# How many AU is the nearest Galaxy from the milkyway?

Oct 4, 2016

It depends what you mean by nearest galaxy, but the conversion factor between light years and AU is about $63000$

#### Explanation:

Let's work out a conversion factor between light years and AU first.

The Sun is roughly $93000000$ miles from the Earth and light travels at about $186000$ miles per second.

So $1$ AU is about $500$ light seconds.

There are $86400$ seconds in a day and about $365.25$ days per year, hence:

$86400 \cdot 365.25 = 31557600 \text{ }$ seconds per year.

Dividing this by $500$ we arrive at:

$\frac{31557600}{500} = 63115.2 \approx 63000 \text{ }$ AU per light year.

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How far away is the nearest galaxy from the Milky Way?

The very nearest galaxy would be one of the small satellite galaxies.

There are about $50$ galaxies within about $1.4$ million light years of the Milky Way. The closest are about $1000$ light years from the edge, which by our reckoning would be about $63000000 = 6.3 \times {10}^{7}$ AU from the edge.

Perhaps of more interest is the distance to the Andromeda galaxy, our largest neighbour in the Local Group. This is about $2.5$ million light years away, which would make it about $160$ billion AU away.