Saturday, April 17, 2021

Goodbye to Summer



By Mike P. Usher

The rainy season is finally over! The unrelenting clouds made it very difficult to do any stargazing this summer; but we can finally see stars at a reasonable hour so we are rolling back the clock on the charts to 9PM.

Tonight is one of the last chances to see a few summer – season stars before they drop into the Gulf of Mexico. Front and center is the not particularly well named Summer Triangle, (this being the middle of Autumn), consisting of the bright stars, Vega, Altair and Vega. Vega and Altair are close neighbors of our Sun being only 25 and 17 light years away respectively. Deneb is the outlier, being 2600 light years from us although the exact distance is rather uncertain.

How do we measure distances to the stars? The traditional method is to use parallax in a manor similar to surveyors. A photograph of a star is taken in January, for example, and another is taken in July when the Earth is on the opposite side of the sun. The star, if it’s close enough, shows a shift in position when compared against background stars. This shift, when trigonometry is used, yields the distance to the star. Such shifts are extraordinarily tiny and distances over a few hundred light years are very uncertain as a result. Fortunately, other methods exist but are thought to be not quite as accurate.

The Summer triangle encloses a section of the Milky Way that is rich with star clusters; feel free to scan the area with your binoculars. Your naked eye however will notice a dark gash through the area, marring the soft whiteness of the Milky Way. This is known as the Great Rift and consists of a large mass of gas and dust blocking the light of the stars behind it. A few stars do glimmer in this area, however these are stars between us and the Great Rift. The nearby Moon probably will wash out this area of the sky; it would be better to wait a week or ten days when the Moon will no longer be in the evening sky.

Comet ISON continues its nose dive into the inner Solar System. Depending on how it brightens I’ll either give an update next column or run the “buying a telescope” guide in time for Black Friday. Either way you will probably be getting up early that morning!


See you next time!

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

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