Saturday, August 17, 2019

Lovely Autumn Evening Last Night

Yes, I know it is still summer, but only in direct sunlight in the day does it feel like it.  I am sitting on my back porch with the cool wind blowing past me.

We had a number of people from church up last night for dinner and astronomy.  The sky was clear and relatively calm.  At 156x, Jupiter's multiple clouds bands were highly visible, with good contrast.  All four Galilean satellites were visible, and bright enough against a dark motionless sky that everyone immediately recognized that they were not stars.  A couple of the adults did not realize that satellites are not always artificial.  But once they mastered that idea, they realized that they are like our Moon.

As expected, no one looked at Saturn without be overwhelmed.  Cassini's Division was very obvious on the east and west sides of the planet.  This was at 78x.  I should probably have gone up in power, but the Moon was rising.  At least one of the adults immediately recognized that he was looking at several of Saturn's larger satellites.  Titan, in particular, is so bright and non-twinkling that it sort of hours itself away.

I showed them Antares to show them why stars twinkle and planets, except of very turbulent nights, do not. The column of light from even the closest stars is at best an arcsecond across.  Planets have light that is tens of arcsecond across, and this less beat up by air currents. Even at 39x, Antares is a little twinkling fireball. 

The Moon rose through the trees a bit north of Bogus Basin and it was a very nice sight to see the trees against the face of a nearly full Moon.  But the burble of the air passing through an extra 4000 miles of atmosphere meant the Moon's limb was alive.  I hope to have them up again with a first quarter or younger Moon, when contrast is higher and there is less burble.

One irritation: while some people use the word "moon" to refer to any natural satellite, this is not correct.  Moon (capital) is the proper name of our satellite, and like Sun should be capitalized.  I wish the built-in spell checker in the Blogger app knew this, instead of trying to force Moon into moon.  If you read The Stand, just spell it M-O-O-N.  If you did not read it, you might enjoy it.


  1. Glad to see your out of the hospital. And that your not suffering the pollen explosion I am having: very high ragweed forecast for the rest of the month.

  2. It's over 100F every day here. Probably will be until the end of the month. Then it will go down into the 90s. Relief!

  3. "One irritation: while some people use the word "moon" to refer to any natural satellite, this is not correct."

    Are you really sure about this? Because the formation "moons of" (which would occur only in discussions of the satellites of Mars and the gas giants, or some fictional planet) has been used since before 1800, at about the same rate as today.

  4. Rick: not surprised, but has our satellite as primary meaning. The secondary meaning would be not capped.