Tag Archives: pretty pics

Pluto! Pluto! Pluto!

Astronomers and planetary scientists are all abuzz as the New Horizons spacecraft draws ever nearer to Pluto. Its closest encounter will be in just a few days on July 14, 2015, but it will spend months sending data back.

I gave a public talk on June 25 about Pluto at a Sigma Xi Science Cafe in Las Cruces. It’s not often that an astronomy talk becomes outdated in real time, but take a look at those “Latest Images” slides and then compare them to these (all credit to NASA, of course):



New Horizons has been traveling since 2006 to bring us this view of an icy, distant world, and Pluto is just our cosmic backyard. Be sure to stay tuned in the coming week for the latest news and images. The best part of a mission like this is following along to see what never-before-known things are revealed each day. Space is full of surprises!


Buckets of Starlight

Have you ever watched rain fall on the pavement? It makes a beautiful, seemingly random pattern. No drop is more or less likely to fall in a spot where another drop has fallen.

Let’s say you wanted to collect as much water as possible during a 30-minute rainfall. What kind of bucket would you make? Tall, short… wide, narrow… orange, green… hot, cold… raised above the ground, in a hole… what would you do?

This is the exact situation astronomers face when designing telescopes. Only instead of rain, we are trying to collect drops of light – called photons. And instead of setting a bucket in a rainstorm, we put a mirror in a dark location and hope for clear skies.

If you took a minute to think about it, you probably settled on using as big of a bucket as possible to collect the most rain. The width of the bucket, or its area on the ground, is more important than its depth, so long as it isn’t going to overflow. And the color, temperature, and height above the ground don’t really matter. This is exactly why astronomers are partial to huge telescopes! The most important part of a telescope is its primary mirror, which is like a bucket for light. Giant mirrors don’t really give us a more “zoomed in” view of the cosmos, but they do let us collect more light – just like a big bucket will collect more rain. Photons of light are always raining down from the cosmos. Bigger mirrors mean more photons, and more photons means fainter stars and galaxies are visible.

Four telescopes, each with an 8.2 m diameter mirror, that together compose the aptly-named Very Large Telescope (VLT). Image credit: Wikipedia via ESO.
The aptly-named Very Large Telescope (VLT) comprises four telescopes, each with an 8.2 m diameter mirror. Image credit: Wikipedia via ESO.

There is another way to get even more rain, or photons, too, of course: leave your bucket out for more than 30 minutes. Maybe even leave it out for hours on end, and carefully set aside all the water – or light – you collect until you can add it all up later. The faintest, most distant galaxies are only visible to those with a big light-bucket and a lot of patience.

The Hubble eXtreme Deep Field. Nearly every object here is a galaxy, containing billions of stars. Hubble spent over 20 days total staring at a tiny patch of sky with its relatively modest 2.4 m diameter mirror to create this image.
The Hubble eXtreme Deep Field. Nearly every object here is a galaxy, and each galaxy contains billions of stars. Hubble spent a total of over 20 days staring at a tiny patch of sky with its relatively modest 2.4 m diameter mirror to create this image.
Image credit: NASA, ESA, et al.

As it turns out, falling rain and incoming photons can both be described by a special set of mathematical rules called Poisson statistics. Each drop hits the ground in a random spot. But the sum total of all of these random events is predictable. So, If you make a graph of raindrops hitting a bucket, or photons hitting a telescope mirror, you get a special shape: a Poisson distribution.

Astronomers use this to know how long we need to stare at a distant star or galaxy, or how big a telescope we need to use. Poisson statistics tells us that the quality of telescope data for a star emitting N photons will be 1/√N. (We like to say the uncertainty, or “standard deviation,” is √N.) This is great news! If you spend some time looking at a star and collect 100 photons, your uncertainty will be 10 photons, which is 10% of 100. That’s not very precise. But if you stare at it longer – or trade up to a bigger telescope – and collect 1000 photons, the uncertainty will be about 32 photons, which is only 3%. Much better.

Image credit: wellhappypeaceful.com
Image credit: wellhappypeaceful.com

The next time you look up at the night sky, remember that your eyes are miniature telescopes. Or perhaps fun-sized light-buckets. How much starlight can you collect?

Lookin’ good, Earth

If you thought you’d already seen that little dot of Earth as viewed from Saturn… well, you had no idea what was coming.

We’re the little blue dot.
This is a zoomed view…

Pretty much all I can do is quote Carl Sagan at this point.

Look again at that dot. That’s here. That’s home. That’s us. On it everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, lived out their lives. The aggregate of our joy and suffering, thousands of confident religions, ideologies, and economic doctrines, every hunter and forager, every hero and coward, every creator and destroyer of civilization, every king and peasant, every young couple in love, every mother and father, hopeful child, inventor and explorer, every teacher of morals, every corrupt politician, every “superstar,” every “supreme leader,” every saint and sinner in the history of our species lived there – on a mote of dust suspended in a sunbeam.

All image credits NASA.


As you may have gathered, I’m an astronomer and my name is merrdiff… er… Meredith.

I like to write, and I think a lot about astronomy. You can find me on twitter @merrdiff. But not everything in astronomy is readily explained in 140 characters or fewer, and thus: a blog.

Why “merrdiff”? It’s a nickname that evolved at summer camp. Only two syllables, easy to shout across a room, similar enough to my full name to generate a response. The original spelling may have been closer to “mur-DIFF!” On a bad day it can resemble more of a dog bark than a word or a name. But with “merrdiff” you have a lower chance of accidentally barking, and a higher chance chance of remembering my real name, which I do prefer in real life.

So, welcome aboard. To kick things off, here is a picture of both of us:

Earth and Moon as viewed from Cassini at Saturn.
Image from http://saturn.jpl.nasa.gov/photos/raw/rawimagedetails/index.cfm?imageID=294988.

This picture was taken on July 19, 2013. The distance of 898,414,528 miles (1,445,858,030 kilometers) makes it a little hard to find yourself in the photo, but trust me, you’re there. Also featured in this image: every place human beings have ever set foot.

Typical reflecting telescope that will result in X-shaped diffraction spikes. The secondary mirror and its supports are conveniently labeled as 3. The telescope tube is 1, and the primary mirror is 2.
Image from http://en.wikipedia.org/wiki/Diffraction_spike.

The bright vertical line on the larger dot (Earth) are most likely due to saturation – in essence, there was too much light in one part of the picture, and some of it bled to nearby pixels. The fainter crosshairs are called diffraction spikes. These show up anytime we take a picture of a bright circular or point-like object with a telescope. This particular pattern (an X) means that the telescope’s mirrors are supported by an X-shaped structure. If you ever see more of an asterisk-shaped spike, that means there are three support structures, and so on.

Cassini is a pretty awesome spacecraft, and it does a lot more than take pictures of Earth from a distance. But that’s more than enough for now. Keep looking up, and welcome to AstronoMerrdiff.