What Time is it in Space?

Keeping tabs on a spacecraft way out at Saturn can get complicated. Unless otherwise noted, all times on this website have been converted to U.S. Pacific Time - the time zone of Cassini mission control at NASA's Jet Propulsion Laboratory in Pasadena, Calif.

Here are some definitions to help you keep tabs on Cassini mission time:

Coordinated Universal Time (UTC)

The worldwide scientific standard of timekeeping. It is based upon carefully maintained atomic clocks and is highly stable. The addition or subtraction of leap seconds, as necessary, at two opportunities every year adjusts UTC for irregularities in Earth's rotation.

Spacecraft Event Time (SCET) or Orbiter UTC

The time something happens at the spacecraft, such as a science observation or engine burn.

One-Way Light Time (OWLT)

The time it takes for a signal - which moves at the speed of light through space - to travel from the spacecraft to Earth. From Saturn, one-way light time can range from about one hour and 14 minutes to one hour and 24 minutes.

Earth Received Time (ERT) or Ground UTC

The time the spacecraft signal is received at mission control on Earth (the Spacecraft Event Time plus One-Way Light Time).

Local Time

Time adjusted for locations around the Earth. This is the time most people use to set watches and alarm clocks.

For example, Cassini began transmitting data from its very first close Titan flyby at 00:16 Orbiter UTC on Oct. 27. The first signal arrived at Earth one hour and 14 minutes later at 01:30 Ground UTC on Oct. 27.

Adjusting for local time, the signals arrived on the screens at mission control in Pasadena, Calif. at 6:30 p.m. PDT (or 9:30 p.m. EDT for folks tuned in at NASA headquarters in Washington, D.C.)

You can use a time zone converter or the chart below to figure out when Cassini's signals would reach your house:

Time Zone
Relative Time (from UTC)
Atlantic Daylight
Subtract 3 hours
Atlantic Standard
Subtract 4 hours
Eastern Daylight
Subtract 4 hours
Eastern Standard
Subtract 5 hours
Central Daylight
Subtract 5 hours
Central Standard
Subtract 6 hours
Mountain Daylight
Subtract 6 hours
Mountain Standard
Subtract 7 hours
Pacific Daylight
Subtract 7 hours
Pacific Standard
Subtract 8 hours
Alaska Daylight
Subtract 8 hours
Alaska Standard
Subtract 9 hours
Hawaii-Aleutian Daylight
Subtract 9 hours
Hawaii-Aleutian Standard
Subtract 10 hours
Samoa Standard
Subtract 11 hours
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