Saturday, June 7, 2014

M8 Lagoon Nebula, M20 Trifid Nebula and M21 Open Cluster in Sagittarius

Binocular and telescope review

I started studying astronomy in the city of Ibague in 2011, after six months of occasional observations I had to move to Bogota in the beginning of 2012.  Even though the city had far more light pollution I wanted to continue my new hobby and I even began sketching in the latter half of the year. In the beginning of my studies I really did not know that there was a nebula called Lagoon, but when I read about it I wanted to see it even if it was from my very light polluted city.

Finally, in November of 2012 my wish
came true and I could find Lagoon Nebula with my 15X70 Binoculars.  Sagittarius is a summer constellation and I think the best time to see it is between May and September when each night it reaches its highest point in the sky for the year. However, I was so eager to see the Lagoon Nebula that I went out the first clear night I had.  At 20:00 hours in the 1st night of November, Sagittarius was setting at 10 degrees over the horizon therefore it was strongly affected by light pollution; the sky seemed reddish blue and the seeing was 5/10; the waning moon was at 90%, just rising over the city. 

As I was scanning through the many stars of that region of Sagittarius, I saw two particularly impressive groups of stars so I decided to stop there and sketch.  In the southern group, there were small, bright, slightly nebulous-like areas around two of the stars. In the western group, there were two areas of interest: a small and bright diffuse patch around the last star located at the northwest position of the group and an almost imperceptible dim area around the first star of the group. I thought the two groups of stars which showed some “nebulosity” were M8 and M20, but what I did not realize was that I had also spotted M21. But the fact is that the almost linear southern group contains Lagoon Nebula (M8) while Trifid Nebula (M20) was the almost invisible dim area I mentioned above situated around the first bright star under the triangle formed by bright stars in the western group. The last star in the upper right part of the sketch resulted in being M21 it appeared like unresolved stars that seemed all together like a small diffuse patch which was an open cluster formed by stars that I could not resolve with the binocular magnification.

In June of 2013 I had the chance to go, for the first time, to the US and spend some time with my wife’s family. I also was blessed to know both coastlines and 2 states in in the center of the country. One of my wife’s relative invited us to her home in Missouri in a nice location 1 hour north of Kansas City.  Usually I recognize the constellations from my home location 4 degrees north of the Ecuador, but  I was a little confused because the constellations appeared to have moved south in the sky. In some way I understood and expected it, but I had a weird feeling when I saw those patterns of stars in the sky.

Sagittarius and Scorpius were stuck on the horizon and there were no more southern hemisphere constellations, although I was able to see for the first time the polar star and the little dipper, while the big dipper and Cassiopeia were in the sky at the same time. What a fascinating experience!

Those nights there were clear and the house was far enough away from the city limits to enjoy a Bortle 5 sky. 

I went out there almost every night to see the sky and on June 30th I decided to check out Sagittarius. Unfortunately, the constellation was at about 30 degrees over the horizon and strongly affected by the light pollution coming I guess from Kansas City. The only instrument I had on hand was a pair of Binoculars 7x35 with some collimation issues; however I decided to take them and try to make a sketch. I did not have a tripod so I had to memorize and sketch quickly the main stars.   Lagoon Nebula seemed like a dim pale spot between four stars, the 3 brighter ones formed an obtuse triangle.  While Trifid Nebula which was an even dimmer spot surrounded by four stars in a kite shape.  M21 was just a tiny diffuse spot northeast from Trifid.

Last May 25th, once again from my current location, the sky was clear enough to stargaze. At 1 in the morning after having sketched another target, I decided to go for Lagoon and Trifid Nebulas.  My intention was to compare the binocular view with the telescope view so I needed the largest field I could get and that’s why I chose to sketch with my 25mm kellner eyepiece. Even with the large FOV, both Nebulas did not fit in the eyepiece at the same time, but with patience and moving the telescope I got to capture them in the same sketch.  

Now let’s talk about the sketch:  In the upper circle of the sketch is Lagoon Nebula, an emission nebula situated about 5,000 light years from us. Around the 9th star of Sagittarii (HIP 88469) which seemed shining with a pale yellow-pink color, there was the brightest part of the nebula which also had the best view with direct vision while the other regions in the nebula were only perceptible with averted vision. In that brightest part of the Nebula is situated the hourglass Nebula, a nebular region that I would compare with the view of the trapezium in Orion nebula, except that this was dimmer, but taking into account that it is almost 4 times farther away than Orion Nebula that is to be expected. 

On the other hand, Trifid Nebula was much less brighter than Lagoon Nebula and was shining shyly around the star HIP88333, a double star system causes the ionization of gas in the Nebula. The reflection part of the Nebula reaches to the star near to HIP88333, but because of the light pollution, this region was imperceptible to my eyes. M8 and M20 seem to be close neighbors: Trifid Nebula is just 500 light years further away from Lagoon Nebula.

Finally, but no less important is the open cluster M21. Made up of some dozen stars, M21 showed up in the Binoculars as a dim patch of light around a star,  while through the 25mm eyepiece (26X) about 5 stars in the middle of a hazy spot could be resolved (including the 2 brightest of about 9 Mag). M21 had an apparent magnitude of 5.90 and compared with the Trifid Nebula which has an apparent magnitude of 6.30 M21 was best perceived with the telescope.

Previously, I had compared both Binocular and telescope view with globular cluster and I did not think there was a significant difference between both of them. But in this case, the telescope view suggests that it’s worth it to invest in a telescope rather than a pair of binoculars and in some way I agree. But the fact is that I felt I needed to learn and see with the binoculars first, otherwise I would feel disappointed with the telescope either because the narrow field of view or because I would take forever to locate those DSOs. I also feel that I needed to train my eyes to see more details and a good way to do it was by trying first the Binos. There is no need for a pair of the big and expensive ones, but even with a small pair of binoculars, several DSOs can be seen with some detail.



Edited by Jennifer Steinberg (editor in chief) 

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