Information about Our Telescopes

Portable Telescopes

The portable telescopes used for monthly stargazing events are Orion Dobsonian telescopes, which reside in Cameron's office (Cahill 343). The Dobsonian telescope is a Newtonian telescope in a very simple alt-az mount popularized by John Dobson in the 1970s. They're easy to operate, small enough to remain portable, and relatively inexpensive for their quality. We possess three telescopes:

• Orion SkyQuest XT6 Plus (The 6 inch)
• Orion SkyQuest XT8 Plus (The 8 inch)
• Orion SkyQuest XT10i IntelliScope (The 10 inch)

For details about their specifications (like focal length), click on the links above and go to the "Specs" tab. They aren't too expensive, in that they were $200-600 each, but some of the eyepieces cost that much too.

Advice for People Buying Telescopes

This is advice for new astronomers seeking to buy a telescope for the first time.

I generally recommend new observers to invest in Dobsonian-style telescopes, as they are relatively inexpensive, easy to use, and long-lasting compared to other telescope designs. A Dobsonian telescope is a Newtonian design on an alt-az mount. It has a steady base and allows for easy movement. It's not ideal for long-duration astrophotography, because the orientation of the view seen through the telescope will change over the minutes and hours if you're tracking on an object. Thus, if you're looking to do astrophotography, it may mean investing in a more advanced telescope with an equatorial mount and automated tracking, but that will cost about 10x more and could be more finicky. Stick with alt-az mounts for beginners, though.

The manufacturer that I've had the best luck with has been Orion, having purchased a number of different Dobsonian telescopes through the years from them for use at both Columbia University and Caltech. The telescopes we're currently using for outreach at Caltech are 6", 8", and 10" aperture Dobsonians from Orion (see above). The downside is that they tend to be a little bit bulky, but they aren't super heavy in that they don't have an electric motor to move where they are pointing. One has to move them manually, but it's pretty intuitive. Here are some photos of our Dobsonians in action.

Astronomical viewing from Pasadena is always going to be a challenge, no matter how powerful the telescope is, because the main limitation is the surface brightness of the sky caused by light pollution. But we've had good luck with our telescopes being able to observe deep sky objects with even the 6" aperture dobsonian on Caltech's campus. When I've taken the 8" or 10" to darker sites like Death Valley, Joshua Tree, and Big Sur, I've been very happy with their ability to view very faint targets. The larger the aperture, the fainter objects you'll be able to see, but also, the more expensive and heavier the telescope. On our outreach wiki, I've assembled a list of what astronomical objects are visible throughout the year in the evening from Pasadena (this will be similar for rest of USA), along with the approximate aperture of the telescope required to view them.

The prices on the Orion Dobs have increased over the last few years, but I think the XT6 or XT6 Plus are a good balance of functionality for price (~$300) for an entry-level scope that should continue to work for several years without any real problems. The ones I bought at Columbia 10+ years ago are still being used, and the ones we have here at Caltech have been going strong for over 5 years. The Classic comes with one eyepiece (25mm), whereas the Plus model for $30 more comes with an additional eyepiece (10mm). The Plus kit for $100 more comes with a solar filter as well, which can be nice when the solar surface is active, so you can see sunspots. If $300 is too steep to start, then there are some smaller versions that still do OK and are less expensive. There's a 4.5" aperture dobsonian for $200 . There's also this nice 100mm (~4") aperture tabletop dobsonian that we use for demonstrations, although it may be best to stick to planets and the Moon with this option as it will be more difficult to see faint objects. A lot of people also start out with astronomical binoculars, but I find that I'm far too shaky when using them, and for the price, I'd just as soon have a real stable telescope. But they are a good alternative for a lower price and a smaller piece of gear. A tripod might help with the shakiness.

In terms of eyepieces, this is also an area where you can potentially spend a lot of money if you want the best. The Plossl eyepieces that come with the Orion telescopes are good, but not amazing quality. I think they make a good starter though before investing in something better. In general, the larger the focal length of the eyepiece (10mm, 25mm, 40mm, etc.), the larger the field of view you'll be able to see in the sky. 25mm is a good medium range, but I really like having a 40 or 42mm eyepiece for seeing a very large region of the sky. These larger focal length eyepieces are great for seeing extended objects like the Double Cluster, Andromeda Galaxy, Pleiades, Hercule Cluster, etc., but they tend to be pretty expensive. When you're viewing smaller objects like planets, or even stuff like the Ring Nebula, you want shorter focal length eyepieces, but I don't like to go much below 10mm because the field of view is so small it's difficult to find objects. I think starting out with a 10mm and a 25mm would be good for most purposes, and then maybe having your next purchase be a 40mm eyepiece (again, maybe a Plossl) would be a good addition unless you have infinite resources.

More recently, a new type of telescope has debuted, which is more expensive, but very easy to use. Unistellar now makes telescopes like the eVscope2 that are reasonably portable, easy to set up, and can see very faint objects, albeit for a $4k pricetag. Their design is different, in that there is a sensor inside the telescope, similar to what is found in a digital camera, that records images of what the telescope is pointed at, and then displays those images on a small screen in the eyepiece (or on your phone). The benefit of this is that it can add consecutive images together to show very faint objects, much fainter than you would be able to see for such a small telescope. The disadvantage is that you're not viewing the actual light rays that are traveling through the telescope to your eye, as is done in a traditional telescope. So it's a trade off. The other disadvantage to this type of telescope is that it's not very good for viewing solar system objects like Jupiter, Saturn, or Mars. But it's very easy to use, especially for a beginner, and provides some amazing views. It also doesn't require lots of different eyepieces, just the equipment that comes in the $4k purchase. I am happy with my purchase of one.

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