AboutTom Whiting Expertise Astronomy has been my hobby/pasttime for over 50 years. Currently own 3 telescopes, the largest of which is a 30 inch Newtonian truss Dob that is portable.I taught Astronomy/Meteorology at the University Level for 13 years before retiring in 1995. Being retired and home most of the time, I am able to answer all questions relatively quickly, unless it's a new moon weekend with good observing conditions. No astrology questions please, or questions about alleged UFO picture identifications.
Experience Experience: Astronomy has been my hobby and study for over 50 years. We currently now own a 30 inch portable telescope (Updated - Pennsylvania`s largest portable telescope). It can be seen on our website at:http://www.velocity.net/~bwhiting and also attend several regional starparties during the year, and have been on 5 total solar eclipse expeditions.
Organizations: President, Erie County Mobile Observers Group for over 15 years.
Publications: Wrote the "Over Erie Skies" newspaper article in our local newspaper for 11 years (1975-86).
Education: Masters Degree- Taught at the University level for 13 years. Retired 20 years -USAF Pilot - KC-135 with 180 combat missions; Also Eagle Scout, Philmont staff 2 Yrs, Order of Arrow Lodge Chief, Ham Radio (inactive).
Awards: two discoveries: The mini-coathanger asterism in Ursa Minor (the little dipper) And the mini-ladle- another asterism in the bowl of Ursa Minor. Clients: Currently President of the ECMOG as mentioned above.
Education/Credentials BS Metallurgical Engineering Grove City College, PAMaster's Degree, Gannon University, Erie, PA
Also retired USAF pilot, 20 years.
What is the difference between large and small radio telescopes? do big telescopes detect weaker signals than small ones? can both sizes detect man made signals?
Thankyou for your time and help,
Alice
ANSWER: Hi Alice,
Yes, bigger radio telescopes can receive weaker signals than
the smaller ones. Yes, both detect man-made radio signals, that's
why Green Bank, West Virginia is settled in a radio quiet region of
the country, and when you visit there, they drive you around in
diesel vehicles because regular car ignition systems put out radio
frequency radiation, so regular cars are not allowed on site.
Neither are cell phones or digital cameras. See http://www.catawbasky.org/September2007Afterdark.pdf
or just google Green Bank.
Smaller radio telescope dishes are used for the higher radio frequencies (say microwave) because they have to be constructed
to a much higher tolerance (much closer to parabolic shape) then
the regular huge radio telescope dishes.
Hope this helps,
Clear Skies,
Tom Whiting
Erie, PA
---------- FOLLOW-UP ----------
QUESTION: Hello,
do large radio telescopes also detect microwaves?
do large telescopes detect more varied signals or do both sizes detect the same signals but different quality?
Thankyou very much,
Alice
Answer Hi again Alice,
In reverse order, (2); all radio telescopes are like normal radio receiving antennae in that all radio wavelengths are hitting the
parabolic (curved) dish antenna. The dish simply makes the instrument highly directional and can listen in on a very small,
specific region of the sky. The operator merely selects the frequency that he wants to record using his "radio receiver equipment", much the same way that you select a particular frequency on your car radio. (Except your vertical radio antenna on your car is omni-directional, or more precisely, non-directional, and catches all wavelengths from all directions).
Yes, size matters; the bigger the aperture (dish), the higher the
resolution of the data (or in visual telescopes, the finer the
details). Plus, the fainter the signal that can be received;
(visual, the bigger the aperture, or mirror, the dimmer the object
that can be detected). So if I had a choice, answer B, both sizes
detect the same signals but different quality, except a very small
radio telescope can't detect extremely faint signals from space.
(1) There is a rule for all telescopes across the entire electromagnetic spectrum for gathering photons of light, and that's
what all radio, Infrared (heat), visible light, UV, X-rays, and
gamma rays are, just photons of light at different wavelengths/
frequencies. And that rule is -- the collection surface has to be
accurate to 1/4 wavelength, or it's a piece of crap....why?
Because worse than that, and all the light or energy is not arriving
at a pinpoint location at the focus point. So that's why visual telescope mirrors have to be ground an figured to several millionths of an inch to work properly (a wavelength of light is about 20 millionth's of an inch). (and that's why the high cost of GOOD telescope mirrors, BTW).
With radio telescopes, the wavelength of radio waves is much much
longer than visible light; some radio waves are several feet long,
so the dish can be off from a true parabolic shape by several inches,
and the dish will perform quite well. But with microwaves, the
wavelength is like only 1 millimeter, so those radio telescopes that
receive microwave radio radiation have to be constructed to within
1/4 millimeter (0.01 inch) or better, to successfully resolve microwave radiation. It's far easier from an engineering standpoint to maintain a small dish to those tolerances, than say an 80 foot wide large dish. So that's why they use smaller radio telescopes for
microwaves, and the really big dishes for non-microwave (read that
longer radio wavelengths) radio signals. So while all radio telescopes can receive all radio wavelengths, the microwave portion
of the radio spectrum can only achieve high resolution with the....
more tightly shaped, smaller, parabolic dishes.
So now you know the rest of the story. ;-)
Clear Skies,
Tom Whiting
Erie, PA
