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 (Telescopes)

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 Next question coming … This question counts double!

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 This question counts double!

: 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 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 Next question coming …

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 Next question coming …

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 $ Next question coming …

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 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

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 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

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

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!

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?

Hubble M101

MAUNAKEAMAUNAKEA MaunaKeaMaunaKea

Questions coming …

sec 45 Question 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.

sec 45 Question 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.

sec 45 Question 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.