MOON PHASES

If you came to this WebPage from another site, you can navigate to our Home Page Denver, CO. However, be sure to close your previous browser window.

Our Moon orbits the Earth at an average distance of 235,000 miles and an average speed of 2,270 mph. Our Moon completes one orbit around the earth about every 27 1/4 days---this is called a sidereal month. This sidereal month is different than a lunar month---also called a synodic month. A lunar month is about 29 1/2 days. Why is this?

The Earth orbits the Sun once a year and travels 360 degrees to do so. Therefore, the Earth moves about 30 degrees each month. The Moon must orbit 360 degrees around the Earth which it does in about 27 1/4 days. However, the Earth has moved about 30 degrees around its orbital path with the Sun, so our Moon must move about an additional 30 degrees to once again be directly between the Sun and the Earth. This relationship is a know as a New Moon.

The Moon makes one full revolution each month---360 degrees. We always see the same face of the Moon.

The eight phases of the Moon around the Earth are shown in the graphic below. The picture is not to any scale. Each phase is shown as you would view it from the Earth.

New Moon:

When there is a New Moon you cannot see it, as the face that is turned toward the Earth receives no light from the Sun to reflect. The New Moon is, therefore, invisible to us viewing from the Earth.

Some of the more astute among you may have a question about the New Moon being invisible, since if the Moon is between the Sun and the Earth, why wouldn't there be a shadow cast upon the Earth. The answer is simple, you are correct, there would be a shadow cast upon the Earth and this is known as a Solar Eclipse. There is a catch though. The Moon is inclined by about 5 degrees to the ecliptic plane. There can only be an eclipse when the Earth and the Moon lie in a straight line with the Sun and the Moon blocks part of the Sun's rays to the Earth, thus causing a shadow. The Moon does not always cover all of the Sun, as there are different types of Solar eclipses.

I will talk more about eclipses at a later time.

Waxing Crescent:

Since the Moon orbits the Earth in a counter-clockwise motion, we come to the next phase which is the Waxing Crescent Moon. The yellow portions ,shown in the graphic above, are the lighted portions of the Moon that you will see from the Earth.

This phase of the Moon is about 45 degrees into the orbit of the Moon around the Earth from the New Moon. Because of the angle of the Sun in relationship to our Moon, you will only see this sliver of the Moon. Remember, that the Earth is moving in its orbit around the Sun also.

1st Qtr:

Next we come to the 1st Qtr Moon. This phase of the Moon is 90 degrees from the New Moon, or 45 degrees from the last phase of the Moon (waxing crescent) that we have just talked about. Once again, In the graphic you will notice that the Yellow part represents the area that the Sun strikes and that we see in the night sky. Once again, remember that we always see the same face of the Moon as the Earth rotates around the Sun and as our Moon rotates around the Earth.

Waxing Gibbous:

The Waxing Gibbous phase of the Moon is another 45 degrees around the orbital path of the Moon. This makes this phase 135 degrees from the New Moon. I will go into more detail of this shortly.

Full Moon:

The Full Moon is directly opposite of the Earth in line with the Sun. Once again, we do not always get an eclipse or the Earth casting a shadow on the Moon every time we have a Full Moon, for the exact same reason as with the New Moon that I described above. Once again, as with the New Moon, there are different types of Moon eclipses. This is a Moon eclipse and not a Solar eclipse, because it is the Earth casting a shadow on the Moon and blocking all or part of the Moon from view.

Waning Gibbous:

With the Waning Gibbous phase some of you may become a little confused. If the Sun is in the location where the graphic shows it, then why is the opposite side (same face) of the Moon lit up?

You need to remember that the graphic shows the Moon as you would be viewing it from the Earth, and the graphic is a two dimensional drawing. Remember, the Moon and Earth are both moving in relationship to the Sun. In the case of this phase of the Moon, the Sun seems to be  behind our Moon. I will explain this shortly.

3rd Qtr:

The 3rd Qtr phase is just the opposite of the 1st Qtr phase. The Sun and Moon just have a different relationship with one another. Hang in there, I will explain it shortly.

Waning Crescent:

With this phase of our Moon we are almost back at our starting point of the New Moon. Once again, this phase is just the opposite of the Waxing Crescent which the graphic shows.

Explanation:

To explain the location of the Sun with our Moon we will use a hypothetical Sunrise and Sunset time of 6:00am-pm. This is only a hypothetical situation and not to be taken literally accurate to the hour, minute, or second.

New Moon:

The Sun rises at 6:00am and the Moon rises at 6am. They both set at 6:00pm.

Waxing Crescent:

The Sun rises at 6:00am, but the Moon will not rise until 9:00am; so the Sun is already 45 degrees into the morning sky before the Moon begins to pop up over the horizon. Notice how in this position you would see the leading part of our Moon being struck by the Sun's rays, just as the graphic shows. The Sun's rays strike the surface of the Moon at an angle that produces this view.

1st Quarter:

The Sun rises at 6:00am, but the Moon will not rise until 12:00pm, or noon. This phase of the Moon is 6 hours behind the path of the Sun in the sky. Once again the graphic shows the leading half being struck by the Sun's rays. This is only logical since the Sun is ahead of the Moon in the sky.

Waxing Gibbous:

The Sun still rises at 6:00am, but now our Moon will not pop over the horizon until 3:00pm. Since we have a Full Moon when the Moon is directly opposite the Earth in line with the Sun, it is only logical that the Waxing Gibbous, which is only 3 h ours from being a Full Moon, to not be that far removed from looking very close to a Full Moon.

The Sun is still above the horizon and ahead of the Waxing Gibbous, so the leading portion of the Moon is lit up by the Sun.

Full Moon:

The Sun still rises at 6:00am, but now our Moon will not pop over the horizon until 6:00pm. The Sun and our Moon are directly opposite one another in the sky. Due to the inclination of the Moon's orbit the Sun's rays light up the whole face of the Moon facing it. Remember, that this is the face of the Moon that is always pointed towards the Earth.

From this point on we will notice a change.

Waning Gibbous:

To some, the graphic may be a little confusing from this point on and it is. However, the graphic shows the view of the Moon that you will see from the Earth during these phases of the Moon which confuses things. With a little thought you can see the effect from the graphic.

The Sun rises at 6:am and sets at 6:00pm. The Moon is not going to pop over the horizon for another 3 hours. Therefore, in the sky the Moon is now ahead of the Sun. Therefore, the Sun appears to be trailing or behind the Moon. This cannot be though, as the Sun has not changed location nor has the Earth changed its orbit around the Sun.

The phases of the Moon going from a Full Moon to the New Moon are the opposite of those going from a New Moon to a Full Moon.

When you start with the New Moon, the surface of the Moon that is always facing the Earth is dark since the entire surface of that face is pointing away from the Sun. As the Moon moves towards the Waxing Crescent more of the surface pointing toward the Earth is exposed to the rays of the Sun. At first there is only a very slim sliver, but as the Moon continues in its orbit around the Earth more and more of the surface of the Moon pointing towards the Earth is exposed to the rays of the Sun; until finally, we come to the Full Moon.

When we move from the Full Moon back to the New Moon the surface of the Moon, that always faces the Earth, is exposing less and less of that surface to the rays of the Sun.

Simple, but it can take some thought to see it.

3rd Qtr:

The Sun still rises at 6:00am, but the Moon will not pop up over the horizon until 6 hours after the Sun has set at 6:00pm. Once again the Sun will be shinning on that portion of the Moon that was shown dark in the graphic before.

Waning Crescent:

The Sun still rises at 6:00am, but the Moon will not pop up over the horizon until 9 hours after the Sun has set at 6:00pm. This means that the Moon will pop over the horizon at 3:00am.

The angle of the Sun with the Moon in orbit gives us the Waning Crescent as we approach the New Moon

As the Moon continues in its orbit we come back to the phase of the New Moon from where we started. Once again the Sun rises at 6:00am and the Moon rises at 6:00am.

BE SURE TO CLOSE THIS WINDOW WHEN YOU ARE DONE If you came to this WebPage from another site, you can navigate to our Home Page by Clicking Here. However, be sure to close your previous browser window.