Hubble’s operators created a picture (started in late 2003 and finished in early 2004) by repeatedly exposing a seemingly-black point in space about the side of a grain of sand. They took 800 exposures over the course of 400 orbits from September ’03 to January ’04. The resulting image is called the Hubble Ultra Deep Field.

A funny thing happened with this photo: there was something there. In that speck of blackness, that speck of nothing in the expanse of space that envelops us, Hubble took a picture of something when given enough time to do it. It turns out that there are galaxies in that void. In fact, in that tiny speck of space, Hubble found ten thousand galaxies.

Let’s have some fun with math. That square was 11.3 square arcminutes, which is 3.3 arcminutes on each side. With 10,000 galaxies in that space, we arrive at approximately 885 galaxies per square arcminute (884.955 to be exactish). Now the celestial sphere is 360º by 360º, or about 41,253 square degrees. From there, we subdivide it into square arcminutes and multiply by 602 to get 148,510,659 square arcminutes in the celestial sphere (since pi is involved, this number changes slightly based on the source’s accuracy for the number).

Now, multiply that by 880 to get 130,689,380,448. There are approximately 130 trillion galaxies visible to Hubble if it takes a couple of weeks to stare at them. :dizzy2:

In any given galaxy, there are on average 100 billion stars (est.). There are, therefore, approximately 13,068,938,044,800,000,000,000 stars visible to Hubble if it takes good look1 (that’s 13 sextillion 68 quintillion 938 quadrillion 44 trillion 800 billion if you want to actually say it, though it’s still far too big to actually rationalize it).

Moreso, this is based only on visible light. How much has yet to reach us? How much is so much further away that Hubble (or the future Webb) will have to watch for months to see?

But, for some more fun, let’s reduce this set a little. Of those 13.7 13.142 sextillion stars, how many have planets? How many of those planets are in the orbital zone that could host life? How many of those could have developed intelligent life?


Think about that when you look up next time. Someone else, somewhere else, is looking up and in some pinpoint in his sky is a speck of light that holds our galaxy, and you.


Curious About Astronomy: How big is the HUDF? (we disagree on some math towards the end, hence the footnote below)

Astronomy 162: Introduction to Stellar, Galactic, & Extragalactic Astronomy; Lecture 32

Wikipedia: arcminute


1 The formula I used is (360^2/3.14159265)60^2880*100000000000. Toss that into bc to get the resulting Impossibly-Large Number.

2 Update: I felt the need to be more accurate. In bc I did the following:

pi=3.14159265 scale=20 (4*pi*(180/pi)^2) * 60^2 * (10000/11.3) * 100000000000 13142536342266155651354.18520428500000000000

What I’m saying is: (number of square degrees in a sphere) * (number of square arcminutes in a square degree) * (number of galaxies in a square arcminute) * (number of stars in an average galaxy).

So that new number comes out to 13,142,536,342,266,155,651,354 or 13 sextillion 142 quintillion 536 quadrillion 342 trillion 266 billion 155 million 651 thousand and 354 stars. Approximately. :grin:

Inspired By


October 29, 2008