R14DSLR

Introduction

Update 9 March:  A free iPhone / iPad  app for timing the occultation, “Occultation 1.0″,  is now available in the Apple App Store here .   A short YouTube video on how to use the app can be seen here .   More experienced observers are still encouraged to use video-recording and UTC-linked apps if possible, but this app should make it easier for less-experienced or first-time observers to participate.  Information on other apps for timing is available on the main Regulus2014 page under the heading “How can I best time the event?”

The principle behind observing the event with a DSLR-type camera is to help precisely measure two times – when the leading edge of the asteroid covers the star (the D or Disappearance event) and when the trailing edge of the asteroid uncovers the star (the R or Reappearance event).  Since the asteroid’s orbital speed is well known, these observations will measure the asteroid’s length in the “along-shadow-path” direction.  The position of the observer across the shadow zone will determine which part of the asteroid they will see Regulus pass behind and thus where on the asteroid their “length” measurement will fall.  Data from many observers will mean we can measure the asteroid along many cross-sections and really get a good idea of its shape (think ‘asteroid CAT scan from 100 million miles away!’)   (Since the shadow zone’s location is not known with perfect certainty, we need lots of observers because only observers who end up in the actual shadow zone will see the star disappear.)

In addition, if enough observers are arrayed across (perpendicular to) the asteroid shadow’s path, it will be possible to precisely determine the “width” of the asteroid (163) Erigone in the “cross-shadow-path” dimension.  (The closest “miss” observation on each side of the shadow’s actual path will be the ones that make this possible.)   Finally, the few video positive observations that end up being nearest the sides of the asteroid shadow (one might call these lucky observations “near hits”) will also help us estimate the size of the star Regulus (HIP 49699).  Regulus is a large blue star with a spectral designation of B7V.  The disk of the star is large enough that gradual disappearance and reappearance is expected. For observers along the path edge, a full occultation many not take place, with a ‘graze’ possible between the extremes of a complete miss and a total occultation.  If the graze zone is observed by enough observers, the size of Regulus can be determined by the width of the graze zone.  Further, the size of Regulus can be estimated by the length of the gradual disappearance and reappearance.  All of these potential observations are scientifically valuable and all can be done by amateur observers with simple equipment such as a DSLR running in video mode and zoomed in on the star during the period of the occultation.  That is a lot of information from just a few seconds of  video, which is what makes this simple technique so powerful.

Call for Observers

If you are an observer with a DSLR or equivalent digital camera with movie capability and zoom lens click on the Google path map to see if your home location is near either of the path edges shown as a blue line.  (The centerline of the path is shown as a green line.)  Potential variation of the path due to uncertainties in the asteroid orbit and star position are shown as red lines.  If your home location (or you are willing to drive to a near edge path location) is between the red and blue lines, or inside the blue line by the same distance between the red and blue lines, then you have a reasonable chance of recording an occultation by the asteroid’s main body.   In addition to the main body, the asteroid (163) Erigone may have undiscovered satellites (many asteroids do have satellites).  For this reason we encourage people to observe this event from any location within 1000 km of the predicted path.

For the simplest set up, all that is needed is a digital SLR or similar digital camera with telephoto lens or zoom lens, a tripod, the capability to record in video mode, and a clear view of Regulus at the time of the event.  Here are some cameras that have already been tested and found to be capable of observing the event under reasonably dark skies:

  • Canon PowerShot SX20 IS at near full zoom
  • Canon T3i, using either a 75mm or 135mm telephoto lens

The above list will be expanded as more test videos are submitted for review.

You can find some basic information on using DSLR video recording for occulations at the DSLR page.  And the paragraphs below provide more specific suggestions for recording the event with Erigone and Regulus.

So, you are interested in participating in the scientific observation of the Regulus occultation using your DSLR camera?  Here are some tips and guidelines to observers to use, as well as instructions on how to submit videos for scientific use by IOTA and professional astronomers.

  • Set the camera on a sturdy and easy-to-adjust tripod.
  • Set the camera to Movie mode.  Use the fastest video frame rate possible, up to a maximum of 30 fps (frames per second).  Slower frame rates can be used, but some of the scientific value of the video will be lost.
  • Use 1/30th second for shutter speed [this is the typical default setting for 30 fps].  If the shutter speed can be adjusted to be faster than that, do not set it faster, since a faster setting will just reduce the brightness of the star on the video.
  • Use a lens with a focal length in the range of 75-300 mm.  A zoom telephoto will work fine. You may find that you cannot see the star until you zoom in to 135 mm or more. You can continue to zoom in, but remember that the earth is turning and so your camera will be carried away from the star over time. This will make the star appear to drift across your viewfinder screen. The more you zoom in, the brighter the star will appear but the faster it will seem to drift, so use the shortest focal length you can while still seeing the star clearly. You don’t want the star to drift off the screen just before the occultation happens!
  • Use the lowest focal ratio possible: f/4-f/5.6 is typical for longer focus lenses or zoom lenses.
  • Use the highest ISO setting possible.  A higher ISO will make the star appear brighter on the video.  Use ISO 3200 or higher if possible.  [Note: some cameras cannot change ISO when in video mode.]
  • When focusing, it is best to use manual focus and easiest to focus on a distant bright object, such as Jupiter which will be not too far away, or a very distant streetlight.  Once you have focused your camera, you can then turn your camera toward Regulus to observe the event.  If you have one, use the viewfinder magnifier option on your camera to help find Regulus
  • Find Regulus well in advance of the predicted event date.  Shoot a 30-60 second test video.  Save the video and send a copy to IOTA for evaluation at least two weeks prior to the event (see uploading instructions below).  If there are any questions or issues with your video, it is best to resolve them before the event.
  • Set up well in advance of the event time, on event day.  Make sure your batteries are fully charged.  If it is cold outside, keep your camera and batteries warm.  Use the settings you used to shoot your test video.  Start recording at least 30 seconds before the predicted time at your site and record for at least 30 seconds after the predicted time at your site.  The predicted time of the event depends on your location as noted in this topic posting.
  • Record your site location coordinates from a GPS device, or from Google Earth, or provide you site location street and city address and location of site on your report to IOTA when you send in your video.

Submitting your video to IOTA. 

It is important that all videos be analyzed by experienced analysts and appropriate software in order to derive the most information from videos submitted. To submit your video to IOTA, do the following steps as appropriate for your device:

  • Transfer the video to a PC.  You may transfer the SD card into a PC SD card reader port, or you may transfer via USB or Firewire, whichever works best for your device.  Transfer the file directly by copying it from the SD card to your computer hard drive.   Do not open the file in MovieMaker or any other program.  For safety, make two copies in two different places on your computer.
    • Rename one of your copies of the video file name as follows:  Erigone_Occultation_YourName_YourCity_YourState.xxx; where xxx will be the file extension of the video format such as .mov or .avi etc.
    • Submit the file in native video format.  Do no open or save the file in any other program.  We want a file of the original data.
  • Upload the file to Google Drive and share the file with triastro@oregontrail.net.  In the share message, include your name, observing site, and video file name submitted to Google Drive.

Good luck if you attempt to video record this event with your DSLR!