Big isn’t always best – in praise of small telescopes
Our Stargazing Live events are always wonderful and our one in January 2014 was probably the best yet because the sky was so brilliantly clear. Also I learnt surprisingly that my 5” telescope gives a better understanding of the Orion Nebula than the best astrophotographs, even those taken by the Hubble Space Telescope.
Looking at the Trapezium stars in Orion
Let me try to justify that unlikely claim. Before the Stargazing event, we are given our target to look at during the evening and we are advised to make sure we knew enough about it to keep the public interested. My target was the Orion Nebula so I did my homework. I read that a nebula is made of gas, which I knew: it is a nursery for new stars as that gas gets pulled together and I knew that too: there is a group of 4 stars in the Orion Nebula called the Trapezium and I even knew that . What I hadn’t realised was that these 4 stars have actually formed from the nebula and are therefore the most obvious of the new generation in the “star nursery”.
I was really pleased that my telescope was just good enough to pick out the Trapezium stars though it wasn’t always obvious that there were 4 of them. I went through my patter about what we were looking at dozens of times during the evening – and loved doing it. More noticeable was a line of three other stars very nearby but I wasn’t sure if they were also young stars born from this nebula or if was just a line-of-sight effect. They might have been hundreds of light years in front of or beyond the nebula, just in the same direction from our point of view.
But you don’t see the Trapezium stars in Hubble images!
Back home after the event, I did a bit more googling to try and find out about these three stars and quickly came to amazing images of the Orion Nebula. The images look beautiful and give a great impression of its gaseous nature. But, wait a minute ! No Trapezium stars. “Goodness, had I looked at the wrong target ?” Then the penny dropped. The images are long exposure, designed to pick up the details you cannot hope to see directly. The effect is that objects you can see without imaging are grossly over-exposed. The Trapezium stars merge into one and just appear at a large bright area within the Nebula itself. In other words, the so-called best images don’t show a really important feature of a nebula – namely the famous examples of young stars forming within it …and yet my telescope does !
To illustrate the difference here are two images. The first one was taken by John Moore and clearly shows the Trapezium stars. I saw roughly this level of detail through my telescope.
Trapezium in Orion imaged by John Moore
Now compare that to a long-exposure image taken from the Hubble Space Telescope (it is Hubble 2006 mosaic 18000), (The circle shows roughly the area of the Trapezium stars). The nebula is much more dramatic and much larger because the image has picked up the fainter parts of the gas cloud. But the Trapezium stars are all but unrecognisable in the general bright area.
Credit: NASA, ESA, M. Robberto ( Space Telescope Science Institute/ESA) and the Hubble Space Telescope Orion Treasury Project Team
It is definitely a case of “horses for courses”. We get a bit spoiled by seeing all the wonderful images of nebulae, galaxies etc that it can be easy to overlook the fact that a telescope serving the human eye can actually show up some features that the “better” views don’t. So if I had to vote on which approach gives the best understanding of what a nebula is , I would choose the simple view through a telescope which includes the Trapezium stars. Definitely the winner. Well done to my telescope.