Observing through the ‘Sucker Holes’

Monday night April 28 was the only night without precipitation in the forecast,  so we took our chances to see if we could peer through the clouds. At 9pm as predicted by the FLO clear sky clock for our area,  Clear Sky Clock near Mill of Kintail , there were patches of clearing. So we decided to observe what we could. We would save the visit to FLO for another night (in case it did rain); instead we went to my place to observe through my 16″ dobsonian and demonstrate how my observatory does science images through the robotic automation of the mount, camera and dome.

The planisphere showed us what might be up there…

And we were seeing small patches of clearing amidst a gray overcast. That’s known as a “sucker hole.”  Astronomers use the term “sucker hole weather” to denote that there might just be limited breaks in the overcast to spot a star or planet. More realistically astronomers define the term sucker hole as:


Sucker Hole:  A clear patch of sky where you point  your telescope only to discover that when you look through the eyepiece, all you see is cloud…


Here’s what we did see for an hour or so…:

First. since the sky was still not completely dark, as defined by astronomical twilight (Sun has to be below the horizon by 17 degrees), and since there were large blocky clouds hither and yon, we used the beacons of the very brightest stars, and planets:

Based on what we know about magnitudes we have:

The bright stars:

  • In the East: Arcturus,  spring constellation Bootes  Magnitude:   -0.1
  • In the West: Capella,  winter constellation Auriga     Magnitude:  0.1
  • In the SouthWest: Sirius constellation  Canis Major Magnitude: -1.5

Obvious constellations:

  • Constellation Leo the Lion – Spring
  • Constellation Ursa Major – Big Dipper (circumpolar)
  • The setting outline of Orion (the Belt was between the trees)


    • Mars    = can be confused with  Arcturus, but actually near Spica in the constellation Virgo
    • Jupiter  – next to the heads of the twins in Gemini- Castor and Pollux




Mars… Even Mars has a Spectral Signature:


Based on the profiler for our time in UT, http://www.skyandtelescope.com/wp-content/observing-tools/mars_profiler/mars.html# we think we saw this region:


Applying the red filter, we were able to transmit red and suppress green and yellow
Because … the atmosphere reveals itself in the spectra


Prism placed in front of a slide projector (not shown)
Unfiltered light through spectrum


Back in the ‘lab’ we can see how the intermediate wavelengths are attenuated
We applied a red filter to the back of the telescope eyepiece. This improved the contrast


This is just another example of learning about atmospheres by filtering on starlight. .. or in this case Reflected sunlight on Mars