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It’s a trap! No it’s THE Trap – the truly awesome Trapezium done DSC-60 style

Hubble photo of Orion Nebulae modifed to put emphasis on the Trapezium. Click on image for larger version.(Flipped left to right as in telescope using a diagonal.)

This is a DSC-60 Project observation for project details go here.
Double Star Club list:
Theta 1 Orionis 05h 35m.3 -05° 23′ 6.7, 7.9, 5.1, 6.7 8.8″,13″, 21.5″ 31° , 132°, 96°

Click for larger image.

Theta 1 Orionis (θ 1 ) – Trapezium 
RA: 05h 35.3m Dec: -05° 23′
Mag: 6.7, 8.0, 5.1, 6.7    Sep & PA: See graphic
Distance: 1350 ly
Spectral type: B1,B0,O6,B0.5

Magnitudes differ somewhat by source – these are from James Kaler and listed A-D, as are the spectral classes. A&B are eclipsing variables.

In my book there is simply no prettier, no more awe inspiring, no more intellectually stimulating sight in the heavens than the Orion Nebulae with the Trapezium at its heart. This four-star trapezoid is easily in reach of any small telescope and positioned near enough to the celestial equator so that it can be observed from just about any where in the world.

When I say this post is “done DSC-60 style”  what I mean is this post  will focus on the four stars in the Double Star Club list  and how they look through a 60mm scope. But these stars are easily reached by even a 50mm refractor.  In fact some say they can be seen with 10X50 binoculars held real steady. I can’t see them that way. My eyes need a 50mm objective and at least 20X to see three of the four stars.  And the sight only gets more interesting – because the surrounding nebula is enhanced – if you use a larger scope and there are two more stars in the Trapezium worth pursuing with larger instruments – and actually more still that are probably out of the reach of amateur observers.

But one of the first lessons the Trapezium offers us is the difference between the human eye and the camera. Look at just about any of the many gorgeous pictures of the Orion Nebula and you will not see the Trapezium no matter how large the telescope used.  You rarely see it in a photograph that even approximates the visual view through a telescope. It certainly doesn’t come through well in the Hubble photo that leads this post, though the nebula is spectacular. But at the telescope your eye will capture the glory of the nebula and the four diamond studs that are the Trapezium.

I’ve been looking at this off and on for more than a half century and it never grows dull, but the view through a 60mm refractor takes me back to my youth and sparks the love affair anew. Here are the pearls you seek – elegantly represented in an out-of-this-world setting. The “C” star glows brightest. I know, we’re used to the brightest star of a multiple star being designated “A,” but in the case of the Trapezium they broke this rule and lettered the brightest four stars in order of RA. The dimmer, more difficult E and F stars do not follow this pattern, however, but they’re out of reach of the 60mm scope so I won’t pursue them here.

Simulation of the low power telescope view of the Trapezium - with the Orion Nebula removed for clarity, but, of course, you will see it with binoculars or telescope. This small image is typical of what the naked eye reveals. Click on it to get a larger version showing the telescope view at low power.

With the naked eye or low power binoculars you see essentially two stars here – the Trapezium looking like one star identified as Theta 1 (θ 1 ) Orionis and what looks like it’s twin, Theta 2 (θ 2 ) Orionis.  Theta 2 is the brightest star in what I call Orion’s Mini-belt. These three stars will probably be the first to catch your eye in a scope and they point to the Trapezium which, of course, unfolds more and more as you increase power. There is about 134 seconds of separation between Theta 1 and Theta 2 – the stars of the Trapezium themselves span about 14-seconds of arc.

I had to play around with the preferences in Starry Night Pro making the stars into tiny specks and get rid of the nebula entirely  in order to simulate the view through my 60mm Unitron refractor at about 36X using a 25mm Ramsden eyepiece – yes, that’s one of the old eyepieces supplied with the scope c. 1970! Of course in the scope I see both the nebula and the Trapesium, so the simulation just can’t do the view justice. What a;ways missing in books and even on the computer screen is the brightness dimension – it gets represented – simulated – by the size of a dot indicating a star, but brightness isn’t size – its – well – brightness! And I think that’s why the live observing experience remains unique and important.

To me there is something magical in such a low power view where the stars are mere pinpoints. I liked this view also because it revealed the nebula for what it is – a burst blister in the surrounding darkness caused by the  huge star-forming region known as the Orion Molecular Cloud. That cloud is far, far larger than what I could see in the telescope field, covering roughly half the constellation of Orion.

I switched to an 18mm Kellner –  I was going completely “retro” on this evening, using the Unitron with its original eyepieces and original Unihex eyepiece holder which includes a less than pristine diagonal.  It just felt right to do this. At this power (50X) the brightness differences of the stars is more apparent and the C star really looks blue to me while across from it the B star still is just a pinprick. (While some have reported color in these stars I see them as white or blue, with duller shades simply a result of the star being fainter.)

Moving up to a 12.5 Kellner (72X) and a 9mm Symetrical (100X) the picture got bigger, but no brighter. Aesthetically I preferred the view at 50X. It had an elegance enhanced by the delicacy of the relatively  dim, B star.

But there are so many things to take in here that you need to just sit and stare and tell yourself what all of this represents. For many years, when confronted with this view, I dreamed of flying in a rocket ship to the Orion nebula – it’s a mere 1,350 light years away – and I imagined looking out the window and seeing these huge, glowing clouds pass by as you do in an airliner.  But the truth is the view would be more like what you see in the simuation above. There would be no clouds! this where the magician of reality  uses great distance to literally pull the wool over our eyes.

My bubble in this respect was broken by Terrence Dickerson in his book “Nightwatch” in which he wrote:

. . . a hypothetical spaceship rocketing through the nebula would encounter only slightly more particles than those recorded in interstellar space. The average density of the nebula is one-millionth the density of a good laboratory vacuum.

Of course it gets much denser near where new stars are forming, since they are pulling material together.

Does that diminish the viewing experience in any way? Heck no! It is a testimony to how distant 1,350 lights years really is. The numbers simply numb us – but try to imagine particles so far apart that there are far fewer of them than in a vacuum on Earth, then imagine us actually seeing them as clouds because we are so far away!

Of course,  the Trapezium at the heart of the nebula is exactly what it appears to be – four hot, young stars that have burned through the dust around them and popped a blister on the huge Orion Molecular Cloud, giving us a look at what is behind that cosmic screen.

And behind the scenes . . .

And then there is the incredible number of stars that are hidden by dust and need to be dug out with infrared observing tools and when they are what we find is the Trap is the tip of the iceberg – an iceberg that holds what is probably the youngest and defintely the most star-packed open cluster we know. The density of this star city is believed to be  6,000 stars per cubic light year – think of what that must be like in comparison to our own region where the nearest star is more than four light years away.  The age is believed to be less than a million years and the Trapezium itself is unstable and will probably vanish in a huge explosion of the C star in the next few million years – so get a look now while you can!

This is all part of what makes the  Trap and surrounding nebula a sight where the sheer majesty overwhelms you. I strongly urge you to click on the following picture to study the larger version. The picture is a composite of what is seen with the Hubble Space Telescope in Visible light and what is seen by the Spitzer Space telescope in infrared light.  As NASA explains it:

Orange-yellow dots revealed by Spitzer are actually infant stars deeply embedded in a cocoon of dust and gas. Hubble showed less embedded stars as specks of green, and foreground stars as blue spots.” All but washed out in the long exposure are the four stars of the Trapezium in the bright area below and to the right of center.

Click image for a larger version of this composite shot in visible light and infra red.

Go here for complete picture and NASA explanation.

Jim Kaler points out more fascinating facts within the Trap itself:

By far the leader of the pack is Theta-1 C, a great 40-solar-mass star with a temperature of 40,000 Kelvin (making it the hottest “naked eye” star, though the 4 are inseparable without optical aid), a huge luminosity 210,000 times that of the Sun (85 percent of the Trapezium’s total), and a 1000 kilometer/second wind with 100,000 times the flow rate of the solar wind. The power of the star is such that it is evaporating dusty disks around nearby new stars that in other settings might form planets.

The other members of the Trapezium pale only in comparison with “C,” all containing over 10 solar masses. A main interest lies in their multiplicity. Theta-1 A is an eclipsing double also known as V 1016 Ori. Every 65 days, the star dips by a magnitude as a star still in the process of formation just one Astronomical Unit away passes in front of the bright component, the whole thing watched by another companion 100 AU off.

Theta-1 D seems to have a companion as well. The champion in this contest, however, is Theta-1 B, which has a companion 60 AU away called “B1.” “B” itself is another eclipser (known also as BM Ori) that drops by nearly a magnitude every 6.5 days, the companion probably much like the Sun. Since “B1” is also double, Theta-1 B is quadruple. Adding them all up (and including fainter Theta-1 E, which lies close by), the Trapezium is a complex multiple of 11 stars!

. . .  Most multiple stars are hierarchical, a distant star going around a close double (like Theta-1 B), or two close doubles going around each other (like Mizar or Epsilon Lyrae), which gives great stability. The Trapezium, on the other hand, is gravitationally unstable, the stars all too close together. As a result, one after the other will be ejected from the group. After only a few million years, the leader of them all, Theta-1 C, will inevitably explode as a great supernova, the others probably doing so as well, all lighting the dusty gases of interstellar space, all providing shock waves that will promote new star formation within the local molecular clouds.

And this is what those little dots of light in your 60mm glass are all about! Awesome. But there’s more.

As I said, the Dickerson statement about the nebula being a vacuum still leaves me a bit confused. It is obviously denser near new stars, else the stars couldn’t form. The question is, how dense does it get and how close to those stars do you have to be  to experience clouds?  More to the point, how dense is matter in the area we actually see in our scopes as nebula? I’m just not sure from what I’ve read. But it is something to think about and while thinking about it, why not sit back and enjoy the Trapezium, the nebula, and starbirth in this wonderful animation.

About this animation

From the Hubble Web site:

This animation reveals the topography and beauty of the Orion Nebula like never before. Based on data obtained by the Hubble Space Telescope, all of the gas clouds, stars and proplyds are positioned as accurately as possible. The animation ends with a close-up examination of the proplyd HST-10, where astronomers see dust grains clumping in the early formation of rocky planets, but whose gaseous envelope is also being burned away by the Trapezium stars in the nebula’s center.

Credit: Greg Bacon (STScI), model based on data by C.R. O’Dell (Vanderbilt University), and The American Museum of Natural History/Rose Center for Earth and Space


One Response

  1. This really is one of the most detailed, eye-catching, and informative pieces on the Orion Nebula/Trapezium area that I’ve read. The Hubble picture at the top of the post is simply hard to get past — somehow I missed that one when it was released. And the perspectives provided by the video are stunning. Truly a pleasure to read, Greg.

    One-millionth the density of a good laboratory vacuum, huh? Geez, that is hard to conceive. In a scope of six inches or more, at low magnification there’s enough light coming from the nebula to play havoc with a person’s dark-adapted vision!

    What really strikes me is how the nebula and surrounding area are so far beyond anything our experience equips us to comprehend. It should put a little humility in all of us.

    Meanwhile, I’ll see what I can do to pry “E” and “F” out of all that dust and gas. 😉

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