30 replies to this topic

[Rutilus]

This fellow CNer has taken some excellent images. The images show how

Uranus will appear at high magnification in the eyepiece. The planet will

show a noticable small disk that will look different to the surrounding stars.

https://www.cloudyni.../#entry12063666

[KBHornblower]

To answer your question "is it too late". The answer is no, Uranus is visible even after sunrise in clear blue sky.  You better be tracking it from darkness or have go to mount in order to find it in daylight though.  I just observed daytime Uranus this past Sunday morn and it was really cool to see that pale green orb suspended against blue sky.  Mars is easy easy in daylight and stunning against a blue sky.  At powers as low as 90x, Uranus will reveal itself as a little orb easily differentiated from a star.  Just pan around with that nagler and you'll find it.  You should be able to find Uranus in a spotting scope at night, Ive seen it with 10x50 binoculars, you could try that to get a feel for its location.

At first I was skeptical about your daylight view, so I tested it by making a simulation in PaintShop Pro, using calculated values for the surface brightness of Uranus and the clear daytime sky.  I could see it with the spot subtending about 10 arcminutes, which is 90x.

[Sketcher]

Do you happen to know any good resources for learning this topic (book / video).

Not really.  After 50 years or so of reading various books etc. I've lost track of what was learned from which source.  Besides, I've never run across a single source that has "everything" in it.  So it ends up being a situation of getting some information from here, some from there, with some supplemented by personal experience.  So I guess the best I can offer is to read all you can on whatever topic is of interest and experiment a bit to determine whether or not any given piece of information is reliable and/or of relevance to you.

 

That being said, In my opinion some of the older sources tend to be of more use than many of the newer sources -- unless one is looking for information that's of particular relevance to one or more of the more modern technological gadgets that are becoming more popular these days.

 

A public library (or used book store) that hasn't "weeded out" most of their older books on amateur astronomy would likely contain a wealth of practical information -- despite the "dated" nature of the state of the science information.

 

can someone give me some advice on distinguishing a planet "disc" vs a "star".  I understand the concept, but I am not sure if I can make out the difference yet.

Are there any sketches or pictures that exist that could help out?

Perhaps better would be the "hands-on" approach.  Start by carefully examining what stars look like with your telescope under high magnifications.  A telescope of high enough quality, tweaked to perform at its best, used under a night of good enough seeing will show (at high enough magnifications) stars as Airy disks with one or more fainter diffraction rings around them.

 

In a 10-inch telescope, Uranus ought to look like a small disk that's 7 to 8 times larger than the apparent diameter of any star's Airy disk -- as seen with the same (10-inch) telescope.  That ought to be a big enough difference in apparent diameter to be quite noticeable.

 

Another thing to practice on would be the moons of Jupiter.  It's possible to tell which moon is which by carefully noting (at a high enough  magnification, on a good enough night, etc.) their apparent differences in apparent diameter.  This is "doable" even with a telescope of half the aperture of yours.

 

Unfortunately, until one has made good progress in understanding one's telescope, how to get the most out of it, seeing conditions, etc; one is going to have a lot more obstacles to overcome besides differentiating a star's Airy disk from a planetary disk that's only a few times larger.  But with perseverance, it's possible to "get there" simply by gaining more quality time behind the eyepiece -- even without any of the "book learning".

 

Note:  stellar Airy disks (particularly those of near "textbook" quality) are much easier to see when using smaller aperture (as in 50 to 60mm) telescopes -- which tend to be less effected by atmospheric seeing conditions, tube currents, mirror cool-down issues, collimation errors, and quality deficiencies.  On the other hand, Uranus will be better seen with your 10-inch telescope.

 

Much is perhaps better learned through experience.  And it takes time and experience to learn how to "see" when observing celestial objects with astronomical telescopes.  Looking at images and sketches and seeing the details therein is very different from looking at the same things through a telescope.

 

It's a wonderful thing (truly, it is!) to accumulate knowledge from books, websites, videos, etc; but none of those resources can replace actual, hands-on, personal experience behind a telescope's eyepiece.  And to me, that personal experience is worth more than the accumulated knowledge that one can gain through the written word, videos, etc.

 

On the other hand, I suppose a lot has to do with the individual, their aptitudes, their attitudes, etc.

[Cpk133]

can someone give me some advice on distinguishing a planet "disc" vs a "star".  I understand the concept, but I am not sure if I can make out the difference yet.

Are there any sketches or pictures that exist that could help out?

 

Thanks!

At low powers, say 100x or 10x per inch, your dob should show stars like this     .      (The airy disc is so small at that magnification, they look like needle points, the brighter ones look bigger due to optical scattering and scatter from your eye).  Uranus on the other hand will look like this    o    The other telltale is uranus will have a unique blue green cast that doesnt look anything like neighboring stars.  At 100x, there should be at least a few stars in the field of view where you'll be able to recognize the difference.  If your eyesight isnt the best, look for something that looks different than everything else, center the object and bump the power up to about 150x. It should be easy to see at that power.  For reference, uranus is about 2x the size of Jupiters moon Ganymede and nearly the same brightness.  

Edited by Cpk133, 07 August 2022 - 04:01 PM.

[Cpk133]

At first I was skeptical about your daylight view, so I tested it by making a simulation in PaintShop Pro, using calculated values for the surface brightness of Uranus and the clear daytime sky.  I could see it with the spot subtending about 10 arcminutes, which is 90x.

I would never lie about the planets :-)

[luxo II]

Here's how it looks visually in most small scopes... even my 70mm APO shows it looking like this.

Attached Thumbnails

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Edited by luxo II, 07 August 2022 - 08:36 PM.