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If you look up at the (clear) night sky, sometimes you will see a bright star-like object going from roughly west to east quite fast. That's the International Space Station (ISS), which travels about 250 miles (400km) above us at a speed of ~17,500mph (28,000 km/h), orbiting the Earth once every ~90 minutes.
Often you will see the ISS have several passes across the sky on an evening or early morning, and with each pass, its path across the sky is different. Sometimes...if you are lucky...the ISS may pass right across the face of the Moon or Sun**...and you can capture these events.
Imagine having an image of the ISS against a beautiful backdrop such the Moon's surface, or a sunspot group on the Sun!
We'll look at what sort of equipment is needed to capture these fleeting transits in a future blog, but firstly, how do you find out if the ISS is going to pass in front of the Moon or Sun for where you live?
Well, there is a website called "ISS Transit Finder" : https://transit-finder.com/ that can help.
ISS Transit Finder main page
On the main page you start off by entering your location by inputting latitude, longitude and elevation above sea level, or you can select where you are from a map or have the your position auto-detected. You then set the start and end date for the transit calculations. Finally, you enter how far in kilometres you are willing to travel in order for the calculation to determine whether or not the transit is visible in the your chosen region. Then simply press CALCULATE.
ISS Transit Finder with location information set for Leighton Buzzard
The page that appears next is the results page. This shows the dates, times and how far away from your current location, any upcoming Solar and Lunar close passes and transits will be visible. So hopefully amongst the close passes you may be lucky with an ISS transit across the Sun or Moon.
Results page for Leighton Buzzard
You can also see the track of the "event" across the ground on a Google Map and also find out more information about the event itself (e.g. ISS velocity) too (see below).
A closer look at the results for one of the close Lunar passes
Why not give ISS Transit finder a go for yourself and see if the ISS is going to get close to, or possibly, transit the Moon or Sun where you live!
** PLEASE NOTE: Observing or imaging the Sun is very dangerous and requires the use of suitable safety equipment such as Baader AstroSolar film for your set up.