Date: July 23, 2011

Title: The Sky Through Two Telescopes

Podcaster: George Kristiansen

Link: http://gkastro.tk/

Description: Choosing a bigger telescope can often be uncertain – will a larger aperture actually make that much difference? What will my favourite objects look like through a larger aperture? Investing in a large telescope can often cost a lot of money, so it’s nice to have a little bit of a hint as to what effect it will have on the popular objects in the sky. This episode compares the views of some of the main objects in the sky as seen through a 5-inch telescope, compared to the view through a 10-inch.

Bio: I’m a student in the UK, and I love to study physics and maths. I do astronomy as a hobby, and I mainly observe variable stars and supernovae, but I find anything in the sky interesting! I also like to learn about computers, and have made a few little pieces of astronomy-related software. I would love to take astronomy and space to a professional level in the future!

Sponsor: This episode of 365 Days of Astronomy is sponsored by the Minnesota Astronomical Society, whose Cherry Grove Observatory provides dark skies and several on-site telescopes for use by members and visitors alike. When you’re in the area, come visit us during one of our star parties at the MAS Cherry Grove observing site.

Transcript:

Hello, my name is George Kristiansen, and I am a student and amateur astronomer from the UK.

There comes a time in the observing career of every amateur astronomer when the desire to buy a larger telescope finally gets the better of you. This was certainly the case with me, after I started observing with my first telescope – a 5-inch reflector, in 2009.

I spent a year touring the skies, observing some of the fine deep space objects such as galaxies and nebulae, and savouring the sights of the cratered Moon, the rings of Saturn, and the cloud belts and moons of Jupiter. I saw things I never could have imagined, and this was the start of an astronomical journey of discovery.

However, I soon found myself wanting more. I was enticed by the beautiful descriptions of deep-space objects from observers with 16-inch telescopes, and was amazed by the stories of Saturn’s rings at high magnification.

Being 16 at the time, I could never hope to buy a massive Dobsonian (and the observatory I would need to store it), but I did manage to purchase a 10-inch Dobsonian reflector, which doubled my aperture, and opened up a whole new universe of possibilities.

In this episode, I will talk about the effect of doubling my aperture on some of the popular objects seen by many amateurs in their first few years, and hopefully, I will be able to help you in making an informed decision as to what some favourite objects look like through a 10-inch telescope compared to a 5-inch one, when aperture fever finally gets the better of you!

Increasing aperture does, of course, allow more light to be channelled into the observer’s eyes, so the main benefit of upgrading from a medium-aperture (like my 5-inch telescope) to a larger aperture, is that fainter objects, most commonly deep-sky objects like galaxies and nebulae, can be seen in the sky. Because of this benefit, I will start by exploring the view of one of my favourite DSOs – the fabulous Orion Nebula, through a 5-inch telescope compared with that through a 10-inch telescope.

The Orion Nebula is the closest active star-forming region to Earth, and it really shows! Visible even to the naked eye as a fuzzy patch, this energetic pool of glowing gas is a common target for amateurs, as the intense energy from the young stars within fuels one of the most amazing sights in the sky.

I have viewed the Orion Nebula many times through my 5-inch telescope, with each observation seeming to show new details in the tendrils of gas and the surrounding star fields. The main feature visible is the glowing heart of the nebula, which, at 90x magnification, fills nearly the whole eyepiece with light. It’s also very easy to see the four main members of the ‘trapezium’ cluster – the grouping of young stars which gives the nebula its glow. Extending from either side of the nebula, I could see two large ‘tendrils’ of glowing gas, almost like two wings jutting out from either side of the main body. These give the nebula some real shape, and curve round for a good distance, getting fainter and fainter further out. That is an indicator of the view of the Orion Nebula through a 5-inch telescope. So what awaited me when I turned my new telescope to this old favourite?

The same main structure was still visible, but the first difference I noticed was the increased extension of the two thin ‘wings’ of nebulosity. They curved further around the main nebula, still fading out of sight before they would re-join at the top. This perfectly demonstrated the increase in light-gathering power that my new telescope brought – a mirror twice as wide easily revealed some of the more subtle details of the nebula. Another large difference was the detail caused by the dark nebulosity – a feature which I had never really noticed while observing with the 5-inch telescope. The main body of the nebula was suddenly dotted with contrasting, mottled areas, where there were subtle variations in the brightness across the glowing gas. The same effect was visible on both of the extensions, with dark nebulosity giving them a subtle knotted and mottled appearance. This really gave the nebula a new texture, and really added something I had never seen (or maybe something I just missed) to this lovely object. The trapezium cluster also yielded two new, faint stars – stars which were probably outside of the visual limit of the 5-inch telescope.
Doubling the aperture seems to reveal more subtle textural details rather than revealing much more nebulosity, but even the small changes were a large improvement on the object (although it looks beautiful through any aperture).

Another common favourite for deep-sky observers is the nearby Andromeda Galaxy – this is also visible to the naked eye under dark skies, and although it looks calm, it is actually racing towards us at hundreds of kilometres per second! So what will it look like through the two telescopes?

My first sighting of the Andromeda Galaxy was a very thought-provoking experience. I found it after around half an hour of searching, and spent ages staring at the unassuming patch of light which was actually the combined glow of hundreds of billions of stars. On my returns to this ‘island universe’, I noticed both of the faint satellite galaxies – one on either side of the disc. They were surprisingly easy to see, despite their small size and relatively low brightness – two small egg-shaped patches; one on either side. The galaxy itself showed up as a glowing oval of light with a perfect core, and a haze of light surrounding it, fading to black before the edges of the eyepiece. This galaxy is probably one of my most viewed objects in the sky, so I couldn’t wait to see what it would have in store for me with my new telescope.

The first time I turned to the Andromeda Galaxy, it looked much the same as through the 5-inch telescope, but as I studied it, I could see more and more of the hazy disc surrounding the core. The satellite galaxies seemed closer in because of the fainter regions of the halo now visible. As I watched, another detail was emerging – two very subtle dark lines following the contour of the disc, passing close to the core. When I finally realised what I was seeing, I was amazed – I could finally see the beautiful, faint dust lanes which show up so well in the images of this wonderful object.

The Andromeda Galaxy is an object which gets better and better with aperture, and I have no doubt that if I upgraded again, I would see even more of this beautiful object, and looking at it will definitely make you feel as though satisfying your aperture fever was a good decision.

Getting a bigger telescope isn’t just good for deep-sky objects. Magnification is important when viewing the Moon and planets, and the rule for determining the maximum ‘sensible’ magnification that you should use with your telescope is to multiply the aperture (in inches) by 50. This means that doubling the aperture also doubles the sensible magnification limit of your telescope. The effect of this is that increasing aperture essentially gives you more resolution, and also gives you clearer views of bright objects such as planets and the Moon. Saturn is probably my favourite planet to view, so I will compare the views of this beautiful member of the solar system.

The firs time I saw Saturn through my 5-inch telescope, it was very low down in the East, so the conditions were not great. Despite this, I could still see the small disc of the rings surrounding a fuzzy yellow orb. Of course I wanted to see more, so I observed it as it got higher and higher in the sky. When the conditions were best, Saturn showed off more detail than any other planet in the sky. I never spotted any weather features on the planet with the 5-inch telescope, but the views of the rings made up for it. On a night of good seeing, the rings were like a sharp edge. They were cutting across and face of the planet and arching visibly round either side. I could often see little areas of dark space between the rings where they curved round the back of the orb, and the contrasting colour of the rings where they crossed the front of the planet gave the image a real 3-D feeling. This planet really does look lovely though any telescope, but how much better did it look when I doubled the aperture?

My maximum magnification with the eyepieces on the 10-inch telescope is currently 240x, which is double the maximum magnification with the 5-inch one. The first thing I noticed about the image was the improved sharpness and contrast. The view was great with the 5-inch telescope, but stepping up in terms of aperture really made a difference.

As a result, with 240x, many more details on the planet and the rings became visible. Under good seeing conditions, it is possible to see Saturn casting a shadow on the rings, and there are occasional weather patterns such as bands of cloud and storms visible in its atmosphere. The real treat is the Cassini division – a steady night will show this dark gap in the rings as a black cut visible all the way around them. The beauty of Saturn is really revealed with the higher magnifications a larger aperture can bring, and the same goes for the other planets and the Moon – Jupiter showed off intricate festoons and small pock-marks in its clouds, and numerous ridges and craterlets were visible across the seas of the Moon.

I hope this little comparison has been useful, and although I only covered three major objects, I hope that you are a little more informed about what changes a larger aperture will bring. As for the rest of the objects? The next clear night is your best opportunity! You can also see some images taken with both telescopes at my website, which is http://gkastro.tk/ Thanks for listening!

End of podcast:

365 Days of Astronomy
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