Photographing the Feb 2013 lunar occultation of Jupiter from southern Australia

Written by Gary on February 3rd, 2013

Those of us who live in the southern parts of Australia may be fortunate enough to photograph this lovely celestial event which will take place about midnight on Monday 18th February 2013 in Victoria, but just after sunset in Perth.

The highest quality images of Jupiter will not be possible in Eastern states due to the event taking place very close to the north-west horizon and thus high resolution imaging will not be anywhere near as detailed as if Jupiter were high in the sky where there is less atmospheric disturbances.

Nevertheless it should be a fun and rewarding event for those who have the equipment and are prepared to do some planning.

As a minimum one would need a super telephoto lens with effective focal length of at least 600mm in 35mm full frame terms – the more the better, plus a sturdy tripod.

Those wishing to taking highly magnified images will need to attach their camera or video cam to a good telescope on a sturdy motor driven equatorial telescope, although with some hard work, a Dobsonian mounted telescope will be possible given the short exposure.

Traditionally, the best images of Jupiter are taken using a video camera attached to a telescope shooting frames at 10-60fps for up to 1 – 2 minutes (longer than 2 minutes causes blurring due to the rotation of Jupiter interfering with images), and then these images are stacked using special sofware such as Registax, then sharpened using wavelet or deconvolution technologies, then contrast is adjusted to get the final image.

The occultation of Jupiter will limit this approach as there is also the confounding movement of our moon.

Interpreting the astronomic data:

  • the moon phase will be 56% which is a touch after 1st quarter being at an angle of 97deg to the sun in relation to earth
  • the northern limits of visibility of the occultation (where it will be a grazing occultation) is an almost linear line running from near Canarvon in Western Australia, through just north of Flinders Ranges in Sth Australia, then to just north of Albury in NSW. there is no southern limit in Australia however, Hobart will not be able to witness the reapparance phase as the moon will be setting.
  • it will not be visible in any other country.
  • for Melbourne (latitude 37deg 43.7 south)
    • Jupiter will disappear behind the dark part of the moon at 12h 32:56 UTC (add 11 hours for AEDT daylight saving to give 23:32:56 local time) and will be 11 deg above the horizon at azimuth 307deg (37 deg north of true west)
    • Jupiter will reappear behind the bright part of the moon at 13h 10:01 UTC (add 11 hours for AEDT daylight saving to give 00:10:01 local time) and will be 5 deg above the horizon at azimuth 301deg (31 deg north of true west)
  • for Perth (latitude 31deg 56.4 south):
    • Jupiter will disappear behind the dark part of the moon at 11h 39:43 UTC (add 8 hours for WST to give 19:39:43 local time, ie not long after sunset) and will be 36 deg above the horizon at azimuth 344deg (74 deg north of true west)
    • Jupiter will reappear behind the bright part of the moon at 12h 45:38 UTC (add 8 hours for WST to give 20:45:38 local time) and will be 30 deg above the horizon at azimuth 327deg (57 deg north of true west)

Choose a camera, preferably a mirrorless one:

If you wish to use a camera instead, the best camera to choose would be one of the latest Micro Four Thirds cameras such as the Olympus E-M5, E-PL5 or the Panasonic GH-3 for the following reasons:

  • the pixel density is higher than on any dSLR and thus Jupiter, which has a diameter of only 0.01 arc seconds, will cover many more pixels (and thus theoretically capture more detail) on one of these cameras than on a dSLR for a given lens or telescope set up – here is the math:
    • if using a 5000mm effective focal length telescope, this will cast an image of Jupiter of only 0.9mm on the sensor
    • if you use a 36mp Nikon D800 full frame camera, Jupiter will cover 150 pixels
    • if you use an Olympus E-M5 camera, Jupiter will cover 240 pixels – that is 60% more pixels available
  • you will generally only need ISO 1600 on a 10″ Newtonian telescope to give a shutter speed of 1/600th sec at f/20, although if using a 3″ refractor telescope, you will need to be using closer to f/66 to achieve 5000mm focal length, and thus you may need ISO 6400 and shutter 1/300th sec
  • there is no mirror so you do not constantly need to be putting the camera in mirror lock up mode (not doing this will destroy your image detail by causing vibrations from the mirror)
  • they are designed for continous live view and magnified live view to assist manual focus is easier to access
  • the E-M5 can shoot at 9fps if you did want to select out the sharpest images or stack them – but you will want a remote shutter cable to avoid shaking the camera, and consider just shooting jpegs to avoid having to wait for the buffer to empty after a burst (use a fast SD memory card to optimise this)
    • hint: use TriggerTrap iPhone app and dongle connected to the E-M5, set E-M5 to Hi Drive mode, set exposure to desired shutter speed (not Bulb as suggested by TriggerTrap), and either use:
      • TriggerTrap “Cable Release” mode and hold iPhone app shutter release down for duration of burst – perhaps the easiest mode to use!
      • TriggerTrap “Timelapse” mode to duration (eg. the minimum of 13secs), and number of photos to desired number, press and release the app button and the app will control shutter release, although, as the camera’s cache is saturated, capture rate declines while the app still keeps pretending photos are being taken at the set rate.
      • works with iPhone 5 as TriggerTrap uses the headphone socket
  • they are amongst the lightest cameras which is handy when mounting on telescopes

First, the super telephoto approach:

  • sturdy tripod
  • super telephoto lens attached to camera of choice, lock the focus and change to manual focus
  • aim to compose image aesthetically in relation to horizon subjects
  • if you are lucky enough to have a few small clouds around, time it so the cloud is covering the moon and not Jupiter to better balance the contrast in brightness
  • consider 2 types of exposures (but bracket these to get the best for your set up and allow for atmospheric extinction if low altitude as they will be this time):
    • one for Jupiter itself eg. ISO 400, f/8, 1/600th sec
    • one for the Jovian moons and earthshine on the dark part of the moon: eg. ISO 400, f/8, 1 sec
  • don’t forget mirror lockup and use the self-timer to reduce camera shake

The telescope approach:

  • ensure telescope temperature has equilibrated by leaving outside for several hours to reduce poor refractive effects inside the telescope
  • if the telescope is a reflector, ensure it is accurately collimated
  • use an equatorial mount where possible and try to get reasonably accurate polar alignment – given the short exposures, precise alignment is not needed unless you are stacking many images
  • don’t forget to have the battery fully charged to drive the mount
  • decide between:
    •  prime focus (no eyepieces but lower magnification, although can use teleconverters)
    • eyepiece projection (use eyepiece and special eyepiece projection adapter for higher magnification)
    • afocal technique (use eyepiece and camera lens – useful for point and shoot cameras where the lens cannot be removed)
  • ensure focus is precise
  • consider 2 types of exposures (but bracket these to get the best for your set up and allow for atmospheric extinction if low altitude as they will be this time):
    • one for Jupiter itself eg. ISO 1600, f/20, 1/600th sec
    • one for the Jovian moons and earthshine on the dark part of the moon: eg. ISO 1600, f/22, 1 sec
  • don’t forget mirror lockup and use the self-timer to reduce camera shake
  • consider burst shots or video mode to help address issues with poor seeing conditions

Choose a location:

  • this is particularly a problematic issue with this occultation given it occurs so close to the N-W horizon
  • in Melbourne, the disappearance phase occurs when it is 11 deg above the horizon and the reappearance phase occurs when it is only 5 deg above the horizon
  • Perths viewer are much more fortunate here, as it starts at 36 deg above horizon with reappearance at 30 deg above horizon, so they should get far better images that the eastern viewers
  • so those in Melbourne would do best to find an elevated position with a clear view to the NW (the disappearance occurs at azimuth 307 deg (37 deg north of west) while the reappearance occurs at 301 deg (31 deg north of west) )
  • the good news is that light pollution is not such an important factor – it could be done in a suburban backyard if you can see the event without trees, buildings or mountains intervening.
  • determine horizon – given it will be just 5 deg above the horizon for the last phase in Victoria, Victorians may well wish to calculate how far east of a mountain they need to be so it does not hide it:
    • a top of a mountain will hide the horizon, if the viewer is within a certain range dependent upon the relative height of the object (eg. mountain or trees) above the viewer:
      •  ignoring refraction of light issues, the approximate distance in km = 3.57 x square root (height difference in metres)
      • thus for a 100m hill, the viewer should be more than 40 kilometres away if they wish to see the horizon without the hill intervening
      • for a 400m mountain, the viewer should be  more than 70km away
      • the Lerderderg State Park rises to over 500m and is NW of Melbourne and one needs to be 80km away
      • Mt Macedon at 615m height requires the viewer to be more than 90km away unless they can stand on another mountain
  • search for a site on Google maps in topography mode (so you can see heights of hills)  and use a paper triangle cut out to ensure line of site is clear of hills or mountains:
    • using A4 sheet of paper, use its width of 21cm as your East-West base, create a triangle with a north-south side of 15.8cm (for 307deg) and mark on it a 2nd hypotenuse line at the 12.6cm mark for the reapparance at 301 deg (assuming you are in Victoria)
    • hold the triangle with the right angle corner in your left hand, holding the base parallel with your screen, and the right side apex on your location.
    • the hypotenuse will then be your line of site to the occultation
    • for other locations with different azimuth readings, use N-S paper measure = E-W paper measure x tan (azimuth-270deg)
    • your selected site should also be able to be easily accessible with a telescope and on public land, and have no trees to the north west
  • lastly, the location should preferably be out of the prevailing wind on the night – in Victoria, this is usually south-westerly but may be westerly or north-westerly and occasionally south-easterly or easterly
  • potential locations near Melbourne include Mt Dandenong, Mt Macedon, south-west of Geelong, north-east of Ballarat, areas north of the Great Dividing Range.

 Then you need the weather to be kind:

  • thick cloud will obliterate your chances, as will any significant cloud on the horizon which does take a long time to move out of your way
  • strong winds will play havoc with your ability to keep the set up still
  • as it is summer, a hot day could really affect your telescope’s seeing if it is left in the hot car so give it plenty of time to equilibrate with the night air
  • seeing is likely to be poor at such low altitudes – unless you are in Western Australia, good details on the planet Jupiter will be hard to capture, you may just have to accept the outline of it’s bands.

If you plan well, practice and are lucky with the weather, you may be able to capture an image similar to this grazing occultation I took using a Canon S30 point and shoot camera through a 10″ Newtonian in 2005:

 

Jupiter

see also my wiki page on photographing occultations which also has links to data and maps for this occultation

BONUS: 2 fairly bright comets to photograph!

You may as well tackle 2 fairly bright comets if the conditions are good, you are away from light pollution and can piggyback your camera on a motor-driven equatorial mount telescope:

  • comet C/2012 F6 Lemmon
  • comet C/2011 L4 (PANSTARRS)

Appendix – examples of Olympus E-M5 for Jupiter:

  • Olympus ZD 50-200mm f/2.8-3.5 lens with EC-20 2x teleconverter:
    • Jupiter measures only 25 pixel diameter at effective focal length in 35mm terms of 800mm f/7; tripod exposure for Jovian moons at 20deg altitude: ISO 800, f/7, 1/4sec
  • Canon FD 500mm f/8 mirror lens:
    • Jupiter measures 30 pixels; exposure for Jovian moons ISO 800, f/8, 1/4-1/8th sec; For Jupiter’s bands: 1/200th sec;
  • Maksutov 500mm f/5.6 telescope with Olympus EC-20 2x teleconverter tripod mounted:
    • Jupiter measures 75 pixels; exposure with Jupiter at 30deg altitude: ISO 800, f/11, 1/4sec for the Jovian moons (the longest without substantial star trailing effect at eq. 2000mm focal length and can use IS set at 1000mm focal length)
  • 10″ f/5.6 Newtonian prime focus plus Olympus EC-20 2x teleconverter:
    • Jupiter measures 145pixel diameter; exposure ISO 1600, 1/200th sec at effective focal length in 35mm terms of 3625mm f/14
  • 10″ f/5.6 Newtonian afocal method using Olympus mZD 45mm f/1.8 lens with 25mm eyepiece:
    • Jupiter measures ~125pixel diameter; exposure ISO 1600, 1/300th sec at effective focal length in 35mm terms of 3125mm f/12
  • 10″ f/5.6 Newtonian afocal method using Olympus mZD 75mm f/1.8 lens with a 25mm eyepiece:
    • Jupiter measures ~215pixel diameter; exposure ISO 1600, 1/100th sec at effective focal length in 35mm terms of 5375mm f/21
    • this is probably the best compromise however resolution is still very highly dependent on timing of the shot in relation to the rapidly changing seeing conditions
    • sequential shooting highly recommended to allow selection of the sharpest images
  • 10″ f/5.6 Newtonian afocal method using Olympus mZD 75mm f/1.8 lens with a 25mm eyepiece plus 2x Barlow lens:
    • Jupiter measures 430pixel diameter; exposure ISO 3200, 1/60th sec at effective focal length in 35mm terms of 10750mm f/42

Don’t forget, this event will be at about 5deg from horizon for Eastern states, so you need to adjust your exposure to allow for about 2 stops of atmospheric light extinction!

 

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