Figuring out Zemanim in the air with Chai Air Tables

This week, I did something that I have never done before. I flew on a fast day. I'm in Israel for a week for a seminar jointly sponsored by Gemara Berura and the Menachem Education Foundation developing standards for teaching Gemara. I might blog about this in the future but first I want to share a nifty web app that I discovered just in the nick of time to help me on my flight.

The website is called Chai Tables and it helps you calculate Halachic Zemanim (the times to daven, say shema, start or end Shabbat, a chag, or a fast) for anywhere in the world. There are many other great websites that do similar functions, most notably What makes Chai Tables unique is its ability to calculate halachic times not just for a stationary location but for a moving target like an airplane. This can be quite difficult especially on a trip from west to east like a trip from the United States to Israel. You see as the plane moves in an easterly direction it is jumping time zones. It if it is also traveling in a northerly direction in the summer your night is also getting shorter. This means that if it is a fast day for example, your fast will be shortened. However, it will also begin sooner. If a fast begins at halachic dawn known as Alos Hashachar and one leaves around 12AM from Newark airport bound for Israel, how does one figure out when dawn will occur? It obviously will start earlier than dawn at your point of departure which in this case began around 4:20AM but how much earlier?

This is where Chai Tables proves itself so useful. You simply click in airplane times, then select Online Tables and you are led to a page where you can enter your flight information: your departure airport, date, and time, followed by your arrival airport, date, and time.

Chai Tables does the rest. It calculates a table with estimated times for dawn, sunrise, last time to say shema, mincha, sunset, and tzeis. All the times you will need to pray and keep halachic occasions like fast days while in flight.

It even shows you a map with your estimated route so you can compare your flight path on the airplane screen with the flight path it used to calculate times in order to make sure that they match. Wow! In my case, I discovered that the fast started much earlier than I had estimated around 90 minutes after takeoff at 1:02AM Newark time.

Thanks to Chai Tables I was able to keep the fast properly and be aware of times for prayer as well. I really don't know how I would have been able to figure this out any other way. This is just another example of how technology can be a great tool to help live a more religiously observant life. It all depends on how you use it.