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So I'm a beginner at astronomy and I was trying to look at the moon but while trying to aim at it I saw a ring-like object in the sky. Does anyone know what this would be? all I could see was a ring with nothing in the middle of it. Was this a special type of star?

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  • $\begingroup$ Possibly an out of focus effect as described at the bottom of this FAQ. $\endgroup$ Commented Aug 6, 2017 at 5:22
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    $\begingroup$ Aaron - I don't mean to discourage you but you really need to provide much more information if you want people to think about your questions: was this with the naked eye, binoculars, finderscope or telescope? What magnification were you using? Date, time, geographical location, which direction (N, S, E or W) and approximately how high in the sky. I suggest you take a look at some of the other questions here and try to imitate the information provided otherwise, at best, you'll only get a series of guesses. $\endgroup$
    – MartinV
    Commented Aug 6, 2017 at 7:50
  • $\begingroup$ Also: Did the ring have a color, what was its size relative to other objects, was it stationary... $\endgroup$
    – user1569
    Commented Aug 7, 2017 at 9:55

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If you were using a telescope with a central obstruction (like a newtonian reflector (including dobsonian mounted ones) or an SCT or MCT, then what you saw is most likely an out of focus bright object (such as a star).

When things are in focus, a star shows as a point (actually, at very high magnifications, a tiny disc with concentric light and dark rings around it - this is called an Airey disc - caused by diffraction effects - but usually the magnification is low enough that it looks like a point).

When things are out of focus, you seen the shape of the telescopes aperture that gets bigger the more out of focus you are. For a refractor, with no central obstruction, this is a circle. For things with a central obstruction, you see a ring (donut) shape. This is what causes donut shaped out of focus highlights on pictures taken with mirror lenses. (and why normal out of focus highlights with normal lenses are round or close to it (the camera iris blades often produce a polygon shape when the lens is stopped down)).

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  • $\begingroup$ This is the most likely answer. In fact, I've often heard these "rings" referred to as donuts. $\endgroup$
    – zephyr
    Commented Aug 7, 2017 at 13:25

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