As we approached September and October 2024, news of a once-in-lifetime visitor to grace our night sky excited many people around the world. Initial estimates identified comet C/2023 A3 (Tsuchinshan-ATLAS) as having possibly last materialised in the night sky above Earth some 80,000 years ago, although other estimates place the comet’s orbital period even longer at over 100 million years. At 80,000 years, Neanderthals would have been walking to earth the last time the comet graced Earth with its presence; at over 100 million years, it puts us in the early Cretaceous period when dinosaurs like the iguanodon were roaming the Earth.

In my last post on shooting the Milky Way from a plane, I introduced using tools like Stellarium to identify where certain cosmic objects are going to be in the night sky at a certain time of night. I introduced using Stellarium as it is a really and accessible tool for everyone since it is free. However, if you are minded to spend a little money on an app to help locate stellar entities in the night sky, PlanIt Pro is a solid choice offering the opportunity for more accuracy.

At the time of writing, PlanIt Pro is available on the Google Play Store for £9.49, and on the Apple iOS App Store for £9.99.

The interface

Stellarium is a planetarium style program which gives a virtual representation of the night sky at a given location at any given time. Whilst it is accurate enough to help identify the direction of a chosen subject, I find PlanIt Pro offers a little more accuracy as the map interface shows the exact location of your chosen object in relation to your camera’s position on a detailed map, as well as showing the field of view which a certain focal length lens will cover. In the example above, PlanIt Pro indicated that comet C/2023 A3 can be seen along the coast at Worthing, looking just south of west from Worthing Pier. PlanIt Pro also has a built-in virtual viewfinder feature which gives you a mock-up of the field of view for the chosen focal length which can help give an approximate assessment of how the landscape might feature in relation to your chosen object to track.

Toward the top of PlanIt Pro’s interface, you’ll notice a feature for the NPF rule. This is a helpful feature which can help you work out what is the slowest shutter speed usable if wanting to avoid any star trails. The shutter speed is worked out taking into account a combination of factors: aperture (“N”), pixel density (“P”), and focal length (“F”). The pixel density can be set in the settings by inputting your chosen camera’s megapixels – the higher the megapixel resolution of the camera, the faster the shutter speed needed to avoid star trails.

Whilst PlanIt Pro has a functionality to track objects in the night sky, the virtual viewfinder can also simply be used to help compose landscapes. The terrain modelling gives a rough idea of how the composition of your landscape might look like when shot from a certain location with a set focal length.

Additional 3D modelling subscription

In addition to modelling terrain, PlanIt Pro offers an additional subscription which allows the addition of 3D models within the app’s virtual viewfinder. I paid £6.49 for a year’s access to having 3D models within the virtual viewfinder as I wanted to use the 3D modelling of the Houses of Parliament to work out where comet C/2023 A3 might be in the night sky in relation to the London landmark. The 3D models can be helpful if you need to get a feel for whether a landmark might obscure the view of your subject because the building rises too high above the horizon when viewed from your chosen location.

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Whilst I found the 3D modelling functionality very useful for planning my shot of comet C/2023 A3 above Big Ben, I am unsure as to whether I will renew the subscription after it ends. The Houses of Parliament and Westminster Bridge are modelled, which were the models I needed for this particular shoot, but apart from that there is only a limited amount of landmarks modelled so even if a specific landmark might not get in the way, other nearby buildings might. Someone on social media asked me about PlanIt Pro after seeing the video above that I had uploaded to Instagram, asking me to check if their closest city, Marseille, France, had any 3D models. Despite being a major landmark, the Cathédrale La Major by the port of Marseille was not featured as a 3D model, but the Basilique Notre-Dame de la Garde did have a 3D model – the only model for the city itself.

Perhaps worth nothing, however, is that PlanIt Pro’s developers have included a feature with the subscription where users can upload their own 3D models and also share with other PlanIt Pro users, so the amount of models available, and ultimately the 3D model functionality’s usefulness, may increase as more and more people share 3D models of buildings to the community.

Closing thoughts

Comet C/2023 A3 and other fleeting celestial events present rare opportunities for photographers to capture the beauty of our universe. While apps like Stellarium are more than adequate for rough planning, I found that PlanIt Pro offers more precise tools with which to plan shots down to the finest details, from optimal positioning to 3D models of selected landmark locations. Though features like the 3D subscription may not suit everyone, the app’s flexibility and accuracy make it a valuable asset for capturing unique compositions. Ultimately, with the right tools, you will be well-equipped to immortalise these celestial moments.