The Beehive Cluster – Praesepe – M44

Open Cluster

The Beehive cluster is located in the constellation of Cancer the Crab. It is quite large and bright and on dark, clear, moonless night away from bright city lights you can just make it out with the naked eye. The secret is knowing where to look. It is a very easy target in a pair of Binoculars.

First Find the constellation of Cancer the Crab. If you have been coming to the star talks at the planetarium this winter you should be familiar with the winter circle that is made of of six of the brightest stars in the winter sky. We can use 2 of those stars to help locate Cancer that does not have any real bright stars in it. Find the bright star Procyon that is part of Canis Minor (the small dog). Slowly scan east (to the right) you’ll see a group of faint stars shaped like the letter ‘Y’ like the chart below shows. You can also find that area of the sky if you scan south from The bright star Pollux in the constellation of Gemini. Don’t despair if you can’t see it right away. A bright moon or some wispy clouds can make it hard too see.

This chart is for the night of March 21^st at 8:00 PM. Overhead is a the top. You are facing Southeast.

You may be able to see a slight glow near the center of the ‘Y’. That’s it! You found it. If not, then its time to break out the binoculars and look at the star in the center of the ‘Y’. Scan around and you stumble across a large grouping of bright stars.

I use 10 x 50 binoculars. Those give me a Field of View of about (4.5 degrees). If you look at the star charts you will see a red circle. This is the area of the sky I am seeing through my binoculars when I am looking through them. The 10x means my binoculars magnify 10 times. The 50 stands for 50 millimeter, the diameter of the main lenses of my binoculars. You may have 7 x 35 binoculars. Can you decode what that means?

Just like telescopes, the bigger the lens, the more fainter the things you can see. Tim, an astronomer at the planetarium often brings his 20 x 80 binoculars to sky watching events. Those are huge.

The Beehive star cluster goes by many other names. Praesepe means manger because some thought that the stars looked like a stable full of animals. Charles Messier, a famous comet hunter, thought this glow in the sky was a comet but was wrong. So he made a list of things in the sky that looked like comets but weren’t so he wouldn’t make the same mistake twice. The Beehive was the 44^th entry on his famous list of 110 objects and is also known as M44.

The Beehive is about 525 light years away. The bright central part that you see in your binoculare are about 13 light years across. You may see a couple of dozen stars in your binoculars, but scientists using huge telescopes that can see real faint stars have counted over 350 stars in this area, but only aroun 200 are actually part of the cluster.

All these stars were born from the same clouds of gas and dust about 10 million years ago according to astronomers. Open clusters are sometimes referred to as Galactic Clusters because they formed from the material that is floating around on our galaxy.

Brian Cieslak

Horwitz-DeRemer Planetarium

Star charts created using Cartes du Ciel, Binocular image from ‘The Binocular Sky’ website

Melotte 111

Open Cluster

It seems that back in the day, an astronomer’s claim to fame was the list of objects he created as he explored the heavens, a memoir of sorts. The most famous is Charles Messier’s Catalog that contains 110 M-objects that could easily be mistaken for comets by early comet hunters. Herschel’s list of deep sky objects included 400 objects. I recently read a book by David Levy, a well known, modern day astronomer, comet hunter, science writer that details Levy’s list of deep sky objects.

But I want to introduce you to another list maker, Philibert Jacques Melotte (29 January 1880 – 30 March 1961). Melotte, a British astronomer, is credited with discovering a moon of Jupiter and an asteroid in the asteroid belt. Melotte’s catalog contains 245 open and globular clusters that he discovered while studying photographic plates taken by an astronomer in South Africa and England. One of the characteristics of Melotte’s objects are they are within reach of modest equipment like binoculars and small telescopes.

Melotte 111 is an open star cluster that fills the field of view my 10x50 binoculars. Too big to be recognized as a star cluster in a telescope, its an easy target to find in binoculars if you know where to look. It is located in the constellation of Coma Bernices and is very near the naked eye star gamma Coma Bernices. First, look southeast for Leo the Lion, easily recognized by the big backwards question mark that is dotted by the bright star Regulus. The ‘Sickle’ as the question mark is also called, is the head and mane of Leo. Scan to the left to a triangular group of stars the some astronomers refer to as Leo’s rear-end that includes a bright star called Denebola. Continue scanning left and you’ll find the faint constellation of Coma Bernices that consists of three stars. The highest ( closest to overhead) is gamma. Focus your binoculars on that star and you’ll see the star cluster Mel 111. A string of stars shaped like swirling letter ‘V’ will stretch across your field of view.

My 10 x 50 binoculars has a field of view of 4.5 degrees. The red circle on the star charts shows how much sky I am looking at when I look through my binoculars. Mel 111 fills my field of view. Telescopes have a much smaller field of view because they magnify the image more. My six inch F/8 reflector has a field of view of a little over one degree at its lowest magnification. I would only see a small portion of the cluster at one time and miss the grand view.

Mel 111 is an open cluster of stars that is 250 light years away and contains approximately 36 stars. The bright star Gamma Coma Bernices is not part of the cluster. Astronomers believe the sparse number of stars, so widely spaced, suggests the stars are dispersing.

Also note the time on the star charts. To observe Mel 111 you will have to stay up a little later, 11:00 PM. We are getting into the time of year when the sun stays up longer than we’ve been used to. On April 21 it sets around 7:30 PM. A few hours later Mel 111 rises to a point in the sky for easy viewing.

Brian Cieslak

Horwitz-DeRemer Planetarium

Star charts created using Cartes du Ciel, Binocular image from ‘The Binocular Sky’ website

FOV Update..Binoculars

FOV Binoculars

If you have a pair of binoculars some manufacturers will indicate the field of view by marking somewhere on the frame..xxx@1000 feet..if it is marked 235@1000 it means if you looked at a 235 foot ruler 1000 feet away it would stretch completely across your field of view.

Author and Astronomer Phil Harrington in his book 'Touring the Universe Through Binoculars' has a formula to determine the FOV in degrees based on that manufacturers mark. Divide the xxx value by 52.5...my 10x50 were marked 235@1000 so 235/52.5 = 4.51 degrees...

To test the formula I went out last night and found a pair of stars, Mizar and Alioth inthe handle of the Big Dipper, that are approximately 4.5 degrees apart. There was a star on each side of the field just as predicted..

Now I can star hop using my binoculars...

BTW I the used ECUlite4 star chart program to find a pair of stars 4.5 degrees apart for the test. It has a feature that can measure angular distances between stars on the chart.

Phil Harringtons book 'Touring the Universe Through Binoculars' has an excellent chapter on binoculars and how to choose a pair.

Ok Lets get out there...The mosquitoes are waiting...

True Field of View

True Field of View

An astronomer not only has to be familiar with the night sky but he also must know his telescope inside and out before he can explore the unknown (at least to him) regions of outer space. One critical characteristic of the telescope that must be determined is its true field of view (FOV), the area of the sky that you see when looking through the eyepiece.

Once you know how big of piece of the sky you’re seeing through an eyepiece, you can plot your course through the stars using a star chart.

To measure the FOV of your eyepiece, find a star located near the celestial equator. You can usually display this line on a star chart program, or locate it on a printed star chart. Use it to help you pick a star. We will take advantage of the fact that a star located on the celestial equator drifts about 1 degree every 4 minutes as the night goes on.

Center the star in the eyepiece and turn off the clock drive. Record the time it takes the star to drift to the edge. If the star takes 2 minutes to drift to the edge, the distance from the center of the eyepiece to the edge is ½ degree or the distance across the whole field of view is 1 degree. Simple, eh?

For my 6-inch f/8 newtonian, the star took 2 minutes 52 seconds to drift from the center to the edge of my 1 inch eyepiece. That’s almost 3 minutes or ¾ of a degree. So the true field of view is 1 ½ degrees. Using the same method I found that my finder-scope has a FOV of 5.25 degrees. I am ready to start plotting star hops on my star charts

Now I can set up my star chart program to create finder circles to match my finders FOV and my eyepieces FOV. Above is a star hopping chart to find M13 in Hercules. I use the freeware program Cartes du Ciel to make my star charts. I have one for each Messier object.

Three the easy way M31 M32 M110

It was a clear cool nite at the observatory tonite. We were able to stay out until 11:00 PM until the dew rolled in. The deep sky team got together tonite to try their hand at locating M31. Thanks to the pictures in all the text books and magazines it is easy for the inexperienced stargazer to miss the Andromeda gallery. They're expecting to see this huge galaxy with spiral arms. Not the little fuzz ball that appears in the eyepiece of their 6 inch reflector.
The team used the star charts they prepared to hop to M31, but tonite it was an easy naked eye object. Once centered on the fuzz ball that is the core the Andromeda galaxy, you could notice a fuzzy star near the edge of the eyepiece. The chart identified this as M32. That meant M110 should be just outside the field of view on the other side of the eyepiece but it was hard to see. All claimed they could pick it out of the gray background in the eyepiece but I think for some it was wishful thinking. We'll break out the 10 inch next time we're out.

BrianC