Lunar Eclipse How To:

1. A Lunar Eclipse Watcher’s ‘How-to’ for the 31 January 2018 and 27 July 2018.
2. A Lunar Eclipse Photography How-To: 7 Tips
3. How-To Demonstrate Penumbral Shadows
Download PDF version of this Handbook here.
Download “Eclipse How-To” in Urdu  here.

Download “Eclipse How-To” in Marathi of the Handbook here.

1. A Lunar Eclipse Watcher’s ‘How-to’ for the 31 January 2018 and 27 July 2018

Planning ahead for viewing the lunar eclipse is highly recommended, because the most important factor for a good experience is the location selected to view the moon rise.

Note that some of the information given here is specific to the South Asian region.

Equipment: No special equipment is really needed to view the lunar eclipse. It can be enjoyed with the unaided eye.

However, if you can manage, having binoculars or a small telescope available at the location attracts  viewers. The binoculars or telescopes can be used to get a detailed view of the moon at various phases of the eclipse. A wide angle view of a binocular is better than a small telescope, especially since with binoculars you are using both your eyes.

Additional optional equipment are watches to note the time of ‘maximum’ eclipse (predicted to be 10:45 PM Indian Standard Time), record the exact duration of totality, etc. and cameras to photograph the moon. Newbies to astrophotography should familiarise themselves with some tips for photography (see below).

Step 1: Determine in advance, the time of moon’s position for your location, and also note the start and end times of the partial eclipse and total eclipse (given in the table below under “What are meant by ‘points of contact’ in the eclipses context?”).

These times can be obtained from various websites, such as www.timeanddate.com.  We have listed detailed information from this site for a few select locations in South Asia in https://www.iiap.res.in/people/personnel/pshastri/grahana/grahana.html

Step 2: Determine a good location for viewing the eclipse well ahead of the 31st January.

  • There should be a clear view close to the Zenith, with nothing obscuring this view in this direction.
  • Going to a height, such as a hill-top or the terrace of a high building could help.
  • The place should also be safe, with enough space to accommodate the number of adults and children expected to participate in the eclipse watching.
  • Choose as dark a site as possible! The darker the site, the better and more enjoyable it will be for watching the totality phase since the moon is rather faint during the eclipse. Areas away from city-light pollution would be highly recommended. Those who live in smaller villages and communities may be able to arrange for switching off of street and building lights to minimise the ambient light during totality which ends at about 19:40 hours Indian Standard Time.

                                                      (Sketch by Juny Wilfred)

Step 3Test out your location if there is some doubt as to whether obstructions such as buildings etc are in the way:

  • If you have regularly seen moon rise during full moon from your chosen spot, you are in good shape. You should be sure of an unobstructed view of the moon at zenith from your chosen location by at most, 01:00 AM (on 28th July) Indian Standard Time.  If not, read on.
  1. First determine the direction of North, which can be done using GoogleMaps or a compass. The latter points at magnetic north, but in South Asia,  magnetic north is within a few degrees of geographic north.
  2. Determine the direction towards which the moon on the 27 July 2018 relative to North, measuring clock-wise from North. Astronomers call this angle as the azimuth. For example, the directions of North, East, South, and West have azimuth angles of 0, 90, 180, and 270º respectively. Note that the azimuth angle of moonrise varies daily and is also varies by location. Sites such as timeanddate.com or mobile apps such as SkyMap or Stellarium will give you the azimuth angle of the moonrise. While using these apps, make sure that you set the date and time to 27 July 2018, 11:00 PM IST.
  3. Locate this direction from your spot and make sure there are no obstructions to your view by trees, buildings, hills etc. There are several alternatives to do this.

One way is to use a mobile app such as SkyMap (for free download), if you have a cell phone that has the ‘accelerometer’ and ‘compass’ hardware features. Download, install and open SkyMap. Calibrate the magnetic compass, for which instructions are readily available on the internet.

Tap on the screen to get the menu and click on ‘Time Travel’. Set the date (27 July 2018) and time to 11:00 PM IST, which is beginning of eclipse. Then enter ‘Moon’ in the search box. The app will lead you to pointing the phone to the approximate position of the moon in the sky. There should be no obstructions such as trees, buildings and hills in this direction as seen from your location.

A second way to do this is to use the mobile app Dioptra. Your mobile needs to have a magnetic compass, GPS, and camera for this application to work, and the magnetic compass needs to be calibrated, for which instructions are readily available on the internet.

Dioptra shows the camera live view with the azimuth angle written in the middle of the screen. Hold the mobile in the landscape position and make sure not to tilt it left/right or up/down. The app helps you with this by showing two angles on the left and right of the screen. The angle on the left shows the left/right tilt and the angle on the right shows the up/down tilt.

You need to make sure that these are both zero before noting down the azimuth reading.  

The displayed angle changes as you move your mobile to locate the azimuth angle for the moonrise corresponding to the day of the eclipse. If you find that this direction is obstructed by a building or a hill, you need to change to a better observing location and retry the exercise. The trick is to iterate this until your location gives enough margin on either side of the direction of moonris

Step 4: Publicise the event as appropriate and be there! Organise refreshments which are bound to be welcomed by the eclipse watchers!!

2. A Lunar Eclipse Photography How-To: 7 Tips

Tip #1: Focus perfectly. Indeed perfect focus is as important if not more important than the correct exposure. Whether you are using a cellphone camera or a DSLR with a zoom lens, focusing is important.

    • Cellphones usually do not have manual focusing, but tapping on the screen on the live moon would bring it into focus. Wait for it to finish its focusing routine before clicking. If the cellphone is moved after focusing, the focus will probably change, so focus again.
    • With SLR cameras, use the manual focus setting, live view and zoom in till the maximum level to check the accuracy of the focusing. Seasoned astrophotographers aim their cameras at a nearby bright star to focus accurately, and then swing back to the moon. Another trick is to use a Tab which has a bigger screen and can show the live view much better. The app on your Tab can also control your camera.

Tip #2: The stability provided by a tripod is a must. One of the most common reasons for blurry moon images is vibration or shake. These days you also get tripods for cellphones (or the cell phone holder that is stuck to the inside of car windscreens). Clicking is a source of shake, and in DSLR cameras there is the mirror shake. You can eliminate all these vibrations or shakes by using a remote control or simply using a 10 second timer.  

    • Shake can also be introduced by putting on the “Image Stabilizer” on DSLR lenses when using a tripod. Keep the IS setting or the VR setting at ‘off’ when using a tripod. During totality the moon can go very dim, and if the atmosphere is not clear, the moon can turn almost black, requiring long exposures. In this situation the earth’s motion might cause blurring. While you can’t stop the earth rotating, you could use high ISO to reduce the exposure time.

Tip #3: In India the moon will rise in eclipse, an opportunity for a landscape eclipse shot, This is a great opportunity to frame a well-known photogenic landmark of your city with the rising lunar eclipse. You will need a good amount planning to make a landscape shot with the eclipsed moon. Usually when you think of lunar eclipse images, a long focal length lens comes to mind. ‘The Photographer’s Ephemeris’ (TPE) app on your phone or similar websites offer excellent help. TPE combines the GoogleEarth and celestial angle/time calculations, to help you locate you and your camera precisely at the point where you can frame the lunar eclipse with the terrestrial landmark. You could also think of positioning yourself on a cliff with a vast landscape stretching down towards the east and the eclipsed moon rising behind that, get the picture?

Tip #4: Get your exposure right! If you are shooting a landscape shot, remember that the sun will be almost the same altitude below the horizon behind. So if you want to shoot the moon at 5° above the horizon, then the sun will be approximately 5° below horizon. Photographers call this the ‘Golden Hour’, and the exposure needs to be tuned to the sunlight conditions on the landscape. As the moon rises, and the sun dips down, at about 12° comes the ‘Blue Hour’, when the landscape is dimmed, and becomes predominantly blue. You must plan for longer exposures at this time to catch the landscape in proper light.

    • While shooting just the eclipsed moon, do note that during totality the moon can get very dim, requiring long exposures or high ISO. In the partial phases, part of the moon is brightly lit in the penumbra, and the other part of the moon is dark, red and in the umbra. Both parts of the moon require different exposures. A short exposure will render the umbra part severely underexposed, and an exposure which is long and correct for the umbra part will render the other part of the moon severely overexposed. You may like to build an image with high-dynamic range by clicking several exposures and merging them together later.

Tip #5: Do not forget to turn off the flash on the camera or cell phone!

Tip #6: Take it easy, enjoy the show, and take your loved ones along to see the lunar eclipse while you shoot in a leisurely manner. The lunar eclipse (unlike a solar eclipse) gives you a long opportunity to make a super image. Rather than shooting hundreds of shots, review your images, check for focus, check its histogram, and make corrections in the next image.

Share an instant image on the social media!

Tip #7: Affix your cellphone camera behind a binocular eyepiece or a telescope eyepiece. For stability you may need to couple the cellphone with an inexpensive adapter available online. You will get a superb shot, ready to be shared instantly!

3. How-To Demonstrate Penumbral Shadows:

Penumbral shadows occur if the source of light is extended. This phenomenon can be easily demonstrated with a torch light from a cell phone. Use the cell phone to cast a shadow of a small  dense object (such as a pencil) on a plane light-coloured surface, e.g., a wall or table top.

Step1: Hold the light (cell phone)  about 20cm or more from the surface, and the pencil very close (a few cm) to the surface so that a shadow of the pencil is cast on the surface. Notice that the shadow of the pencil has a sharp outline.

Step 2: Now keep the source of light in the same position as before and move the pencil away from the surface and much closer to the light while keeping the shadow of the pencil at roughly the same position. Notice that the shadow of the pencil becomes more blurred. A careful look will reveal a dark shadow surrounded by a much lighter “narrower” shadow.  The latter is the penumbra. If the light were a point source, such a penumbra will not occur.  The reason the penumbra is not visible in Step 1 above is that, even though the source of light is extended, the pencil is sufficiently far away from the source that the source functions as if it is almost a point source (see diagram).

The sketches show how the phenomenon of penumbral shadow can be demonstrated using an extended light source such as the ‘torch’ light from a cell phone, and an object with a sharp outline such as a pencil, casting a shadow on a light-coloured surface. When the object whose shadow is cast is far away from the light source the shadow is seen as sharp because the light source behaves almost point-like with respect to the object and so the penumbral shadow is negligible. When the light source is brought relatively close to the object, the shadow begins to blur at the edges and lighter shadow, viz., the penumbra can be seen around the main shadow. (Figure by Juny Wilfred)

 

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