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Test Stars for Checking Limiting Magnitude

Started by Barry Simon, 04/21/2003 01:38PM
Posted 04/21/2003 01:38PM Opening Post
A good grouping of stars for testing the limiting magnitude of binoculars and small telescopes up to about 80 mm aperture (from an urban or suburban location) can be found in Gemini just east of the bright star Pollux. At this time of year Pollux is between 50 and 60 degrees up at about 10 pm, so it is well placed for this test. The test group of stars is found by simply going "up" from Pollux approximately 2/3 degree in an easterly direction.

In binoculars you will note two stars in a line from Pollux that are approximately 7th magnitude. At the 2nd (brighter star) take a sharp turn to the left (south) and you will see two more stars in line with the brighter star where you turned. Note that in a refractor with a star diagonal the view will look a little different, just remember to turn your scope in the correct celestial directions.) These two are about 8th magnitude. Continuing on you will see another 7th magnitude star, about the same distance beyond the fainter 8th magnitude stars as is the other 7th magnitude star back to the north. Slighly east (up) between this last star and the last 8th magnitude star was a fainter 9th magnitude star. It was not initially noticed in the binoculars, but was eventually seen. It's visibility was not easy in the binoculars but was essentially constant. Subsequently another faint star was discovered "west" or below the imaginary line connecting the 7th magnitude star to the 8th magnitude stars in the middle. This one was a little fainter than the first 9th magnitude star. It's visibility was in and out in the binoculars.

From the city under 4.5 magnitude skies, these fainter 9th magnitude stars should be seen in 80 mm binoculars or telescopes and should be a challenge for 60 mm and 70 mm binoculars. From a dark rural location, these fainter stars should be easily seen in mounted 12x50 binoculars.


Barry Simon