q & a

Here are some of the questions which visitors to Inconstant Moon have asked. They have been divided into six sections...

movement: the moon's orbit and phases
physical: form, characteristics and geology
phenomena: unusual lunar events
observation: what can be seen... and what can't
terminology: naming of the moon, phases and features
miscellaneous: anything not covered avove

If you cannot find the answer to your question, go ahead and ask it!

telescopic detail

q: I have a 675 power telescope and would like to know how much detail I can hope to see with it. (John Barnett, Petersburg, Kentucky)
a: Power is much less important in selecting a telescope than aperture. It is this, the size of the telescope's main mirror or lens, which defines how much light the instrument can collect and what detail you can resolve with the right eyepiece. It limits the maximum useful power, which is roughly 60x the aperture in inches or 24x the aperture in centimetres. So for a 2.4" (60mm) aperture, the maximum useful power will be 144x. Nothing smaller than an 11" instrument could usefully use a 675x eyepiece.

A telescope's theoretical limit of resolution (the Dawes limit) is 4.56 / aperture in inches (11.58 / aperture in centimetres), so an 11" telescope could resolve detail down to .41 seconds of arc.


q: On Saturday night (august 21st at about 2:20 am) I went camping on the beach I saw the moon get dimmer and dimmer then it finally went all the way down. I have never seen the moon go down before - why did that happen?
a: Although this was during an eclipse season (a period when eclipses can occur) it was several days before the new moon (when lunar eclipses happen) so can only have been an atmospheric effect, such as airborne dust, smoke or water vapour.

orange moon

q: Why is the moon sometimes orange? (Mikey Talley, 6, Golden)
a: There are two probable reasons for the Moon appearing orange. The more common one is dust or smoke in the atmosphere. The more unusual possibility is a lunar eclipse.

visibility of artefacts

q: Is it possible to see the manmade objects such as the lunar lander, and rover on the moons surface? I am working on a school project and nobody seems to know the answer to this. (Steve Schwertfeger)
a: Even the most powerful telescopes, such as the Hubble Space Telescope, the Keck telescopes on Mauna Kea, Hawaii and the European Southern Observatory's Very Large Telescope at Cerro Paranal, Chile are unable to resolve anything as small as the Apollo vehicles at the range of the Moon. Hubble's threshold, for instance, is around 85 metres across. However, in theory the long shadows cast by the landers at sunrise and sunset could be visible, though this has not yet been tried.

ring around the moon

q: Tonight (1/27) I saw what appeared to be a 3 colour ring around the moon. It resembled more of a rainbow and was quite a distance away from the moon, but equal in distance all the way around. What was it? (Kathy Wills, Middletown, Ohio)
a: It was almost certainly the effect of ice crystals high in the atmosphere. These would typically create a circular halo some 20° from the Moon.

daytime visibility

q: Why we can see the Moon during the day? (Kim, Bothell, WA)
a: Every 29.5 days, the Moon travels right the way round the Earth, so it is actually up during the day as much as during the night. However, it tends to be bigger and brighter at the times when it spends more time in the dark, nighttime sky, and vice versa. The brightest, fullest Moon rises around sunset and sets around dawn, but when (two weeks later) it is in the sky throughout the day it is a thin, dim crescent and just can't be seen against the bright sky. The best time to see a daytime Moon is around the first and last quarters, when it is fairly bright and is up for half the day and half the night.

flag on the moon

q: Can the US flag left on the moon in '69 be seen through an earth-based telescope? And where is it, anyway? (Ken, Atlanta)
a: Apollo 11 landed in the Mare Tranquillitatis (Sea of Tranquility) near its southern edge. See the Apollo Landings map in Cyclopedia Selenica.
The Hubble Space Telescope was recently trained on the Moon for the first time. It can theoretically resolve lunar features down to 85 metres (280 feet) across, which means that although it could never directly observe the lunar module's base section (much less the flag) it could possibly see its shadow near lunar sunrise or sunset. No Earth-bound telescope could match this feat.