Whilst driving my daughter to school one morning she said to me, “Look Daddy, I can see the Moon”. She sat quietly for a moment and then pondered, “But why can we see it now Daddy, when I thought it only comes out at night?”.
When we are children we get so used to the idea that the Moon is out at night and conversely the Sun is out during the day. As a result of this many of us don’t really think about why we can still see the Moon during the day time?
In fact, when we do stop and think we realise, of course, that the Moon and the Sun are always “out”. It is the orbit of our planet around the Sun, and the orbit of our Moon around us, that dictate where and when we can see which (and not to forget the fact that our planet is tilted on it’s axis).
Firstly, the Moon is not always visible during the day (unless you wished to chase it around the planet…)
For starters, for the Moon to be visible to you during the day it must be above the horizon.
On average the Moon is above the horizon for 12 hours and 25 minutes every day. However, the length of time the Moon is above the horizon will depend on a number of factors.
- The latitude from where you are observing the Moon
- The position of the Moon in its orbit, relative to the Earth’s equator
- It’s distance from the Earth
- The height of the local horizon
As the Moon orbits around the Earth it moves to a point where it is closest (Perigee) and furthest away (Apogee).
On average the Moon is a distance of 384,400 kilometres from the Earth. At Perigee it is 363,300 kilometres from the Earth and at Apogee it is a whopping 405,500 kilometres from the Earth.
As children we get used to the Sun rising and the Sun setting, but we never really think of the Moon as rising or setting. In fact the Moon also has times when it will rise and set as well as Moon phases.
When looking up at the Moon its shape appears to change with four different phases depending on the Moon’s position as it orbits around the Earth, and also dependent on the Earth’s position as it orbits around the Sun.
There are four main Moon phases, also known as Lunar Phases.
- First Quarter
- Full Moon
- Third Quarter
- New Moon
An additional four phases make up the eight total phases that comprise the “Phases of the Moon” in the following order.
What are moonrise and moonset? Well, moonrise and moonset are defined as the moments when the upper edge of the Moon’s disk touches the horizon.
So does the moon rise and set everyday? You might think that it does, but in fact the answer to this question is “no”. As the Moon is constantly in motion, the time between one moonrise or moonset, may be a little longer than the 24 hours in a day. Let’s look at an example – if the Moon was to rise in your location just before midnight on one day, it may not rise again until just after midnight on the third day – in that example there would be no moonrise on the second day! Now wouldn’t it be strange if the Sun worked like that – well in fact – it can also exhibit some strange sunrise and sunset characteristics. For example, in some places around the globe, at certain times of the year – the Sun may never rise and it may never set!
Hopefully that helps us to understand why we can see the Moon during the day.
Primarily this is due to a number of factors, such as the Moons phases, how close it is to Earth, and how luminous it can appear at times. So next time you look up at the sky during the day, you might just see a ghostly pale Moon reminding us of the beautiful dance that never ends between our Earth and it’s only Moon.
Image Credits: [credit – rudall30], [credit – PeterHermesFurian], [credit – jemastock], [credit – gyd_zyk].