MVNSC: Mississippi Valley Night Sky Conservation:
Stars and Star Clusters Within the Milky Way:
Program developed by:
- Mississippi Valley Conservation Authority
- Royal Astronomical Society of Canada
- Ottawa Astronomy Friends
- Instructor: Pat Browne
- Assistants: Andrew Lindstrom, Bob Hillier
- References used in this course: http://mvc.on.ca/night-sky-references/
- Course runs each Friday during the month of April
- Course time: 19:45 – 22:00 formally with priority given to observing when clear sky .
- Note: Donations can be receipted as charitable . Donations can be made online at CanadaHelps – (choose Night Sky Conservation fund):
Here are some examples of objects that can be seen in our Spring Night Sky. The distances to these stellar systems range from 100 to 10,000 light years. All of these objects are in or around the disk of the galaxy.
Our Galaxy: A collection of Billions of Stars. As with all galaxies, it is a massive, gravitationally bound system consisting of stars, stellar remnants, an interstellar medium of gas and dust, and dark matter, an important but poorly understood component. The word galaxy is derived from the Greek galaxias, literally “milky”, a reference to the Milky Way. – courtesy Wikipedia
- Binary Stars
- Variable Stars
- Stars with Nebulosity: Small Clusters of stars embedded in Nebulosity (Interstellar Gas and Dust)
- Reflection Nebulae
- ‘Planetary’ Nebula – Dying stars that look like planetary disks
- Emission Nebulae
- Star Clusters : Hundreds to Thousands of Stars in and around the plane of the galaxy
- Open or Galactic Star clusters
- Globular (densely packed) spherical clusters
- Mizar and Alcor – Optical and true Binary System
Variable Stars – Cepheid Variables
A variable star is not just a star that’s there, it’s a star that’s happening – Leslie Pelletier. Variable stars change brightness. Example Delta Cepheus (in the consellation Cepheus).Delta Cepheus changes in brightness over a period of 5 days. As the stars expands in size, it fades. As it contracts, it brightens.
Stars with Nebulousity (Gas and Dust)
There are two basic types of bright nebula (as opposed to dark (dust and gas) nebula):
Emission Nebula – are clouds of hydrogen gas glowing because their atoms have been ionized by the young, hot (blue) stars embedded within them. These nebulae shine from the energy they receive from the stars.These are interstellar clouds of ionized gas emitting light of various colours. The most common source of ionization comes from high-energy photons emitted from a nearby hot star.
- Star Formation: Sites of emission nebulae with H II regions, in which star formation is taking place and young, massive stars are the source of the ionizing photons.
Example: Orion Nebula Complex See: Orion’s Stellar Distances<a href=”AboutOrion.html”: About Orion </li
- Stars no longer on the Main Sequence – Stellar disks that resemble planets (because they are not point sources). These are planetary nebulae, in which a dying star has thrown off its outer layers, with the exposed hot core then ionizing them. – courtesy wikipedia
Example: M57 – the Ring Nebula
Image – courtesy P. Browne (120 ED refractor using maximDL)
Reflection nebulae are composed of cosmic interstellar dust which reflects the light of a nearby hot young stars. The energy from the nearby stars is insufficient to ionize the gas of the nebula to create an emission nebula, but is enough to give sufficient scattering to make the dust visible. Thus, the frequency spectrum shown by reflection nebulae is similar to that of the illuminating stars. Among the microscopic particles responsible for the scattering are carbon compounds (e. g. diamond dust) and compounds of other elements such as iron and nickel. – courtesy wikipedia
Example: Pleaides in Taurus
NOTE- In a telescope eyepiece or binoculars, you do see whisps of gas and dust – but NO colour and NO detail. Suffice to say you are receiving the photons from these objects directly from the object into your eye.
Star Clusters …
Naked Eye Open Cluster – Messier M44 – the Beehive cluster
The Beehive Cluster consists of about 400 stars in a loose ‘swarm’. Most of the stars are in a region of about 15 light years. The cluster is only about 500 light years away – farther than the Pleiades. The bright orange stars are the ones that have had time to evolve into red giants. (Given the estimates of mass for those stars still remaining on the main sequence, we can use our models of stellar evolution to calculate the age of the cluster members – in this case – 400 million years or so). This is a young collection of stars). Typical of Open Clusters:
- Loose collection of stars forming from the same diffuse cloud of gas.
- Open clusters are often called ‘galactic clusters’ since they are found within the disk of stars which makes up the Milky Way (as opposed to Globular clusters which are not confined to the plane of the galactic disk).
Globular Clusters: A group of 100s or thousands of stars bound together in a densely packed spherical swarm of stars orbiting around the center of the Milky Way Galaxy. (Other galaxies have globular Clusters too). Stars in globular clusters are extremely old. They may have been the first parts of the galaxy to form (Billions of years old).
We find the age of the cluster by noting which stars have had the time to evolve into red giants. Such calculations, according to the model for stellar evolution are at least as old as the galaxy itself. Stars in this collection belong to a population of stars whose chemical composition consists mostly of hydrogen and helium.
Messier Object M3 shown below is a collection of stars in a ball more than 200 light years in diameter. These stars are held together by mutual gravitational attraction. There are more than 50,000 members that can be resolved in large telescopes. … Probably a true value of 1/2 million in this spherical volume. M3 is estimated to be 40,000 light years distance.
/> Globular clusters swarm above and below the disk
Question: How are Distance and Brightness of the Objects that we saw related?
Here is where some of these objects are located in the Milky Way: