Astronomical telescopes How do they work? Use eyepiece to watch image Refractor: Lens collects light Use eyepiece to watch image Reflector: Mirror collects light 2”-5” toy 6”-30” amateur 3’-10’ professional 10’-33’ super Large lens/mirror collects much light - the diameter of the telescope is the important indicator!
Why do we need telescopes? To collect much light - need large diameter To make small objects look large - need magnification Limits to light collection: Diameter ~ 10 m (30 feet) will be too heavy to hold Limits to magnification: “Seeing” - stars jump around (related to twinkling) - caused by air turbulence little light Notice: all stars twinkle but planets twinkle less - why? Answer: planets are disks in a telescope, but stars are always points much light
Questions coming …
sec 10 9 11 12 15 14 13 8 7 1 2 3 5 4 6 16 26 17 27 28 30 29 24 25 23 19 18 20 21 22 Question 9 Which of the following is the most important measure of a telescope? A The magnification. B The diameter of its mirror (or lens). C The focal length of its mirror (or lens). D The length of the telescope. E The distance of the farthest object it can see. Next question coming …
sec 10 9 11 12 15 14 13 8 7 1 2 3 5 4 6 16 26 17 27 28 30 29 24 25 23 19 18 20 21 22 Question 10 The largest telescope we have at Ole Miss is 15 inches. What category is that? A Large professional. B Average professional. C A decent amateur size. D A small amateur size. E Uselessly small for astronomy. Next question coming …
How large is the Big Dipper? Angular sizes How large is the Big Dipper? 250 apparent size Stretch out your hand: 1 cm = 1o 25o 1o = 60 am (minute of arc) 1 am = 60 as (second of arc) How large is the Moon? 1/2 0 apparent size 1/2o = 30 am = 1800 as 0.5o
Much more detail is visible Resolution Resolution of the human eye is 1 am = 60 as Smallest visible detail is as small as this. Stars are points in all telescopes: Calculated size of a star: ~ 0.001 as, Resolution of best telescope: ~ 0.1 as. Much more detail is visible Resolution of a simple telescope is ~ 1 as
The handle of the Big Dipper: the middle star is a double Alcor and Mizar Alcor 25 am 25 am Mizar A & B 14 as The handle of the Big Dipper: the middle star is a double How far apart are they? 25 am
Questions coming …
sec 8 9 10 12 11 7 6 1 2 3 4 13 30 35 40 45 14 25 16 15 18 17 19 20 5 Question 11 How do stars look in the largest telescope of the world? A They look like large disks and we can see a lot of detail on them. B They look like large disks but there is not much detail to see, although telescopes would have been able the resolve the details. C They look like tiny disks but few or no details can be seen on them. D They look like points (no details visible). E They look like “star-shaped” objects with rays emanating from them. Next question coming …
sec 10 9 11 12 15 14 13 8 7 1 2 3 5 4 6 16 26 17 27 28 30 29 24 25 23 19 18 20 21 22 Question 12 How large does the Moon appear in the sky? A A few inches. B A few thousand miles. C A few arc seconds. D A light year. E A half a degree. Next question coming …
sec 10 9 11 12 15 14 13 8 7 1 2 3 5 4 6 16 26 17 27 28 30 29 24 25 23 19 18 20 21 22 Question 13 How large is the Big Dipper? A A few miles. B A few light years. C Five million light years. D More than twenty degrees. E A half a degree. Next question coming …
sec 10 9 11 13 14 8 12 7 2 1 3 4 6 5 15 17 26 25 27 28 30 29 16 24 19 18 23 20 22 21 Question 14 The two stars Alcor and Mizar are easily separated by the human eye. This means that they must be farther apart than … A a few degrees B one arc minute. C a few light years. D a few million kilometers. E a million light years.