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Night SkyNight Sky Lecture 3

Night Sky Lecture 3

  • III Observing the Moon – Observing is best at First (or Third) Quarter

The Night Sky Around Us

The Local NightSky as it appears May 17 2013 at 10pm – courtesy ECU

Where are all the Messiers Gone?

When the moon transits in the evening, the ‘faint fuzzies’ fade away… Now is the time to observe the moon.

  • Early Observations:   Galileo Galilei – Italy 1610


Galileo improved the construction of a telescope, which he used to observe the night sky and the moon.In his observations of the Moon,Galileo observed that the line separating lunar day from night (the terminator) was smooth where it crossed the darker regions of the moon, but quite irregular where it crossed the brighter areas.

From this observation, he deduced that the darker regions are flat, low-lying areas, while thebrighter 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

















For a general understanding of our satellite, take a tour with  the LRO satellite of our satellite:

See: Evolution of the Moon

See LRO’s (Lunar Reconnaissance Orbiter) Tour of the Moon

How does he moon effect earth and earth effect the moon (mutual effects)

  • Eclipses
  • Tides
  • Libration

Lunar Eclipse (Earth between Sun and Moon) – at Full Moon.The Moon is being eclipsed by the Earth
Solar (Moon between Earth and Sun) – at New Moon. The Sun is being eclipsed by the Moon

The Moon Is Earth’s Natural Satellite –Proximity Produces Observable Effects

How do the Tides Effect the Earth:

Because the moon is the Earth’s satellite, there are differential forces between the two bodies which produce the tides of the oceans. The near point is being pulled more strongly toward moon while the far point is being pulled less strongly, than the Earth’s centre. Relative to the centre, the near point is pulled toward Moon, while the far point is pushed away from the Moon. The difference between these (vector) forces is the tidal force. This force is responsible for the two bulges of water on opposite sides of the earth.

Right Arrow: Earth – Ocean pull from moon… Left Ocean – Earth pull becomes a push

Earth feels 3.5 times more tidal force than the Moon from their relationship, because the Earth is bigger, and thus has a bigger differential. Note about the Sun (and tidal force): The Sun’s effect on Earth is only half the Moon’s because, while more massive, it is much farther away

Earth Moon Interaction: 1 Lunar Revolution ~ 1 Lunar Axis Rotation

Astronomers who have studied the moon for centuries felt frustrated that they
could see only one side! The moon turns on its axis in exactly the same time period that it takes to go around the earth, 27.3days. It rotates slowly 13 degs per day as well as travels slowly at 13 deg/day so it keeps the same side always toward the earth (but not toward the sun). This synchronous rotation of the moon around the earth is the result of a tidal locking of the moon to the earth. Torques (twisting forces ) are applied to the moon which slow down the rotation and keep it aligned, pointing to the major axis of the earth-moon system


Standard names for Phases of the Moon

New Moon – Our first session was before new moon (after third quarter phase). Itis 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’. 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.

 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.
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
  • Craters

























This image is taken from the Virtual Moon Atlas available for both windows and linux>






Tips to Getting your ‘bearings’ on the Moon:

Start at the terminator.  This gives you a good sense of your x-axis.

  1. Locate a unique easy-to-identify feature like the Montes Apennines
  2. Then locate the craters you are supposed to study either North or South of there
  3. NOTE BENE: Find out what kind of image you are seeing:
    1. Reflector telescopes produce an image with South Up
    2. Refractor telescopes  (if you are using an additional diagonal mirror) produce Left-Right reversed
    3. Binoculars produce the magnified  image of the moon.





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