to see the type of stuff we see on the web.

I did something very interesting though. Even though we cannot really look at stars because they are so far away, I used my Barlow and zoomed anyway. What I saw was unbelievable. I couldn't believe it. You know you've seen those pics of the sun where you can literally see the sun boiling and spewing out stuff? I saw the exact same thing. I was amazed. I was staring at dim, blazing suns and I could see that stuff exploding. It's absolutely amazing. Please try it out and let me know how it goes. I tried it on many stars and some of the "explosions" were slower on some stars, but I couldn't believe what I was seeing.

 

[marine1]

Merc what scope you using?

 

[mercurial]

12" Dobsonian. Maybe it's time for some elite eyepieces

 

[marine1]

Merc is mine a good one? Do you think it is worth even trying to do that?
Merc, can you please explain maybe the difference between 5" and 12" and also what would be the benefit of yours over mine or vice versa?
Thanks man
I have the Sky-Watcher SK127MAKEQ3 Maksutov-Cassegrain 5"

Am I right in saying that the 12" will let in far more light than a 5"?
What would the point of having such a small Aperture (is that right?) be?
I mean your focal length is not really the most important thing now is it?

 

[Crusader]

I had my first look at the Orion nebula last night, but it was nothing like the stuff I see on the web I'm so disappointed. All I could see was a cloud. The filters helped a bit but I was expecting to see the type of stuff we see on the web.

First mistake, there's absolutely no comparison between what you see in pictures on the web and what you will see visually. The images you see on the web has been created by taking long exposures (45min etc) and stacking them and then postprocessing them adding and enhancing colors etc.

Your eyes simply can't do that. They can collect light for only around 1/30th of a second. Since your dark adapted vision can only distinguish between black and white you won't see color in almost all objects. The only exception are the bright planets. Some people can however see a very slight greenish and even redish color in the Orion Nebula.

What you saw is exactly what you were supposed to see. Nebulae do look like greyish mist. The difference between visual observing is that you are actually collecting the photons that left the object millions or thousands of years ago and travelled light years to reach your eye. You are viewing it live... and not many people can say that!

I did something very interesting though. Even though we cannot really look at stars because they are so far away, I used my Barlow and zoomed anyway. What I saw was unbelievable. I couldn't believe it. You know you've seen those pics of the sun where you can literally see the sun boiling and spewing out stuff? I saw the exact same thing. I was amazed. I was staring at dim, blazing suns and I could see that stuff exploding. It's absolutely amazing. Please try it out and let me know how it goes. I tried it on many stars and some of the "explosions" were slower on some stars, but I couldn't believe what I was seeing.

Sorry to burst your bubble, but I doubt that you were actually seeing blazing suns. The only star where you can see anything like that would be the Sun (with proper filters of course!). There is no way, regardless of the magnification that you could resolve any other stars into something more than just pinpricks of light.

My guess is that you were actually seeing severe atmospheric disturbance, otherwise known as bad seeing. The stars will seem to have movement and be boiling. They could even seem to show different colors. That's caused by atmospheric conditions, and will be much more severe if you view something low on the horizon.

Check out the explanation of the pickering seeing scale. If the images are close to what you saw then it was definitely due to severely bad seeing.

No matter how expensive your EPs are they won't be able to help with that.

 

[Crusader]

Merc is mine a good one? Do you think it is worth even trying to do that?
Merc, can you please explain maybe the difference between 5" and 12" and also what would be the benefit of yours over mine or vice versa?
Thanks man
I have the Sky-Watcher SK127MAKEQ3 Maksutov-Cassegrain 5"

Am I right in saying that the 12" will let in far more light than a 5"?
What would the point of having such a small Aperture (is that right?) be?
I mean your focal length is not really the most important thing now is it?

Ok, this can get to be a long explanation so bear with me.

Aperture size governs the amount of light that any telescope can gather. The more light, the fainter the objects you will be able to see and the brighter the object will appear. Also larger scopes will be able to provide more resolution - bringing out more details.

The light gathering ability of a certain aperture is equal to the diameter of the scope squared so in your case with a comparison between a 5" and a 12":
(5x5) : (12:12) = 25: 144 = 1:5.76. So that means a 12 inch scope will be able to gather almost six times more light than a 5". (My math might be faulty since I'm working from memory).

Now the f/ratio and focal length comes into play. The higher the f/ratio the smaller the FOV. Maks have a smaller FOV than a Newt (for the same aperture). Maks provide higher magnifications since they have a longer focal length for the same EP size.

5" Mak: Focal length = 1500mm, F/ratio = f/11.8, Limiting mag = 13.2, Max mag = 254x, Resolving power: 0.92 secs of arc (smallest feature on moon is 2.2 miles across), Fov with 25mm = 0.917°

12" Newt: Focal length = 1500mm. F/ratio = f/4.9, Limiting mag = 15.2, Max mag = 600x, Resolving power: 0.5 secs of arc (smallest feature on moon is 1.1 miles across). True Fov with 25mm = 0.917 °

10" Newt: Focal length = 1200mm, F/ratio = f/4.7, Limiting mag = 14.7, Max mag = 500x, Resolving power: 0.5 secs of arc (smallest feature on moon is 1.1 miles across). True Fov with 25mm = 1.15°

Ok, those numbers can be confusing. But basically what they mean is this.
Limiting magnitude determines the faintest object you will theoretically be able to see, the larger the aperture the fainter the object visible. A larger scope will be able to resolve more details. The smallest moon feature visible is used as an indication of the theoretical size. In practice it means that a larger scope will be able to better separate double stars and show better resolution if conditions permit.

The True Field of View is the amount of sky you will be able to see with the same eyepiece (25mm with AFOV of 55°). As you can see your Mak and the 12" will show the same size of field, although the 12" will have a brighter image and could show fainter objects. My 10", since it has a shorter focal length will show a larger area, since the magnifcation will be smaller (48x vs 60x). Where this comes into play is when deciding between eg a f/8 10" or a f/4.7 10". The f/8 will have a smaller FOV when compared to the f/4.7 and the f/8 scope will also provide higher magnifications for the same EP size.

The difference between your Mak and and the 12 Newt can be summed up as having less light gathering power. Objects will be fainter and you might not be able to resolve the same faint objects. The resolution in the Newt will also be slightly better, but more often than not atmospheric conditions will negate it.

Your Mak is definitely not a bad scope by any means. It's got enough aperture to show all of the Messier Objects, should work nicely on nebulae and be very good with the planets. You also don't need to collimate quite as often, and more importantly your scope will be quite a bit more portable.
The downside is that Maks require long cool down times (I've read around 40min to 1 hour) but that's about the same as a large Newt.

Hope that helps. If I've confused you more feel free to ask questions and I'll do my best to answer. Just remember I'm a newbie myself.

 

[marine1]

Wow thanks so much for the information. Really helps.
When you say cool down, what exactly do you mean?

 

[Crusader]

Wow thanks so much for the information. Really helps.
When you say cool down, what exactly do you mean?

Basically it' s just jargon to say that the telescope needs time to reach ambient temperature. Regardless if the ambient temperature is warmer than where the scope was kept the process in known as "cool down" - guess because it's much easier to type than "reach ambient temperatures, or acclimate to the current temperature".

This is important to do because the air inside the tube can cause air currents similar to bad seeing conditions.

 

[marine1]

So basically you need to wait about 40 minutes with the scope out before viewing?

 

[Crusader]

So basically you need to wait about 40 minutes with the scope out before viewing?

That's right. Of course you can start viewing immediately but the image will be degraded. Once the scope reaches ambient you should be able to see a big improvement.

And I neglected to add with regard to the maximum magnification of the various apertures that they will in all likelihood be limited to around 240x by atmospheric conditions regardless of the size. Only on nights of exceptional seeing will you be able to use very high magnifications while still increasing the amount of detail visible (as opposed to making the image larger but fuzzier).

 

[marine1]

Wow it is really complicated and a sicence in its own.
So basically the key is to have a high rated scope in terms of diameter of the lense (is that right) and in terms of Focal Length.
I imagine the real big ones are damn expensive

 

[marine1]

I want:

http://shop.technopro.co.za/celestr...ed-telescope-14-schmidt-cassegrain-p-528.html

 

[Crusader]

Wow it is really complicated and a sicence in its own.
So basically the key is to have a high rated scope in terms of diameter of the lense (is that right) and in terms of Focal Length.
I imagine the real big ones are damn expensive

It depends on what you want to view. For nebulae and galaxies (the faint fuzzies) you want as much aperture as you can get (if portability isn't an issue) and a shortish focal length so you can view a large area at a time since most DSO's are extended objects. You'll likely only use low magnifications as well, but with a fast focal ration you'll need premium EPs to prevent coma etc. - which gets expensive.

For planets higher magnification is better and the aperture doesn't need to be that big since the planets (at least those worth viewing) tend to be bright in any case. So less aperture and a longer focal length would be better. Also a mount that can track will be essential for the really high mags if the conditions are favourable.

I want:

http://shop.technopro.co.za/celestr...ed-telescope-14-schmidt-cassegrain-p-528.html

That's one of my dream scopes as well. Heck I'll settle for a CPC 1100 at R60k. Too bad both those scopes will require some type of permanent mount since they definitely don't fall into the portable category.

 

[marine1]

Crusader thanks for sharing some knowledge with me.

 

[Crusader]

Crusader thanks for sharing some knowledge with me.

No problem, it's my pleasure. I just hope I haven't let you astray I still get some things mixed up on occasion.

 

[Kalvaer]

I had my first look at the Orion nebula last night, but it was nothing like the stuff I see on the web I'm so disappointed. All I could see was a cloud.

Keep on looking at it when ever you can. You need to start training you eyes to see things.

The more you use it, the more you will start noticing things you never noticed before and the easier it will become to find things when you know what your looking for. The first time I looked at Orion I hardly saw anything, Now though I pick up the green clouds as soon as I put my face to the EP. There are other really interesting things as well like realising that a star1 you are looking at with the naked eye is actually 4, and then when you really start looking at it knowing that you look for, you realise there are actually 15 in a small concentrated spot

The "Trap" in orion is a very nice place to start as its very easy to find and start "spliting" the stars.

Also agree very much with cooling down the scope as Crusader mentioned. I usually take my scope out when I get home in the afternoon if I want to use it. Allows me to check collimation, and adjust everything with sunlight and not battling with a torch later, and then leave it out until its dark. The main reason is for the "cooling down". It allows the scope to reach ambiant and settle down while the sun is setting so I dont have to worry when I go out.

You also need to be carefull with your hands. If you put your hand on the tube, you can create a "hot" spot on the tube where you warmed it up. While not a real train smash, it can cause heat waves to appear while viewing for a few minutes until it cools again

 

[Crusader]

Keep on looking at it when ever you can. You need to start training you eyes to see things.

The more you use it, the more you will start noticing things you never noticed before and the easier it will become to find things when you know what your looking for.

I have to agree completely with this and I can't see why I didn't mention it myself. The more you look at something and train yourself to see the more details will become visible.

Going back through my observation log I can see that when I stared, I spotted the Lagoon nebula (at least the right area) but I couldn't notice the nebulosity. A month or so later after having much more eyepiece experience I could make out the nebula with ease and describe the dust lanes and the double star at the centre. Quite a difference in descriptions.

You can test this by having someone (after allowing them to get dark adapted) look at a nebula you can easily see and make out details. 9 times out of 10 they won't be able to see it or know what you are talking about. (M42 is an exception because it's very bright, but try the Trifid or Helix).

 

[marine1]

Space Weather News for Monday, Dec. 1, 2008
http://spaceweather.com

When the sun goes down tonight, step outside and look south. Beaming through the twilight is one of the prettiest things you'll ever see--a tight three-way conjunction of Venus, Jupiter and the crescent Moon. The event is visible from all parts of the world, even from light-polluted cities. People in New York and Hong Kong will see it just as clearly as astronomers watching from remote mountaintops. Only cloudy weather or a midnight sun (sorry Antarctica!) can spoil the show.

The great conjunction offers something extra to Europeans. For more than an hour on Monday evening, the crescent Moon will actually eclipse Venus. Astronomers call such an event a "lunar occultation." Venus emerging from the dark edge of the Moon is a remarkably beautiful sight. Sky watchers across Europe will be able to see this happen.

 

[mercurial]

Thanks guys.

 

[w1z4rd]

Guys go check out the moon now.. Im sure thats two planets next to it. Orsm to look at.