MVNSC – Mississippi Valley Night Sky Conservation
How-To Observe the Moon around First Quarter
– courtesy Michael Watson, member RASC
Equipment you will need:
- Moon chart – Overview with labeled sections near the terminator (line between sunlight and shadow portion)
- Telescope –
- If reflector, your image of the moon will be ‘upside down’ . You will need to rotate your chart N/S
- If refractor, your image of the moon will be left/right reversed. You will need to flip your chart E/W
- or.. Binoculars – no adjustment necessary
- Camera (optional) – can be hand held
References to use:
- Get an overall map – The classic Atlas of the Moon by Antonin Rukl shows the first overview map “Observing the Moon at First Quarter”. The Virtual Moon Atlas is a good electronic one.
Notice that for the image in a reflector telescope it is rotated 180 degrees so that North is down. This is what you see in the eyepiece.
- Orient it for your instrument (South is up for reflectors)Look for big features like Mare
- Camera Snapshot [optional] Put your camera close to the eyepiece and view through the viewfinder
- Turn off the flash (if you have not already done so)
- Shield stray light from the image – hint make a ring around the camera lens with your index and thumb
The camera was not close enough to the eyepiece in this shot. Need to look for the viewfinder and patiently wait for the image to come through…
This shot is just a lot closer in when the ‘seeing’ was steady. We can see all the features in the blue moon chart.
Look for the Northern Mountain chains
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Identify what’s completely defined near the terminator
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Identify craters South, Middle, North
Moon Features – Overview:
The Isabel Williamson Lunar Observing Manual provides a complete guide to ‘what to observe’. RASC – Lunar Guide
To find out what to observe at first quarter, you need to consult a map and then pick out the targets:
Start with the Maria – these are large dark lava-filled basin features – excellent markers for navigating the lunar surface (also tells you which phase you’re looking at).
Mare “Seas” (Lava-filled basins)
- Mare Serenitatis (Serenity) north of Tranquility note Posidonius Crater to right Landing site of Apollo 17 at southeast.
- Mare Tranquillitatis (Tranquility) to north of Nectaris, Its southwest region was the landing site of Apollo 11 in 1969
- Mare Fecunditatis (Fertility) –dark volcanic plain to the east (right) below equatorial centre
- Mare Nectaris (Nectar) lies southeast of Fertility they are separated by many deep craters and valleysMare Imbrium, near the Terminator
Mountains
Mountain chains are also excellent markers
- Apennine Mountains on southwest border of Serenity. A plain separates them from Caucus to North, appearing near the Terminator. The Appennine Front area was the location of the Appolo 15 site.
Craters
- Ptolemaeus – probably close to the Terminator at first quarter
- Arzachel makes a nice trio with Ptolemaeus and Alphonsus
- Note: It is much easier to identify the craters on the terminator of the moon. You can easily find them on the map, and the deep shadows make their shapes obvious. The terminator is your friend!
Measuring Features on the Moon
We can measure the diameter of the craters just by knowing the diameter of the moon which we have roughly known since antiquity.
Given a good enough map to the terminator (our friend ) we can determine the distance in kilometers of the crater diameter as a proportion of the lunar radius – easiest to see around first or third quarter
Here we have 4 mm/ 84 mm X 1763 km = 80 km.
We can use the free software Virtual Moon Atlas and use the measuring tool to yield a slightly larger value.
