Arcsecond facts for kids
An arcsecond (also called a "second of arc") is a very tiny unit used to measure angles. Think of it like a super-small slice of a circle! It's shown with the symbol 
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We use arcseconds in subjects like mathematics and astronomy (the study of space).
To understand how small an arcsecond is, let's break it down:
- A full circle has 360 degrees.
- Each degree is divided into 60 smaller parts called arcminutes (or "minutes of arc").
- And each arcminute is divided into 60 even smaller parts called arcseconds.
So, an arcsecond is 1/60th of an arcminute, and an arcminute is 1/60th of a degree. This means an arcsecond is 1/3600th of a degree (1/60 × 1/60 = 1/3600).
In a full circle, there are 360 degrees × 60 arcminutes/degree × 60 arcseconds/arcminute = 1,296,000 arcseconds! That's a lot of tiny slices!
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Why Do We Need Arcseconds?
When we look at objects far away, like stars or planets, they appear very small. Even small changes in their position or size need to be measured with great precision. Arcseconds allow astronomers to measure these tiny angles accurately.
For example:
- Astronomers use arcseconds to describe how big a planet appears from Earth.
- They also use them to measure how much a star seems to move over time (this is called "proper motion").
- Even the tiny wobble of Earth as it orbits the Sun can be measured in arcseconds.
How Small is an Arcsecond?
To give you an idea of how incredibly small an arcsecond is:
- Imagine a coin, like a US quarter, placed about 4.8 kilometers (3 miles) away from you. The angle that coin takes up in your vision would be roughly one arcsecond!
- Or, think about the width of a human hair. If you held a human hair at arm's length, its width would be about 30 arcseconds. So, one arcsecond is even smaller than that!
These tiny measurements are super important for making accurate maps of the sky and understanding how the universe works.
Related pages
See also
In Spanish: Minuto y segundo de arco para niños
Images for kids
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Example ballistic table for a given 7.62×51mm NATO load. Bullet drop and wind drift are shown both in mrad and minute of angle.
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Comparison of minute of arc (MOA) and milliradian (mrad).
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