Observational Astronomy Laboratory PHSC 1051/3051

1. Observational Astronomy LaboratoryPHSC 1051/3051 • #4 McEver Hall (across from the BIG fish tank) • Course Information and Lecture Notes can be found at http://cosmos.atu.edu/bigjay • Then Go To ATU Courses (PHSC1051/3051) http://pls.atu.edu/physci/physics/people/psjr/courses/ • Find and Browse the ATU Observatory Web Site http://cosmos.atu.edu/observatory

2. Astronomical Resources • Magazines • Sky & Telescope http://www.skypub.com • Astronomy http://www.kalmbach.com/astro/astronomy.com • Observing Books • Norton’s Sky Atlas ISBN 0-582-31283-3 • Burnham’s Celestial Handbook ISBN 0-486-24064-9 • 365 Starry Nights ISBN 0-13-920570-5 • Sky Calendars and Events • Star Date http://stardate.utexas.edu • Abram’s Planetarium http://www.pa.msu.edu/abrams/ • http://www.skypub.com/sights/skyevents/skyevents.shtml

3. Excerpt from SkyWatchers Diary Tuesday, August 29 A small, faint constellation in this evening's sky is Corona Borealis, the Northern Crown. One and a half hours after sunset find two bright stars: Arcturus, a third of the way up in the west, and Vega, overhead. One- third of the way from Arcturus toward Vega look for a semi-circular pattern of faint stars, reminiscent of a laurel wreath crown.

4. Star Atlases • Norton’s 2000 Star Atlas and Reference Handbook • Uranometria Vol. 1, 2 & Deep Sky • Sky Atlas 2000 http://www.skypub.com/store/sa2000polakis.html http://www.icstars.com/HTML/AmazonBooks/books_staratlas.html

5. Celestial Navigation • Constellation Atlas http://www.slivoski.com/astronomy/ • Creating Star Charts 101 http://skyview.gsfc.nasa.gov/skyview.html • The Star Finder • match current time with the date • face south • place south on the map at your belly • look down at the map • now swing the map overhead • look up at the map • the map is the sky in 360o

6. Celestron C8’s • Celestron 101 http://www.celestron.com/tb-2ref.htm • Celestron 8 inch reflectors • C8 Schmidt-Cassegrain

7. Meade LX 200 12-inch • Meade 12 inch reflector • LX200 Schmidt-Cassegrain

8. James Clarke Telescope • Custom Telescope • 16 inch newtonian or cassegrain reflector

9. Optica Reflectors • Optica Telescopes • 6 inch newtonian reflectors

10. Newtonian 8-inch • Custom Telescope • 8 inch newtonian reflector

11. Refracting and Reflecting Telescopes

12. Refractor Focal Length

13. Chromatic Aberration

14. Reflector Focal Length

15. Telescope Configurations

16. f-number (f/#) The f/# refers to the ratio of the focal length to the diameter. An f/10 optical system would have a focal length 10 X bigger than its diameter. The f/10 celestron C8 has a focal length of 80 inches. (8 inch aperture times 10) Our 16 inch telescope in the newtonian f/4 configuration has a focal length of 64 inches (16 x 4).

17. Magnification Magnification depends on the ratio of the focal lengths for the primary aperture to the eyepiece. M = focal length of objective / focal length of eyepiece = fo/fe Therefore for the same eyepiece, in general, the telescope with the longest focal length can achieve the greater magnification.

18. Magnification Isn’t Everything Magnifying something spreads the light out into a larger and larger area. An object is only so bright and magnifying an image too much causes it to become so diffuse that it ceases to be visible. Magnifying power for a telescope is not what you are looking for. Besides, increased magnification can be achieved by changing eyepieces. What do you want in a telescope?

19. Bigger Light Bucket

20. Light Gathering Power Light Gathering Power Telescope diameter (D) Light Gathering Power (LGP) is proportional to area. LGP = p (D/2)2 D = diameter

21. Light Gathering Power Light Gathering Power Telescope diameter (D) Light Gathering Power (LGP) is proportional to area. LGP = p (D/2)2 D = diameter A 16 inch telescope has 4 X the LGP of an 8 inch. LGP 16 inch = p (16/2)2 LGP16/LGP8 = 4 LGP 8 inch = p (8/2)2 A 16 inch telescope has 2800 X the LGP of the eye. LGP 16 inch/LGP eye (0.3inch) = (16/0.3)2 = 2844

22. Size Does Matter Same magnification, different telescope primary apertures. Which telescope is bigger?

23. Resolution

24. Resolving Power Telescope diameter = D (cm) Resolution = a (arcminutes) a = 11.6/D Larger D = smaller angular sizes resolved

25. Clock Drive Last but NOT least. You and telescopes are on the moving observatory we call earth. A clock drive is required to counter earth’s rotation and provide tracking for telescopes and cameras.

26. Night Vision It takes nearly 15 minutes for your eyes to make adjustments to see in low light levels. WHY? First, your pupil dilates. This allows more light to be collected by your eye. When it is really dark out, your pupil opens up and lets you see things that were too faint to see when you first walked outside. Even more important to night vision is a chemical called rhodopsin. You've probably heard that human eyes have rods and cones. The cones help you see color, and the rods help you see when it gets dark.

27. Sensitivity Curve For approximately the first 10 minutes in the dark, the cones require less light to reach a threshold response than do the rods. Thereafter, the rods require less light. The point at which the rods become more sensitive is called the rod-cone break. It is after this break where you can start to really see detail well in the dark.

28. Photopigments Our visual system is most sensitive when the photopigments have not absorbed any light for about 30 minutes. Under these conditions we say that the photopigments are fully regenerated. When the rod photopigments are exposed to light they undergo a process called bleaching. It is called bleaching because the photopigment color actually becomes almost transparent. In the dark they regenerate and regain their pigmentation again. In the rod receptors the unbleached photopigments appears purple. The technical name for the rod photopigment is rhodopsin. The photopigments in the cones also bleach when exposed to light. There are three classes of cone photopigments (RGB). Each class is photochemically a little different than the other and therefore their spectral absorbencies are different.

29. Bleaching (After Image) Demo Concentrate on the black checkerboard for at least 20 seconds. Your pigments become bleached. Afterwards you will see an inverse image in the box at the right. And just what are those illusionary gray dots at the white cross intersections?!

30. Microspectrophotometry Bowmaker & Dartnall (1980) projected a known amount of light directly through the outer segments of photoreceptors and measured how much light was absorbed by the photopigment molecules at each wavelength.

31. RGB and Grey Photopigments The wavelength of maximum absorbance is indicated at the top of each curve. The 420 nm curve is for the short wavelength cones, the 498 nm curve is for the rods, and the 534 nm and 564 nm curves are for the middle and long wavelength sensitive cones respectively.

32. Night Vision The rhodopsin is in the rods. It takes 15 minutes or more for the rhodopsin to get back to a good level after you look at white light. But, because this chemical is not as sensitive to dim light, the good astronomer carries a dimmed or reddened flashlight instead of a bright one. This allows them to look at their star chart and find the next object. When they look back up at the stars, their night vision is still good. The smart astronomer doesn't have to wait after looking at the chart. Why? Because smart astronomers use dim red flashlights!

33. Advanced Red Flashlight Project

34. Red LED Flashlight Project RadioShack and ~ $7.00 • one project case • bright LED and holder (LED1) another LED and holder (LED2) • a 22 ohm resistor (R1) • a 47 ohm resistor (R2) • one AAA battery holder • two AAA batteries • two switches

35. Averted Vision Rods are actually densest outside the central 1-degree foveolar area. Since the rods have a lower threshold than the cones, they are much more sensitive at low light levels. A person attempting to see in light dimmer than moonlight, has to depend entirely on their rods. To best detect small targets with the rods under such circumstances, the individual must look approximately 15-20 degrees to one side, above, or below an object to place the object of interest on the part of the retina that possesses the highest density of rods.

36. Blind Spot Note the almost complete absence of rods on the fovea. The fovea is that position on the retina where the best focus of the eye is located. This and the optic nerve bundle give humans a day and night blind spot.

37. Blind Spot Demo I Close your right eye. With your left eye look at the on the right. At the correct distance the will disappear.

38. Blind Spot Demo II Close your right eye. With your left eye look at the red dot At the correct distance the gap in the blue lines will disappear.