If I am asked..."how far can you see?"...
Posted 19 May 2013 - 12:09 PM
A penny to an unaided eye has an angular size of 1" if 2.5 miles away. Using an FL scope of 1625mm at f/8 and an eyepiece FL 21mm with an apparent field of 68 degrees will that penny 2.5 mi away look 77x bigger?
Leaving atmospheric factors out of the equation let me know if I am on the right track .
Posted 19 May 2013 - 02:32 PM
But yes, the penny will look 77 times bigger.
Hope this helps.
Posted 19 May 2013 - 04:43 PM
Posted 19 May 2013 - 07:23 PM
Posted 20 May 2013 - 06:05 PM
Posted 20 May 2013 - 09:32 PM
When I'm asked that question I reply it's not how far but how bright that matters. then explain a streetlight can be seen farther away then a single xmas tree bulb or house light point out how the stars aren't all the same brightness. this also works for why I can show a galaxy but not pluto with a 8" scope
The "how far can you see" is quite a vexed one, and I too struggle with it. Most people who ask aren't upto speed with things astro, and to get technical with them can make one seem arrogant, a smartarse, or even too much of a rocket scientist. It's always been a challenge for me to come up with a reply that isn't over the top, and doesn't make assumptions of the understanding to astro novices.
Wirenut, I like your comparative reply. I might look at first mentioning how the perceive lights at night from an aircraft, a bright light doesn't mean it's closer - it could be a spot light in the far distance, or a feeble torch up close. Astro is the same. A galaxy is that massive spotlight, & Pluto the torch. Pluto's closer, but we can't see it. Then we can start to talk about distances.
I've got a viewing night coming up next month at a high school. I'm sure this question will come up. I'll see how it goes. I could just end up with egg on my face...
Posted 21 May 2013 - 12:37 PM
Posted 21 May 2013 - 12:48 PM
I see things that happened before the Earth even existed....
I don't see objects, I see the past.....
Posted 22 May 2013 - 10:24 AM
Posted 22 May 2013 - 12:38 PM
Posted 25 May 2013 - 06:12 PM
I used to be able to see this group in an 8" scope from home, but light pollution in the last 2years has made them a dark sky option now for visual. My little video rig will now make this group a centre piece again,
Great thread this one! Has stirred up some good discussion & provoked some new outreach ideas with targets.
Posted 26 May 2013 - 12:41 AM
When asked "How far can that telescope see?" or the companion question, "How high a power can that telescope go?", I turn it into a bit of a telescope technology discussion by saying "Technically, all telescopes see to infinity and to infinite power. WHAT you can see is dependent on, first of all, the aperture which is how much information can come in. Then atmospherics, telescope technology, and other criteria play into the answer." Then specific examples follow, like ideal power per inch versus actual under real conditions, how even the Hubble can't get down to the resolution needed to see man's traces on the moon, maximum power capable on any scope at sea level, etc., always ending up with aperture and reality, and why their 10X50 binoculars can't see the flag on the moon, and why their 60mm refractor can't do 750X or spot every moon of Saturn or the entire Virgo cluster. But why portability can still bring the gorgeous star fields in context as great fields to sweep, and double stars, selected planetary nebulae, and even galaxies under the right circumstances are achievable with low to moderate cost (compare the cost of an 8" f/6 Newtonian on a dob mount with, say, same tube on an Atlas EQ-G). I usually have a crowd at the scope, so if one person asks, all are thinking the same thing so it's work the pause for a reality check versus the dime store scope boxes or Hubble pictures.
Posted 26 May 2013 - 02:01 PM
Posted 26 May 2013 - 02:52 PM
Posted 26 May 2013 - 03:21 PM
Posted 26 May 2013 - 06:07 PM
I use a 20 inch model of the MW to help with the scaling of things. I can point to the fact that Andromeda is twenty something MW diameters distant...and that at the scale of the MW model, the SS diameter out to Neptune's orbit is 1/2 of a millionth of an inch.
Long winded, but it gets to a lot of the themes that I like to address in public programs. Using a video display allows me to address a group and display some of the objects as the discussion progresses.
Posted 16 July 2013 - 09:10 AM
I will, however, try to figure out the farthest thing I have observed with a given telescope. What are the quasers that can be seen in smaller scopes?
Posted 16 July 2013 - 10:03 AM
The obvious one is 3C273 which is usually about mag. 12.5 (visible with 3" aperture under good conditions) and is approximately 2.4 x 10^9 light years distant ... that's approximately 1.4 x 10^22 miles. This number is somewhat hard to grasp but if you think of one mile for every grain of sand on all the beaches on Planet Earth you're somewhere in the right ballpark. Or, think of it another way: if there was a whacking great mirror on 3C273 and you had a hugely powerful telescope, if you looked in the mirror you'd still have to wait another 300 million years or so to see the reflection of the solar system forming.
What are the quasers that can be seen in smaller scopes?
Posted 16 July 2013 - 06:50 PM
The model is also good for putting the solar system in perspective, being a fraction of a micro inch.
It also helps to show visitors where the scope is pointed.
Posted 06 August 2013 - 03:58 PM
I tend to steer it into a resolution question. Ideally, you have a really sweet termination line on the moon, and then I start to talk about how when you drop a pebble into water, how you see the little "blip" in the middle from the water rebounding. I tell them that rock behaves the same during impact, and you can see the frozen remnants in the moon.
The first response is always "no way!", then I let them have a peek works every time! On very nice nights, Saturn works great too!
Sorry, just noticed the last comment was nearly a month ago, sorry to bring up an old topic!
Posted 24 August 2013 - 06:01 PM
Oversimplified, yes. But it works.