All Eyes on Boötes

In May, the constellation Boötes' is the featured pattern for sky surveys. To quantify the night sky above the New Carlisle Economic Development Area, we want to determine the limiting magnitude of visible stars, both objectively with meters and subjectively with visual estimates. For the latter, you will select the one of eight star charts made by Globe at Night of the constellation Boötes that most closely matches the sky you see above each respective observing site. You will enter that chart's whole magnitude number on the Globe at Night website.

I have also made two star charts that depict the constellation Boötes with limiting magnitudes of 5 and of 6 with the fainter stars labeled. The purpose is to see which of the faintest stars is at the limit of visibility for your eyes. The fainter the star, the higher the magnitude number. The two-digit red numbers are actually the magnitude and fraction of magnitude, with the intervening decimal point not depicted in order for it not to be confused with a plotted star. For example, if the faintest star you can see has a red number 47 next to it, then that star's magnitude is approximately 4.7.

The magnitudes are printed in red so they are deliberately harder to see under a red flashlight compared to the faint printed star points. When you are in the field, simply circle the stars you can see on a printout of the star chart. Hang on tight--that's your observing record. You can later determine which was the faintest visible star.

The next viewing window for the Globe at Night campaign is May 5-14 using the constellation Boötes. However, their dates are designed for general public viewing hours. You can expand your observing opportunities if you select observing times that are after astronomical twilight (when the sun is 18 degrees or more below the horizon and is contributing no light to the night sky) and when the moon phase is negligible or the moon is below the horizon.

Stars of Boötes with magnitudes < 5 (decimal points hidden).

Stars of Boötes with magnitudes < 6 (decimal points hidden).

Finding Boötes

Boötes is the constellation of the herdsman. The bright orange star Arcturus dominates the sky at magnitude 0.2. To find Boötes, first find the Big Dipper. You may recall that the two pointer stars at the end of the bowl will guide you to Polaris, the north star. However, if you follow the rest of the stars the other way, continuing along the handle of the Big Dipper, you "arc to Arcturus." Much of the constellation Boötes is alongside that arc. In May, the constellation rises on its side.

This blog post is adapted from, which focuses on the constellation Leo.

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