Stargazing: Big Dipper’s appearance is purely by chance

Stargazing: Big Dipper’s appearance is purely by chance

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The overwhelming majority of books dedicated to casual stargazing usually contain significant amounts of information about constellations, their location in the sky and maybe some mythological background as to their naming. All that is a good.

The word constellation means “stars together” and it was the very early sky watchers who played a game not unlike Connect-The-Dots and then come up with names for them. Some of those names are familiar others are not.

Looking at the vast array of stars overhead at night it is easy to understand how those ancient cultures thought all of the stars were at equal distances, all attached to some gigantic celestial dome.

A case in point is the familiar formation of stars we refer to as the Big Dipper. This arrangement of stars we see year round is purely by chance because of our position on Earth.

As I’ve mentioned in several past columns dealing with constellations, we only see the star patterns as we do because of our “fixed” position here in southwest Iowa. It is here that the illusion of what we see gets confused with reality.

The brightness, or magnitude of stars is based on two things: the star’s distance from us and the star’s actual brilliance.

Comparing apparent and absolute magnitudes of stars is much like looking at light fixtures on our streets. All streetlights are basically the same strength but the ones closer to us appear brighter than those further away.

This is particularly true with the Dipper. Its home constellation is Ursa Major, the Great Bear, which is now well placed in the northern sky.

Although each of the seven stars which make up the dipper appear to be the same brightness this familiar form is seen as it does purely by chance.

Alkaid, the star at the very end of the dipper’s handle is the furthest lying at a distance of 160 light years (LY). Moving along the handle, the next stars and their distances are Alcor, 95 LYs, Alioth, 80 LYs, Megrez (the star in the upper left portion of the dipper’s cup) is 60 LYs, which puts it nearest to us. Dropping down to the lower left is Pecda, 84 LYs, Merak (lower right) 90 LYs and lastly, Dubhe, 130 LYs.

Again when observing the Big Dipper each of the stars appear of equal brightness. If Alkaid is almost three times further away from Megrez and yet they appear the same, Alkaid must be a star of tremendous proportions.

After observing the Big Dipper, take a look around at the other constellations and their shapes. Truly things are not always as they appear.

As I mentioned in last week’s column Comet SWAN is making news in astronomical circles but everyone is still anxiously awaiting the comet’s nearest approach (perihelion) to the Sun that occurred yesterday and whether the comet was able to withstand the tremendous pressures being placed on its nucleus.

If everything went well, Comet SWAN should begin to be the brightest and will be moving through the constellations of Perseus and Auriga both visible in the early-morning low north-western sky.

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