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 A Setup: Please take a moment to mute your cell phone! Use a pencil, not a pen! P/f coming – next Tuesday + Lunar eclipse – Sept. 27 (Sun) Recall reading assignment Chapter 6, pp. 165-190 (Telescopes)

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

3. 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 This question counts double!

4. : 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

5. 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!

6. 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?

7. 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

8. Questions coming …

9. sec 30 Question 6 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 …

10. sec 30 Question 7 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 …

11. sec 30 Question 8 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 …

12. sec 30 Question 9 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 …

13. sec 30 Question 10 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

14. Must put telescope on a mount that follows the daily motion of stars ( “ tracking ” ): Equatorial mount (one axis points at the North Star) What do you think the most expensive part of an amateur/professional telescope is? The optics (lens/mirror - needs to be as precisely manufactured as 0.00001 inch!)? The mount? The observatory (building and dome)? The light detectors that register and analyze the light? Must put the telescope in a dome to protect from bad weather stray light - light pollution kills astronomy Mounts and observatories

15. Mt. Palomar Mt. Palomar Observatory California Diameter: 200 in (Length of tube: 16 yards) Observer in cage Main mirror

16. Adaptive optics How do you fight seeing? (1) Put your observatory on a mountaintop: seeing at best: ~ 0.4 as (2) Use adaptive optics: seeing at best: ~ 0.05 as Deform your mirror to compensate for seeing Observe a “ guide ” star and have a computer tell how to deform mirror Do this ~ 100 times each second No guide star? Make one!

17. The Hubble (3) Put your telescope on a spaceship: seeing: 0 as Hubble Space Telescope is a “ small ” telescope Diameter: 2 m; resolution: 0.06 as More discoveries than all other telescopes combined. How do you fight seeing?

18. Hubble M101

19. MAUNAKEAMAUNAKEA MaunaKeaMaunaKea

20. Questions coming …

21. sec 45 Question 11 403530252019181716151413121110 9 8 7 6 5 4 3 2 1 0 Next question coming … What is an equatorial mount? A A design of the telescope ’ s mechanics that allows tracking stars in the sky. One axis points at Zenith (that is, straight up). B A design of the telescope ’ s mechanics that allows tracking stars in the sky. One axis points at the North Pole. C A scientific term that explains the motion of stars in the sky. D A design of a telescope ’ s optics with a mirror to collect the light. E A design of a telescope ’ s optics with a lens to collect the light.

22. sec 45 Question 12 403530252019181716151413121110 9 8 7 6 5 4 3 2 1 0 Next question coming … Why does the Hubble Telescope make very detailed images? A Because it has the largest diameter of all telescopes. B Because it is of exceptionally good quality. C Because it is in space where the atmosphere does not blur the image. D Because it can use infrared radiation that other telescopes cannot. E Because it is in space, closer to the stars than other telescopes.

23. sec 45 Question 13 403530252019181716151413121110 9 8 7 6 5 4 3 2 1 0 What is adaptive optics? A When the telescope follows the stars as they move in the sky. B When some of the telescope ’ s lens or mirror is covered according to changes in the atmosphere. C When the shape of the optics is changed according to the changes in the atmosphere. D When appropriate color filters are used as the atmosphere absorbs more or less red or blue light. E When the magnification of the telescope is chosen according to how turbulent the atmosphere is on the day of the observation.