Tuesday, January 14, 2014

Globular clusters in Ophiuchus

A comparison between binocular and telescope view

When I received my first pair of binoculars, Celestron skymaster 15x70, in 2011, I became even more seriously interested in astronomy (after starting with naked eye recognition). Almost one year after I received them, my wife gave me a telescope, just what I needed then. I have seen in several posts and forums that when people say astronomy they assume telescope, but astronomy is so much more, from naked eye viewing to binoculars and more, so that’s why I am dedicating this blog to those who are interested in starting astronomy.
Two sketches in different conditions with two different “tools”: the first one from a sub-urban sky with a pair of astronomical binoculars and the second one in my very light polluted skies with the 5 inches telescope and a 25mm kellner eyepiece. Several times I had tried to spot these two messier either with my binoculars or my telescope. Unfortunately, even when Opiuchus is in the Zenith providing one of the best views from the city, there are two factors against my search: with the binoculars, the light pollution makes the sky seems clear making the cluster “invisible”; and with the telescope, the main star visible with the naked eye is too far from either M10 or M12 to make it useful for using the star hopping technique I usually practice.
In June of last year we traveled to a very little city just about 84 miles from our city for a short vacation so I included the binoculars in our baggage. They are light and easy to set up, so I considered them to be useful in our trip.

The second night there had good conditions to observe the sky: moonless, constellation at ±45° above the horizon, transparency 2/3, Temp. ±25° C, Bortle scale: 5-6.  I found M10 and M12 at about the middle of the distance from ζ Oph to ĸ Oph.  Both clusters just fit in the binoculars field of view. Both clusters are similar in apparent magnitude (6.60) and because the better sky they seemed much brighter than some others DSO’s I had seen previously from the city like M4 (5.90) or M2 (6.50) which should look brighter in the same conditions.
M10 (down in the sketch)  and M12, look like twin clusters with a slightly difference: M12 looks just a little fainter than M10 and is at 16000 LY from us while M10 which is at 14300 LY from us has an apparent diameter of 15.1 arc minutes.
Now, let’s talk about the second sketch.  After I performed the first one, I tried unsuccessfully some other nights to spot M10 and M12 with the telescope. Lots of nights were cloudy and some others with the moon between me and the deep sky. Finally, in early October, there was a night with good conditions: clear, moonless, Bortle scale 9, Antoniadi II.  Opiuchus was setting off, just 25°above the horizon. Unfortunately M10 and M12 were just behind my neighbor’s building so I looked up for M9 instead. Sabik (η Oph) was visible to the naked eye and it was a good point of reference. With the star hopping technique and with the help of the flip scene of Stellarium, I could spot M9 which is located at about 3.30 arc degrees from Sabik in a straight line to γ Sgr in Saggittarius.  In the view with the 25mm kellner eyepiece, M9 seems not as large as its brothers M10 and M12, but seems like a very tiny spot, perhaps 5 times bigger than the stars around. M9 has an apparent magnitude of 7.9 (much less than M10 and M12) and it is situated at the farthest distance from us: 25800 LY. At 2pm of M9 (in the sketch view) a very tiny star of the cluster could be resolved.
Now, let me review some things about the two observations: in same conditions and with the same instrument M9 would be seen fainter than M10 and M12, so this was a disadvantage for the telescope view plus the very light polluted skies but however, the binocular view in middle of a better sky, is at least for globular cluster a good view comparable with a telescope (of medium aperture) view in a polluted sky.  About planets and nebulas, I still consider that the telescope has the advantage, even in polluted skies.

But my point is not to choose telescope or binoculars; my point of view is that who is interested in astronomy with a tight budget, could begin with a good pair of binoculars and even those who already have a telescope could enjoy the binocular view as much as they enjoy the telescope view.
I have to admit that some nights I don’t want to spend time setting the telescope or searching in the sky so I just take my binoculars and look at the sky. Binoculars are a good and serious start in astronomy and provide an easy and quick set up for those whose every hour of clear sky is a treasure.

Please enjoy this marvelous creation of God and have good skies!!!


Edited by Jennifer Steinberg (editor in chief)



  1. hola amigo vivo en bogota vivo cerca al aeropuerto, estaba pensando comprar un telescopio profesional un refractor de 100 mm o un catadioptrico de 8" para usar principalmente desde mi casa, pero me pregunto si en realidad vale la pena despues me decepcionare mas que todo por la contaminacion luminica de bogota , se que la luna seria facil de observar, pero galaxias nebulas o otros planetas, por ejemplo como se ven segun su experiencia, saludos.

  2. Yo tengo un reflector de 5" y creo que ha sido una buen inversión. Al principio fué un poco frustante porque pasar de manejar los binoculares al telescopio implicó un poco mas de lectura y disciplina. De seguro no habrá problema con planetas o la luna, pero ya hablando de galaxias y nebulosas, es mejor optar por un telescopio (o binoculares si es el caso) que puedas transportar a cielos rurales. Ambos telescopios que dices creo que tienen unas buenas características , sin embargo pienso que no dan ventaja comparada con su precio, para objetos de espacio profundo (especialmente nebulosas, cúmulos glubulares y galaxias) con respecto a telescopios mas pequeños o incluso un buen par de binoculares.
    Conozco un sitio aquí en Bogotá donde puedes conseguir buenos aparatos usados y cuando veas buen tiempo, sería un placer para mi compartir un poco mas de mis dibujos.

    Si quieres me puedes contactar a mi mail lgcarvajalre@unal.edu.co.



  3. gracias amigo, voy a ver si puedo conseguir unos buenos binoculos para empezar aunque con este clima puedo esperar un poco.