Recall reading assignment: Prepare your scantron: Use a pencil, not a pen! 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 C Question # 3: answer B Setup: Recall reading assignment: Chapter 6 (Telescopes) pp. 165 – 189 Test 2 on Wednesday! Please take a moment to mute your cell phone!

Review questions coming …

This question counts double! sec 10 9 11 13 14 8 12 6 2 1 3 4 15 5 7 16 26 17 27 28 30 29 24 25 23 19 18 20 21 22 Question 4 Which of the following is the most important measure of a telescope? A The magnification. B The distance of the farthest object it can see. C The focal length of its mirror (or lens). D The length of the telescope. E The diameter of its mirror (or lens). Next question coming …

This question counts double! sec 10 9 11 13 14 8 12 6 2 1 3 4 15 5 7 16 26 17 27 28 30 29 24 25 23 19 18 20 21 22 Question 5 How large is a small research telescope? A 2-3000 magnification. B 5-10 meters in length. C 1-2 meters in diameter. D 10 centimeters in diameter. E At least 10 meters in length. Next question coming …

This question counts double! sec 8 9 11 7 10 4 1 2 3 13 6 12 25 30 35 40 14 19 16 15 17 18 45 20 5 Question 6 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 …

This question counts double! sec 10 9 11 13 14 8 12 6 2 1 3 4 15 5 7 16 26 25 27 28 30 29 17 24 19 18 23 20 22 21 Question 7 How much is the resolution of a telescope? A a few degrees. B ½ to 2 arc seconds. C a few light years. D a few million kilometers. E a million light years.

Seeing : 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 limits magnification to a few hundred at best Look at a double star in good and in bad weather: Good seeing Bad seeing

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 Practical limits 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 A scam! Resolution: 2.4 as Blur is 350 x 2.4 as = 840 as = 14 am

Magnification computed M = fobjective/feyepiece Example: Meade, diameter = 12 inches, fobj = 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?

The smallest detail we can see on the Moon Smallest detail Moon The smallest detail we can see on the Moon 1 mile wide Resolution limit (atmospheric) 0.5 as at very best Moon is 0.5o = 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.

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 8 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. 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 9 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. 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 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. 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 11 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. 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 12 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

Mounts and observatories 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 Must put telescope on a mount that follows the daily motion of stars (“tracking”): Equatorial mount (one axis points at the North Star)

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

How do you fight seeing? Adaptive optics (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!

How do you fight seeing? (3) Put your telescope on a spaceship: 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.

Hubble M101

Mauna Kea M A U N K E

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 13 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. Next question 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 14 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. Next question 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 15 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.