Where are We?

"Hubble Ultra Deep Field" by NASA ESA is in the Public Domain A photograph taken from the Hubble space telescope. Almost all of the objects depicted are entire galaxies each containing around 100 billion stars!

We live in a vast universe. The photograph above was taken in a portion of the night sky that looks void of stars to the naked eye. What we see through the Hubble telescope is innumerably many galaxies. Astronomical distances like those in the photo are so vast that we define a new unit to describe distances - the light year. The light year is the distance light travels in a year. This distance is easy to calculate given the speed of light and the number of seconds in a year:

Some distances measured in light time are:

To moon is 1.25 light seconds
To sun is 8.3 light minutes
To former planet pluto is
To next nearest star (proxima centauri) is
To next nearest galaxy (Andromeda) is
To most distant object visible to naked eye (Triangulum galaxy) is
To edge of visible universe is .

"Andromeda" by ESA/Hubble is licensed under CC BY 4.0

Andromeda

Above is our galactic neighbor, the Andromeda galaxy. The photo is the largest composite photo ever assembled by NASA and the ESA. In this photo are over 100 million discernible stars in a narrow band of the galaxy. At the distance of 2.5 million light years, the ability to see individual stars is equivalent to taking a landscape photograph of a beach from a sailboat and seeing individual sand grains.

Where are We?

Andromeda

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