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Home Bilking Network

(May 31, 2000)

Usually, I can laugh off the things said about astronomy on TV. Other times though, what I see makes me boiling mad. Yesterday I saw such a thing.

The Home Shopping Network occasionally sells telescopes. This time, they were selling the Galileo 3 inch reflector, a rather small telescope. This kind of telescope, selling for about $100-200, makes a decent starter 'scope, but in general most people would find the view through them disappointing. Planets would be fairly small, and most other objects would be hard to see. The Moon would look nice, and you can view the Sun with them by projecting the image on a piece of paper, but that's about it. Amateurs know these types of telescopes are usually not mounted well, making them shaky, and tend to be hard for a novice to use.

This did not stop the people on HSN though. The on-air sales personality gushed about the telescope's ability, just as you might expect. With her was a Galileo company representative, whom I have seen before on that network. I have heard him say shady things, but I've never heard any real lie. That changed yesterday.


image of galaxy M51 taken through a good 'scope The first thing I saw when I stopped on the channel was a picture of a galaxy called M-51, also known as the whirlpool galaxy. This is a classic spiral galaxy, and is a staple of amateur observing. However, it is also a faint object, and can barely be seen at all in a 3" telescope! Implying it would be an amazing object through that 'scope is at best misleading.

However, they didn't stop there. They showed an image of the galaxy which they claimed was taken by the Hubble Space Telescope, even displaying it with the word "Hubble" on it. The picture was not from Hubble! Hubble's field of view is too small to encompass the shot they displayed. Clearly the picture was taken with a small ground-based telescope, probably something around 8-10 inches in aperture. There was even a hair in the print! As someone who uses Hubble on a daily basis, I can assure you: there are no hairs in its images. So this was lie number 1: they claimed a picture was from Hubble when it wasn't. The company rep must have known it wasn't from Hubble; he sells telescopes for a living. He was either lying or grossly incompetent. It's your call.

After they showed the faux Hubble image, they then showed a picture taken through the 3" telescope they are selling. The picture wasn't bad, as they go. It looked pretty much like the other picture, which was their point. A small 3" telescope for $100 can do as well as they $6 billion Hubble! If you fall for that line, perhaps you deserve to get bilked out of a hundred bucks. Still, lying to sell something is illegal.

Anyway, a picture taken through a telescope is not what you would see with your own eyes. A camera can collect light for a long time, letting the image build up. Faint objects can be seen in images that would never be seen by your own eye. They then implied that this is what you'd see through the telescope, which is again another lie, at least by implication. To further this, they showed two more images of objects that would be at the absolute very best faint smudges through that telescope. For the record, they were the Sombrero Galaxy, also known as M104, and the Ring Nebula, aka M57. The Ring is a favorite of mine, and I can see it just barely from my back yard through my own telescope, which is more than ten times more sensitive than the 3" they were selling.

As if that weren't bad enough, more was to come. The on-air rep said (and I quote): "Pluto is no problem for this telescope." The telescope company rep standing behind her nodded his head and said "Yup". This is a complete bald faced lie. It's possible that the on-air rep simply didn't know what she was talking about (but then she shouldn't have said what she did), but for the company rep to agree is simply and plainly a complete lie. Pluto is way way beyond the capacity of that telescope to see. It would be hard in my own telescope, which again is much larger than the 3" they were hawking, even from a very dark site. While technically, it is possible to just barely glimpse Pluto through a telescope as small as the one they are selling, it takes a very high quality telescope, extraordinary viewing conditions and a lot of experience behind an eyepiece. [Note added June 1 2000: I initially calculated it would take a 'scope twice the size as the Galileo one to see Pluto; I was in error. I had input the wrong brightness of Pluto. I have updated that calculation below.]

Perhaps in a way they were telling the truth. Pluto really wouldn't be a problem for that 'scope; it's not even an issue. It would be like using a $30 microscope to look at individual nitrogen molecules. It's ridiculous.

Incidentally, she also said that any 'scope can show you the Moon, and a few can show you Jupiter and Saturn. Actually, those two planets are naked eye objects, so any telescope can "show them to you". This was just a mistake on her part, but again, if she doesn't know any better, she shouldn't be talking about the product.

I called HSN and asked to talk to someone in charge, but instead was given this address to write a letter:

Home Shopping Network Customer Accounts
P.O. Box 9000
Clearwater, FL
33758

I decided not to write a letter, since I doubt it would ever get read; HSN is extremely popular and I am sure they receive hundreds or thousands of letters a day. Hopefully, posting this webpage will warn lots of people about their practices.


Bad Addendum (July 21, 2000): The other big shopping channel, QVC, also sometimes sells telescopes. They had a segment last night. Bragging about the remote controlled focuser on one 'scope (which is actually pretty convenient), the sales rep said it's useful for looking at "craters on the Moon... the rings of Saturn, the spot on Jupiter or the canals on Mars." Um. There are no canals on Mars. Astronomers 100 years ago thought they saw a network of fine lines criss-crossing the surface, but these turned out to be illusions. They were shown not to be real in the 1960s! Someone needs to drag QVC into the 2000s.

Second Bad Addendum (July 21, 2000): This page was quoted heavily by Astronomy Now! columnist Adrian Berry. That was pretty cool, though he actually misquotes or misinterprets me in two places. I'll see if I can get a copy of the article to post here.


Here is the math involved with calculating how big a 'scope you need to see Pluto. First, you need to know that the bigger the 'scope, the fainter an object you can see. It's like a bucket collecting rain water; the bigger the bucket's opening, the more rain it collects. It depends on the area of the opening, which is proportional to the square of the radius of the bucket. So a bucket twice as wide collects 4 times as much rain. The same with a telescope. The pupil in your eye is about 0.5 centimeters in width when it's fully dark adapted. A telescope 5 centimeters across has 10 times the diameter, so you can see objects 100 times fainter (10x10=100) if you look through it. So

(faintness of object through a 'scope)/(faintest by eye) =
(radius of pupil)2 / (radius of telescope mirror)2

Solving for the size of the 'scope, we get

radius of 'scope = radius of eye x square root(faintness of eye/faintness through 'scope)

Say you want to see something 25 times fainter than you can with your eye:
'scope = 0.5 centimeters x square root(25) = 2.5 centimeters, which is a pretty small 'scope. But what about Pluto?

(Some of the math below was corrected July 21, 2000 to give more detail.)

Pluto has a magnitude of about 13.5, and the visual limit without a telescope, being very generous, is about 7. At this point I won't go into details about magnitudes (which involve logarithms), but this means that Pluto is about 100.4x(13.5-7) = 400 times fainter than the faintest star you can see with the naked eye. So the size of a 'scope needed to see Pluto is:
'scope = 0.5 x square root(400) = 0.5 x 20 = 10 centimeters. Ten centimeters = 3.9 inches, so the minimum 'scope you need is still about 25% bigger in diameter than the size of the 'scope sold by Galileo. This in turn means it has (3.92)/(32) = 1.7 times the light gathering capability of the Galileo 'scope. In other words, the Galileo 'scope is nowhere near up to the task of seeing Pluto. And even the 10 cm 'scope assumes it has superior quality optics, and that the user has a trained eye and an observing site that is as absolutely dark as possible. No matter what, the line "Pluto is no problem" is incorrect.



©2008 Phil Plait. All Rights Reserved.

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