What Time is it?

(printable version)

So you've paid attention to all our cool data, but you've become confused about time. Time is supposed to be simple to understand, right?

Well, unfortunately time isn't always a still concept.

There are two reasons you may be confused. Some of the times on our site may be listed using hours greater than 12, for instance 2100. Another reason is that some of the data appears to be from the future. Far out man! But how can this be?

Understanding GMT

Scientific research is done all over the globe. But when scientists come together, they need to be able to speak in the same language of time.

To do long-term studies, many scientists use a time called GMT (Greenwich Mean Time). Recently, scientists have agreed upon an even more precise standard called UTC (Coordinated Universal Time). Essentially GMT and UTC are the same time (save a few decimal places in the seconds), but UTC is becoming more and more the preferred standard.

Essentially, GMT is the time at 0 degrees Longitude, which coincides with Greenwich, England. When a scientist on the East Coast of the United States measures an event at, say, 6:00 AM Eastern Standard Time (EST), he will record the simultaneous time in Greenwich, England, which is 5 hours ahead of the US East Coast, or 11:00 in the morning.

Perhaps, even more importantly, GMT never uses Daylight Savings, thus it never skips or repeats hours during the year. This means that in the summer, when Eastern Daylight Savings Time (EDT) is in effect on the East Coast and we are one hour "ahead" of standard time, GMT is only 4 hours ahead of the local time (EDT). In the the winter, GMT is 5 hours ahead of local Eastern Standard time.

To put this simply, scientists all over the world basically all use one time zone, that of Greenwich, England. By doing so scientists are able to compare their data without having to translate for various time zones or daylight savings.

The 24 Hour Clock

GMT also has another quirk. Normal clocks go through twelve hours twice in one day. This makes it very confusing for machines like computers to determine which hour it really is. So, many large scale systems use the 24-hour clock, sometimes called "military time." In the 24-hour time system, Midnight is represented by 00:00, 1:00 AM by 01:00, and so on. When you get to 1 PM you simply add twelve to the hour, hence 13:00. The last minute in the day is then 23:59 (11:59 PM) which then turns into 00:00 (midnight) on the next day. Notice that in the 24-hour time system there is no need for AM or PM. The time already indicates which half of the day the hour is in.

Putting it all together

All of our satellite and coastal radar data is collected using GMT. Thus, in the winter, you will need to subtract 5 hours from the timestamp to determine the time in Eastern Standard Time (EST) that the data is from, and in the summer you will need to subtract 4 hours to obtain Eastern Daylight Time (EDT). Our chart below can help you figure this out.

For more information on Time and how to understand it, check out the cool Exhibits and FAQ at the Division of Time and Frequency's web site, part of the National Institute of Standards and Technology (NIST).

* These hours are from the next day. When converting from GMT back to EDT or EST, you will have to subtract 1 from the date.