What is UTC?

UTC (Coordinated Universal Time) is the world’s primary time standard. All time zones are defined by how many hours they are ahead of (+) or behind (–) UTC. In many places, this offset changes twice a year because of Daylight Saving Time (DST). Some locations do not change their clocks. For example, Altamira stays at UTC-3 year-round. UTC is computed by the Bureau International des Poids et Mesures (BIPM) using data from about 450 atomic clocks in 85 national laboratories worldwide.

Why use UTC offsets instead of just timezone names?

UTC offsets are unambiguous. Time zone abbreviations like “EST” or “CST” are not, because they are used in multiple unrelated regions. For example:

• “Eastern Time” exists in both North America (UTC-5/UTC-4) and Australia (UTC+10/UTC+11).
• “CST” can mean U.S. Central Standard Time, China Standard Time, Cuba Standard Time, and more.

A UTC offset always indicates a clear, fixed relationship to UTC.

What is the difference between GMT and UTC?

For most everyday purposes, GMT and UTC are the same, since both represent UTC+0. The difference is technical:

• GMT is the older term, based on the average solar time at the Royal Observatory in Greenwich, London.
• UTC is the current global standard, introduced in 1972. It is based on atomic clocks, making it more precise.

What is Daylight Saving Time (DST)?

Daylight Saving Time (DST) is when clocks are moved forward by one hour in spring ("spring forward") and moved back by one hour in fall ("fall back"). The purpose is to extend evening daylight. During DST, a location may use a different time zone name and a different UTC offset. Not all places observe DST. Some regions, such as most of Arizona and Hawaii in the United States, stay on the same time all year. For example, Altamira stays on Brasilia Standard Time (BRT, UTC-3) all year and does not switch for DST.

Does Altamira observe Daylight Saving Time?

No. The clock stays the same all year, and the UTC offset does not change.

What time zone is Altamira in?

Altamira is in the Brasilia Standard Time (BRT).

What is an IANA time zone identifier?

IANA (Internet Assigned Numbers Authority) time zone identifiers are the official, permanent names used by computers to handle time correctly, including DST rules. They use the format Continent/City, such as America/New_York or Europe/London . These identifiers ensure that devices automatically use the correct offset and DST transitions for each region.

The IANA time zone identifier for Altamira is America/Santarem .