Why a Stargazing Weather Forecast Matters for Astro

A stargazing weather forecast is important for Astrophotography. After all, we all know we need clear skies, don’t we?

Yes, of course, but it is not as simple as that, as I have learned as I got deeper into astrophotography. In this post, we’ll uncover what types of weather and atmospheric conditions affect backyard astrophotography. We’ll also discuss what you can do to overcome the challenges that certain weather conditions create for astrophotographers.

Believe me, it is more complicated than you think, and just because the sky looks clear doesn’t mean that your astrophotography images will be unaffected by other aspects of astronomical weather.

Cloud Cover and Its Effects on Night Sky Imaging

Clear skies are ideal for astrophotography¹ as they allow for the best visibility of celestial bodies. This seems fairly obvious, right?

Not so, in my experience! Poor “seeing,” mist, or humidity can ruin what appears to be a clear sky. We’ll look at what “seeing” is later.

Cloud cover can obstruct the view of stars and other celestial bodies, making it difficult to capture clear images.

There are few things more infuriating than setting up, as happened to me recently, having clouds roll in to stop you before you even get started!

Before you polar align your telescope, you need clear conditions, or your camera will not be able to capture those bright stars that your alignment software needs to gauge where your telescope is pointed in relation to the Polar Axis. No polar alignment, and no imaging session.

Just recently, I had to wait for a half hour or more just to polar align, and I thought about giving up and taking my equipment inside for the night. Then, after going inside and returning after 30 minutes, I saw that the sky had cleared!

The stargazing weather forecast is your friend as it will help you decide when to plan an astrophotography session and when not to. However, there is also always a level of inaccuracy in these forecasts. Your local weather may suddenly change and be quite different from the forecast app you’ve used. 

Severe Weather Signs While Stargazing

The night sky can provide clues about impending severe weather if you know what to look for. Here’s how you can read the sky to prepare for any unexpected turns in the weather:

Cloud Formations

Clouds are silent messengers, offering insight into upcoming weather conditions. Keep an eye on:

• Cirrus Clouds (“Mares’ Tails”) and Altocumulus Clouds (“Mackerel Scales”): These clouds often signal changes in weather. Their presence, especially together, hints at rain approaching within the next day or so.
• Cumulus Towers: Standard cumulus clouds are quite typical on a warm day, but if you notice them building into towering formations (cumulonimbus), it could suggest severe weather is on its way.

Celestial Rings

Rings or halos around the Moon or the Sun, are created by ice crystals in high-altitude clouds. These rings are a sign that rain might be coming.

Wind Patterns

While not as reliable as cloud formations, wind can still provide hints about changing weather. Be alert to:

• Increasing Winds: These often foreshadow rain.

By paying close attention to these natural signs, you can be ready for any change in weather conditions. Keep these tips in mind next time you’ set off with your’re out under the stars.

Effects of Temperature and Humidity on Astrophotography

Here are some of the main effects that temperature and humidity have on your equipment:

• High humidity can cause dew to form on the lens of a camera², potentially ruining astrophotography shots.
• Temperature changes can affect the camera sensor’s performance³, with cooler temperatures often resulting in less noise in the final image. For every 20°F drop in temperature, digital noise in an image can decrease by up to 50%.⁴
• Extremely cold weather can drain camera batteries faster⁵, affecting the duration of astrophotography sessions.
• Snow and ice⁶ can reflect moonlight and other light sources, potentially overexposing the image or washing out faint stars.
• Temperature changes can also alter the focus of your telescope or camera, so this needs to be monitored if you expect a larger swing of temperature at night when you are imaging. 

Let’s take a look now at how these stargazing weather effects can influence how we plan for a night’s astrophotography.

Planning Your Astrophotography Shoot: The Stargazing Weather Forecast

To have a trouble-free night of imaging, it’s vital to look at your chosen astrophotography app and consult your local stargazing weather forecast. Here are the things you need to consider:

• Will it be clear for the whole night or part of the night, and when exactly?
• How strong will the wind be?
• Consider the effect of high cloud because it sometimes appears to be clear but isn’t. This kind of cloud can spoil your images, but sometimes you may be able to image despite some of this light, high cloud.
• Is it going to be misty or humid?
• It’s not weather per se, but the phase of the moon is an important factor in astrophotography. The light from the moon has a negative impact on stargazing conditions. As long as the moon is not too close to your astronomical target and as long as it is not in one of the fuller phases, it may be possible to image successfully. This is a judgment call. 

Strategies for Overcoming Weather Challenges in Astrophotography

Where I live, it is often windy. The weather can be very clear, and the only thing that stops me from having a perfect night of astrophotography is the wind. The effect is to cause images to be blurry because gusts move the telescope before the telescope’s auto-guiding system can correct the movement.

However, for short gusts an auto guider can help to adjust your telescope so that any movement is minimized. Here’s what I use:

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Wind can also cause camera shake⁷, resulting in blurry images in astrophotography. Wind speeds above 10 mph can cause blurring in long-exposure astrophotography⁸ due to the movement of the camera or telescope.

In these windy conditions, I’ve found that shortening my exposure time can fix this problem. Normally, I expose for about six minutes, depending on my target, but in windy conditions, I reduce this to two minutes or even less. The images then become significantly sharper.

An obvious but sometimes difficult-to-implement solution for windy weather is to put my equipment in a sheltered position. This can be a problem, depending on which direction I am pointing my telescope. Building an observatory or viewing area with some shelter from the wind is a good idea. 

Stargazing weather forecasts also should consider humidity levels because high humidity can mist optics and cause dew to drip onto lenses and drop inside the tube of the telescope. Many use dew heaters to reduce this problem, especially in the winter months when the weather is colder.

I find that in the climate where I image, the Mediterranean, humidity can be a problem on colder winter nights and also because I am very close to the sea. I use a long cover over the aperture of my scope to stop this, and I don’t normally need to use a dew heater.

As regards the phase of the moon, I have learned to make sure I choose a target not too close to where the moon will be and also to limit my astrophotography to times when the moon is lower in the sky or less than 80% illuminated, but this is only a guide; this may vary. Using a dual-band filter removes much of the moonlight and allows me to photograph my targets even when the moon is relatively bright.

Let’s now look at what you need to do to understand what your stargazing weather forecast is saying to you and whether or not you should go ahead and do astrophotography. Some tools and apps can help, so what do I use? And what else do you need to do to stay ahead of the weather?

Staying Ahead of the Weather: Apps and Tools for the Modern Astrophotographer

Before consulting apps or tools, learn about and monitor the phases of the moon. They are very consistent and follow an ever-repeating pattern. Once you understand the details of the movement and appearance of the moon’s phases, this can help improve your astrophotography.

Drawbacks of Using General Weather Apps for Stargazing

General weather apps are commonly used but they have several drawbacks when it comes to stargazing.

• Limited Astronomy Features: These apps usually focus on basic astronomy information, such as sunrise and moonrise times. Occasionally, they might cover special celestial events like meteor showers, but the depth and breadth of their astronomical data are quite limited.
• User Interface Challenges: On a dark observing field, these apps often become impractical. They typically require extensive scrolling through screens and tiny font sizes make it difficult to retrieve specific details quickly. This can be particularly cumbersome during nighttime stargazing sessions.
• Ad Clutter: Advertisements are another hassle, as many of these apps are saturated with ads that can distract and interrupt the user experience, complicating your focus on the sky.

For those who are serious about stargazing, these limitations might outweigh the convenience that general weather apps offer for day-to-day weather updates.

I use a free app called Clear Outside. The great thing is that it tells me what I need to know about my local stargazing weather forecast and conditions. How much cloud will there be? Will it be, low or high cloud? It also tells me the temperature and wind conditions. Importantly, it tells me the rising and setting times of the moon and its level of illumination on any given night.

This is mostly all I need to know before planning my astrophotography session.

In addition, Clear Outside also tells me what level of light pollution the local area has. It gives this in terms of its Bortle number. See more about light pollution here.

Another good choice is the Clear Sky Charts app, a go-to tool for precise night sky predictions. This app pulls data from the Canadian Meteorological Centre to provide detailed forecasts tailor-made for stargazers, extending up to 180 hours.

How It Works:

• Data Visualization: The app uses rows of colored squares to simplify complex data. Each square delivers insights on three key factors: cloud cover, atmospheric transparency, and astronomical seeing conditions.
• Color Coding: The darker blue squares are your best friends here; they signal optimal conditions for an unobstructed view of the stars, ensuring minimal cloud interference and excellent transparency.
• Wide Coverage: Whether you’re planning to stargaze in a remote area or attend star parties, the app offers charts for thousands of locations throughout the U.S. and Canada, ensuring you’re never far from a perfect spot to gaze at the night sky.

By breaking down dense meteorological data into clear, visual charts, this app provides an intuitive and effective guide for all your stargazing needs.

Astrospheric sets itself apart from other stargazing forecast apps with its wealth of detailed information designed specifically for North American astronomers. While some apps may only offer basic weather forecasts, Astrospheric goes beyond by providing satellite imagery, an extended cloud outlook, and comprehensive lunar data, such as moon phase and precise rise/set times.

A notable feature of Astrospheric is its use of intuitive visuals, like colored squares, to represent weather conditions. Unlike typical forecast apps, these visuals provide a quick summary when hovered over, revealing specifics such as cloud cover percentages, transparency status, and average seeing conditions. This level of detail makes it a powerful tool for both amateur and professional astronomers seeking precise weather forecasting data for their stargazing sessions.

The Scope Nights app is a must-have tool for amateur astronomers, offering a comprehensive set of features designed to enhance stargazing experiences. This app compiles data from global resources like the U.S. National Oceanic and Atmospheric Administration (NOAA) and European forecast models to provide precise stargazing forecasts worldwide.

One of its standout features is the dual forecasting options, delivering both daily and hourly predictions. This allows users to plan their stargazing activities with precision, optimizing their time under the stars. The app’s visually appealing interface uses simple graphics, making it easy to assess viewing conditions at a glance.

Beyond just weather, Scope Nights integrates light pollution data and presents it on an interactive map, helping users find the darkest skies nearby. The primary screen of the app showcases a detailed astronomy forecast for six consecutive nights, ensuring you can plan your celestial observations well in advance.

With these features, Scope Nights becomes an essential companion for anyone passionate about exploring the night sky.

I hope this page has been helpful to you and put you on the path to mastering your stargazing weather forecast so that the weather doesn’t present too many problems for you.

References

[1] NASA Science. How to Find Good Places to Stargaze. Retrieved from https://science.nasa.gov/solar-system/skywatching/how-to-find-good-places-to-stargaze/

[2] Cory Schmitz (2024-08-12). How to Dew-Proof Your Camera Lens • PhotographingSpace.com. Retrieved from https://www.photographingspace.com/dew-proofing/

[3] Quora. How exactly does the temperature of camera image sensors affect the image? Retrieved from https://www.quora.com/How-exactly-does-the-temperature-of-camera-image-sensors-affect-the-image

[4] Cloudy Nights Forum. Retrieved from https://www.cloudynights.com/topic/563601-dslr-in-camera-noise-reduction/page-2

[5] Capture Landscapes. No title. Retrieved from https://www.capturelandscapes.com/extend-battery-life-for-winter-photography/

[6] MIT Climate Portal. Can we cool the Earth by covering more of it with snow? Retrieved from https://climate.mit.edu/ask-mit/can-we-cool-earth-covering-more-it-snow

[7] Cloudy Nights Forum. No title. Retrieved from https://www.cloudynights.com/topic/803594-shaky-images-how-to-avoid-it/

[8] Cloudy Nights Forum. No title. Retrieved from https://www.cloudynights.com/topic/664700-jetstreams-affect-on-astrophotography/