Table of Contents
The moon is perhaps the most noticeable feature we see in the night sky. For astrophotographers, the phase of the moon on any given night is extremely important as it lights up the whole sky when it is full. This can impact deep space photography because it lightens the background and reduces contrast in the image.
Current Phase of the Moon
Above you can see today’s current phase of the moon, the percentage illumination of the moon, the age of the moon in days and which constellation the moon is in. There is also additional information about lunar events to come soon such as lunar eclipses and so on.
This is updated daily to give the most accurate lunar cycle information.
Lunar Calendar for this month
This moon phase calendar shows you how the moon looks for each month of 2024:
What is the present phase? How to know
The first way to determine what phase the moon is in is to look at it and estimate it. You can’t tell if it is waning or waxing by looking at it, but you can see approximately what percentage is illuminated. Another way the moon changes is its position in the sky. This can affect what target you should choose because a bright moon can impact your imaging negatively.
If the moon is full, you may find it better to choose an astrophotography target far away from the moon to reduce the effect of the glare. Remember that the light from the moon is no different from other forms of light pollution and will impact your images, especially if your astrophotography target is too close.
The second way to discover where the moon is in its cycle is to use a calculator or app. In order to help you out with this, here is a calculator that you can use to find out exactly how much of the moon is illuminated in the sky at any date you want.
You can also use the calculator to find out when the next new moon or full moon is, which can be very helpful in astrophotography as it is very challenging to image under a full moon and is best at the time of a new moon because that is when the sky is darkest and not illuminated by the moon’s light.
I regularly check my phone app, Clear Outside, to answer the question “What moon phase are we in right now?” I also want to see how it will change over the next week or so. Clear Outside also includes weather information, so it is extra helpful. Here is a list of useful apps you can use for astrophotography.
The main reasons I check the lunar cycle and to find moonrise and moon set are because it affects the brightness of the sky, and sometimes I may want to photograph our beautiful satellite. In this article, I will discuss how the moon affects astrophotography, but elsewhere on this website, I’ll explain more about how to photograph the moon.
Let’s be clear about the meaning of the appearance of the moon.
The Lunar Cycle Explained
At any given time we are at a certain stage in the Lunar Cycle. As the moon orbits around the earth, the illumination of the moon changes as it moves around the sun.
Here’s a diagram of the Lunar Cycle that should make this easy to understand:
What causes the moon’s appearance to change?
There are many websites (including Nasa’s page about the Lunar Phases2) that talk about this in detail if you want a deeper explanation, but basically, here is my explanation.
The Moon orbits the Earth in under four weeks (27.32 days in fact). This means that it moves about 13 degrees along its path each day towards the east. I’ve observed while waiting for the Moon to decrease in brightness that it rises a little bit later each day, and this is because the Earth has to rotate a bit more to put it in the same position as the night before.
The moon travels anti-clockwise around the Earth. Therefore, every four weeks or 29 days to be exact, the lunar cycle repeats. If we are at a certain point in the lunar cycle today we will be at the same point in four weeks time.
As the Moon changes its position in relation to us on Earth, the sun shines on the lunar surface from a different angle, causing one part to be illuminated and one part of the face we see to be in shadow. When the Moon is directly facing the Sun from our perspective (i.e., the Moon and Earth are aligned), we see a full moon, but when it is on the other side of the earth in a position 180 degrees from this, the side we see faces away from the Earth and is in complete darkness.
When the moon is in complete darkness, there is no light reflecting from it and, therefore, no skyglow to affect our astrophotos. The New Moon is the best time to image, as the sky is at its darkest level.
Check out my page: Why does the moon glow? The answer is not so simple.
The same part of the moon always faces toward us as it does not appear to rotate3. However, the angle between the moon and our viewpoint here on Earth changes to create the phases.
The moon moves from full through the waning stages, including the new moon, when we see no illumination. The crescent then appears to grow larger until we have 100% lit up again. The lunar cycle is then complete and begins again.
The lunar phases can be divided into two, waxing (when the illuminated area of the moon is increasing, and waning, (when the illuminated area is decreasing). The two most obvious periods of the lunar cycle that affect astrophotography are around the full and new moon.
To check where we are in the lunar cycle today, consult a lunar calendar4, use an app, or observe it if it is a clear night. It’s easy to spot the different phases.
Description of the Phases
Here is a brief description of the lunar cycle and the appearance of the moon. This cycle lasts approximately 4 weeks and constantly repeats throughout the year.
- New Moon: This is the first stage of the lunar cycle, and it occurs when the it is positioned between the sun and the earth, with its illuminated side facing away from the earth. During this period, the moon is not visible in the sky.
- Waxing Crescent: As the moon orbits the earth and begins to move away from the sun, the portion of its illuminated side that is visible from the earth begins to increase, creating the appearance of a thin crescent shape. This is called the waxing crescent.
- First Quarter: When the moon is at a 90-degree angle to the sun and earth, with half of its illuminated side visible from the earth, it is in the first quarter phase.
- Waxing Gibbous: As the moon continues to orbit the earth and its illuminated side becomes more visible, it enters the waxing gibbous stage, in which more than half but less than all of its illuminated side is visible.
- Full Moon: When it is directly opposite the sun in its orbit, with its illuminated side fully facing the earth.
- Waning Gibbous: As the moon moves away from this point, the portion of its illuminated side that is visible from the earth begins to decrease, entering the waning gibbous stage.
- Third Quarter: When the moon is at a 90-degree angle to the sun and earth again, with half of its illuminated side visible from the earth, it is in the third quarter of the cycle.
- Waning Crescent: As the moon continues to orbit the earth and its illuminated side becomes less visible, it enters the waning crescent phase, in which less than half of its illuminated side is visible.
After waning, the lunar cycle begins again with the new moon.
- Fascinating facts about the moon
- Paperback
- 149 pages
- Rating 5.0
Beliefs about the Moon
Since ancient times the phases have had meaning. The full lunar disc set our calendars and is still used today to set the dates for religious festivals.
Let’s take a look at some of these traditional beliefs. For example, the new moon signifies new beginnings and renewal. The waxing crescent stands for progress, and it is a time to make decisions. Other meanings of the moon’s appearance5 include:
- The first quarter (half moon) – overcoming problems and increased energy.
- Waxing gibbous – time to finalise preparations for an event to take action.
- The meaning of the full moon – celebrating achievements.
- The waning gibbous moon – being thankful and sharing knowledge.
- The last quarter (half-moon but opposite side to the first quarter) – acceptance and reassessment.
- the Waning crescent – precedes the new moon – rest and inner reflection.
Why the Moon affects the Planning of Astrophotography
Asking “what is the moon phase today?” is so important for astrophotography because of its brightness. When it is illuminated by the sun and begins to light up the sky, it impacts the contrast of any images you take. I have found that more than 60% illumination and less than about 45 degrees between the moon and my deep sky target are enough to negatively impact my astrophotos.
It is possible to mitigate the effects of a bright moon using a narrowband filter rather than the normal RGB filters often used.
When doing landscape astrophotography you want to have lower illumination, the moon’s position and brightness are crucial.
When the moon is very bright and illumination is more than about 40 or 50 percent, I use my ZWO Duoband filter. This filter captures the two wavelengths of light found in the deep sky objects I normally image, nebulae. It can also be used to capture the hydrogen alpha in a galaxy such as M33, the Triangulum Galaxy.
The filter I use has a bandpass of 15 nm, which means that some light pollution and moonlight can pass through, which does mean that I have to be careful to image away from the moon and only image when the it is less than a maximum of approximately 70%.
I would like to add a comment here that the exact percentage of the moon when you decide to go ahead and take photographs of the night sky depends on your experience. So, while using narrowband techniques and after having improved my processing techniques, I can easily image with even an 80% or more illuminated moon.
Other filters can cut out more light pollution and moonlight, such as the Optolong L-Extreme or L-Ultimate, which I believe has a bandpass of 3nm. This could make it possible to even image under a full moon, as long as you do not point your equipment too close to the moon.
In summary, the moon is a source of light pollution, scattering light that will increase the gradient and mask details in your astronomy photos. Wait until it gives off less light.
For astrophotography, another thing I’ve found helpful is understanding that the moon rises later each day by an average of about 50 minutes or so, which means that I have often been able to get a few hours of imaging in before the bright moon comes up. As long as it is below the horizon, it has not affected my imaging at all since I also make sure to image at least 30 degrees above the horizon.
Research Survey: How Do Astrophotographers Adapt To the Brightness of the Moon?
I decided to conduct a survey and ask members of forums such as StargazersLounge about what they do when there is a bright moon and how this affects their astrophotography. Below are the results I got from three basic questions.
Results of the Survey
As expected, I found that many astrophotographers are not put off by a full or bright Moon. However, I was surprised at the percentages. My research showed that 77% of astrophotographers surveyed continue imaging under a full moon, and 22% do not. As confirmed by the comments I received from many respondents, under the full moon, imaging in narrowband is the best way to capture deep-sky objects.
In my second question, I tried to get respondents to be more specific about any limitations they had regarding when they would decide, if at all, that the moon was too bright for them to image. A large majority, (62.5%), said that they image when the moon is more than 80% illuminated. Almost 21% said that their limit was when the Moon was 50% illuminated.
Finally, I asked how close an angle to the bright Moon they generally image. One in three chose 90%, while the other answers were all equal in number.
One thing I did notice in the comments I received was that some of the respondents appeared confident enough in their ability to post-process images that they could image under a full Moon and go a bit closer to the Moon. Generally, of course, there is an admission that this processing is more difficult and not always ideal.
If you do find yourself wanting to photograph the moon you may ask yourself the question is tonight a full moon? Normally the full moon last for possibly two or three days. Probably best to plan and I would recommend consulting a lunar calendar or even buying one so you always know in advance how much illumination from the moon might affect your astrophotography.
Conclusion
We need to know the phase of the moon is in because of the effect it has on the brightness of the sky. The current phase of the moon can determine how and when we can image and capture astrophotos. Some astrophotographers prefer to avoid imaging during a full moon or around that time of the month, while others continue to image using narrowband filters and by imaging a certain distance away from the moon. It’s ultimately up to you to decide what is best for you. Good luck with your astrophotography!
References
[1] MoonPhase.guide. Daily lunar ephemeris. Retrieved from https://moonphase.guide/
[2] NASA. Moon Phases. Retrieved from https://moon.nasa.gov/moon-in-motion/moon-phases/
[3] Space.com. Does the moon rotate? Retrieved from https://www.space.com/24871-does-the-moon-rotate.html
[4] Time and Date. Moon Phases 2024 – Lunar Calendar. Retrieved from https://www.timeanddate.com/moon/phases/
[5] CircleDNA. How The Moon Affects Us: 5 Common Beliefs About The Power And Influence Of The Moon. Retrieved from https://circledna.com/blog/how-the-moon-affects-us-5-common-beliefs-about-the-power-and-influence-of-the-moon/
Leave a Reply