Gaia and the Cosmic Distance Ladder

I first heard about Gaia (Global Astrometric Interferometer for Astrophysics) during my undergraduate studies around 8 years ago. Although the impending space mission was hailed as one of the most important of the 21st century, it seems like it hasn't received nearly enough press in the last little while, which is why I wanted to talk about it in this blog post. The Gaia spacecraft was first proposed in 1993, on the coat tails of the Hipparcos mission, and was finally launched in December of 2013. And, as of a European Space Agency press release on July 29th, Gaia is now ready to do science!

Credit: "Gaia spacecraft". Via Wikipedia.

Gaia's motives range from discovering extra-solar planets to detecting quasars, but its most important purpose, in my opinion, is to precisely measure the distance to over 200 million stars within our galaxy to an accuracy of 10%, and out to a distance of 30,000 light years, well beyond the Milky Way's galactic centre. These distance measurements are obtained through a process called stellar parallax, where the apparent motion of a star is observed compared to more distant background stars as the Earth moves around the Sun.

Credit: "Stellarparallax2" by Original uploader was Booyabazooka at en.wikipedia - Originally from en.wikipedia; description page is/was here.. Licensed under Public domain via Wikimedia Commons.

Not only will the precise determination of the distance to this many stars in the Milky Way provide us with a detailed representation of the structure of our galaxy, but parallax is the most important fundamental measurement in the cosmic distance ladder. The cosmic distance ladder (or CDL) is a series of methods for determining distances in the cosmos which are calibrated to each other to greater and greater distances. The first rung in the CDL is the distances within our own solar system, which have been determined to great accuracy with radar. Once the Earth-Sun distance is determined precisely, accurate parallax measurements can be made.

Credit: The Worlds of David Darling

The next rung on the CDL is a class of objects called a Standard Candles. These are objects which have a known brightness, and therefore, when their apparent brightness is observed, one can calculate how far they are (sort of like figuring out the distance of a car based on how bright its headlights look). A couple of famous examples of standard candles are Cepheid Variables and Type Ia Supernovae, which are used to calculate the distance to objects much further than can be achieved with parallax (such as with distant galaxies). However, in order to calibrate the intrinsic brightness of these objects, the distance to nearby standard candles must be computed via some fundamental measurement, such as parallax. Thus, having accurate parallax measurements for nearby objects allows astronomers to determine the distance to bodies which are much further away.

It becomes apparent, when the determination of distance to far-away objects must be calibrated in this way, that an error in a lower rung of the CDL can seriously affect the distance measurements to very faraway galaxies. This problem became clear in the early 20th-century when Edwin Hubble was making his first distance measurements to nearby galaxies. When he discovered that the Universe is expanding, he calculated the age of the Universe to be only about 2 billion years, which was a problem because the age of the Earth had been estimated to be at least 3 or 4 billion years! This was later resolved when the brightness of Cepheid Variables was properly calibrated, which more than doubled the calculated age of the Universe. We now know the age of the Universe to be 13.8 billion years, and the value is mostly obtained from the distance measurements of far-off galaxies.

In conclusion, accurate distance measurements to objects within our own galaxy can have implications for our understanding of the history of the Universe! Even though the primary purpose of Gaia is to map out the structure of our galaxy, it will have a great impact on our knowledge of cosmology.

Bullet Journaling for a more productive life

Folks, so, so, so much has happened since I last wrote! First, the Relay for Life was a great success (you can read my buddy Erin's recap for a good summary). I also picked up a part-time job at a math tutoring centre called Mathnasium (I actually started end of February, but it's still news!), and then, mid-June, we found out about a really gorgeous house for rent that was actually within our price range. I'm talking back yard, in-suite laundry, central A/C… the whole nine yards! So, at the end of July, we moved! I promise to write a post about our new home, but perhaps when it's a little neater after we've unpacked a bit more.

So, here we are, in a new home for just about two weeks, still with what seems like a gazillion boxes left to unpack (though I have been making progress). I've felt like there's just so much to do that it sometimes gets overwhelming. This is why, at the beginning of August, I decided to start a Bullet Journal. You can read more about the process on the creator's website, but the basic idea is that you just write down things as they happen and distinguish between tasks, events, and notes with little bullets. I bought a cheap unlined notebook at the dollar store because I wasn't sure I'd enjoy the process, and I didn't want to waste a lot of money, but I'll probably go for a Moleskine or something similar for my next journal.

On the very first page, instead of making an index, I gave my contact information and wrote a little legend to keep track of the different bullets and signifiers. I put the index at the back of my journal instead of at the front so that if I ran out of space, I'd be able to continue on earlier pages. I've also seen some people use multiple indexes at random points in their journal. That could work too, I suppose, but it seems confusing. Here's my first page, decorated with colourful doodles on a slow day at work:

The next spread is my monthly calendar and tasks. On the left side, I made a list of all the days in the month, with the date and day of the week, and then started to fill in the more important events I already had planned. One small change I've made since I scanned these pages is I put a little event bullet to the left of each date so I can check them off as the days go by, which makes it a little easier to see where I am in the month. For my September spread, I'll definitely give my days a bit more room! On the left side, I started listing all of the tasks I could think of that I wanted to accomplish in August. I keep looking back on these and attempt to tackle one each day. The especially important and urgent tasks, I mark with an asterisk (for example, Daphne's sweater, which I need to finish before she leaves for England at the end of the month).

Then, we get into the meat of the journaling. Each day is a series of bullets. Tasks are demarcated by empty boxes, events are unfilled circles, and notes are filled in smaller circles. Every morning, I write down the things I want to get accomplished and the events for the day, adding more as I think of them. I check off tasks as I complete them and events as they happen. If, by the end of the day, there is a task left unaccomplished, I migrate it to the next day (with a little arrow) or cross it out if it became irrelevant. For the future, I think I'll probably only migrate tasks when I change pages, since they're still visible until I turn the page. As you can see, I've been pretty good at getting stuff done this way! It feels unnerving to still have little unchecked boxes at the end of the day, and just so good to add in that little checkmark when a task is complete.

Once I have enough tasks (or events or notes) that are similar in nature, I migrate them to collections, which I note in the index. The ones I show in the image below are for Blog Ideas and Crafting Projects. Some other collections I've added since are: Books to Read, Movies to See, and Songs to Learn on the Ukulele. I also added a collection for Future Dates. One minor issue with the Bullet Journal system is that it's difficult to plan for events further in the future than just the current month. So, as things come up, I just add them to the master list of future events, and when I start a new month, I'll migrate them there. Easy!

I've also personalized it a little with some Dalek post-its. I have a black one to indicate the current month, and a blue one to bookmark which page I'm currently on.

So that's my bullet journal! I've only been at it for two weeks, but so far, I think I'm enjoying it a lot. I'll admit to spending a lot of time fooling around on the internet, trying to find the perfect bullet journaling system, but overall, I think I'm getting more done this way. I'll certainly give a progress report once I've been at it for a bit longer.