Monday, December 6, 2021

Summer triangle shines

The Zenith.

The Zenith.


We talked about the Summer Triangle consisting of Vega, Altair and Deneb last year, and once again like last year the Moon is washing out all the lesser stars. You may wish to wait a few days until the Moon is out of the way before you go star gazing.

The three stars of the Summer triangle are buried deep in the Milky Way and their constellations are rich in Deep Sky objects. But before looking for any of them examine the shape of the Milky Way itself. If you are at a dark sky site you can’t help but notice the Milky Way is not a continuous stream, but is in fact rather irregular in shape. In particular, between Cygnus and Aquila there is a dark streak largely devoid of stars. This is the Great Rift – not really a starless region but a vast dust cloud that blocks the starlight behind it.

Rather than hunt for a particular deep sky object with your binoculars, lay down on a lawn chair with them and sweep the sky along the length of the Milky Way. There is nothing like the thrill of discovery! Most of the deep sky objects seen in this area of the sky are known as open or galactic clusters. These are groups of stars of perhaps a dozen to several hundred that were born at nearly the same time and are still associated with each other. Our Sun was born in such a cluster long ago, now dispersed. Open clusters are short lived objects perhaps lasting no more than 100 million years before gravitational forces from the rest of the galaxy pry them apart. Somewhere in the sky tonight are the long lost siblings of the Sun.

Also visible in this region of the sky is the asteroid Pallas, visible in 9×50 binoculars as a 9.75 magnitude dot. Now embedded in the stars of the Milky Way, it would be a major challenge to locate. Pallas is a good example of why asteroids were not discovered until two centuries after the invention of the telescope. They often spend a large part of their time far from the ecliptic, and when one does happen to see an asteroid they look exactly like a star.

See you next time!

Mr. Usher is President of the Everglades Astronomical Society which meets every second Tuesday at 7:00PM at the Norris Center, Cambier Park, Naples.


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