A2 - Lunar disk Flashcards
What shape is the Moon?
oblate spheroid (wider at equator)
What are craters/ejecta?
-asteroid/comet impact locations
-material thrown outwards, forming ejecta rays around crater
What are maria, and how do they form?
-asteroid/comet impacts leave craters
-fills with lava that cools
-forms flat basaltic plain
What are terrae?
-the lunar highlands
-brighter (higher albedo), more mountainous parts of the Moon
What are mountains (on the Moon)?
rim of an impact crater
What are valleys? What are their alternate name?
-lava channel flow
-cools and contracts
-forms a valley structure
-rille
Draw the diagram of the Moon labelled with 3 maria, 3 craters and 1 mountain range:
What is special about the Moon’s orbital period, and how long is it?
-27.3 days
-its orbital period is equal to its rotational period
-ie tidally locked
What is libration, and why does it happen? What does it allow observers to do?
-apparent oscillation of the lunar disk
-happens because the Moon’s rotational axis is tilted relative to its orbital plane
-allows observers to see parts of the Moon that aren’t always visible
When would be the best time to observe the Sea of Tranquility and why?
-full Moon
-it is a mare, and a flat feature which doesn’t cast shadows
-it is best observed when fully illuminated
When would be the best time to observe Tycho and why?
-half Moon (specify the quarter it is in if asked)
-the crater has height, and casts shadows, so the added contrast when it lies along the terminator line helps observations be more detailed
-or full Moon to see its bright ejecta rays being fully illuminated
How do lunar eclipses show that the Earth has a curved surface?
-the shadow of the Earth appears curved when cast onto the Moon’s surface
-the curvature of the shadow is different to the curvature of the Moon
Describe a method that allows you to work out the relative size of the Moon, using a lunar eclipse:
Assume you know the Earth’s diameter and the times of each of the umbral contacts, but not the Moon’s orbital period
-calculate difference in time between 3rd contact and 1st contact to find how long the Moon took to cross the umbral shadow of the Earth
-do the same with the 2nd and 1st, to see how “long” the Moon is
-divide one by the other to find out their relative “lengths”, and then multiply/divide by the Earth’s diameter
Describe a method that can allow you to figure out the length of the lunar phase cycle:
-need to measure time between 2 Full Moons, use a clock to record start time and end time
-observe from same location every time
-repeat over several cycles to improve reliability
