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[Chicago Astronomer - Astro Joe]

Astronomers Measure Distance to Milky Way's Spiral Arm

36,000,000,000,000,000 miles

A team of astronomers has taken an important step toward mapping the Milky Way by accurately measuring the distance to the star-forming region W3OH in the Perseus spiral arm, the nearest arm to us. This long strand of stars streaks out of the Milky Way’s disk in the same manner as others seen in galaxies across the universe.

Until now scientists had difficulties figuring just how far away spiral arms are, and various measurements and techniques had discrepancies ranging by a factor of two.

The new results are from a telescope nearly the size of Earth. The astronomers used the Very Long Baseline Array, taking observations from several telescopes stretching from Hawaii to the Virgin Islands, to create the resolution of a telescope nearly 5,000 miles in diameter.

Full story here: www.space.com/scienceastronomy/051208_spiral_arm.html

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That's a whole bunch of miles!

[Maddad]

Thirty six thousand trillion. Yeah, big number. Astronomically big you might say. You might, but i'd just say honkin' big number.

[Chicago Astronomer - Astro Joe]

Here's more on the measurement of the Spiral arm...

Perseus Spiral Arm of the Milky Way much closer than thought

Dr. Xu Ye, an astronomer at Shanghai Observatory now working at the Max-Planck-Institut für Radioastronomie and one of the members of the international team who made the measurements, stated that "we measured distance by the simplest and most direct method in astronomy - essentially the technique used by surveyors called triangulation." Specifically, the team used the changing vantage point of the Earth as it orbits the Sun to form one leg of a triangle. Measuring the change in apparent position of a source, they could calculate the source's distance by simple trigonometry (resulting in 6357±130 light years).

"Studies such as ours are the first steps to accurately map the Milky Way," says Dr. Mark Reid, a member of the team from the Harvard-Smithsonian Center for Astrophysics. "We have established that the radio telescope we used, the Very Long Baseline Array, can measure distances with unprecedented accuracy--nearly a factor of 100 times better than previously accomplished." To get a feeling for this measurement one may visualize a person standing on the moon, holding a torch in his stretched-out hand. Let her turn around herself like an ice scater, but only making a single turn in the course of one year. The VLBA measurement is equivalent to measuring the torch's motion with an accuracy comparable to the torch's size.

Much more here: www.physorg.com/news9124.html

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I think....

That it is much too early to stand on definite numbers on the distance thru triangulation now. Given the vast amount of time it takes galactic objects to move in relation to one another, and for the galaxy itself to rotate....much more time is needed for comfortable ongoing measurements.

But we start somewhere, and it's a good thing.