Air thins on high, black holes trap light, canary holds smallest egg record
Why does the air get thinner at high altitude? Katie, Oregon, Wisconsin
Ultra long duration balloon flies where the air is thin ó
above 99 % of Earthís atmosphere. [NASA]
A: Air seems nebulous but is massive. Earthís gravity pulls
air molecules down, squeezing them together.
Air languishing at Earthís surface has 200 miles of atmosphere
above and a weight of 14.7 pounds (6.67 kg) on each square inch (6 square
centimeters). At 18,000 feet high, the weight above halves and the air is twice
The Weather Book by Jack Williams
Black holes trap light
I was taught in school that gravity is a force between two masses. And that the
speed of light is the fastest something can travel, because light has no mass.
So why can light not escape from a black hole? If it has no mass, how can it be
under the influence of gravity? Leland, Lakenheath, England
How gravity bends light. The actual star is
depicted in red. It appears to be in the position of the yellow star. The bent
curve (solid line) shows how light travels from the actual (red) star to an
observer on Earth. [Rod Nave, Georgia State University]
A: Much of what you were taught is valid even under the
terrible constraints of a black hole. The speed of light is, indeed, the fastest
any object can go. Gravity is an interaction between two masses. Photons (light
particles) are massless. Then, how does a black holeís gravity trap light or,
more generally, how can gravity influence light?
"This is deep water," says Rod Nave, physicist at Georgia
State University but suggests thinking about how gravity bends light.
We first tested Einsteinís General Theory of Relativity with
this effect. His theory predicted that a massive object, like the Sun, would
bend light. Sure enough, during the solar eclipse of 1919, we observed the light
from a star behind our Sun only because the Sunís gravity field bent the starís
light. Otherwise, the Sun would have blocked the starlight. So, we have observed
gravity influencing light.
The reason behind gravityís ability to bend light is something
called the principle of equivalence. Einstein stated we canít tell the
difference between the effects of gravity and those of a reference frame (like
an elevator) thatís smoothly accelerating with the same acceleration as gravity.
A ball released in an elevator rising with 1G (32 feet/sec/sec
or 9.8 m/sec/sec) acceleration will look exactly like itís falling from a
personís hand in a stationary room. The ball will get closer and closer to the
rising elevator floor until it hits.
Thus, the released ball in the rising elevator has an
"inertial mass", which is exactly equivalent to its "gravitational mass" when it
falls to the ground.
Moreover, photons have inertial mass (similar to that of air
particles moving in the wind). Photons, for example, bop against a solar sail.
The sail moves away from the bounced photon like a struck punching bag.
Since photons have inertial mass, they have an equivalent
gravitational mass. Gravity influences light (for instance, bending it) via the
photonís gravitational mass.
Inside a black hole, gravity is so extreme it can bend light
back down into the black hole. "Itís like the trajectory of a tossed baseball
that has no chance of escaping Earth," says Nave.
WonderQuest: Black holes die, but it takes a while
HyperPhysics by Rod Nave: Black holes
Canary holds smallest egg record
Whatís the record for the smallest bird egg? Someone, World
A Yorkshire canary [Sid Golding, artist; Brian Keenan,
Yorkshire Canary Club, © 1988, used with permission.]
Guinness World Records says the smallest bird egg was laid on
Oct. 5, 1998 by a posture canary. It was a piddling 0.275 inches (7 mm) long and
0.2 inches (5.25 mm) in diameter ó about the size of a pea.
Q: Is there a record for the worldís smallest chicken egg?
Chelsea, Tippecanoe, Ohio
A: I canít find it if there is. About the closest I can come
is Farm Life talk: "I found a brown egg the size of an acorn in the coop," says
Tim R. Lambert, Maine farmer, about the smallest chicken egg his bantam and
Barred Rock hens ever laid. (Related figure:
This just in: We went out to the coop and found a
fully formed brown egg that is 1 1/4" x 7/8" and weighs 12 grams (0.4 oz). It is
smaller than the egg on your website, and it came from full-sized (not bantam)
chickens. Amy, Mequon, Wisconsin
Canary Classics: The border fancy canary (a Victorian-times posture canary)
(Answered Feb. 6, 2004, updated: June 15, 2007)