MVNSC – Mississippi Valley Night Sky Conservation The Night Sky Around Us Lecture 2
Program developed by:
Mississippi Valley Conservation
Authority Royal Astronomical Society of Canada
Ottawa Astronomy Friends
Instructor: Pat Browne
Assistants: Andrew Lindstrom, Bob Hillier
Course runs each Friday during the month of April Course time: 19:45 – 22:00 formally with priority given to observing when clear.
Lunar Observations when the Moon is around First Quarter
Some reflections from last week …
Local Reference Lines that help us Observe the Night Sky Around Us
As we look again at our Celestial Sphere, we see two important reference lines:
- Our Local Meridian (Blue line) – The North South line about our local horizon that traces through the poles and the Zenith
- The Ecliptic (Yellow line) that traces the plane of the Ecliptic where the planets rise and set. This line goes through the common zodiacal constellations, and there’s lots of stuff to explore up there!
What line is our Local Meridian?
It is the line along the great circle perpendicular to our celestial equator that starts due North at the horizon, then rises up and crosses the Zenith and touches down directly South at our local horizon. Because the meridian is fixed to the local horizon, a celestial object (star, planet, sun) will cross our meridian as the Earth spins. It reaches its highest point in the sky when crossing the meridian. We say the object “culminates” when it reaches its highest point on the meridian
As we apply it to our study of locating stars:
The earth rotates around its own axis every 24 hours. If we extend the Earth’s rotational axis into space it intersects the North Celestial Sphere in two places, the North Celestial Pole (NCP) and the South Celestial Pole (SCP) . The Great Circle (circle that passes through the center of the sphere) that goes through the observer’s zenith (directly overhead) and the North Celestial Pole is called the Meridian. Stars are at their highest point when they cross the Meridian. Similarly the Sun crosses at its highest point roughly at noon on our local Meridian.
Question: Why do we, as observers in the Northern Hemisphere face towards our Southern Horizon? In other words, why do we set up our planisphere usually to face South?
Answer: Because the majority of the objects in our celestial sphere including the planets, culminate along our meridian as we face South. As you can see from the diagram: Most Stars are located above the Celestial North Pole axis. In our case that would be at an Altitude of 45 degrees (our Latitude) . All stars, planets, clusters and galaxies will culminate along the meridian with an altitude : (90 − L + D), where L is our latitude and D is the object’s declination (Celestial latitude) courtesy http://en.wikipedia.org/wiki/Culmination.
So as long as the star or other celestial object has a declination between +45 and -45, we will see it culminate when we face south.
Question: What Causes the Seasons on Earth?
Answer: The Earth’s axial tilt towards and then away from the Sun, with respect to its path along the ecliptic, (the orbit around the sun). For the explanation, let’s go to https://millstonenews.com/2014/04/night-sky-course-planets-earth-and-orbits-around-the-sun.html
Lecture 3 Introduction: The Effect of Moonlight on viewing Deep Sky Objects or… (Where have all the Messier Objects Gone?)
If we go out and try to observe the objects circled in red, (our list of Messier Objects like M1 (in Taurus), M42 (in Orion), M44,(in Cancer) (M65, M66) in Leo), we will not be able to see … WHY…
Light from the Moon …
Light from Artificial Sources
When the moon transits in the evening, the ‘faint fuzzies’ fade away… Now is the time to observe the moon.
Lunar Observations: Early Observations: Galileo Galilei – Italy 1610 – Lunar Features as Mountains and Craters measured from shadow lengths
From this observation, he deduced that the darker regions are flat, low-lying areas, while the brighter regions are rough and covered with mountains Based on the distance of sunlit mountaintops from the terminator, he estimated that the lunar mountains were at least 6kms in height
Because of the view during first quarter week (1/2 lit) we can see the mountain height from light rays straight to the moon and perpendicular to us. : Measuring Mountain Heights – Galileo
Note also that the diameter of the moon in terms of Earth radii was estimated during a lunar eclipse: … Based on a total eclipse of the Moon, the Greeks found that the Earth’s shadow in terms of the the Earth’s diameter is 3.5 Moon diameters.
So the lunar diameter was estimated at roughly ~ 12,756/3.5 ~ 3700 km courtesy http://www.nuffieldfoundation.org/practical-physics/diameter-moon
Understanding the reason behind other Lunar Phenomena, the Origin and Evolution of the Moon, and the Interactions between the Earth and the Moon – see: https://millstonenews.com/2014/03/lunar-science-understanding-our-lunar-explorations.html
Standard names for Phases of the Moon
New Moon – Our first session was before new moon (after third quarter phase). It is the period when the moon rises and sets with the sun (roughly). This is the time to observe Deep Sky objects (such as objects in the Messier Catalog – which include stellar nebulae, Open Clusters, Globular Clusters and Galaxies).
First Quarter – One week after new moon, and the moon appears in the night sky, and sets after midnight. It is said to be ‘waxing’ or growing. It is roughly 50% illuminated. Deep Sky objects are hard to see. This is a good time to view the features of the moon near the terminator where light and shadow are apparent. (More on that later)
Full Moon – One week later (2 weeks after New Moon) we see the fully illuminated moon, and not much of the deep sky! The moon appears like a flat disk. Shadows have fled, and the bright, washed out appearance is good for a going for a walk in the moonlight.
Third Quarter – The moon is said to be ‘waning’ . Again, a good time to see the features on the moon.
To understand the lighting on the moon – try this:
At Full Moon there are no Shadows to Observe
Features remain in darkness and gradually become illuminated from 0-14 ‘day-old’ moon For these features and more, one of the best ways to make a project study out of the moon is to observe with the Royal Astronomical Society of Canada’s (RASC) Isabel Williamson Lunar guide. This is the guidebook we use to work on the RASC Lunar Certificate program. http://www.rasc.ca/sites/default/files/IWLOP2013c.pdf
See: See Lunar Observing and the Isabel Williamson Lunar Guide (Millstone News article)
Here is a list of such objects, and we can check them with MoonGlobe or Virtual Moon software:
For a beginner:
Make sure the feature is visible for the day of the lunar cycle.
It’s good to pick three basic types of features to study:
- Mountains – Montes
- “Seas (basins)” – Maria
This image is taken from the Virtual Moon Atlas available for both windows and linux http://ap-i.net/avl/en/start
Tips to Getting your ‘bearings’ on the Moon:
Start at the terminator. This gives you a good sense of your x-axis.
- Locate a unique easy-to-identify feature like the Montes Apennines
- Then locate the craters you are supposed to study either North or South of there
- NOTE BENE: Find out what kind of image you are seeing:
- Reflector telescopes produce an image with South Up
- Refractor telescopes (if you are using an additional diagonal mirror) produce Left-Right reversed
- Binoculars produce the magnified image of the moon.
For detailed Lunar Observations – go to our Night Sky News page! https://millstonenews.com/2014/04/lunar-road-map-how-to-observe-the-moon.html