I took my telescope out tonight (I am new, just got the telescope a few days ago, it's my first one) and I was observing Mars, however all I see is just an bright orange circle, with no surface detail, regardless of magnification. The telescope I'm using is a 8in Newtonian, 1200mm focal length. Here's what I saw with a 8mm eyepiece and 2x Barlow: Mars 8mm 2x

Mars was about 32° above the horizon when I took this image.

Did I just do a poor job with collimation? Is the the observation angle? Please let me know!

  • Hi. I want to ask if you were looking through the scope and not able to see details, or only photographing it? – JohnHoltz Nov 4 at 13:58
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    Looks overexposed, or perhaps you've got high level cirrus? – Wayfaring Stranger Nov 4 at 16:15
up vote 7 down vote accepted

There's another answer here claiming that an off-axis aperture mask will improve things. That is a fairly popular meme, but it's entirely incorrect, and makes misleading claims about the effects of the central obstruction. All that does is it hides existing problems with the instrument.

If the off-axis hole appears to improve things, something else is very wrong and you need to fix that first; it's not a solution, it's a symptom pointing at serious issues. More importantly, it reduces precious aperture, therefore capping the resolving power of the instrument in a situation (observing Mars) when you need all the resolving power you can get. Please don't do that. Ignore the off-axis mask altogether.

Now, what to do to get better results with Mars?

Collimation

Make sure your telescope is in perfect collimation. There is no one technique to rule them all. There are many ways to collimate a telescope. Whichever method you choose, make sure you actually use it before observing Mars. Small deviations from perfect collimation will affect results on this difficult target.

Your instrument's manual, or the manufacturer's website should provide some info. Here are some links to get you started:

https://garyseronik.com/a-beginners-guide-to-collimation/

https://www.skyandtelescope.com/astronomy-resources/how-to-align-your-newtonian-reflector-telescope/

Some info about the importance of collimation:

http://www.astrophoto.fr/collim.html

Regarding laser collimators, which are very popular: A laser collimator is very quick and can be very good, but provided the laser itself is perfectly centered. Plug the laser into the focuser, watch the laser spot on the primary mirror, and slowly turn the laser like a knob - if the spot moves in a circle as you turn the laser, then it's not centered. Some lasers can be adjusted until they are centered (2 or 3 adjustment screws on the barrel), others can't. A laser that's not centered will not provide good collimation for your telescope.

There are many other collimation techniques, keep learning.

You don't need to be in perfect collimation every single time - a lot of faint fuzzies (galaxies, etc) don't require any careful collimation. But for Mars and the Moon you better do it right. Don't obsess over it, but try and do a good job. Personally, I at least check collimation every time no matter what, but with practice now it only takes me 5 minutes to fix any deviation, so it's not a chore.

Thermal equilibrium

If your telescope is not at the same temperature as the air, convection vortices will appear inside which will affect performance. Take the instrument outside at least 1 hour before the observation and let it vent out all the heat.

Some reading material:

https://garyseronik.com/beat-the-heat-conquering-newtonian-reflector-thermals-part-1/

https://garyseronik.com/beat-the-heat-conquering-newtonian-reflector-thermals-part-2/

Seeing

This is basically atmospheric turbulence. When it's bad, the image is distorted and fuzzy. When it's good, the image is clear and you can see small details. Basically, Mars is impossible to watch if seeing is not good or very good. Sometimes, spells of bad seeing can last for days or weeks. There's not much you can do except put the scope in the car and drive someplace else where seeing is good at that time.

https://en.wikipedia.org/wiki/Astronomical_seeing

Seeing is basically weather-related, so it can be predicted to some extent. Go on the Clear Dark Sky website, search for a location close to your home, and pull up the chart:

http://www.cleardarksky.com/csk/

enter image description here

Look at the row called Seeing. If it's dark blue for the time when you plan your observation, chances are good that seeing will not get in the way. If it's light blue or white, the forecast is not good.

Opposition

Mars is only worth trying around oppositions, when it's closest to Earth. This happens roughly every two years.

The previous opposition was in July 2018 when Mars had an apparent size of 24 arcsec.

Currently (November 2018) the apparent size of Mars is 11 arcsec, less than half the size at opposition.

The next opposition is in October 2020, when it will be about 22 arcsec.

A few weeks before and after opposition Mars is worth trying.

https://www.wolframalpha.com/input/?i=mars+apparent+size+in+october+13+2020

Focus

Make sure the scope is perfectly focused. Point it at a fixed star (Polaris is quite convenient since it does not move), and adjust the focuser until the image of the star is as small as it can be.

It's pointless to try fine focusing if the scope is not collimated (see above). Collimate first, then you'll be able to achieve a sharper focus.

Also, if there are seeing issues, or thermal issues, a sharp focus will be hard to achieve.

Other factors

Mars is a difficult object to observe. Good quality optics are important. Aperture is important (more is better - please disregard the memes about limiting the aperture). Experience is important - you'll get better in time.

  • Thanks so much! How close do I have to get with the collimation? Is there a tolerance or is it absolute? – Krystian S Nov 7 at 1:44
  • @KrystianS As close as allowed by the tools and technique you're using. Small errors result in a small loss of performance. Large errors result in a large loss. I'll edit the answer to add some extra info about collimation. – Florin Andrei Nov 7 at 4:16

Surface details on Mars are very low contrast (except for ice caps). Sometimes you just can't see anything. Poor collimation may be a problem, or bad seeing (turbulence in the atmosphere, especially a problem when Mars is low in the sky); sometimes you have to look for a while for a moment where you can glimpse detail on the surface.

A newtonian's central obstruction will always reduce contrast on planetary details. One answer to this is to use an off-axis aperture mask for planetary and lunar observation; they are not that hard to make (sometimes they will come with your scope). This will essentially convert your 8" newtonian to a 2.5" (or so) obstruction-free off-axis reflector. This will make the overall image dimmer, but can improve contrast and lessen the impact of bad seeing.

  • What a great answer! – Fattie Nov 6 at 9:39
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    The off-axis aperture mask is bad advice. All it does is it reduces the aperture and limits the resolving power of the instrument. Please don't do that. Make sure the telescope is perfectly collimated. Make sure the telescope is at thermal equilibrium with the air. Try and do your observations while atmospheric turbulence is low. And most importantly, observe Mars around oppositions, when its apparent size is greatest - it's quite pointless to try when it's not at opposition. – Florin Andrei Nov 6 at 19:38
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    Also, the effects of the central obstruction are one of the most misunderstood topics of amateur astronomy. When the central obstruction is invoked as a reason for decreased performance, in 9 cases out of 10 the argument is wrong from the beginning. OP, please disregard the central obstruction topic completely. You have other things to worry about, which are legitimate concerns. – Florin Andrei Nov 6 at 20:12

You wrote that your telescope comes with 1200mm focus. Your diameter is 200mm. Check out the length of your telescope. If it's less then 600mm, then you have troubles, because your telescope could use "corrector" lense in front of your ocular lenses. Such "corrector" is weak part, because it most likely corrects the aspheric error of main mirror and making such correctors is very costly. Producers could use cheaper parts which destroy your telescope, but increase their profits. If you find out that there is corrector, then you got solution: buy proper corrector. But such task is not for beginners. Consult with other peers!

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As both Earth and Mars move in their orbits, the actual distance between us varies. We past the close-approach point in this orbit in July, and now we are further ahead of Mars in the orbit. As distance increases, the angular size of Mars decreases. Right now, Mars is about 11 arcseconds in diameter from Earth. The size of details you can make out depends on the aperture of the telescope. As light enters the telescope, the wave-fronts begin to break down in a process known as diffraction. The practical result of this is that the interference patterns between the wavelets limits the amount of detail that can be resolved. This is a bit different from, but analogous to, the way a photographic sensor can only capture so much data and as you enlarge the image you lose detail through pixellation. In theory, magnification is unlimited.... but USABLE magnification is limited primarily due to the aperture of the instrument.

Diffraction effects are also somewhat dependent upon the wavelength of the light - shorter wavelengths are less affected than longer ones. For deep-blue light around 425 nanometers, the diffraction limit of an 8" (203 mm) telescope is about 0.57 arcseconds. This means that the smallest details it can resolve will be about that size or larger. For redder light, say around 675 nm, the diffraction limit is about 0.84 arcseconds. At 425 nanometers, and at the current distance to Mars (as I write this, about 131,443,000 km), .57 arcsec equates to about 363 kilometers. Thus, the smallest details you should be able to see on Mars are about 363 km in size - if they're blue. For redder objects (most of Mars), something would have to be about 510 km in size to be visible. Anything smaller is just lost in the blur, and even object that size are going to be a significant challenge. Of course, these numbers are based on the theoretic limits of the instrument. This doesn't take into account the quality of the optics or the effects of the atmosphere.

The generally accepted rule of thumb is that the highest usable magnification of a telescope can be calculated by multiplying the aperture in inches by 50x or the aperture in mm by 2x. For an 8"/203 mm scope, this gives a value of 400x. However, this is maximum and assumes ideal conditions.

For average conditions with humidity in the air, turbulence in the atmosphere, dust, pollen, and other pollutants, etc... as well as the air density itself, the practical limit for most observers under normally experienced conditions is probably closer to 20 to 30x per inch or 1x or so per mm. This would mean a maximum normal usable magnification between about 180x and 240x. Beyond that, the image gets too blurry to be worth viewing.

Because of this, a Barlow lens doesn't necessarily help maters. Further, most Barlow lenses suffer from some amount of chromatic aberration, worsening the view. A good quality Barlow is usually apochromatic, but the more common ones aren't.

Now, looking at the image you posted, it's hard to get a good idea what the issues are for sure. Camera sensors and human eyes work differently, and don't equate well. But, most likely your primary issue is simply that of distance and resolution. This gets worse as Mars gets closer to the horizon. If it's under 40° above the horizon, you're starting to get into substantially more atmosphere between you and the object. Like looking through a glass of water, the atmosphere will distort the view more and more. If Mars wasn't high in the night sky when you were observing, this could be part of your problem.

Unfortunately, Mars won't be a good target again until October 2020, at which time it should pass within 62.12 million miles, at which time its angular size should be more than twice what it currently is, and you should be able to resolve details half the size you currently can see.

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