THE SOUTHWORTH PLANETARIUM
207-780-4249 <%28207%29%20780-4249> www.usm.maine.edu/planet
70 Falmouth Street Portland, Maine 04103
43.6667° N 70.2667° W
Founded January 1970
Julian date: 2457785.16
"I don't enjoy writing. I wouldn't wish writing on a dog."
-James Cameron
*THE DAILY ASTRONOMER*
*Wednesday, February 1, 2017*
*Weight and the Way*
How many Pandoras should we have answered by now in order to meet our 100
Pandora parchment goal by early August? We'll look now.....
Well, never mind that, let's reach into the vessel and proceed!
Our two parchment questions are both based on word-related confusions.
*PANDORA PARCHMENT # 14: "Is it true that an astronaut can move any
object in space easily because objects in space are weightless?" -M.B,
Richmond, VA*
Excellent question!
First, a note about "weightlessness."
NASA no longer uses the term "weightless" in reference to objects in orbit
around Earth because that term wrongly implies that orbiting objects aren't
experiencing any gravity. Orbiting objects are experiencing Earth's
gravitational pull, but to a lesser extent than ground based objects. For
instance, here on the planet's surface, we're experiencing a downward
acceleration due to gravity of about 9.8 meters/second squared. This
means that if, for instance, you inadvertently knock over the tea cup your
daughter gave you for Christmas and, damn, you don't have a clumsy dog to
blame it on, that tea cup will accelerate toward the ground at 9.8 meters
per second squared. However, if you are on the International Space
Station, the gravity is weaker because you are about 250 miles away from
Earth's surface. The acceleration due to gravity is only about 90% as
strong as the pull on the ground. Yet, if you drop a tea cup on the
Space Station, it doesn't crash to the floor with a 120-decibel bang. It
floats! Why? Because the International Space Station is falling toward
Earth at the same rate. Consequently, objects aboard the ISS seem to be
floating, when they are merely falling. Fortunately, as the ISS falls
toward Earth, its horizontal speed assures that Earth will move away from
it so it won't crash to the surface.
All objects in Earth orbit have "weight," which measures the pull of
Earth's gravity on those objects.
*Couch potatoes. ** Three astronauts aboard the ISS watch a World Cup
match. Even though the men appear to be "weightless," they are actually
experiencing Earth's gravitational pull. So, too, is the ISS, itself. For
this reason, the ISS and the astronauts fall at the same rate and it
appears as though they are "floating." Image courtesy of NASA. *
All objects, no matter where they are,also have "mass." Mass measures an
object's inertia, or its resistance to changes in its motion. An
object careening through interstellar space will not just stop with a index
finger nudge. One will have to exert a force on it to either impede or
halt its motion altogether. The more massive the object, the more
difficult it will be to alter its motion, even in deep space.
*PANDORA PARCHMENT # 15: "Why do we see the Milky Way if we are inside
it?"*
*-Maia V, Old Orchard Beach.*
Great question!
The confusion arises from the definition. The name of our home galaxy
is the "Milky Way." Our solar system is tucked away in the Orion-Cygnus
Arm of this galaxy, as we can see from the image below:
*Home. Our solar system occupies a small region within the Orion-Cygnus
Arm (or the Orion Spur) of the Milky Way Galaxy. Image:
Universetoday.com *
The luminous "cloud band" that traverses our sky is also called "the Milky
Way." However, that band is just the plane of the galaxy, itself. Within
this plane one finds the greatest concentration of stars per unit area.
These stars therefore appear like a diffuse arc of light, as opposed being
a series of well resolved pinpoints.
The Milky Way Galaxy is our home galaxy.
The "Milky Way" we see in the night sky is just a part of that galaxy.
(c) 2017 Edward Gleason
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