Object of the Week, July 12, 2015 - Messier 20, the Trifid Nebula

[Howard B]

Messier 20, the Trifid Nebula

Emission nebula
Sagittarius
RA 18h 02m 23s
DEC −23° 01′ 48″
Magnitude: 6.3
Apparent Size: 28 arc minutes
Distance: 5200 ly
Discovered by: Charles Messier on June 5, 1764

Messier-20.jpg

If I have a favorite deep sky object – and I’m not sure that I do – the Trifid Nebula might be it. There are a couple of reasons it might be my favorite though. First, I remember being mesmerized by its black and white photos I grew up seeing in books and being intrigued by its name, especially because its dark lanes seemed to slice it into four sections.

Secondly, it just looked so ephemeral, and even though my views through the suburban light glow I grew up in where tantalizing, it wasn’t until my first trip to darker skies that I realized I could see much of this detail for myself. Under these darker skies it looked beautiful through my 8 inch, and it really did look like it was divided into three sections.

With each larger scope – 12, 20 and now 28 inches, I’ve come to appreciate it even more. The dark lanes have structure and depth through my 28 inch scope, the brighter parts of the nebulosity has a warm hue while the fainter part to the north looks cooler. The hues seem more prominent when using a binoviewer but I’ve seen them quite well with a single eyepiece during exceptionally clear observing conditions.

My sketch is a rough draft of a long term project, which I hope to add to in the next couple of months. I find large, diffuse nebulae like the Trifid are the most difficult objects to draw realistically.

Trifid for Hawaii presentationSMALL.jpg Trifid for Hawaii presentation_invertedSMALL.jpg

Also fascinating is the multiple star in the center of the Trifid, ADS 10991, but there are other stars nearby that under steady seeing make it look even more interesting.

The color photo here is from http://www.constellation-guide.com/t...la-messier-20/ which also has a nice facts and figure article about the Trifid. Good stuff, but for me the best reason to look at the Trifid Nebula is to enjoy its sublime beauty and recall my youthful enthusiasm while under a starry summer sky.


GIVE IT A GO AND LETS US KNOW!

[Ivan Maly]

A big favorite of mine as well, and I too notice a slight color contrast. Here is the sketch I did last summer. 16", remote dark site, various magnifications with and without an OIII filter.

[Howard B]

Ivan and I can't be the only one's with observations of the Trifid - come on, let us know!

Howard

[Ivan Maly]

Wrong forum to discuss Messiers (laughing).

[RolandosCY]

Wrong forum to discuss Messiers (laughing).

True!!! But still a worthwhile object for all size telescopes. I have observed this object many many times with all my scopes. The view through the 18" is definitely breathtaking and the detail amazing. Yet at the same time the view through my 4,5, and 6 inch refractors are also quite impressive, both with and without filter (provided the view is under nice dark skies). I have made a mental note to prepare a sketch during next new moon weekend...

[Steve Gottlieb]

Ivan and I can't be the only one's with observations of the Trifid - come on, let us know!

Howard

I was also hoping others would post as this is such a well-known popular target, but I'll add an observation ...

18" (8/12/10): the emission component of M20 was sketched and observed carefully at 175x. At the intersection of the dark lanes is the multiple central star HN 40 with a mag 7.6/10.4 pair at 6" and a tight mag 8.7/10.5 pair at 2.3", with the two pairs are separated by 11". Four lanes (B85) emanate from the bright central hub. A narrow lane starts NW of the multiple star and heads 2.5' due N, where it stops at a mag 10 star. Near the base of this lane another branch heads west to the edge of the nebula. Another lane heads SSE for ~2.5', tapering at the end. A prominent lane shoots 3.5' NE and has a few short branches, including one just NE of the central stars. This lane is bordered by a couple of mag 10.5-11 stars on its south edge. There is an extension at the NE end that bends to the north and exits the main nebulosity and merging with a dusty region just SE the reflection component to the north. A mag 9.4 star is at the north edge of the main emission component. The blue reflection component surrounds mag 7.3 HD 164514 and extends ~6' with an irregular structure.

[wvreeven]

This is my observation with my 6" telescope from July 22, 2007. Apparently I didn't notice that the dark nebula splits up the nebula in four parts.

I started with my 9.7 mm eye piece. Using OIII I clearly saw three lobes with the double star inside and the reflection nebula to the north. The three lobes are separated by B 85 which clearly is visible. The OIII makes the reflection nebula disappear largely but it enhances the view of the lobes. Using my 20 mm eye piece it becomes clear why this object is called the Trifid Nebula. Without OIII it seems that the dark lane makes the west part f the nebula disappear but peripheral view makes it visible again. The reflection nebula to the north seems to fan out to the west quite a bit. So does the emission nebula while it ends sharply to the north and east. Pretty impressive considering that this observation was done in evening twilight.

[nicoscy]

I will skip comments about past observations of this object with my 12" dob in favor of my last observing session on Saturday the 19th this month.

I have this passion about investing a couple of observing sessions every summer with a rich field instrument every summer, travelling from Scorpio, being swept up by the river we call The Milky Way Galaxy, floating down the river to disembark close to Cassiopeia.

I used this, a 60mm f5.5 (fl 330mm) ED APO:

TS 60mm.jpg

True field of view of 7.29 degrees. 10.6 times magnification. 5.36mm exit pupil. A trip that lasted a couple of hours and will be repeated soon, but just for you to get a feel of the FOV, I think the image below shows how crazy the FOV is in the specific area of interest:

Sagitta.jpg

Some structure in both M8 and M20 was visible, resting on a velvety rich layer of stars. I could barely see dark lanes on M20 but they were there, appearing as hairline fractures on the body of the nebula. Later I changed the FOV to include M8, M20, M21 and M28 in the same FOV and a bit later I switched clusters, ditching M28 in favor of M23, while keeping M8, M20 and M21 in the same FOV

I plan to repeat the experiment in order to squeeze more information out if what I was seeing but this time I will mount my Ethos 21mm, sacrificing some exit pupil and TFOV in order to get a slightly higher magnification 15.7x.

Although I love my dob, I am not shy about using small instruments to make observations - the Trifid Nebula (and friends in the surrounding area) make for wonderful objects in smaller aperture but ultra wide field instruments. Sometimes it's about the big picture as well and M20 and friends definitely fit the bill.

So, anybody else do any observations with their smallest instead of their largest instruments? How did you find the experience? Or am I the lone ranger in this case, reporting on observations with a 330mm FL telescope weighting in at 1.8 kilos (probably less than the weight of some people's finderscopes on this forum!!)?

[Ivan Maly]

Wide field is great, Nicos. The last time though I observed with my smallest instead of the largest telescope after my 16" slid off its bearings as I tried to look low in the south from uneven terrain. So I took out my 80 mm. Which incidentally was indeed bought as a sort of finder to ride on another scope. The stuff was so dim in it!

[svdwal]

Would love to, but at 51 degrees north it is too low in the sky. And a Summer object too.

M17 looks reasonable, everything below it, especially the nebulae, are not very good to look at.

[Uwe Glahn]

Wow Howard! Extremely well done your sketch, simply perfect. Your sketches are so close to reality that I often became the feeling - yes, exactly this is i what it looks like in the eyepiece. Same feeling here.
Unfortunately I did not sketch this object, because under normal transparency it is also to low in the sky, even for southern Germany. You loose to much detail, so I did not start an attempt. For Namibia this object is to "north" difficult decision but I have to try it in the future.