Presentation on theme: "Program developed by Mississippi Valley Conservation Authority"— Presentation transcript:
1 IV Spring 2012 Astronomy Course Mississippi Valley Night Sky Conservation The Sky Around Us Program developed byMississippi Valley Conservation AuthorityRoyal Astronomical Society of CanadaOttawa Astronomy FriendsInstructors:Pat BrowneStephen CollieRick ScholesCourse Assistant:Amy BoothSpecial Treat:AstroPhotography Presentation,Sanjeev Sivalvurasa …Agenda –Nightsky Around us = MoonlightLecture/ObservationsField trip to FLO – weather permittingEarth Centered Universe software for illustrations –courtesy David Lane
2 Review Last Week III Sky Around Us The Sky around us … starsStellar evolution and distances viaAbsolute magnitude and stellar spectraon the main sequenceLunar Study – Courtesy Stephen CollieFollowed by Lunar and Double StarObserving – ‘Running a telescope’using the red dot, the finder and themain eyepieces(at different magnifications)Doubles – Polaris, Castor, ,AlgeibAlkaidFollow the Arc to Arcturus and Speed on to Spica… (diagram courtesy Helen Sawyer Hogg).
3 Lunar Exercise – How To… Lunar Certificateprogram provides ahandle on howto study the moonObserving 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 ECONOMICUniformity of lighting in the town 3:1 Illuminance level in urban areas.Maintain and standardize onminimum wattage levels to dothe 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/poleReducing wattage from 200W 100W saves the town $315/luminaire over 20 yearsFor 1000 lamps (now) = $ over 20 years in reduced wattage
6 In a nutshell…Uniformity – work to the minimum difference in lighting levelLower Wattage – work to the lowest specified lighting level according to IESNA standards… i.e. 1.2 FootCandles for road surfacesPole Spacing increase on roadways with less traffic – reduces Pole Count of luminairesReduce Wattage and save Energy Costs From 200 -> 100 WSmart Lighting - extinguish when not being usedLight 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 towork withWhy is the moon a sphere rather than themore irregular shape of an asteroid ?Roche Limit:The critical distance between a planet and its satellite belowwhich, the satellite is broken up by tidal forces.In our case, the moon is not broken up by tidal forcesbecause it orbits outside of Earths Roche Limit.L =2.5 Earths Radius ~ 16000kmMoon’s distance 365,447 km .It is also held together by self-gravitation – that makes itspherical as gravity and hydrostatic pressure shape the bodyas a sphere. However, When the orbit decays, to within theRoche limit, it would have to have enough self-cohesivestrength to resist tidal breakup. As the sample exerciseshows, bodies within the Roche limit (like people) aretypically not spherical, but irregularly shaped.It is only if self-gravitation dominates over internal cohesiveforces (tensile strength) that the body is spherical.This implies a density (kg/m^3) , a tensile strength ofmaterial (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 bondsTo 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 - IIIBeyond the solar system and the clusters…Question Raised: What is cosmological redshift ?It is the spectral shift in wavelength due to the velocity ofthe space-time fabric between the observer and thedistant object (galaxy).It is a measurement of the recession velocity – a velocitythat is not intrinsic to the motion of the object, but dueto the fact that the universe is expanding according toHubble’s Law:Recessional Velocity = Hubble's constant times distanceV = Ho DIn cosmological redshift, the wavelength at which theradiation is originally emitted is (only) lengthened as ittravels through (expanding) space. A Cosmologicalredshift results from the expansion of space itselfand not from the motion of the object. So the recessionalvelocity is not the galaxies motion, but the motion ofspace-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 burningAlready evolved…The most massive main-sequence stars will also have the highest absolute magnitude, and thesewill 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, bendingto the upper right from the main-sequence line.The absolute magnitude at this bend is directlya function of the age of globular cluster, so anage scale can be plotted on an axis parallel tothe magnitude.By estimating from energy considerations, how rapidly the stellar evolution takes place, weput 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 Orioncourtesy astronomy sketch of the dayasod.info
14 Globular Clusters – North East WHOHelen Sawyer Hogg's work focused on globularclusters, in particular the variable stars withinthem. She published more than 200 papers,the Catalogues of Variable Stars in GlobularClusters, and a number of historical articles,mostly in the Journal of the Royal AstronomicalSociety of Canada, JRASC, and was activemember in a number of professional societies.She also began categorizing clusters according tothe degree of concentration the system hastoward the core. The most concentrated clusters were identified as Class I, with successivelydiminishing concentrations ranging to Class XII.This became known as the Shapley–SawyerConcentration Class.A Gift of Stars
15 Personal Introduction to … personal experiences of the Night Sky … Sanjeev will share his experience next…