Our Moon

[Ant]

Hi All,

Just thought I'd jot down some things that I've been thinking about.

I'm starting my quest (again) to take an image of the moon at every phase through from New moon to New moon. The hardest of this is New Moon - which luckily I have (the partial eclipse of May 04).

Why is it that sometimes the last quater moon is visible before midnight and sometimes it isn't, well it's all due to the declination of the sun and the moon.

We all know that the sun follows a pattern each year, high in the sky in the summer low in the sky in the winter and half way between duringf spring and Autumn (fall).

But what isn't so widely known is that the Moon follows the same pattern but in reverse, i.e. high in the winter, low in the summer.

What this means is that the moon is best seen (high in the sky) at first quarter in the spring and last quarter in the Autumn.

So for an observing / imaging point of view (unless of course you want to observe the moon), the moon is a pain in the Bottom in the spring from First quarter to a few days after full. The same in the summer but when you get to the Autumn and winter the troublesome period lasts a lot longer, from first quarter to last quarter.

Well these are my thoughts on the moon, it's not explained very well, even though I've given it quite a bit of thought I just haven't explained it very well. Hopefully you'll get my drift from this.

What I was trying to get at was there are beter times of the year for observing specific phases of the moon.

Ant

[Astroman]

I wish you well in your quest! It is worthy, indeed. If you could get it all in one month, that would be even better. Put it together in an animated gif and you could see how the Moon tilts her head to us during the month.

Which brings me to your ponderances. 8)

Close, but no cigar, as we say. There are changes in the ability to view the Moon, but they are not strictly seasonal. They are actually tied to the inclination of the Moon's orbit with relation to the Earth's equator. This inclination is 5º. Each month, the Moon orbits 5º above and 5º below. So, depending on when you view during the month, it may be higher or lower in the sky Coupled with our attitude in the sky, you can add those angles to the height. Right now, it so happens, the Moon is in a particularly low attitude, meaning it rises pretty much as far south as it can get- minus 27º for Earth's tilt, minus another 5º for the Moon's inclination. This adds up to an apparent short cycle for the Moon from new to full. Keep heart though, in 6 months, it will be farthest north, and take longer! Perhaps spring would be a better time to fulfil your quest?

[Ant]

I knew that it was related to the ecliptic, where the ecliptic is is sseasonal (at least I thought so).

The sun during the winter is very low in the sky so I supposed that the ecliptic is low and the opposite for the summer (i.e. ecliptic high). and in the spring it about half way.

So in the spring when the the sun is at about half way (0degrees dec) and the moon is at first quarter the moon will be in the furthest part north of the ecliptic (not taking into the account of the 5 degrees inclination which can either exagerate the effect or partially negate it).

This also accounts for the fact that when we are in the winter(1/4 of an orbit before spring) and the moon is full (half way further round the ecliptic the moon is also high in the sky)

Go back to the autumn and it's last quarter that's in the furest noirth part of the ecliptic and thus the LQ moon is very far north.

Does that make more sense?

Ant

[Astroman]

Right, Ant. I'm just saying it's not solely seasonal. The ecliptic is just part of it. You're right though. Summer Moons will be higher than winter ones. Unless, you're in Australia, but let's not open that can of worms, ok?