It all depends on your point of view

In Space, Some directions are Better than Others

by Bob Berman
November 11, 2010 11:07 AM | 0 0 comments | 5 5 recommendations | email to a friend | print
In the 1920s, astronomers found that if you gaze in some directions (like southwest just after sunset these nights), you stare into the obscuring dusty gas of the Milky Way and see no galaxies at all. By contrast, a peek toward the north carries our eyes through an open window to the larger universe beyond. Images from large telescopes show more background galaxies here than foreground stars. That’s why all three of Hubble’s “Deep Field” pictures – long-exposure images of the farthest reaches of the Cosmos – were not of random sections of the sky. Instead, the great telescope pointed at carefully selected directions from Earth, aimed most directly through the thinnest sections of the galaxy. One of these transparent zones is marked by the Big Dipper.

Directionality – or its absence – can be critical in solving cosmic riddles. Fifteen years ago, when many astrophysicists believed that the mysterious and powerful Gamma Ray Bursters were nearby phenomena in our own galaxy, a Princeton astrophysicist solved the puzzle by pointing out that their random distribution throughout the sky proved that they were distant extragalactic objects; otherwise their locations would match our galaxy’s shape.

The reason why more meteors are seen after midnight each night is that, starting at that time, the observer faces forward in the direction in which Earth moves around the Sun. We then smash into meteors head-on. Before midnight, the only shooting stars that we’d see are those that catch up to Earth from behind.

On a grander scale, the way that we’re forced to face due to the rotation of our entire galaxy causes us to pivot toward interesting new vistas over time. The Andromeda spiral – now high in the east as a smudgy blob – will totally vanish when we’ve wheeled around to our galaxy’s opposite side in 100 million years. That nearest and brightest major galaxy will then be blocked for millions of years by the bulge at the Milky Way’s center, like the middle of a carousel hiding the spectators beyond.

At nightfall an upward gaze takes our eyes to Cygnus, the forward direction toward which our galaxy is spinning. In late winter we peer out the rear-view mirror, back toward where we’ve been. Some researchers are using this difference in their search for Dark Matter, under the assumption that hypothesized Dark Matter particles not rotating with the galaxy will therefore strike us at different speeds, depending on the season. Indeed, when we gaze from Orion to Cassiopeia we’re looking along our galaxy’s flat plane – but outward from the center of our galaxy, where stars should be moving more slowly but are not: slam-dunk evidence of Dark Matter.

Then, too, early this fall, researchers announced that the value of a fundamental force (Alpha, the strength of electromagnetism) is stronger in the southern than in the northern direction – which may indicate (as I pointed out a couple of weeks ago) that the Cosmos has “neighborhoods” with different properties.

In sum, a beginner may think that space is the same everywhere, and that gazing in various directions merely displays different constellations. But serious explorers, both professional and amateur, know that the brightness, content, type of phenomena and speed of celestial objects all critically depend on something very basic: the sky direction.

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