Learning aim B: Astronomical measurements and observations

Transcription

1 Learning aim B: Astronomical measurements and observations

2 Types of telescopes There are 2 different types of telescopes, each with their own advantages and disadvantages: Reflecting telescopes Refracting telescopes

3 Refracting use lenses Reflecting use mirrors

4 Reflecting telescopes (D) Newtonian reflector Cassegrain reflector Coude reflector

5 Where can we position telescopes? 1) On Earth Earth-based telescopes 2) In space space-based telescope

6 Earth-based telescopes Mauna Kea observatory in Hawaii

7 Earth-based telescopes Advantages Easy to fix and maintain. Cheaper 10 to 20 times cheaper than space telescope. Disadvantages Can only be used at night. Cannot be used in cloudy weather. They are limited by atmospheric conditions Earth s atmosphere absorbs much of the infrared and UV that passes through it.

8 Your turn Telescopes How many are there? Type of radiation detected Keck telescopes Very large baseline array James Clerk Maxwell telescope

9 Space-based telescopes The Hubble space telescope.

10 Space-based telescopes Advantages No atmospheric gases in space so the image is not distorted. Can observe near-infrared and UV that normally would be blocked by the atmosphere. Disadvantages Cost to operate. Cost to fix and upgrade. Cultural conflict. Can detect all parts of the EM spectrum.

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12 Telescope Section of EM spectrum detected Website Wilkinson Microwave Anisotropy Probe Microwaves James Webb Space Telescope Infrared james-webb-space-telescopecomplete-2018-launch.html Hubble Space Telescope Visible and ultraviolet es/hubble/story/index.html Chandra X-ray Observatory X-rays Fermi Gamma-ray Space Telescope Gamma rays mi-gamma-ray-space-telescope NOTE: These telescopes are ALL space based. YOU NEED AN IMAGE OF EACH AND TO WRITE A BRIEF DESCRIPTION ABOUT THE MISSION OF EACH TELESCOPE THIS NEEDS TO BE PRESENTED AS A POSTER!!

13 General mode of operation refracting telescope: A refracting telescope works bending light through a lens so that it forms an image. There are a few problems with refracting telescopes: some of the light reflects off the lens so the image is very faint large lenses are needed to improve the magnification this can be difficult to do perfectly.

14 General mode of operation reflecting telescope: In a reflecting telescope the image is formed by reflection from a curved mirror. It is then magnified by a secondary mirror.

15 Determining the focal length of a refracting telescope CONVERGING LENS 1. Set up the equipment. 2. Measure the distance u and write it in the table (THIS NUMBER WILL BE NEGATIVE). 3. Move the paper back and forward slowly until you see a sharp bright spot on the paper. The distance between the lens and the paper when the light is focussed is distance v (THIS NUMBER WILL BE POSITIVE). 4. Calculate 1/u (which will be negative) and 1/v. Once you have found those, calculate 1/f and then find f. 5. REPEAT 3 TIMES.

16 Determining the focal length of a refracting telescope DIVERGING LENS 1. Set up the equipment. 2. Move the paper towards to CONCAVE lens until you see a focussed bright spot. f 1 f 2 Measure this distance f1. 3. Move the paper away from the lens until you see another bright focussed spot and measure the distance f2. 4. Find 1/f1 and 1/f2 and then use the equation to find 1/F. 5. Then find F by doing 1/1/F. 6. REPEAT 3 TIMES.

17 Determining the prime focus of a CONCAVE mirror 1. Set up the equipment. 2. Measure the distance between the light sources and the mirror (this is o). 3. You will need 2 ray boxes, and a small piece of card. Move the card towards to CONCAVE mirror until you see a focussed bright spot. Measure this distance i. 4. Find 1/o and 1/i and then use the equation to find 1/f. 5. Then find f by doing 1/1/f. 6. REPEAT 3 TIMES. THESE NUMBERS WILL ALL BE NEGATIVE.

18 Determining the prime focus of a CONVEX mirror 1. Measure the radius of curvature of lens Divide this number by 2 to get the focal length. 3. Repeat 3 times for lens No try it with lens 2.

19 Effectiveness of mirrors over lenses LOOK IN YOUR BOOKLET HERE PAGE 13 has some general reasons why mirrors are better than lenses for LARGE telescopes. Mirrors are advantageous over lenses because they aren t affected by: 1) Spherical aberration 2) Chromatic aberration

20 Spherical aberration You must talk about: 1) What is meant by spherical aberration? (include the diagram to the left to aid your answer) 2) Why is it a problem? 3) What can we do to reduce its effects? Use this web link: at-is-spherical-aberration

21 Chromatic aberration You must talk about: 1) What is chromatic aberration? 2) What effect does it have on images? (You may want to include a diagram. Include my diagram (not the one in the booklet) and use this web link: Only talk about longitudinal chromatic aberration you don t need to use the word longitudinal though.

22 Moon phases You should have done this by the time you read this slide: You MUST have at least 7 drawings of the Moon including: The phase with a label (waxing gibbous etc.) The labelled constellations around each diagram. The labelled planets around each diagram. The location of the moon right ascension and declination

23 Moon phases: discussion and conclusion To get that distinction you must include results, discussion and improvements: What do your results conclude about the Moon s rotation? Are your results accurate and how do you know this? (Compare with others and astronomical data) Are your results reliable and how do you know this? What were the main sources of error? (Hint: visual aspects, inaccuracies of measurements, suitability of equipment for purpose). What could you do to improve the accuracy and reliability of your observations?

24 Right ascension and declination Comparable to latitude and longitude on Earth but in space. Tells you the position of the Moon, sunspots etc. in space.

25 Sunspots Your task: Observe sunspots over a 5 day period. We will project the Sun spots on to paper and then you can draw round them so they are to scale (scaled down of course). You will need to write down the RA and D of the sunspots and observe the same group of them everyday to show the Sun rotates about its axis. We will perform a calculation to find how long it takes for the Sun to rotate on its axis once.

26 Sun spots: discussion and conclusion To get that distinction you must include results, discussion and improvements: Did any spots appear to change size or shape? What did you notice about their positions over the days?(did other groups sunspots move the same amount over these four days?) If the Sun spots rotate by degrees every day, how long does it take the Sun to complete a complete rotation? Are your results accurate and how do you know this? (Compare with others and astronomical data) Are your results reliable and how do you know this? What were your main sources of error? (Hint: visual aspects, inaccuracies of measurements and suitability of equipment for purpose). How could you improve your results?