IV Spring 2012 Astronomy CourseMississippi Valley Night Sky ConservationThe Sky Around Us

Program developed byMississippi Valley Conservation AuthorityRoyal Astronomical Society of CanadaOttawa Astronomy Friends

Instructors:Pat BrowneStephen CollieRick ScholesCourse Assistant:Amy Booth

Special Treat:

AstroPhotography Presentation,Sanjeev

Sivalvurasa …Agenda – Nightsky Around us = MoonlightLecture/ObservationsField trip to FLO – weather permitting

Earth Centered Universe software for illustrations – courtesy David Lane

Review Last Week III Sky Around Us

The Sky around us … starsStellar evolution and distances via Absolute magnitude and stellar

spectra on the main sequence

Lunar Study – Courtesy Stephen Collie

Followed by Lunar and Double StarObserving – ‘Running a telescope’ using the red dot, the finder and

the main eyepieces (at different magnifications)

Doubles – Polaris, Castor, ,AlgeibAlkaid

Follow the Arc to Arcturus and Speed on to Spica… (diagram courtesy Helen Sawyer Hogg).

Lunar Exercise – How To…

Lunar Certificate program

provides a

handle on how to study the

moon

Lunar Exercise How to

Observing out the Summer Kitchen … or on the Balcony

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

http://millstone.typepad.com/files/lunarsampleexercises.doc

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/poleReducing wattage from 200W 100W saves the town $315/luminaire over 20 yearsFor 1000 lamps (now) = $315000 over 20 years in reduced wattage

Points to Ponder 1 On Earth as in Heaven…

Responsible Lightingis ECONOMIC

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

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 ~ 16000kmMoon’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) aretypically 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 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

The Ultimate Spectral Distance Ladder

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 the distant 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 D

In cosmological redshift, the wavelength at which the

radiation is originally emitted is (only) lengthened as ittravels 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!

Points to Ponder - IIIBeyond the solar system and the clusters…

Deep Sky Objects - II

Night Sky IVClusters – 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…

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.

http://www.sciencebuddies.org/science-fair-projects/project_ideas/Astro_p016.shtml

WHEN: HR diagram for Globular Clusters tells us the AGE (billions of years)

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.

Already

evolved…Statistical Age--- still burning

Observing = “Faint Fuzzy”Observing Spring Globular Clusters M53, M3,

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. http://uncle-rods.blogspot.ca/2011/12/my-favorite-fuzzies-unks-globular-star.html

                                                                                                                                    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.

Spring Globular Cluster M3 – What it contains (because its

sooo old)

Courtesy Turn Left at Orion

courtesy astronomy sketch of the day

asod.info

Globular Clusters – North East

A Gift of Stars

WHOHelen 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

clusters were identified as Class I, with successively diminishing concentrations ranging to Class

XII. This became known as the Shapley–Sawyer Concentration Class.

Personal Introduction to

… personal experiences of the Night Sky

… Sanjeev will share his experience next…