1. Prepare your scantron: Fill in your name and fill the bubbles under your name. LAST NAME FIRST, First name second Put your 4-digit code instead of “ IDENTIFICATION NUMBER ”. --- (The last 4 digits of your OleMiss ID.) Question # 1: answer A Question # 2: answer B Question # 3: answer B Setup: Please take a moment to mute your cell phone! Use a pencil, not a pen! Recall reading assignment Chapter 6, pp. 165-189 (Telescopes)

2. Angular sizes How large is the Big Dipper? 25 0 apparent size Stretch out your hand: 1 cm = 1 o 25 o How large is the Moon? 1/2 0 apparent size 1/2 o = 30 am = 1800 as 0.5 o 1 o = 60 am (minute of arc) 1 am = 60 as (second of arc)

3. Resolution Resolution of the human eye is 1 am = 60 as Smallest visible detail is as small as this. Resolution of a simple telescope is ~ 1 as Much more detail is visible Stars are points in all telescopes: Calculated size of a star: ~ 0.001 as, Resolution of best telescope: ~ 0.1 as.

4. Alcor and Mizar The handle of the Big Dipper: the middle star is a double How far apart are they? 25 am 14 as Alcor Mizar A & B

5. Questions coming …

6. sec 45 Question 4 403530252019181716151413121110 9 8 7 6 5 4 3 2 1 0 Next question coming … 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.

7. sec 30 Question 5 29 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. 282726252423222120 19 181716151413121110 9 8 7 6 5 4 3 2 1 0 Next question coming …

8. sec 30 Question 6 29 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. 282726252423222120 19 181716151413121110 9 8 7 6 5 4 3 2 1 0 Next question coming …

9. sec 30 Question 7 29 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. 282726252423222120 19 181716151413121110 9 8 7 6 5 4 3 2 1 0

10. : air moves  stars jump around and twinkle 2 to 4 arc seconds in Mississippi 1 arc second in good location 0.1 arc second on Mauna Kea, Hawaii Size of “ seeing ” Seeing Seeing limits magnification to a few hundred at best Look at a double star in good and in bad weather: Bad seeing Good seeing

11. Practical limits Practical limits on magnification Atmosphere limits resolution to “ seeing ” (0.5 as to 2 as): magnification 30 - 120 x already brings out all the detail there is for convenience, 200 - 300 x is used in really stable weather The telescope ’ s optics limits resolution to 12 as / D[cm] (D is diameter of telescope) for very small telescopes max magnification is: 5-10 times D example: D=3 cm (small binoculars) - at most 15-30 x What is a pair of 6 x 30 binoculars? 6 x magnification 30 mm = 3 cm diameter A small but acceptable telescope What is a 2-inch diameter telescope with magnification 350 x ? 350 x magnification 5 cm diameter Resolution: 2.4 as Blur is 350 x 2.4 as = 840 as = 14 am A scam!

12. Magnification computed M = f objective /f eyepiece Example: Meade, diameter = 12 inches, f obj = 3048 mm Resolution:0.4 as (optical) 1-2 as atmospheric With f=26 mm eyepiece, M = 117 x With f=10 mm eyepiece, M = 305 x With f = 4 mm eyepiece, M = 762 x Which ones make sense?

13. Smallest detail Moon The smallest detail we can see on the Moon Resolution limit (atmospheric) 0.5 as at very best Moon is 0.5 o = 30 am = 1800 as in diameter 1800 as/0.5 as = 3600 counts of the smallest detail fits in one line on the Moon Moon is 3476 km, so 3476 km / 3600  1 km. Anything smaller than a km is blurred. 1 mile wide

14. Questions coming …

15. sec 30 Question 8 29 What is seeing? A The amount of air starlight passes through to reach our eyes. B The diameter of the blur caused by the atmosphere. C The amount of light passing through the atmosphere. D The brightness of a star as it appears to us in the sky. 282726252423222120 19 181716151413121110 9 8 7 6 5 4 3 2 1 0 Next question coming …

16. sec 30 Question 9 29 Which of the following limits the magnification of all but the smallest telescopes? A Optical effects. B Quality of the lens/mirror. C Seeing. D The shaking of the telescope mount. E Inaccurate tracking. 282726252423222120 19 181716151413121110 9 8 7 6 5 4 3 2 1 0 Next question coming …

17. sec 30 Question 10 29 What is an 8 x 50 pair of binoculars? A Diameter = 8 cm, magnification = 50 x. B Length = 8 cm, magnification = 50 x. C Magnification = 8 x, diameter = 50 mm. D Magnification 8 x, length 50 cm. E One that cost $50 but is only worth $8. 282726252423222120 19 181716151413121110 9 8 7 6 5 4 3 2 1 0 Next question coming …

18. sec 30 Question 11 29 How small is the smallest detail we can still discern on the Moon with a very good telescope? A 100 miles. B 1 mile. C 10 feet. D 1 foot. E 1 inch. 282726252423222120 19 181716151413121110 9 8 7 6 5 4 3 2 1 0 Next question coming …

19. sec 30 Question 12 29 The large refractor in Kennon observatory is 15 inches in diameter, and the focal length of the objective is 15 feet. What is the magnification with a 1-inch (=25 mm) eyepiece? A 12 x B 15 x C 180 x D 3,000 x E 30,000x 282726252423222120 19 181716151413121110 9 8 7 6 5 4 3 2 1 0