We’ve had many new people join Planet Hunters over the past several months (Welcome to all of you), and I thought it would be good to spend a blog post answering some of the recurring questions that get asked on the forums that our Talk moderators, the science team, and other members of the Planet Hunters community have answered in one spot for both new and veteran volunteers.
Q: How many people look at each light curve?
A: Currently 5 people review the same 30-day light curve. We combine the results from all the classifications of that light curve to make an assessment to decide if there is a transit or not. This is known as the wisdom of the crowd. By combining the results of many non-experts you can match or outperform an expert classification. You can read more about how we do that for Planet Hunters here. Once there are 5 classifications the light curve it is retired and a new unclassified light curve makes the list. We do have some preferences for what light curves get shown, but it’s roughly a random draw with a few rules. Those rules prioritize the light curves so that for example we show new light curves that don’t have known planets more than showing Kepler favorites or known eclipsing binaries to optimize changes of discovering something new.
Q: Is it possible go back and reclassify a light curve I’ve already classified?
A: No, once the classification has been submitted you can’t go back and change it. It’s okay if you’ve missed something or made a mistake. Usually if you see something other people who classified a light curve will as well and will have marked it.
Q: I just started with Planet Hunters. Am I starting from the beginning and seeing old data that’s already been classified by previous classifiers months ago?
A: You’re seeing the newest data we have on the website. Though we are currently showing data that has already been searched for planet transits by the Kepler team’s automated routines, we think there may be transits that the computer algorithms may have missed. Starting in 2013, the Kepler light curves will be released publicly at the same time as the Kepler team gets to see it, and we’ll be uploading that data as fast as we can go through classifying Quarters on the Planet Hunters website.
Q. What’s a Kepler favorite, and why doesn’t it show up under My Candidates?
A. A Kepler favorite is a star the Kepler team thinks has planets of its own and have identified what they believe to be planet transits. We don’t list those on your planet candidates list. We only list things Planet Hunters has identified as new planet candidates.
Q. What’s an eclipsing binary (or what’s an EB)?
A. An eclipsing binary or EB is a pair of stars that are gravitationally bound to each other and orbiting their common center of mass,. We call this an eclipsing binary because the smaller star passes behind and in front of the larger star along our line of sight. When the smaller and cooler of the two stars transits in front of the larger hotter star you get a drop in light like with a planet . We call this drop in light a primary eclipse. The difference from a transiting planet is that a planet has no significant light in the optical compared to a star, so when it passes behind you typically don’t see anything observable in the optical. In this case we have two stars that are luminous so we loose the light of the second star when it passes behind the larger star. That produces a smaller drop in light we call a secondary eclipse. So for a eclipsing binary light curve you get a big dip small dip repeating pattern. The light curve looks something like this if the stars are well separated:
Q. I can only mark 18 transits before the Finish button goes away. What do I do?
A. This is a known bug in the interface. We won’t be fixing that in this version of the site. Just mark as many as you can before the Finish button goes away (that should be about 18).
Q. How do you want me to mark EBs in the classification interface?
A. Mark the primary and secondary eclipses or as many as you can before the submit button goes away. The science team will sort out if those are planet transits or stellar eclipses in the light curve.
Q. What if I discovered a planet, will you let me know?
A. Yes, if you were the first to identify a candidate that we can confirm is a planet or the science team writes a paper where the majority of it is devoted to a specific candidate we will ask you to be a co-author on the paper. The Zooniverse has your contact info from when you signed-up. So not to worry we’ll email you. Also since we can’t stick 200,000 co-authors on a paper, every we paper write references our authors page to acknowledge the contributions from all our volunteers who make the science possible.
Q. What are those gaps in the light curve? Is that a big planet transiting?
A. If you see gaps like the ones shown above, that’s not from a really big planet or star that blocks out all of the light from the Kepler target star. It just means that Kepler isn’t collecting data. Usually that’s because Kepler is pointed away from the Kepler field so it can aim it’s antenna towards Earth to send its observations back to NASA. The other reason there might not be data is because something has happen on Kepler and it has entered safe mode to protect itself. When that happens the spacecraft isn’t taking data.
Q. What is the difference between SPH number and APH number?
A. Kepler is monitoring about 160,000 stars. We have chosen to show sections of the light curve that are the same size as the first quarter (35 days), and therefore Quarter 2+ light curves are broken into three sections of roughly 30 days (each quarter is typically 90 days except for Quarter 1). We have 5 days worth of overlap in each section, so that we don’t miss any transits that happen at the starts and ends of where we separated the light curves. You can tell which part of the light curve you are looking at by the APH#. The first two numbers are quarter and section. For example, APH22332480 is section 2 of Quarter 2. Quarter 1 light curves start with APH10. We use APH for the light curve sections and SPH for referring to the star itself. For the SPH numbers the first two numbers refer to what quarter the star first appeared in the public data set. For example, SPH21332480 first appeared is Quarter 2 Section 1. The star source pages (like http://www.planethunters.org/sources/SPH10129795) contain all the sections of light curve (we have available on the site) for you to review and the x-axis is the days from the first observation, so you can look for repeat transits in other sections of the light curve easily. Also available on the source page is a downloadable CSV file which contains all the available light curve data we have on the site.