This week in Starwatch I want to tell you about one of the crown jewels of the Butler summer night skies. I also want to get you prepared for the best celestial happening in the United States so far this century, a total solar eclipse on Aug. 21.

In the meantime, with even a small to moderate telescope you can view a cluster of a million stars crammed together in a tight ball. It's called the great Hercules star cluster, and it's one of the true treasures of the entire night sky.

As it is with any worthy treasure you have to dig for it a bit, but not all that much. It's even visible in moderately light polluted heavens, but if you can see it in the darker countryside it will be all the better.

The Great Hercules cluster, known astronomically as Messier object 13, or M13, is categorized as a globular star cluster.

Throughout the celestial dome there are hundreds and hundreds of star clusters. All you have to do is lie back on the ground or in a reclining chair and randomly scan the heavens with a pair of binoculars and I'm sure you'll find some.

Most of these are what's known as open star clusters, made up of groups of young stars that recently formed gravitationally out of a huge hydrogen gas cloud. Most open clusters are occupied by stars less than a couple of hundred million years old. In the lifetime of stars that's a blink of an eye.

Globular clusters like M-13 are different. They are spherical swarms of thousands or even hundreds of thousands of stars packed in a small area, usually less than 300 light years in diameter.

Just one light-year equals nearly 6 trillion miles. Globulars are made up of old stars generally more than 10 to 12 billion years old, and more than 140 globular clusters form a giant halo around our Milky Way galaxy.

In a way they are part of the outer structure of our home galaxy, or what some astronomers call satellites of our Milky Way. That makes them a heck of a long ways away. The best one to see in our part of the northern hemisphere is without a doubt M-13, about 25,000 light years away.

This is a great time of summer to find the Hercules globular cluster. As soon as it gets dark enough begin your quest. Start out by facing south and look for Vega, a very bright star, shining nearly overhead. Then look for Arcturus, an even brighter star perched in the fairly high western sky. Draw a line between Vega and Arcturus and M13 will be just short of the halfway point between the two stars. Scan that area with your binoculars or telescope and see if you can spot what looks like a little fuzz ball. It's on the right side of the moderately bright trapezoid of stars that make up the central area of the faint constellation Hercules the Hero.

Through a telescope that fuzz ball appears as a dazzling sphere crammed full of stars, about 150 light years in diameter. It's celestial congestion to the max.

With enough magnification and light gathering, you may see some individual stars at the cluster's edge. Many astronomers estimate there are maybe a million-plus stars living there.

Also keep in mind that because of its vast distance and the speed of light we're seeing the Hercules globular cluster now as it looked in 23,000 B.C. Chances are it's still about the same now, though.

I know you'll love viewing M13. I sure love showing it off to fellow stargazers at my star parties. It's a wonderful telescope destination.

Eclipse coming

Pray for clear skies on Aug. 21 for the first total eclipse seen the United States since 1979. Here in Butler it won't be a total eclipse, but will be a deep partial eclipse that begins at 1:10 p.m. and continues until 3:54 p.m.

At the eclipse maximum at 2:35 p.m. 79 percent of the sun will be obscured by the moon.

Never stare at the sun directly during a partial eclipse or at any other time. You can easily permanently damage your eyes.

You can safely view the partial eclipse with specially filtered eclipse glasses to protect your eyes. You'll find eclipse glasses for sale all across the Internet when you Google “solar eclipse glasses.”

I've seen them for sale as low as about $2. I would get several pairs as soon as you can, because I know they will be a lot harder to get as we get close to Aug. 21.

Another way to view the partial eclipse safely is to hold a piece of white cardboard with a pencil diameter hole in it over another piece of stiff white cardboard. The best and safest way to aim the piece with the hole at the blank card is to stand with your back to the sun and hold the pinhole piece back toward the sun. Use the shadow of the cardboard to aim it over the blank cardboard and you should be able to see the eclipse with absolutely no danger. It really works.

If there's any chance for you to travel to the path of totality, be there.

The 60 to 70 mile-wide strip of the country with totality runs from Northern Oregon to South Carolina. It's so worth the trip.

I've seen a total solar eclipse before, and as hard as I try it's impossible to describe in words. The temperature drops, stars come out, and you can see solar flares shooting out from the edge of the sun and corona, the sun's outer atmosphere.

During totality is the only time you can view the eclipse without eye protection. Totality in most of the band lasts less than two minutes. My advice is to stop viewing the totality directly and use special eclipse glasses or other protection a good thirty seconds before totality ends. Safety first.

If you do plan to travel into the path of totality be sure to make your choice of destination as fluid as possible. Keep a close eye on the weather forecast within a few days of Aug. 21.

It might be hard to find lodging within the eclipse band, but since totality is in the midday hours you can wake up early and drive into the band.

There's a great app that can help you with the best place for you travel. It's Eclipse 2017.org. One of the great tools I use to help predict cloud cover for any given place is Clear Sky Clock.

Again, it is so worth the journey. You'll thank me later.

Make the stars your old friends

If you have any astronomical questions or want me to write about something you're seeing in the night sky, drop me a line at mikewlynch@comcast.net. I will read them.

Mike Lynch is an amateur astronomer and professional broadcast meteorologist for WCCO Radio in Minneapolis/St Paul and is author of the book, “Stars: a Month by Month Tour of the Constellations” published by Adventure Publications available at bookstores at http://www.adventurepublications.net.