Observing Assignment 2 Casey Pidsadny Student # PHYS Jennifer West October 29, 2015

Transcription

1 Observing Assignment 2 Casey Pidsadny Student # PHYS Jennifer West October 29, 2015

2 Objective: To become familiar with the functionality of a telescope, practice locating objects in a telescope, and begin with the concept of field of view (FOV). Apparatus: Logbook & Pencil Watch and Timer (Smart Phone) Telescopes: Times in CDT Glenlea Ewen Time Start 20:22 20:00 Time End 21:06 20:30 Long. 97 7' '53 Lat '43" '41" Elevation 239m 239m Sunset 18:24 18:42 Sunrise 08:01 07:47 Moonset 01:37 19:14 Moonrise 16:01 08:19 Moon Phase 1 st quart. New Astro Twilight Ends 20:12 20:30 Clouds Clear Clear Transp. Average Poor Seeing Average Poor Temp. 7 C 5 C Wind SE 20km/h W 20km/h Celestron 8 Schmidt-Cassegrain Meade LX200 EMC 16 Schmidt-Cassegrain Focal Length 2032mm Focal Length 4064mm Focal Ratio f/10 Focal Ratio f/10 Finderscope 6x30 View Finder 8x50mm Telescope Type GOTO Optical Design ACF Highest Useful Magnification 480x Optical Coatings UHTC Lowest Useful Magnification 29x Pointing Precision ±1" Limiting Stellar Magnitude 14 Resolving Power (Dawes Limit) 0.28 Resolution (Rayleigh) 0.69 Colour Black Resolution (Dawes) Light Gathering Power (Compared to Human Eye) Optical Tube Length Optical Tube x 432mm Weight 5.9kg Mount Equitorial Method - Part 2 - Glenlea: Repeat the following observations for two different eyepieces with different focal lengths. A partner can do some of these if working in

3 groups. Group member: Tetyana D 1. Locate Altair in the telescope (declination: +8 55') 2. Observe its motion westward through the field of view. (Remember that the view of the telescope is flipped) 3. Adjust the declination of the telescope until Altair is directly in the centre of the field of view. 4. Have a timer ready. 5. Adjust the right ascension of the telescope so that Altair is just out of view through the eyepiece (East). Start timing when Altair first appears in the field of view and stop timing when Altair leaves the field of view in the West. 6. Record this time in seconds. Include an estimated error in this measurement 7. Repeat steps 5 and 6 two more times, for a total of three time measurements. Method - Part 3 - Ewen: 1. Use manual telescope controls to find Vega. 2. Use control panel to set this as the location of Vega in the telescope computer. 3. Performing steps 1 and 2 with Altair and Deneb will lead to a proper calibration of the telescope. 4. Now we can use the telescope catalogue to find objects; We can type in the object number and the telescope will automatically move to that object. 5. Find the ring nebula, M57, in the telescope object library and set the telescope to move their. 6. Sketch M57 and all stars within the field of view of the telescope and make a description of what was seen. 7. Estimate the field of view of the eyepiece based on the sketch and a reference star chart. Calculations: field of view = time*cos(declination Altair)*0.2507, where is the conversion rate from seconds to arcminutes. Declination of Altair: +8 55' = Average Time = (Time1 + Time2 + Time3)/3 Estimated error in time measurements = ±2s Adjusted Time = Time * cos( ) = Time * Error of FOV (based on timer error; use lower times) = ±0.49' Eyepiece 32mm 24mm Average Time 195.8s Adjusted Time FOV 48.49' 40.47' angular magnification = telescope focal length / eyepiece focal length Focal Length Magnification Celestron mm Eyepiece 1 & Celestron x Eyepiece 1 32mm Eyepiece 2 & Celestron x Eyepiece 2 24mm estimation of Ewen Telescope FOV = 1.1 = 66', based on the star count of sketch vs star count in Stellarium

4 Discussion: 1. Explain how one can use the drift time to calculate the FOV of an eyepiece. The drift time is time it takes an object to move across the fov of an eyepiece modified by an adjustment factor based on the declination of the observed object. If the object has a declination of exactly 0 0'0, then the drift time is simply the time it took to cross the fov of the eyepiece. In other, and most cases to get the drift time we would have to multiply the observed time by the cosine of the declination of the object. One can then calculate the fov (in arcminutes) by a simple formula. FOV = (drift time*0.2507), where is the conversion rate of seconds into arcminutes. For Example, if the observed (measured) time of the object going across the e yepiece is 195.8s and the declination of the object is +8 55' which equals Then we use the formula: FOV = (drift time*0.2507) = time * cos(declination Altair)* = 195.8*cos( )* = 48.49'. 2. How does the focal length of the eyepiece relate to the field of view? For a larger eyepiece focal length there would be a larger field of view. An eyepiece of focal length 32mm would have a field of view of 48.49'±0.49' and an eyepiece of focal length 24mm would have a field of view of 40.47'±0.49', according to the calculations made in Calculations. So, for a larger eyepiece, you would have a larger field of view. 3. What is the magnification of each eyepiece? The magnification of each eyepiece is calculated by taking the focal length of the telescope and dividing it by the focal length of the eyepiece. So, the magnification of the 32mm eyepiece is 2032mm/32mm which is 63.5x magnification and the magnification of the 24mm eyepiece is 2032mm/24mm which is 84.67x magnification. Conclusion: In summary, the field of view of the 32mm eyepiece is 48.49'±0.49' and the field of view of the 24mm eyepiece is 40.47'±0.49'. The observations and calculations went well with all values and concepts being consistent with each other. Errors could have occured in the accuracy of the timing of observing Altair drift across the field of view, as there is an uncertainty, errors could also be made with the sketches of M57 and the comparison of the sketch to a star chart because sketches cannot possibly be completely accurate. The objective was achieved and there were no inconsistencies.

5 References: Bishop R Optics and Observing: Telescope Parameters. Observer's Handbook 2015, ed. Chapman DMF. Toronto, ON, Canada: Royal Astronomical Society of Canada. 49 pp. Celestron LLC Advanced VX 8 Schmidt-Cassegrain Telescope. Torrance, Ca., USA: Celestron LLC. (Accessed 28 October 2015). Meade Instruments LX200 ACF 16 f10 - No Tripod. Irvine, Ca., USA: Meade Instruments. (Accessed 28 October 2015). Stellarium development team Stellarium Version [Computer program]. Available at stellarium.org (Accessed 29 October 2015).