10" Newtonian

[Dave-7 (David)]

Hi Guys, I recently purchased a 10inch reflector and have used it a handful of times. Ive observed a few planets and noticed that im not getting the quality and size that i should. For example i was looking at mars one night using my 10mm eyepiece and a 2x Barlow which gives me 240x however from some of the images ive been seeing on this forum and youtube, what i see through the eyepiece looks no where near as good (compared to other people using the same scope). Mars was simply a red dot and i could just make out the north polar cap. Does this sound right?



The scope i am using is as follows

Optical Design Newtonian (Parabolic)
Diameter 254mm
Focal Length 1200mm
Secondary Mirror Diameter 58mm
F/Ratio f 4.7
Highest Practical Power 508x
Faintest Steller Magnitude 14.7
Resolving Power 0.56
Finderscope 9x50 Finderscope
Focuser Diameter 2" with 1.25" adapter
Focuser Crayford
Eyepieces Plossl 25mm and 10mm (1.25")
Solid Tube style


Also i should mention that my scope is collimated and cooled at ambient temp while viewing

[raymo]

Hi Dave, Firstly, It's no good comparing images with what you are seeing,
unless you know exactly how and where the images were obtained. Many,
if not most, planetary and lunar images are the result of tens, hundreds,
or thousands of video frames stacked and processed. Your visual experience is never going to anywhere near equal those images.
Also, the seeing where you are may not be the best. Another also is the
fact that an experienced observer will see more in an image than a
novice.{assuming that you are a novice}. As has been said in another thread recently Mars is very small at the moment; it will get a little larger
over the next couple of weeks, but then you'll have to wait a couple of years to see it much larger. I suggest you try and get a look through
someone else's scope, so you can better judge whether your's is performing correctly.
raymo

[barx1963 (Malcolm)]

David
Mars is a very small target, currently it is only 15" wide, so even at 240x it will only appear as a small disc. In my 20" I have pumped it up to 315x and can just make out some details and a hint of a polar cap.
The images you see are often done as mentioned with lots of frames that are stacked and processed and using very long focal length and barlows.
Patience is often the key as there will be fleeting glimpses of steady air which will suddenly reveal much more detail.

Cheers

Malcolm

[astro744]

"The observation of planets is a delicate art." M. du Martheray.

(As quoted in Introduction to Observing and Photographing the Solar System by Dobbins, Parker, Capen, Willmann-Bell publisher).

At 240x an object 15 arc seconds will be 1 degree in diameter.

i.e. 15 x 240 = 3600 arc sec = 1 deg.

The Moon is 1/2 degree in diameter.

Try the following next full moon which happens to be an eclipse so it will look reddish like Mars:

Look at the Moon unaided and see what features you can see. Try and sketch light and dark features to scale. If you can do this with a 1/2 degree object then Mars at 240x will be no problem.

Use filters; Red, Orange, Yellow, Green, Blue & Violet all give different views.

The art of observing is being able to detect small low contrast detail. Filters help bring out such detail but a trained eye will begin to detect such detail without filters.

Back in the days of film a visual image was always better than the photograph because your eye sees brief very steady views amongst prolonged periods of not so steady views due to our atmosphere. Film used to record the not so steady moments during the few second exposures. Nowadays video recordings capture the view and then only the good frames are selected and combined to form views that are better than any large ground based telescope in the days of film could ever have recorded.

You will not see Mars in the telescope as you do in some of the recent pictures being posted. However, you can still detect many markings on the planet that really stand out including the poles, Syrtis Major, Hellas Planitia, Sinus Sabaeus, Sinus Meridiani and Solis Lacus to name a few. The latter is also known as the Eye of Mars and is my personal favourite since it is small and not always easily detectable.

Note too Mars has dust storms that can engulf the entire planet and then no features are visible although such large storms are rare. Often smaller dust storms are seen covering some features.

Find yourself an observing guide to Mars for this opposition showing a map of the entire planet and a table showing the longitude of the central meridian for any given night. Mars spins 24h 40m so the same feature will be on the central meridian 40 minutes later each night.

There is plenty of info at http://alpo-astronomy.org/

Enjoy!

[-George-]

Hi, If I may ask...

The moon is 1/2 degree in diameter looking at it with your eyes. That means mars through the telescope at 1 degree should look like 2 moon sizes by eye - no scope.

A moon generally looks big at night... if mars is 2x the size of that (1 degree vs 1/2) then Mars should look absolute huge. I am confused on this degree business.

And when is the moon 1/2 degree because some nights it looks as big as the sun. So what is all this degree based on and why isn't mars double the size of a big moon since its 1 degree not half?

Originally Posted by astro744

"The observation of planets is a delicate art." M. du Martheray.

(As quoted in Introduction to Observing and Photographing the Solar System by Dobbins, Parker, Capen, Willmann-Bell publisher).

At 240x an object 15 arc seconds will be 1 degree in diameter.

i.e. 15 x 240 = 3600 arc sec = 1 deg.

The Moon is 1/2 degree in diameter.

Try the following next full moon which happens to be an eclipse so it will look reddish like Mars:

Look at the Moon unaided and see what features you can see. Try and sketch light and dark features to scale. If you can do this with a 1/2 degree object then Mars at 240x will be no problem.

Use filters; Red, Orange, Yellow, Green, Blue & Violet all give different views.

The art of observing is being able to detect small low contrast detail. Filters help bring out such detail but a trained eye will begin to detect such detail without filters.

Back in the days of film a visual image was always better than the photograph because your eye sees brief very steady views amongst prolonged periods of not so steady views due to our atmosphere. Film used to record the not so steady moments during the few second exposures. Nowadays video recordings capture the view and then only the good frames are selected and combined to form views that are better than any large ground based telescope in the days of film could ever have recorded.

You will not see Mars in the telescope as you do in some of the recent pictures being posted. However, you can still detect many markings on the planet that really stand out including the poles, Syrtis Major, Hellas Planitia, Sinus Sabaeus, Sinus Meridiani and Solis Lacus to name a few. The latter is also known as the Eye of Mars and is my personal favourite since it is small and not always easily detectable.

Note too Mars has dust storms that can engulf the entire planet and then no features are visible although such large storms are rare. Often smaller dust storms are seen covering some features.

Find yourself an observing guide to Mars for this opposition showing a map of the entire planet and a table showing the longitude of the central meridian for any given night. Mars spins 24h 40m so the same feature will be on the central meridian 40 minutes later each night.

There is plenty of info at http://alpo-astronomy.org/

Enjoy!

[simmo]

Hi Dave,

Just like you I have a 10" newt so I possibly can understand some of your position. Please don't think of me being presumptious with my post as i'm just not sure of your experience.

Firstly I would agree with everyone that you need a steady atmosphere for good seeing in relation to Mars and for mostly anything else. If the conditions are average then Mars will not look like much more than a red round ball.

A rough guide I use for how good seeing is first - any twinkling in the stars. If they sparkle like a diamond then there is something going on in the atmosphere and therefore the viewing may not be so good. You can get a better idea of your night sky by looking on
www.skippysky.com.au/Australia
or something similar. Transperancy has to do with the amount of cloud in your area and seeing is related to the atmosphere, the darker the blue the better.

Secondly your mirror cooling down and tube currents, if you have a solid tube, can really affect your seeing and you might have noticed that already. The best time I have found to view planets is just on dusk when the stars start to appear. Or later on when the scope has sufficiently cooled down.

And lastly if you are using the 10mm eyepiece that came with your scope then you are already a step behind. While the 25mm is ok the 10mm that came with your scope is pretty much something you should think about replacing if you want better planetary views. You will notice the difference with a better eyepiece.

On the good side if you can get the great seeing conditions, a good eyepiece and your scope cooled you will get a pretty good view of Mars. About a month back I viewed Mars at a dark sky site with very good seeing condtions and could easily see the polar caps and a dark lane with detail that ran from top to bottom so don't worry.

Good luck with it.

simmo

[astro744]

Originally Posted by -George-

Hi, If I may ask...

The moon is 1/2 degree in diameter looking at it with your eyes. That means mars through the telescope at 1 degree should look like 2 moon sizes by eye - no scope.

A moon generally looks big at night... if mars is 2x the size of that (1 degree vs 1/2) then Mars should look absolute huge. I am confused on this degree business.

And when is the moon 1/2 degree because some nights it looks as big as the sun. So what is all this degree based on and why isn't mars double the size of a big moon since its 1 degree not half?

OK the Moon is 1/2 degree in diameter or 30 minutes of arc. One degree = 1/360 of a circle. (360 degrees in a circle).

Note:
1 degree =60 minutes of arc
1 minute = 60 seconds of arc
1 degree = 3600 seconds of arc

MARS WITH THE UNAIDED EYE WILL NOT LOOK TWICE AS BIG OR EVEN AS BIG AS THE MOON WITH THE UNAIDED EYE. This is important as there is a hoax that goes around every Mars opposition claiming so.

Lets just forget about Mars for the moment and look at the Full Moon without any telescope or binoculars, i.e. unaided eye. It fills 1/2 degree of sky. How much detail can you see? You should be able to see the dark and light markings easily but no craters. If the Moon was twice as big OR twice as close OR you magnified by 2 you would get a 1 degree Moon and you may be able to make out the larger craters.

Now back to Mars. With the unaided eye it is 15 arc seconds in diameter. This is 15/3600 = 0.0042 degrees in diameter. Very small and for all intentional purposes a point of light.

Magnify Mars by 120x i.e. 0.0042 x 120 = 0.50 degrees. Mars will appear THROUGH THE TELESCOPE the same diameter as the MOON when the Moon is viewed unaided.

Magnify Mars by 240x i.e. 0.0042 x 240 = 1 degree. Mars will appear THROUGH THE TELESCOPE the twice as big as the MOON when the Moon is viewed unaided.

This is easily observed when Mars and the Moon are in the same part of the sky. Look at Mars through the telescope with one eye at say 120X and look at the Moon unaided with the other eye. They will look the same diameter. (This is easier if the telescope is a refractor or SCT with no diagonal, i.e. straight through mode.

Therefore you should be able to detect detail even at 120x on Mars although the more magnification the better provided seeing is good and the image is not too dim.

I hope this clears things up.

[julianh72 (Julian)]

Originally Posted by -George-

Hi, If I may ask...

The moon is 1/2 degree in diameter looking at it with your eyes. That means mars through the telescope at 1 degree should look like 2 moon sizes by eye - no scope.

A moon generally looks big at night... if mars is 2x the size of that (1 degree vs 1/2) then Mars should look absolute huge. I am confused on this degree business.

And when is the moon 1/2 degree because some nights it looks as big as the sun. So what is all this degree based on and why isn't mars double the size of a big moon since its 1 degree not half?

The full sphere of the sky is 360 degrees around, or 180 degrees from horizon to horizon. The discs of the Moon and the Sun are 1/2 degree across - or to put it another way, you would need a "train" of 360 Moons (or Suns) to reach from one horizon to the other.

The Moon and the Sun are BOTH 1/2 degree across (plus or minus a small amount) - it's one of the great coincidences of the universe. The Sun is much bigger than the Moon, but it is also much further away, so they are the same size as viewed from Earth. That's why we can get total solar eclipses (where the Moon JUST covers the disc of the Sun) and annular eclipses (when the Moon is a little further away, so it doesn't quite cover the disc of the Sun).

The fact that the Moon looks bigger on the horizon than it it does when it is higher in the sky is just an optical illusion - it is basically 1/2 degree across wherever it is in the sky (barring minuscule effects of refraction etc). Somehow, having nearby reference points to compare it against (the horizon, etc) tricks us into thinking it is bigger. You can prove this yourself if you check out how much of the eyepiece it fills when low in the sky (and looks huge to the naked eye), and when it is higher - it is the same size.

If you can get a clear 240x view of Mars, it will look about twice as big through the eyepiece as the full Moon does with the naked eye (but probably not as bright) - and you should be able to see some surface shading etc.

Remember though that Mars is significantly bigger and further away than than the Moon, so even with 240x magnification, features of a size of a few hundred km that you can see on the Moon with the naked eye (the dark Mare, etc) will still be smaller in your 240x telescope view of Mars, so you will not be able to see mountains and craters on Mars. If you point your telescope at the Moon, however, and get a 240x view, you will be able to see features that are just a couple of km across.

Hope this helps!

[cometcatcher (Kevin)]

Originally Posted by -George-

Hi, If I may ask...

The moon is 1/2 degree in diameter looking at it with your eyes. That means mars through the telescope at 1 degree should look like 2 moon sizes by eye - no scope.

A moon generally looks big at night... if mars is 2x the size of that (1 degree vs 1/2) then Mars should look absolute huge. I am confused on this degree business.

And when is the moon 1/2 degree because some nights it looks as big as the sun. So what is all this degree based on and why isn't mars double the size of a big moon since its 1 degree not half?

The moon looking big is an optical illusion brought about by foreground objects. Notice how the moon looks bigger at the horizon than it does at the zenith. But it's not. You can prove this by sighting the moon through a long thin pipe, or a telescope with micrometer eyepiece, although the moon is slightly "flattened" very near to the horizon. Mars through the eyepiece has no foreground objects to give it size perspective.

The "apparent" size of the moon just happens to be the same "apparent" size of the Sun, most of the time. There is some slight variation due to apogee and perigee but roughly they are both about 30 minutes of arc apparent diameter.

Degrees are easy to understand. They are much like time. 60 arc seconds = 1 arc minute. 60 arc minutes = 1 degree. There's 360 degrees of azimuth. It would take 720 moons or suns end to end to go around the horizon. In R. A. 15 degrees = 1 hour. It takes 24 hours to rotate 360 degrees (24 x 15 = 360)

I have a similar telescope to you, a 10 inch f4.5 Newtonian (and a few others). As others mentioned, Visually, Mars is very demanding on perfect conditions and perfect collimation. Most of the time all I see is a red dot and maybe an icecap. Many amateurs are very skilled these days at producing amazing images that rival professional photos of only a few years ago. If you want the "eye" view, it would be comparable to one sub out of the hundreds or thousands of subs that are used.

Edit, beaten by Julian as typing with a kitten on lap is slow work lol.

[-George-]

Ok so the moon is 1/2 degree even when it looks 4 times its normal size on the horizon. Through the telescope, it will fill up the same amount of space (even though you literally are seeing it 4x bigger unaided) as when its high up and 1/4 of its size?

Why does the moon look larger on the horizon? Is there some natural magnification happening by the atmosphere in that position? Would not the telescope 'magnify' the already magnified image and thus it should be bigger?

Mars at 1 degree means it fills up the eyepiece as 2 moons by naked eye?

That is fairly large and pleasing. I thought it would be like 5mm on a page or something not worth seeing. However if it is that big... that would be pleasing.

How big does Jupiter/Saturn/Neptune/Uranus/Venus end up in degree, and how much would one need to magnify to have each 1 at least the size of 1-2 moons naked eye?

[MrB (Simon)]

Originally Posted by -George-

Why does the moon look larger on the horizon? Is there some natural magnification happening by the atmosphere in that position? Would not the telescope 'magnify' the already magnified image and thus it should be bigger?

As Kevin has said, it is an optical illusion. In other words, it is our brains making it appear larger, not atmospheric effects or anything else, just our stupid brains

http://en.wikipedia.org/wiki/Moon_illusion
Just to make things interesting: " In fact, the Moon appears about 1.5% smaller when it is near the horizon than when it is high in the sky, because it is farther away by nearly one Earth radius. "
'Appears' is perhaps the wrong word to use in the above quote.

http://blogs.discovermagazine.com/ba.../#.UzzO4fmSyCk

[astro744]

When the Moon is directly overhead the distance is from you to the Moon. When the Moon is on the horizon the distance is from you to the Moon plus the radius of the Earth. It should therefore be slightly smaller on the horizon not accounting for any refraction effects.

[astro744]

Just to throw some more spice to the mix; do a search for "moon at apogee and perigee" and you will see that the apparent size of the moon changes significantly from apogee to perigee. See also https://www.fourmilab.ch/earthview/moon_ap_per.html

(Note really sure why the blink comparison was re-scaled but there is an explanation in the text).

[julianh72 (Julian)]

Originally Posted by -George-

Ok so the moon is 1/2 degree even when it looks 4 times its normal size on the horizon. Through the telescope, it will fill up the same amount of space (even though you literally are seeing it 4x bigger unaided) as when its high up and 1/4 of its size?

Yes, the Moon is the same size (1/2 degree, give or take a couple of %) wherever it is in the sky. You might think it looks 4x bigger when it's on the horizon, but it isn't really.

We "think" the Moon looks big - probably because it's familiar and interesting, and we can make out some detail on it with the naked eye. There's a nice demonstration of what the naked human eye can actually make out on the Moon here:
http://www.astro.umd.edu/~thuard/ast...ure6-notes.pdf

An average human eye can resolve down to about 1 arc-minute or so, or about 1/60 degree, which is equivalent to about 1 metre at 4 km distance.

Think for a moment how "small" 1/2 degree actually is:

Printed a nice detailed photograph of the Moon so that it just fits across the width of a piece of A4 paper (210 mm wide). Now take that photo and walk away from it by 25 metres and turn back to the photo - THAT'S how big (small) the Moon REALLY looks!

[Dave-7 (David)]

Thanks for the replies guys it helped a lot.
So i just had another look through my scope at mars and tonights seeing conditions were much better. I could make out the north polar caps and syrtis major but just. One thing i did notice was that mars was exceptionally bright, so bright that it had difraction spikes, not sure if this is because my scope is not collimated. I also noticed it looked rather "washed". but that aside im happy with what i saw.
Oh and thanks for hijacking my thread George....

[Steffen]

Originally Posted by -George-

A moon generally looks big at night... if mars is 2x the size of that (1 degree vs 1/2) then Mars should look absolute huge. I am confused on this degree business.

Yes, apparent angular sizes in eyepieces can be tricky. Even though Mars at 240x will have twice the apparent size of naked-eye Moon keep in mind that in your typical Plössl eyepiece the entire field of view has an apparent size of 50 degrees, i.e. a hundred Moons wide.

Cheers
Steffen.

[barx1963 (Malcolm)]

Originally Posted by Dave-7

Thanks for the replies guys it helped a lot.
So i just had another look through my scope at mars and tonights seeing conditions were much better. I could make out the north polar caps and syrtis major but just. One thing i did notice was that mars was exceptionally bright, so bright that it had difraction spikes, not sure if this is because my scope is not collimated. I also noticed it looked rather "washed". but that aside im happy with what i saw.
Oh and thanks for hijacking my thread George....

No the diffraction spike occur because of the spider holding the secondary.

Malcolm