Expert: Tom Whiting - 4/21/2011

Question
QUESTION: can the moon cause the clouds to act differently, if they have high water compositions.

ANSWER: Hi John,
No. (All low clouds by definition, have high water composition because the air temperature is at the dew point temperature, by definition, so the relative humidity is 100% in any cloud).  
  But the moon can affect the color of the clouds and shows us whether they are dark heavy
clouds loaded with dust, ice, and rain, and thinner clouds like cirrus. The light of the moon also creates the haloes we see around the moon, and on rare occasions, a moonbow. But the moon at 238,000 miles is too far away to physically cause the clouds to "act differently" in the physical sense.  (Even if the moon were only 10000 miles distant, there would be no physical effects on our atmospheric clouds, except we would see a much brighter moon alighting... them.)
Hope this helps,
Clear Skies,
Tom Whiting
Erie, PA

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QUESTION: well it is true that the moon pulls on the ocean right. i just dont understand why it wouldnt affect the water in the air to

ANSWER: Air is fully saturated when there is about 4% water vapor content, or completely saturated air for 100% relative humidity. (So there is still 96% air in fully saturated samples of air.)
And remember, that's water vapor... read that gaseous, not liquid water.
Water vapor (molecular weight 18) is lighter than air (average molecular weight 29), that's why moist air rises because it's slightly lighter than the heavier dry air.

The moon's differential gravity affects the entire earth, simultaneously, not just the ocean's water. Since water is, unlike land surfaces, mobile; we see it (large bodies only) as "tides"... but the entire ground surface facing the moon also is affected like 1/1000 of an inch. (Likewise, the lunar surface rises like 1/10 inch due to the Earth's differential gravity...much more stronger... too.)  So I guess you could say that the moon also lifts the Earth's entire atmosphere facing the moon (along with the clouds and water vapor too) but it would hardly be measureable, let alone catastrophic. (I'd hate to be the person that has to measure that one because of the sub-microscopic effect on the atmosphere)!

And here's another tidbit for you... IN reality, tides are not caused by gravity! If it were, we'd only have one high tide and one low tide per 24 hours, right?... but we have TWO, each day. It's because tides are caused by "differential gravity", not gravity... the difference between the pull on one side of the Earth as compared to the pull on the far side of the Earth away from the moon.  So this causes 2 "bulges" and 2 "dips" on the surface (not one). Thus we have 2 highs and 2 low tides per 24 hours, due to differential gravity, and not gravity by itself.  It only happens because of the closeness of the moon. If the moon were as distant as the sun, we would have ocean tides that only rise and fall by several inches every day, because it's distance squared in the denominator of the force equation, and because at the solar distance, the difference in distance between near side (93,004,000 miles) compared to the far side (92,996,000 miles)... that ratio percentage  (differential)  is very small compared to if you use the moon's 238,000 miles smaller distance. Thus the moon's differential gravity is much stronger on us, than the sun.  But the sun's TOTAL gravity is far more than that of the moon... because it's much more massive, containing 99.86% of the total mass of the entire Solar System.
(I know, it can be confusing, even trying to explain it.  But... it's all true and accurate.)
So... bottom line is, I see no effects on clouds and water vapor solely due to the moon's differential gravity. Besides, cloud mass is just way too small. I don't even see measured tidal effects from the moon on Lake Erie in my backyard, and it's certainly far more massive than clouds.
Hope this helps,
Clear Skies,
Tom

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QUESTION: okay thanks for your response on the last question.... but i was also wondering why is it possible for us to see the stars at night. i mean cause they are just so far away.

Answer
Well, fortunately our very thin atmosphere (and it IS very thin compared to Venus, Jupiter, Saturn, all the gas giant planets)... is transparent to visible light.  So with a dark black sky at night, we can even see the Andromeda Galaxy out there at about 3 million light years with our naked eye, as a little fuzzy blob of light.  So the distance is not a factor, only the brightness. Anything brighter than +7th magnitude can be seen by the human eye, although I've read where owls can see down to +9th magnitude objects if we could communicate with them with their bigger eyes.
Our telescope "eyes" can see much much dimmer objects because our atmosphere is transparent to visible light. And that's why many of us own rather large scopes, to see better (dimmer objects) in that wavelength of the electromagnetic spectrum.
Light intensity drops off as the square of the distance, so most of the stars we DO see with the naked eye are the "whales among the fishes". There are many nearby (within 50 light years) little red dwarf stars that we can't see naked eye because they are just too small and dim (Barnard's star, Wolf 359, Proxima Centauri, etc.) In fact, those little red dwarfs are said to make up over 80% of our Galaxy, and we can't see them very far away. So we only see, naked eye, the large giant stars in our local region of the Milky Way (out to about only 5000 light years, on average). That's not very far, considering our Galaxy is over 100,000 light years across. So we're still only seeing "our large, bright neighbors" with our human naked eye.
So when you see a light (any light) at night... remember you are just seeing brightness and that's all. Not diameter, not distance, not even direction of flight... only brightness and that's all. The eye cannot determine any other quantity, unless you have 3 separate observers and can triangulate on said object. That's why you can laugh out loud at these so-called UFO nutzys that report, lights at night, that are 100 feet in diameter and 3 miles distant, it's speed,  and all sorts of other details... when we know that the only determinant quality available is brightness, (and maybe color)... but not size or distance or even correct direction of true flight or true velocity.
Look at a star and tell me it's correct size and distance and true direction of movement (called proper motion)... you can't, and no one else can either, without some pretty sensitive scientific equipment, and sometimes it takes 2 or more observers at different locations at the same time.
Clear Skies,
Tom

FOLLOW UP:
Even our sun, an averaged size star, would drop below the naked eye limit of 6th magnitude, at a distance of only 100-120 light years. So we can't even see, naked eye, solar type stars, out much more than a measly 100 light years. So we're only seeing the supergiant, giant, and sub-giant stars much beyond that short distance with naked eye, unless a solar-type star has an intrinsically (self-generated) high brightness (very high surface temperature).
tom