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Program developed by Mississippi Valley Conservation Authority

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1 IV Spring 2012 Astronomy Course Mississippi Valley Night Sky Conservation The Sky Around Us
Program developed by Mississippi Valley Conservation Authority Royal Astronomical Society of Canada Ottawa Astronomy Friends Instructors: Pat Browne Stephen Collie Rick Scholes Course Assistant: Amy Booth Special Treat: AstroPhotography Presentation,Sanjeev Sivalvurasa … Agenda – Nightsky Around us = Moonlight Lecture/Observations Field trip to FLO – weather permitting Earth Centered Universe software for illustrations – courtesy David Lane

2 Review Last Week III Sky Around Us
The Sky around us … stars Stellar evolution and distances via Absolute magnitude and stellar spectra on the main sequence Lunar Study – Courtesy Stephen Collie Followed by Lunar and Double Star Observing – ‘Running a telescope’ using the red dot, the finder and the main eyepieces (at different magnifications) Doubles – Polaris, Castor, ,Algeib Alkaid Follow the Arc to Arcturus and Speed on to Spica… (diagram courtesy Helen Sawyer Hogg).

3 Lunar Exercise – How To…
Lunar Certificate program provides a handle on how to study the moon Observing out the Summer Kitchen … or on the Balcony

4 First Experience really observing the moon. Location: ‘Summer Kitchen’ – peering out at the first quarter moon… just a peak Equipment: 6” F8 Dobsonian using a 24 to 8mm zoom eyepiece providing 60 to 120 power Camera and sketch activity. I was really taken by the southern pole at first quarter, the deep brooding shadows with little detail and all shadow. This will be hard to identify. So I did look at the overall view – for this I needed to switch to the 40 mm (30 x) eyepiece so that the exit pupil of light going into the camera made a complete and easy shot. Hint – Full view with camera – use low power

5 Points to Ponder 1 On Earth as in Heaven…
Responsible Lighting is ECONOMIC Uniformity of lighting in the town  3:1 Illuminance level in urban areas. Maintain and standardize on minimum wattage levels to do the job. Luminaire Saving: Pole Spacing standardize and maintain schedules: from 3:1 to 10:1 based on usage (traffic, residential,etc) Economic Saving: Cost considerations  lower wattage, well-placed poles: .043$/kwh*10h* (.2kw) *365d* 20years = $628/pole Reducing wattage from 200W  100W saves the town $315/luminaire over 20 years For 1000 lamps (now)  = $ over 20 years in reduced wattage

6 In a nutshell… Uniformity – work to the minimum difference in lighting level Lower Wattage – work to the lowest specified lighting level according to IESNA standards… i.e. 1.2 FootCandles for road surfaces Pole Spacing increase on roadways with less traffic – reduces Pole Count of luminaires Reduce Wattage and save Energy Costs From 200 -> 100 W Smart Lighting - extinguish when not being used Light the Surface not the underbellies of aircraft

7 Points to Ponder - II Lunar and Planetary
Planetary and Lunar: Why do we use the temperature units – Degrees Kelvin ? 0 Deg Celsius = 273 . Handy, units are scaled the same – just a larger offset to work with Why is the moon a sphere rather than the more irregular shape of an asteroid ? Roche Limit: The critical distance between a planet and its satellite below which, the satellite is broken up by tidal forces. In our case, the moon is not broken up by tidal forces because it orbits outside of Earths Roche Limit. L =2.5 Earths Radius ~ 16000km Moon’s distance 365,447 km . It is also held together by self-gravitation – that makes it spherical as gravity and hydrostatic pressure shape the body as a sphere. However, When the orbit decays, to within the Roche limit, it would have to have enough self-cohesive strength to resist tidal breakup. As the sample exercise shows, bodies within the Roche limit (like people) are typically not spherical, but irregularly shaped. It is only if self-gravitation dominates over internal cohesive forces (tensile strength) that the body is spherical. This implies a density (kg/m^3) , a tensile strength of material (Kn/m^2) in order to define a critical radius. Small satellites and moons can survive inside their planet’s Roche Limit because their electrochemical bonds are more significant than their gravitational bonds To find the critical Radius for a given body orbiting in the Roche Limit, we compute the Radius of the Sphere which can be held together by self- gravitation rather than internal cohesive strength: Fgravity = Tensile Strength x Sphere Surface Area  Rcritical for spherical object

8 The Ultimate Spectral Distance Ladder
Points to Ponder - III Beyond the solar system and the clusters… Question Raised: What is cosmological redshift ? It is the spectral shift in wavelength due to the velocity of the space-time fabric between the observer and the distant object (galaxy). It is a measurement of the recession velocity – a velocity that is not intrinsic to the motion of the object, but due to the fact that the universe is expanding according to Hubble’s Law: Recessional Velocity = Hubble's constant times distance V = Ho D In cosmological redshift, the wavelength at which the radiation is originally emitted is (only) lengthened as it travels through (expanding) space. A Cosmological redshift results from the expansion of space itself and not from the motion of the object. So the recessional velocity is not the galaxies motion, but the motion of space-time. This is a very special spectral shift indeed!

9 Deep Sky Objects - II Night Sky IV Clusters – Where…
From Galactic to Globular… By now we have studied and observed clusters within the disk of our galaxy and in our western sky in the Spring. These clusters are thousand or so light years away. They also are known to be in the active process of star formation. Now it is time to go beyond the disk of the Milky way to observe Globular Clusters… Deep Sky Objects - II

10 Globular Cluster – What we can glean
Since most galaxies contain globular clusters and since globular clusters are so old, the properties of globular clusters can be used to learn about not only the universe today, but also the universe in the past. Using modern telescopes and computers, astronomers have studied numerous properties of globular clusters. Here are just some of the quantities that we can measure for globular clusters: size (radius), mass, distance from galactic center, distance from Earth, brightness, age ** color.

11 will be the first to evolve into the giant star stage.
WHEN: HR diagram for Globular Clusters tells us the AGE (billions of years) Statistical Age --- still burning Already evolved… The most massive main-sequence stars will also have the highest absolute magnitude, and these will be the first to evolve into the giant star stage. As the cluster ages, stars of successively lower masses will also enter the giant star stage. Thus the age of a single population cluster can be measured by looking for the stars that are just beginning to enter the giant star stage. This forms a "knee" in the HR diagram, bending to the upper right from the main-sequence line. The absolute magnitude at this bend is directly a function of the age of globular cluster, so an age scale can be plotted on an axis parallel to the magnitude. By estimating from energy considerations, how rapidly the stellar evolution takes place, we put an age to these clusters.

12 Observing = “Faint Fuzzy”
Observing Spring Globular Clusters M53, M3, Observing = “Faint Fuzzy” Globular Clusters: Fuzzy blobs of thousands ofstars which are resolvable with telecopes!!! 6. M3 (NGC 5272). Magnitude 6.3, 18.6’x18.6’, Class VI. M3, yeah, M3. It’s a beauty, of course, but it suffers by being in the spring sky where it must compete for our attentions with the hordes of spring galaxies.                                                                                                                                      7. M53 (NGC 5024). Magnitude 7.7, 14.4’x14.4’, Class V. If M3 is sometimes ignored, M53 is the forgotten man of the Messier globs. It has three strikes against it. Like M3 it is in the spring sky when amateurs tend to be focused on intergalactic space, it’s a little lackluster at nearly magnitude 8, and it’s somewhat hard for small instruments to resolve at Class V. And yet, and yet… It’s still a Messier, and that means g-o-o-d. If nothing else, this one provides a welcome break when you tire of observing yet another faint fuzzie in Coma - Virgo. You do need 8-inches of aperture before M53 begins to look like much, but when you have at least that you may be surprised at how good it is.

13 Spring Globular Cluster M3 – What it contains (because its sooo old)
Courtesy Turn Left at Orion courtesy astronomy sketch of the day

14 Globular Clusters – North East
WHO Helen Sawyer Hogg's work focused on globular clusters, in particular the variable stars within them. She published more than 200 papers, the Catalogues of Variable Stars in Globular Clusters, and a number of historical articles, mostly in the Journal of the Royal Astronomical Society of Canada, JRASC, and was active member in a number of professional societies. She also began categorizing clusters according to the degree of concentration the system has toward the core. The most concentrated cluster s were identified as Class I, with successively diminishing concentrations ranging to Class XII. This became known as the Shapley–Sawyer Concentration Class. A Gift of Stars

15 Personal Introduction to … personal experiences of the Night Sky
… Sanjeev will share his experience next…

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