Astronomy Definitions and Terminology

Terminology and Astronomy Basics

The main thing you need to know, in case you don’t want to read all the info below, is that the bigger the telescope (the bigger the diameter of the telescope), the fainter the objects are that you will be able to see, the more detail you will be able to see in those objects, and the more magnification you can put on them. Once an object is well resolved, viewing it under “high power,” or more magnification, makes the object appear really up close, almost like you’re inside it, or able to reach out and touch it.


A common misconception amongst the general public is that more magnification is better. This is not true. More magnification only makes an object appear larger. If it is not a CLEAR (ie. well resolved) object, it is still a fuzzy object. A cotton ball under high magnification is still a cotton ball. Looking at it under high magnification will not make it appear more detailed. What people REALLY want when looking through a telescope is RESOLVING POWER. This is why astronomers keep building bigger and bigger telescopes.



Resolving Power        

The ability of a telescope to resolve objects depends on the area of the mirror or lens. A mirror or lens with twice the diameter (astronomers use the term aperture for diameter) will have FOUR times the resolving power. Remember that Area equals pi times radius squared from math? That’s what we’re getting at.



This is a term astronomers use to state how bright or faint an object is. Much like in golf, a higher score is “worse”. The more “negative” an object’s magnitude is, the brighter it is. The Sun is about magnitude minus 27, and the full moon is about magnitude minus 13. The Hubble Space Telescope has located objects down to about 30th magnitude. The scale is logarithmic, and the human eye, unaided, in perfect conditions can see objects down to about 6th magnitude.

So, what will I be able to see?

Most of the really cool deep sky objects (galaxies, nebulae, and clusters) need a telescope of at least 10” in diameter. Where an 8” enables you to see them as small, faint, blurs through an eyepiece, a 10” makes them appear larger and with greater detail. An 8” telescope usually is limited to about 10th magnitude for observing. A 12” is even better yet, and can usually resolve objects down to about 12th magnitude. My OuttaSightBridge™ is well suited for nice, relatively portable observing, and a wide range of objects, without requiring a tall ladder and other logistics for viewing. My 28” telescope, SkyClops™, is rated to resolve objects down to about 18th magnitude, and can make those faint, blurry, blobs in an 8 or 10 inch seem like you could just reach out and touch them. I have personally viewed galaxies 150 and 300 million light years away through SkyClops™. This is not possible through telescopes smaller than 24”, generally. Remember: The Magnitude scale is logarithmic, with the difference between each digit on the scale being a factor of 2.512. So, even though 12th magnitude vs. 10th magnitude doesn’t seem like much, it is. A larger telescope will also provide greater detail, and permit much more magnification of the object, once it is viewable and resolved.

Any Questions:

Contact Me!!! I will be happy to answer any questions, and offer you opportunities to view for yourself.

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