http://www.citydeepsky.com/wiki/index.php?title=Limiting_Magnitude&feed=atom&action=historyLimiting Magnitude - Revision history2024-03-29T12:02:24ZRevision history for this page on the wikiMediaWiki 1.19.17http://www.citydeepsky.com/wiki/index.php?title=Limiting_Magnitude&diff=3124&oldid=prevEvilscientist: /* Theoretical Limiting Magnitude */ add units for d2018-06-01T15:40:38Z<p><span dir="auto"><span class="autocomment">Theoretical Limiting Magnitude: </span> add units for d</span></p>
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<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div><math>m_v\approx2.7+5\log_{10} d</math></div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div><math>m_v\approx2.7+5\log_{10} d</math></div></td></tr>
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<tr><td class='diff-marker'>−</td><td style="background: #ffa; color:black; font-size: smaller;"><div>where d is the diameter of the objective lens/mirror of the optical system. This formula makes the assumption that the magnification used is greater than the diameter of the objective in mm, so telescope with a 70mm objective needs an eyepiece that gives at least 70x of magnification for this formula to be accurate. It also assumes clear and dark skies <ref name="birney">Birney, D.S., Gonzales, G., Oesper, D., 2008, Observational Astronomy, 2nd ed, (Cambridge)</ref></div></td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div>where d is the diameter of the objective lens/mirror of the optical system <ins class="diffchange diffchange-inline">in mm</ins>. This formula makes the assumption that the magnification used is greater than the diameter of the objective in mm, so telescope with a 70mm objective needs an eyepiece that gives at least 70x of magnification for this formula to be accurate. It also assumes clear and dark skies <ref name="birney">Birney, D.S., Gonzales, G., Oesper, D., 2008, Observational Astronomy, 2nd ed, (Cambridge)</ref></div></td></tr>
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<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>So for example, a dark adapted human eye with an aperture of about 7mm has a limiting magnitude of about 6.7 at a dark site. A 50mm set of binoculars has a limiting magnitude of 11.0 and a 127mm telescope has a limiting magnitude of about 13.0.</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>So for example, a dark adapted human eye with an aperture of about 7mm has a limiting magnitude of about 6.7 at a dark site. A 50mm set of binoculars has a limiting magnitude of 11.0 and a 127mm telescope has a limiting magnitude of about 13.0.</div></td></tr>
</table>Evilscientisthttp://www.citydeepsky.com/wiki/index.php?title=Limiting_Magnitude&diff=3005&oldid=prevEvilscientist: add references tag2011-08-31T03:07:18Z<p>add references tag</p>
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<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>M67</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>M67</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>[[Image:m67_map.png | thumb | 640px]]</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>[[Image:m67_map.png | thumb | 640px]]</div></td></tr>
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<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div><ins style="color: red; font-weight: bold; text-decoration: none;"><References/></ins></div></td></tr>
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<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>[[Category:Observing Concepts]]</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>[[Category:Observing Concepts]]</div></td></tr>
</table>Evilscientisthttp://www.citydeepsky.com/wiki/index.php?title=Limiting_Magnitude&diff=2987&oldid=prevEvilscientist: Major rewrite of this page.2011-07-12T04:49:00Z<p>Major rewrite of this page.</p>
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<tr><td class='diff-marker'>−</td><td style="background: #ffa; color:black; font-size: smaller;"><div><del class="diffchange diffchange-inline">==</del>Limiting <del class="diffchange diffchange-inline">Magnitude and City Skies==</del></div></td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div>Limiting <ins class="diffchange diffchange-inline">magnitude </ins>is the [[magnitude]] <ins class="diffchange diffchange-inline">of the dimmest object that </ins>can be <ins class="diffchange diffchange-inline">seen </ins>with a <ins class="diffchange diffchange-inline">particular optical system be it </ins>unaided eye's <ins class="diffchange diffchange-inline">binoculars or </ins>a [[<ins class="diffchange diffchange-inline">telescope</ins>]]<ins class="diffchange diffchange-inline">. Several factors can affect what </ins>the <ins class="diffchange diffchange-inline">actual limiting magnitude will be</ins>.</div></td></tr>
<tr><td class='diff-marker'>−</td><td style="background: #ffa; color:black; font-size: smaller;"><div><del class="diffchange diffchange-inline">Of course the problem with observing from within a city </del>is <del class="diffchange diffchange-inline">that </del>the <del class="diffchange diffchange-inline">sky itself has a visual </del>[[magnitude]]<del class="diffchange diffchange-inline">. This limits what </del>can be <del class="diffchange diffchange-inline">observed, though </del>with <del class="diffchange diffchange-inline">larger instruments, you can see fainter objects. For example, from </del>a <del class="diffchange diffchange-inline">light polluted back yard within the city of Calgary, the </del>unaided eye <del class="diffchange diffchange-inline">on a good night can see down to 4th magnitude which is much brighter than the 6th to 7th magnitude that could be seen at a good dark site. At this magnitude, most constellations are missing stars and other than the moon and planets, there</del>'s <del class="diffchange diffchange-inline">not </del>a <del class="diffchange diffchange-inline">heck of a lot to look at. Even so the </del>[[<del class="diffchange diffchange-inline">M45|Pleiades</del>]] <del class="diffchange diffchange-inline">and </del>the <del class="diffchange diffchange-inline">[[Hyades]], for example, are visible in the winter time, albeit missing stars</del>.</div></td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div></div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"></td></tr>
<tr><td class='diff-marker'>−</td><td style="background: #ffa; color:black; font-size: smaller;"><div><del class="diffchange diffchange-inline">If you move up to 10x50 binoculars</del>, the limiting magnitude <del class="diffchange diffchange-inline">moves to around 7. This </del>of <del class="diffchange diffchange-inline">course brings many more items into visibility, at least in theory. There are at least 50 deep sky objects that would fit into this category, that are visible from Calgary's, and hence Canada's, latitude. Now this </del>is <del class="diffchange diffchange-inline">a theoretical 50, as for many objects, </del>the <del class="diffchange diffchange-inline">actual surface brightness will be less than what </del>the <del class="diffchange diffchange-inline">magnitude suggests</del>. This <del class="diffchange diffchange-inline">is because for extended objects, i.e. non-stars, the magnitude is the aggregate of the total brightness of the object. The more spread out an object is, the dimmer it actually appears for a given magnitude. So two objects </del>can <del class="diffchange diffchange-inline">have the same magnitude, but if one is spread </del>out <del class="diffchange diffchange-inline">more, it would appear dimmer. This is one reason why this list isn't simply generated from a planetarium program as </del>the <del class="diffchange diffchange-inline">magnitudes listed won't necessarily translate into observability at a given limiting magnitude.</del></div></td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div><ins class="diffchange diffchange-inline">==Theoretical Limiting Magnitude==</ins></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div><ins class="diffchange diffchange-inline">All other factors equal</ins>, the limiting magnitude of <ins class="diffchange diffchange-inline">an optical system </ins>is <ins class="diffchange diffchange-inline">based solely on </ins>the <ins class="diffchange diffchange-inline">aperture of </ins>the <ins class="diffchange diffchange-inline">objective lens</ins>. This can <ins class="diffchange diffchange-inline">be worked </ins>out <ins class="diffchange diffchange-inline">with </ins>the <ins class="diffchange diffchange-inline">following formula:</ins></div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"></td></tr>
<tr><td class='diff-marker'>−</td><td style="background: #ffa; color:black; font-size: smaller;"><div><del class="diffchange diffchange-inline">The list also include objects visible </del>with a <del class="diffchange diffchange-inline">small [[telescope]]</del>. <del class="diffchange diffchange-inline">For </del>example, a 127mm <del class="diffchange diffchange-inline">(5 inch) [[Maksutov]] </del>has a <del class="diffchange diffchange-inline">theoretical </del>limiting magnitude of about 13. <del class="diffchange diffchange-inline">However </del>due to light <del class="diffchange diffchange-inline">pollution within </del>the <del class="diffchange diffchange-inline">city </del>this <del class="diffchange diffchange-inline">becomes </del>something <del class="diffchange diffchange-inline">around 9 </del>to <del class="diffchange diffchange-inline">10</del>. <del class="diffchange diffchange-inline">Again with surface brightness differing from </del>magnitude, <del class="diffchange diffchange-inline">it's unlikely </del>there <del class="diffchange diffchange-inline">will </del>be <del class="diffchange diffchange-inline">many 9th mangitude galaxies on </del>the <del class="diffchange diffchange-inline">list</del>, <del class="diffchange diffchange-inline">but what </del>can be seen <del class="diffchange diffchange-inline">through </del>the telescope <del class="diffchange diffchange-inline">will be</del>.</div></td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div><ins class="diffchange diffchange-inline"><math>m_v\approx2.7+5\log_{10} d</math></ins></div></td></tr>
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<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div><ins class="diffchange diffchange-inline">where d is the diameter of the objective lens/mirror of the optical system. This formula makes the assumption that the magnification used is greater than the diameter of the objective in mm, so telescope </ins>with a <ins class="diffchange diffchange-inline">70mm objective needs an eyepiece that gives at least 70x of magnification for this formula to be accurate</ins>. <ins class="diffchange diffchange-inline">It also assumes clear and dark skies <ref name="birney">Birney, D.S., Gonzales, G., Oesper, D., 2008, Observational Astronomy, 2nd ed, (Cambridge)</ref></ins></div></td></tr>
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<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div><ins class="diffchange diffchange-inline">So for </ins>example, <ins class="diffchange diffchange-inline">a dark adapted human eye with an aperture of about 7mm has a limiting magnitude of about 6.7 at a dark site. A 50mm set of binoculars has a limiting magnitude of 11.0 and </ins>a 127mm <ins class="diffchange diffchange-inline">telescope </ins>has a limiting magnitude of about 13.<ins class="diffchange diffchange-inline">0.</ins></div></td></tr>
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<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div><ins class="diffchange diffchange-inline">These magnitudes are limits for the human eye at the telescope, modern image sensors such as CCD's can push a telescope 4-6 magnitudes fainter<ref name="birney"> </ref>.</ins></div></td></tr>
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<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div><ins class="diffchange diffchange-inline">==Factors Affecting Limiting Magnitude==</ins></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div><ins class="diffchange diffchange-inline">Now the theoretical limiting magnitude calculated with the formula above  is the limiting magnitude under ideal conditions. As conditions are never ideal, the value may be less than that calculated. The atmosphere above the observing site has an effect. The closer to sea level a site is, the more atmosphere one has to look through and this has a negative effect on limiting magnitude. The weather has another effect, on how transparent the air is </ins>due to <ins class="diffchange diffchange-inline">water and dust in the atmosphere. Turbulence causes stars to be smeared making them seem dimmer. </ins></div></td></tr>
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<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div><ins class="diffchange diffchange-inline">The telescope optics also have an effect on the limiting magnitude beyond the diameter of the objective. Poorly produced or aligned optics will spread the </ins>light <ins class="diffchange diffchange-inline">of an object out and make it seem dimmer. Dirt and dust on </ins>the <ins class="diffchange diffchange-inline">optics will also absorb and diffract light, again making the object seem dimmer than it really is. Higher magnification can, to a point, improve contrast by making the sky appear blacker. This works especially well on stars as their light doesn't get spread out as much under magnification as does that of extended objects.</ins></div></td></tr>
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<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div><ins class="diffchange diffchange-inline">The age and skill of the observer is also a factor. As we age, our pupils don't dilate as much as they did when we were younger, limiting how much light gets into our eye. This is less a factor with a telescope as carefully selected telescope-eyepiece combinations can compensate for </ins>this <ins class="diffchange diffchange-inline">somewhat but still </ins>something to <ins class="diffchange diffchange-inline">consider</ins>. <ins class="diffchange diffchange-inline">Further skilled observers can generally see dimmer objects than novice observers once they learn and master techniques such as averted vision.</ins></div></td></tr>
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<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div><ins class="diffchange diffchange-inline">Finally the sky itself has a </ins>magnitude<ins class="diffchange diffchange-inline">. Even at the darkest site</ins>, there <ins class="diffchange diffchange-inline">is a faint glow to the sky called air glow caused by starlight being scattered by the atmosphere. Other natural phenomenon such as the Zodiacal light and aurora also cause the sky to </ins>be <ins class="diffchange diffchange-inline">less dark than it could be. Beyond natural phenomenon, </ins>the <ins class="diffchange diffchange-inline">light pollution from city lights causes an incredible degradation to the brightness of the night sky. Human light pollution can push limiting magnitudes to values around 4 or higher</ins>, <ins class="diffchange diffchange-inline">so only the brightest stars </ins>can be seen <ins class="diffchange diffchange-inline">with </ins>the <ins class="diffchange diffchange-inline">unaided eye. Binoculars and telescopes also see a corresponding reduction in their limiting magnitues such that 50mm binoculars can only see around magnitude 7 or so and a 127mm </ins>telescope <ins class="diffchange diffchange-inline">is limited to around 10th magnitude</ins>.  </div></td></tr>
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<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>==Determining Limiting Magnitude==</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>==Determining Limiting Magnitude==</div></td></tr>
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<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>==Maps==</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>==Maps==</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>===Limiting Magnitude Maps===</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>===Limiting Magnitude Maps===</div></td></tr>
<tr><td class='diff-marker'>−</td><td style="background: #ffa; color:black; font-size: smaller;"><div>The limiting magnitude maps are .pdf and .ps files. They are held in the file repository on <del class="diffchange diffchange-inline">my </del>blog. The links below provide access to the files:</div></td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div>The limiting magnitude maps are .pdf and .ps files. They are held in the file repository on <ins class="diffchange diffchange-inline">the </ins>blog <ins class="diffchange diffchange-inline">evilscientist.ca</ins>. The links below provide access to the files:</div></td></tr>
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</table>Evilscientisthttp://www.citydeepsky.com/wiki/index.php?title=Limiting_Magnitude&diff=2967&oldid=prevEvilscientist: /* Limiting Magnitude and City Skies */ clean up - remove first person2010-10-05T21:22:40Z<p><span dir="auto"><span class="autocomment">Limiting Magnitude and City Skies: </span> clean up - remove first person</span></p>
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<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>==Limiting Magnitude and City Skies==</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>==Limiting Magnitude and City Skies==</div></td></tr>
<tr><td class='diff-marker'>−</td><td style="background: #ffa; color:black; font-size: smaller;"><div>Of course the problem with observing from within a city is that the sky itself has a visual [[magnitude]]. This limits what can be observed, though with larger instruments, you can see fainter objects. For example, from <del class="diffchange diffchange-inline">my </del>light polluted back yard within the city of Calgary <del class="diffchange diffchange-inline">(or as we like to call it</del>, <del class="diffchange diffchange-inline">light pollution central), my </del>unaided eye<del class="diffchange diffchange-inline">, </del>on a good night can see down to 4th magnitude which is much brighter than the 6th to 7th magnitude that <del class="diffchange diffchange-inline">I </del>could <del class="diffchange diffchange-inline">see </del>at a good dark site. At this magnitude, most constellations are missing stars and other than the moon and planets, there's not a heck of a lot to look at. Even so the [[M45|Pleiades]] and the [[Hyades]], for example, are visible in the winter time, albeit missing stars.</div></td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div>Of course the problem with observing from within a city is that the sky itself has a visual [[magnitude]]. This limits what can be observed, though with larger instruments, you can see fainter objects. For example, from <ins class="diffchange diffchange-inline">a </ins>light polluted back yard within the city of Calgary, <ins class="diffchange diffchange-inline">the </ins>unaided eye on a good night can see down to 4th magnitude which is much brighter than the 6th to 7th magnitude that could <ins class="diffchange diffchange-inline">be seen </ins>at a good dark site. At this magnitude, most constellations are missing stars and other than the moon and planets, there's not a heck of a lot to look at. Even so the [[M45|Pleiades]] and the [[Hyades]], for example, are visible in the winter time, albeit missing stars.</div></td></tr>
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<tr><td class='diff-marker'>−</td><td style="background: #ffa; color:black; font-size: smaller;"><div>If <del class="diffchange diffchange-inline">I </del>move up to <del class="diffchange diffchange-inline">my </del>10x50 binoculars, <del class="diffchange diffchange-inline">my </del>limiting magnitude moves to around 7. This of course brings many more items into visibility, at least in theory. There are at least 50 deep sky objects that would fit into this category, that are visible from Calgary's, and hence Canada's, latitude. Now this is a theoretical 50, as for many objects, the actual surface brightness will be less than what the magnitude suggests. This is because for extended objects, i.e. non-stars, the magnitude is the aggregate of the total brightness of the object. The more spread out an object is, the dimmer it actually appears for a given magnitude. So two objects can have the same magnitude, but if one is spread out more, it would appear dimmer. This is one reason why this list <del class="diffchange diffchange-inline">won</del>'t <del class="diffchange diffchange-inline">be </del>simply generated from a planetarium program as the magnitudes listed won't necessarily translate into observability at a given limiting magnitude.</div></td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div>If <ins class="diffchange diffchange-inline">you </ins>move up to 10x50 binoculars, <ins class="diffchange diffchange-inline">the </ins>limiting magnitude moves to around 7. This of course brings many more items into visibility, at least in theory. There are at least 50 deep sky objects that would fit into this category, that are visible from Calgary's, and hence Canada's, latitude. Now this is a theoretical 50, as for many objects, the actual surface brightness will be less than what the magnitude suggests. This is because for extended objects, i.e. non-stars, the magnitude is the aggregate of the total brightness of the object. The more spread out an object is, the dimmer it actually appears for a given magnitude. So two objects can have the same magnitude, but if one is spread out more, it would appear dimmer. This is one reason why this list <ins class="diffchange diffchange-inline">isn</ins>'t simply generated from a planetarium program as the magnitudes listed won't necessarily translate into observability at a given limiting magnitude.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"></td></tr>
<tr><td class='diff-marker'>−</td><td style="background: #ffa; color:black; font-size: smaller;"><div><del class="diffchange diffchange-inline">I will </del>also include objects visible with a small [[telescope]]. <del class="diffchange diffchange-inline">My </del>127mm (5 inch) [[Maksutov]] has a theoretical limiting magnitude of about 13. However due to light pollution within the city this becomes something around 9 to 10. Again with surface brightness differing from magnitude, it's unlikely there will be many 9th mangitude galaxies on the list, but what <del class="diffchange diffchange-inline">I </del>can <del class="diffchange diffchange-inline">see </del>through <del class="diffchange diffchange-inline">my scope </del>will be.</div></td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div><ins class="diffchange diffchange-inline">The list </ins>also include objects visible with a small [[telescope]]. <ins class="diffchange diffchange-inline">For example, a </ins>127mm (5 inch) [[Maksutov]] has a theoretical limiting magnitude of about 13. However due to light pollution within the city this becomes something around 9 to 10. Again with surface brightness differing from magnitude, it's unlikely there will be many 9th mangitude galaxies on the list, but what can <ins class="diffchange diffchange-inline">be seen </ins>through <ins class="diffchange diffchange-inline">the telescope </ins>will be.</div></td></tr>
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<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>==Determining Limiting Magnitude==</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>==Determining Limiting Magnitude==</div></td></tr>
</table>Evilscientisthttp://www.citydeepsky.com/wiki/index.php?title=Limiting_Magnitude&diff=2800&oldid=prevEvilscientist: add telescope link2009-11-19T01:44:23Z<p>add telescope link</p>
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<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>If I move up to my 10x50 binoculars, my limiting magnitude moves to around 7. This of course brings many more items into visibility, at least in theory. There are at least 50 deep sky objects that would fit into this category, that are visible from Calgary's, and hence Canada's, latitude. Now this is a theoretical 50, as for many objects, the actual surface brightness will be less than what the magnitude suggests. This is because for extended objects, i.e. non-stars, the magnitude is the aggregate of the total brightness of the object. The more spread out an object is, the dimmer it actually appears for a given magnitude. So two objects can have the same magnitude, but if one is spread out more, it would appear dimmer. This is one reason why this list won't be simply generated from a planetarium program as the magnitudes listed won't necessarily translate into observability at a given limiting magnitude.</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>If I move up to my 10x50 binoculars, my limiting magnitude moves to around 7. This of course brings many more items into visibility, at least in theory. There are at least 50 deep sky objects that would fit into this category, that are visible from Calgary's, and hence Canada's, latitude. Now this is a theoretical 50, as for many objects, the actual surface brightness will be less than what the magnitude suggests. This is because for extended objects, i.e. non-stars, the magnitude is the aggregate of the total brightness of the object. The more spread out an object is, the dimmer it actually appears for a given magnitude. So two objects can have the same magnitude, but if one is spread out more, it would appear dimmer. This is one reason why this list won't be simply generated from a planetarium program as the magnitudes listed won't necessarily translate into observability at a given limiting magnitude.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"></td></tr>
<tr><td class='diff-marker'>−</td><td style="background: #ffa; color:black; font-size: smaller;"><div>I will also include objects visible with a small telescope. My 127mm (5 inch) [[Maksutov]] has a theoretical limiting magnitude of about 13. However due to light pollution within the city this becomes something around 9 to 10. Again with surface brightness differing from magnitude, it's unlikely there will be many 9th mangitude galaxies on the list, but what I can see through my scope will be.</div></td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div>I will also include objects visible with a small <ins class="diffchange diffchange-inline">[[</ins>telescope<ins class="diffchange diffchange-inline">]]</ins>. My 127mm (5 inch) [[Maksutov]] has a theoretical limiting magnitude of about 13. However due to light pollution within the city this becomes something around 9 to 10. Again with surface brightness differing from magnitude, it's unlikely there will be many 9th mangitude galaxies on the list, but what I can see through my scope will be.</div></td></tr>
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<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>==Determining Limiting Magnitude==</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>==Determining Limiting Magnitude==</div></td></tr>
</table>Evilscientisthttp://www.citydeepsky.com/wiki/index.php?title=Limiting_Magnitude&diff=2407&oldid=prevEvilscientist at 20:04, 9 February 20092009-02-09T20:04:08Z<p></p>
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<tr><td class='diff-marker'>−</td><td style="background: #ffa; color:black; font-size: smaller;"><div>[[Category:<del class="diffchange diffchange-inline">Astronomical</del>]]</div></td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div>[[Category:<ins class="diffchange diffchange-inline">Observing Concepts</ins>]]</div></td></tr>
</table>Evilscientisthttp://www.citydeepsky.com/wiki/index.php?title=Limiting_Magnitude&diff=2268&oldid=prevEvilscientist: fix grammar and add wikilinks2009-01-30T13:22:59Z<p>fix grammar and add wikilinks</p>
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<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>==Limiting Magnitude and City Skies==</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>==Limiting Magnitude and City Skies==</div></td></tr>
<tr><td class='diff-marker'>−</td><td style="background: #ffa; color:black; font-size: smaller;"><div>Of course the problem with observing from within a city is that the sky itself has a visual magnitude. This limits what can be observed, though with larger instruments, you can see fainter objects. For example, from my light polluted back yard within the city of Calgary (or as we like to call it, light pollution central), my unaided eye, on a good night can see down to 4th magnitude which is much brighter than the 6th to 7th magnitude that <del class="diffchange diffchange-inline">you </del>could see at a good dark site. At this magnitude, most constellations are missing stars and other than the moon and planets, there's not a heck of a lot to look at. Even so the Pleiades and the Hyades, for example, are visible in the winter time, albeit missing stars.</div></td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div>Of course the problem with observing from within a city is that the sky itself has a visual <ins class="diffchange diffchange-inline">[[</ins>magnitude<ins class="diffchange diffchange-inline">]]</ins>. This limits what can be observed, though with larger instruments, you can see fainter objects. For example, from my light polluted back yard within the city of Calgary (or as we like to call it, light pollution central), my unaided eye, on a good night can see down to 4th magnitude which is much brighter than the 6th to 7th magnitude that <ins class="diffchange diffchange-inline">I </ins>could see at a good dark site. At this magnitude, most constellations are missing stars and other than the moon and planets, there's not a heck of a lot to look at. Even so the <ins class="diffchange diffchange-inline">[[M45|</ins>Pleiades<ins class="diffchange diffchange-inline">]] </ins>and the <ins class="diffchange diffchange-inline">[[</ins>Hyades<ins class="diffchange diffchange-inline">]]</ins>, for example, are visible in the winter time, albeit missing stars.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>If I move up to my 10x50 binoculars, my limiting magnitude moves to around 7. This of course brings many more items into visibility, at least in theory. There are at least 50 deep sky objects that would fit into this category, that are visible from Calgary's, and hence Canada's, latitude. Now this is a theoretical 50, as for many objects, the actual surface brightness will be less than what the magnitude suggests. This is because for extended objects, i.e. non-stars, the magnitude is the aggregate of the total brightness of the object. The more spread out an object is, the dimmer it actually appears for a given magnitude. So two objects can have the same magnitude, but if one is spread out more, it would appear dimmer. This is one reason why this list won't be simply generated from a planetarium program as the magnitudes listed won't necessarily translate into observability at a given limiting magnitude.</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>If I move up to my 10x50 binoculars, my limiting magnitude moves to around 7. This of course brings many more items into visibility, at least in theory. There are at least 50 deep sky objects that would fit into this category, that are visible from Calgary's, and hence Canada's, latitude. Now this is a theoretical 50, as for many objects, the actual surface brightness will be less than what the magnitude suggests. This is because for extended objects, i.e. non-stars, the magnitude is the aggregate of the total brightness of the object. The more spread out an object is, the dimmer it actually appears for a given magnitude. So two objects can have the same magnitude, but if one is spread out more, it would appear dimmer. This is one reason why this list won't be simply generated from a planetarium program as the magnitudes listed won't necessarily translate into observability at a given limiting magnitude.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"></td></tr>
<tr><td class='diff-marker'>−</td><td style="background: #ffa; color:black; font-size: smaller;"><div>I will also include objects visible with a small telescope. My 127mm (5 inch) Maksutov has a theoretical limiting magnitude of about 13. However due to light pollution within the city this becomes something around 9 to 10. Again with surface brightness differing from magnitude, it's unlikely there will be many 9th mangitude galaxies on the list, but what I can see through my scope will be.</div></td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div>I will also include objects visible with a small telescope. My 127mm (5 inch) <ins class="diffchange diffchange-inline">[[</ins>Maksutov<ins class="diffchange diffchange-inline">]] </ins>has a theoretical limiting magnitude of about 13. However due to light pollution within the city this becomes something around 9 to 10. Again with surface brightness differing from magnitude, it's unlikely there will be many 9th mangitude galaxies on the list, but what I can see through my scope will be.</div></td></tr>
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<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>==Determining Limiting Magnitude==</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>==Determining Limiting Magnitude==</div></td></tr>
</table>Evilscientisthttp://www.citydeepsky.com/wiki/index.php?title=Limiting_Magnitude&diff=1579&oldid=prevEvilscientist at 22:26, 16 January 20092009-01-16T22:26:18Z<p></p>
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<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>[[Category:Astronomical]]</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>[[Category:Astronomical]]</div></td></tr>
</table>Evilscientisthttp://www.citydeepsky.com/wiki/index.php?title=Limiting_Magnitude&diff=1401&oldid=prevEvilscientist at 21:55, 12 January 20092009-01-12T21:55:05Z<p></p>
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</table>Evilscientisthttp://www.citydeepsky.com/wiki/index.php?title=Limiting_Magnitude&diff=1388&oldid=prevEvilscientist at 16:55, 12 January 20092009-01-12T16:55:39Z<p></p>
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</table>Evilscientist