Amateur Meteor Observing

An invited talk for the Irish Astronomical Association,
given ahead of the 2011 Draconids meteor outburst,
5 October 2011, Belfast.

Transcript

3. What are meteor(oid)(ite)s?
4. video!
5. Meteoroid – a solid object moving in interplanetary space, of a size considerably smaller than an asteroid and considerably larger than an atom or molecule. Definition by the International Astronomical Union (1961) (i.e. the stuff between ~0.01 mm and 10 m in size) (Jenniskens, 2006)
6. Who cares about meteor(oid)s?!
10. Kinetic energy = ½ · mass · velocity2 Getting hit by a 2000 kg car at 50 mph: E = ½ · 2000 kg · (22 m/s)2 = ~500 000 Joule Getting hit by a 0.5 g meteoroid at 100 000 mph: E = ½ · 0.0005 kg · (45 000 m/s)2 = ~500 000 Joule
11. Where do meteoroids come from?
12. Comet 103P/Hartley (NASA image, 2010) Surface charcoal-like dust; reflects just 4% of light Jets of sublimating ices 79% H2 O, 13% CO, 3% H2 CO, 3% CO2 Dust particles most likely dragged along by jets; pushed to slightly different orbits. (video)
13. Are comets mostly made of ice or dust?! Density of water ice: ~1.0 g/cm3 Density of silicate rock: ~3.5 g/cm3
14. (Jenniskens 2006) Comets must be very porous; perhaps containing caves and voids („rubble pile model“) Possible explanation for jets: 1) Outgassing spins up nucleus 2) Centrifugal forces expose 'cracks' of fresh ices
16. When do we see them?
17. „The south gets the pretty deep-sky objects, but we get all the big meteor showers!“ (Jenniskens, 1994) Southern Hemisphere Northern Hemisphere Meteor activity through the year
18. Shower meteors move on parallel paths! „Radiant point“
19. What we thought meteoroid streams looked like before powerful computers ...
20. Dust trails from comet Churyumov-Gerasimenko (model: Jeremie Vaubaillon) What meteoroid streams really look like! Key insights: 1) Comet trajectories change every revolution (slightly or dramatic) 2) Trails can remain narrow for decades to centuries (dispersion due to gravity and radiation pressure often a slow process!)
21. 10P/Tempel 2 7P/Pons-Winnecke 2P/Encke (IRAS, 1983; Mark Sykes, William Reach)
22. (Arlt & Barentsen, 2006) Leonids 2006 Alpha-Aurigids 2007 Dust trails regularly produce ~1-hour outbursts! Time Meteor rate Meteor rate Increase in the meteor rate by a factor x2 to x10, but sometimes x1000!
23. Need continuous and worldwide observations; only possible with support from „citizen scientists“ Perseids 2009
24. Observing projects 1) Using your 'naked' eyes 2) Using a video camera
25. watching vs observing personal definition observing: recording data in a manner suitable for objective analysis (PS: There is nothing wrong with watching!)
27. Fast-readout chip Human eye Resolution 1 ~ 2 megapixel 120 megarod Sensitivity @ 50 fps 10-6 ~ 10-7 lux (1 - 4th magnitude) 10-8 lux (6th magnitude) Dynamic range 1 : 1 000 ~1 : 1 000 000 000 (delay) Why use our eyes when we have video cameras?! Answer: the human eye is incredibly sensitive to faint, fast-moving objects!
28. Visual observing • Be comfortable - monitor the sky without interruption! • Camping bed, water-proof sleeping bag, hat ... • Watch • Tape recorder (or pencil + paper) • Backup batteries and tapes • Plenty of chocolate, but avoid alcohol!
29. At the start • Record your details in such a way that they can easily be understood "in 20 years from now" • Your full name and location • Date (e.g. "Night from 8 to 9 October 2011") • Timezone used (!) • Meteor showers you will classify • Starting time of the observation
30. Interval counting In intervals of 5 to 30 minutes (~10 meteors), we need to know: 1) Sky quality ("limiting magnitude") 2) Number of meteors per shower 3) Brightness of each meteor (optional) For example: 20:04 - 20:12 UT Limiting magnitude = 5.2 2 Draconids (mag. 1 & mag. 3) 1 Sporadic (mag. 4)
31. 1. Count the number of stars in one of the 'reference fields' (include corner stars) 2. Look up the corresponding Limiting Magnitude (Lm) in the tables at www.imo.net Stars in field #14 Limiting magnitude 1 2.23 2 2.49 3 3.90 4 4.65 5 4.73 ... ... 1. Estimate the sky quality Your count needs to be independent, do not be influenced by colleagues!
33. 2. Number of meteors per shower Classify each meteor by shower. Take into account: 1) Direction Must appear to come from within ~20 degrees of radiant 2) Length meteors near the radiant must be short 3) Speed Draconids are very slow! Note: 5 to 15 meteors per hour do not belong to any known shower; we classify these as „sporadic“.
34. Which showers to consider? Handy „working list“ at http://www.imo.net/calendar/2011
35. 3. Brightness of each meteor Compare each meteor to reference objects, e.g.: Make a best-effort estimate - do not be afraid to be wrong, and do not listen to your colleagues! Object Magnitude Full Moon - 13m Jupiter -3m Sirius -1.5m Vega 0m Aldebaran 1m Polaris 2m
36. http://www.imo.net/visual/report
37. Time observed in hours (e.g. 15 minutes = 0.25 hours) Cloud correction (no clouds = 1.00)
38. Magnitude distributions
39. Automated analysis at http://www.imo.net We encourage observers to report data directly to the IMO as well as to their local group(s)
40. Never worry about your rates, just report what you see! By averaging data from hundreds of observers, we obtain the meteor rate as seen by the average human under average conditions
42. Perseids 2009 - visual counts
44. Camera (200-300 GBP), + lens (10-50 GBP) + video capture card (50 GBP) + old PC. SONY „ExView“ chips
45. IMO MetRec Software - www.metrec.org
47. So what about the Draconids meteor shower?
48. (Credit: David Asher) Period = 6.6 yr
49. 21P/Giacobini-Zinner 2011 July 3rd; magnitude 19.1
50. (Credit: David Asher) The history of the comet's orbit is uncertain due to interactions with Jupiter!
51. October 8, 6-9 pm BST Draconids: Saturday 8 October Model by Jeremie Vaubaillon / IMCCE Paris video
52. 1933 1946 2011 +10 000/hr !
53. Rev. W. F. A. Ellison (Armagh Observatory) Belfast Telegraph, 11 October 1933. "Just before 7 pm, I observed a brilliant meteor drop from the constellation Lyra. Five minutes later I counted a dozen meteors during the few minutes occupied in walking up the Observatory avenue. Between 7 and 7-35 pm I counted 300 meteors. ... Called indoors for the evening meal at 7-35. I was out again at 7-58. Then it was apparent that a really great meteoric storm was in progress. I counted 200 meteors in two minutes, and then counting became impossible. The fire- stars became as thick as the flakes of a snowstorm.“ This event was followed by another major outburst in 1946 (Ellison died 1936), and smaller peaks in 1952 (250/hr), 1985 (550/hr) and 1998 (500/hr).
55. Trail (year) Encounter (2011 October 8) 1880 17:31 BST 1887 18:00 BST 1894 19:03 BST 1900 21:11 BST Predictions for 2011 by multiple scientists agree with respect to the timing (Credit: Watanabe & Sato, Vaubaillon, Maslov, Cooke & Moser, et al.) Confirmation by David Asher: Uncertain (comet not observed). Meteors might be bright. Trail known to exist, ZHR 60-600? Meteors likely faint. Solar altitude Time 0 (Sunset) 18:45 BST -6 (Civil) 19:23 BST -12 (Nautical) 20:03 BST -18 (Astronomical) 20:45 BST Darkness in Armagh:
56. NASA Meteoroid Environment Office (Times in UT)
58. How many meteors can we really expect?
59. ZHR = 60 - 600 meteors/hr ZHR: „Zenithal Hourly Rate“ Assumes perfect sky: 1) Radiant in zenith 2) Limiting magnitude = 6.5
60. Radiant at zenith Radiant at horizon Good news: radiant at 80 degrees altitude! => only ~2% of meteors lost due to this effect. Our atmosphere is thin!
61. # meteors of magnitude < m # meteors of magnitude < m+1 = population index r # m < 3.5 # m < 6.5 = r^3 = 3^3 = 27 Worst case: Draconids r = 3.0 (uncertain) and Limiting Mag. = 3.5; We would only see 1 out of every 27 meteors! (ZHR 600 => 22 ) Magnitude Meteors 0 1 2 3 4 5 6 x r x r x r x r x r x r „power-law“ Sky quality
62. Reasons for optimism 1) We encounter the *very same* dust trails which caused the major storms in 1933 & 1946! 2) The 1933 & 1946 storms ALSO took place under a full moon! ... but, the trail is more dispersed now! (how much?!)
63. Many uncertainties • What really was the level in 1933 & 1946? • Where was the comet before its discovery in 1900? • When did it lose most material? • How did the dust spread out? • Does the stream contain large grains? This meteor shower will teach us about the comet and the likelihood of future outbursts! (e.g. 2018, 2037) Two aircrafts will be deployed! (Vaubaillon et al.)
64. „Fireballs as bright as Venus or Jupiter, and occasionally much brighter appeared in a momentary splendour. These exceptional objects had long luminous trains which lasted for a few seconds after the meteor had vanished. Also the character of their light was very bright, diamond- like, and sparkling.“ Let's hope for 1 or 2 beautiful fireballs, and be happy with any extras! 1933 Belfast Telegraph:
66. (Pete Gural) Lunar „flashes“ 1 to 2 hours after main peak?
68. Backup slides
69. Scientific observations produce scientific minds!
70. (Verbelen, 2008) Radio observing Time Frequency