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 (Telescopes)

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)

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: ~ as, Resolution of best telescope: ~ 0.1 as.

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

Questions coming …

sec 45 Question 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.

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 Next question coming …

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 Next question coming …

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

: 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

Practical limits Practical limits on magnification Atmosphere limits resolution to “ seeing ” (0.5 as to 2 as): magnification x already brings out all the detail there is for convenience, 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 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!

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?

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

Questions coming …

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 Next question coming …

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 Next question coming …

sec 30 Question 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 $ Next question coming …

sec 30 Question 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 30 Question 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