Appreciating the Heavens

 

Since acquiring a dog...  about four years ago this week, as a matter of fact...  Norene and I have been paying more attention to what's above us.  That's because Riqui's (officially 'Suncatcher's Periquita') last walk of the day happens between 10:30pm and 11:30pm.  We have started to pay more attention to things like 'summer constellations' and 'winter constellations' and phases of the moon (because we can walk the golf course's cart paths from about half-moon through full-moon and for a few days after).

The moon rises about 50 minutes later every day.  Because the moon's cycle is about 28 days (more or less), it rises 1/28th of a day later each day.  There are 1,440 minutes in a day, and 1/28th of that is 51 minutes and 20-some-odd seconds.  Seven days' worth of that is 358+ minutes — pretty close to 6 hours.  At 'new moon', the moon rises just around dawn.  Half-moon (first quarter) is seven days later and has the moon rising around noon.  At full-moon, the moon rises near sunset — the sun and moon are on opposite sides of the Earth.  That's what makes the moon 'full'.  From full moon on, the moon rises closer to sunrise than to sunset.  Last quarter has the moon rising around midnight.

The stars are a different matter.  The stars make a complete circuit (360 degrees) over the course of a year — 365 days — close enough for government work.  The stars rise 1/360th of a day earlier each day.  That comes out to about four minutes (plus or minus).  Thirty days times four minutes is 120 minutes, two hours, 1/12 of a day, and one sign of the zodiac.

Over the course of a year, someone who looks up at the sky about the same time every night will watch the sky gradually change as the moon and the constellations creep across the firmament.

I recommend it highly.

 

The Grass Rainbow

 

It's Sunday and since I don't have to go to work, the dog gets an extra-long walk.  A few months back, I realized I was being followed on those early-morning walks... by a rainbow on the grass which matched my pace the way the moon sometimes seems to follow you at night.

Investigating, I discovered a few surprising things:

• The Sun has to be relatively low in the sky — it has to be early in the day.
• The grass has to be wet with dew, and the wetter the better, although there must be such a thing as 'too wet'.  This also requires 'early' because after the Sun has been up for a while, the dew will evaporate.  The droplet size also appears to affect the visibility — the smaller, the better.  This seems a reasonable assumption: the best rainbows are those seen at a distance when apparent droplet size is very small.
• The viewer has to be walking West, that is: away from the Sun, with the Sun at the viewer's back.
• The viewer has to be looking through polarized lenses.  I have polaroid clip-on sunglasses, but probably any polarization will do the trick.  I know this is true because when I flip up the lenses to get a better look at the colors, they vanish.

When all these things are true, you may find yourself seeing two rainbows, one on each side, emanating from about where your feet are, and arcing away at (Wikipedia says) 42 degrees, although most times I can see it only on one side, if at all.  The shape of the grass rainbow is not circular as we're used to seeing with rainbows in the sky.  Instead, it's parabolic or possibly hyperbolic.

They're very hard to see, even under the best conditions.  I find it's easiest if I'm moving because then the rainbow itself moves against the grass and it's easier to pick out.  If you go looking for a grass rainbow, I hope you find a good one.