Wandering through the realms of the cosmos, pondering its huge vastness

Posts tagged “lunar occultation

Lunar Occultation of Jupiter – August 12, 2012

During the early morning hours of August 12, Philippine sky observers had a great chance of witnessing a relatively rare occultation of Jupiter (and some of its largest satellites) by our Moon. In astronomy, an occultation is an event that occurs when an apparently larger body passes in front of an apparently smaller one. In this case, the moon passed in front of the planet Jupiter; the pair being visible in the morning sky in the Philippines about 5 hours and 53 minutes before the Sun. At the moment of closest approach, the Moon was at mag -11.3, and Jupiter at mag -2.2, both in the constellation Taurus.

Despite the presence of hazy skies and thin clouds, we were lucky to have been able to observed the occultation event. Once I located the moon with my naked eye, I immediately pointed my superzoom camera  to it and took an image. I found Jupiter close to the moon but it was covered with haze. A few minutes later, Jupiter slipped behind the bright lunar limb and was visible no longer. Half an hour later, I tried to capture a video of the reappearance of  Jupiter, but the clouds had thickened to the point where I could no longer find the moon. When the clouds  had finally gone out of sight, Jupiter was already emerging from behind the dark limb.

Still, considering the less-than-ideal conditions, it was quite a successful observation. 🙂

Sky condition: 70-80% cloudy
Camera used: Canon Powershot SX40 HS

I observed this event from Marikina City.

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When Luna Occults Subra

Last March 17, 2011 , the University of the Philippines Astronomical Society (UP AstroSoc) set up at the PAGASA Astronomical Observatory in UP Diliman to observe the  occultation of the 3.3 magnitude star, Omicron Leonis (or Subra) by the 92% illuminated waxing gibbous Moon.

This event was headed by UP AstroSoc associate member and alumni, Anthony Urbano of EtenyWorks. Kuya Eteny, as the members fondly call him, was experienced in observing occultations.

During this observation, he brought his 6″ Newtonian Equatorial Reflecting Telescope (NERT) with a self-designed home-built clock drive attached to the telescope’s equatorial mount. To record the occultation event, a Canon S3IS connected to a laptop was mounted to the telescope’s eyepiece by means of a fabricated camera adapter. This modified camera can show it’s system time on its on-screen display. According to Kuya Eteny, the default precision of the on-screen timer is limited to 1 second, but a patch, currently made available only for Canon S3IS, increased the clock’s precision to 1/100 of a second — the maximum precision of the camera’s built-in clock.

The telescopes set up which included the 6" NERT (left-most)

You can learn more about this improvised clock drive project, the camera modification and  the rest of observation set up by visiting his site where he posts a lot of cool stuff about observation and instrumentation. His inventions are most fit for those amateur astronomers interested in modifying their own telescopes and cameras especially for the purpose of doing astrophotography. 🙂

The event was from 10:20 UT (ingress) and ended at 11:10 UT (egress). Although it can be classified as a ‘bright star occultation’,  the light coming from the target star wasn’t bright enough to pass through the thick clouds during the entire event. By around 11:50 UT, we decided to packed up since there was still no trace of the star near the Moon.

On-screen display of Canon S3IS (with the CHDK firmware upgrade) showing the Moon under the dark patches of clouds. The system time (upper right corner) in this screenshot reads 19:18:44 PST (11:18:44 UT) The occultation event during this time was over, yet there was still no sign of Subra which should be located a few degrees above the Moons upper right limb.

When the Moon passes in front of a background star during occultations, the shadow of the Moon cast by the star sweeps across the Earth. When the leading or trailing edge of the Moon’s shadow crosses an observer, the observer sees the star “disappear” or “reappear”. These events are usually very sudden, and timing the instant of occultation is an important astronomical measurement.

But why is it important to observe lunar occultations?

  • Observing lunar occultations is important because the results improve our knowledge of the position and motion of the Moon. For example, when you time the disappearance of a star behind the edge of the Moon to 0.1 second accuracy (a value easily attainable), you are actually fixing the position of the Moon’s edge in space to an accuracy of about 80 metres. i.e. you are making a measurement with a precision of only 80 metres over a distance of 384,400 km. (This is one of the most accurate measurements an amateur observer can make in any branch of science!)
  • Combining many such measurements of the Moon’s position over a long time gives astronomers new information about the Moon’s motion and orbit. For example, total occultation observations have shown that the Moon is spiralling away from the Earth at a rate of a few centimetres per year.
  • Total lunar occultations have also been used to provide valuable information about star positions, about the hills and valleys on the edge of the Moon, and to discover new double stars.

Aside from occultations by the Moon, there were also Planetary Occultations and Asteroid Occultations. Just as the Moon passes in front of background stars, so too do planets and minor planets (also called asteroids).

Planetary occultations are occultations of stars by the passing of a planet in front of it. However planetary occultations occur less frequently than lunar occultations because the planets appear so much smaller in our sky than does the Moon. Nevertheless, observing occultations of stars by planets has yielded some stunning discoveries – for example, the rings of Uranus, and the atmosphere around Pluto.

On the other hand, Asteroid Occultations are occultations of stars by the passing of an asteroid in front of it. Asteroid occultations can occur anywhere on the surface of the earth. A few naked eye stars have been occulted during the past 20 years, but most occultations are of quite dim stars typically between magnitudes +9 and +12. An occultation might occur at any time of night, on any day of the week. More and more fainter asteroid occultations are being predicted, so that it is likely that at least 5 events will likely cross your area in the coming year.

While occultations of bright stars by major planets are very rare, occultations by asteroids are a little less so. This is not because any one asteroid has a greater chance of passing in front of a star. Rather, it is because there are so many more asteroids to choose from!

Anyway, asteroid occultations are the only way — apart from spacecraft missions to asteroids and radar observations of nearby objects — to determine the approximate size and shape of those bodies and are, of course, much cheaper.

If, as an amateur astronomer or telescope owner, you would like to be part of history, contribute something relevant to the study of astronomy, or would love to see sights that few have witnessed, then occultations are the thing for you. The occultation process offers discovery and research. It is possible for amateur astronomers to discover new companions of stars, help to improve the polar diameter of the sun and moon, identify the existence of possible satellites orbiting asteroids, to improve knowledge of heights of lunar mountain peaks and depths of valleys in the polar regions, determine corrections to ephemeris errors and assess star position errors, improve knowledge of the shape and sizes of asteroids, and more through occultation science. It does not matter where you live in the world. If you have access to a computer and possess a telescope of at least 4-6 inches, know your geodetic position either from GPS or a good topographic map, have a source of time signals and tape recorder, you can make your own observations of these rare and critical events.

The International Occultation Timing Association (IOTA) web site can be found here and that of the International Occultation Timing Association/European Section (IOTA/ES) web site can be found here.

 The IOTA web site contains predictions that are updated frequently.

To be able to observe and correctly record an occultation event, you should first have knowledge to find your way about the sky. Most stars that are occulted by asteroids have average apparent visual magnitude of 10.

The program Win-OCCULT, authored by David Herald in Australia, provides accurate predictions of all types of occultations and related phenomena. You can obtain a copy of Win-OCCULT by downloading it from here.

Good luck! 🙂

Lunar Occultation of Omicron Leonis — 17 March 2011

For Philippine observers, a star-moon eclipse will occur on March 17, 2011, from 6:20 pm to 7:10 pm (PHT). The event will be visible to the naked eye, but is best observed with a pair of binoculars, or with an astronomical telescope.

image reposted from eteny.wordpress.com

DETAILS (from AstronomyLive.com)

VISIBILITY: This will be the second time this year that OMICRON LEONIS or Subra will be occulted. This time it’s again visible in south-east Asia and the Phillipines but now also Australia and New Zealand can join the party! The star will disappear on the dark side, meaning easy to spot and very interesting to broadcast.

STAR & MOON: Omicron Leonis is a +3.5 magnitude star. The waxing Moon will be 92%, so there is some lunar disturbance. It all starts in Iba, the Phillipines at 10:50 Universal Time. Check the link below, to see when it starts and ends at your location.

LIVE BROADCASTING SCORE: Good. Although the Moon phase is not optimal, this occultation is beautiful to watch mainly because it disappears behind the dark side of the Moon. Another thing that makes broadcasting this occultation interesting is that the white line on the map – locations where the star will disappear and reappear behind the mountains on the lunar edge during darkness- is near the densely populated cities of south-east Australia. So when living near those white lines you should really find yourself a telescope and watch this occultation taking place.

HOW TO READ THE MAP BELOW?: The white line indicates that the occultation takes place during darkness. Blue is occultation at twilight and the dotted red line indicates occultation during daylight. Cyan means the occultation takes place when the Moon rises or sets. Another important feature of these maps is that you can check grazing locations (on the lines), places where the star will ‘scrape’ the Moon and thereby is occulted for a very short period of time.


Skywatching Highlights: March 2011

March is filled with several exciting conjunctions, lunar occultations, planetary displays and other celestial events which will take place alongside with some big astronomy-related projects geared toward promoting the appreciation of the night sky to many people globally.

March Event Time Notes
5 New Moon 04:45 AM
6 Moon at apogee (farthest distance to Earth) 04:00 PM
7 Final close pairing of Jupiter and the moon for 2011
10 Moon shines near the Pleiades star cluster
11 Moon near star Aldebaran
12 Moon in between Capella and Betelgeuse
12 Juno at Opposition 6:00 PM
13 Moon shines in front of Winter Hexagon
13-18 Close pairing of Mercury and Jupiter dusk These appear low in western horizon
13 First Quarter Moon 07:45 AM
15 Gamma Normids Active from Feb 25 – Mar 22. ZHR 6
16 Minimum separation Mercury Jupiter dusk Mercury 2° to the left of Jupiter
16 Mercury 2° North of the Moon 01:00 AM
17 Lunar occultation of omicron Leonis Start: 6:20 PM End: 07:10 PM
17 Moon and Regulus are less than 10 degrees apart
19 Sun-Earth Day
20 Full Moon 02:10 AM This will also be the largest full moon of the year because it will be near perigee, its closest point to the Earth.
21 Vernal Equinox 07:20 AM

6th worldwide GLOBE at Night 2011 campaign

March 22 -April 4 for the Northern Hemisphere

23 Moon near red star Antares before dawn
23 Mercury greatest elongation East(19°) 09:00 AM
26 Last Quarter Moon 08:10 PM
26 Earth Hour 2011 8:30 PM
31 Venus 6° South of the Moon 09:00 PM

Note: Dates and sky displays are based on Philippine settings. Philippine Standard Time (PST) = UT + 8


Astronomy Terms:

Occultation – An event that occurs when one object is hidden by another object that passes between it and the observer.

Opposition – When two celestial bodies are on opposite sides of the sky when viewed from a particular place (usually the Earth).

  • it is visible almost all night, rising around sunset, culminating around midnight and setting around sunrise;
  • at this point of its orbit it is roughly[1] closest to the Earth, making it appear bigger and brighter.
  • the half of the planet visible from Earth is then completely illuminated (“full planet”)
  • the opposition effect increases the reflected light from bodies with unobscured rough surfaces
Greatest  (Eastern) Elongation When an inferior planet is visible after sunset, it is near its greatest eastern elongation. A planet’s elongation is the angle between the Sun and the planet, as viewed from Earth
Vernal Equinox The Sun will shine directly on the equator and there will be nearly equal amounts of day and night throughout the world. This is also the first day of spring (vernal equinox) in the northern hemisphere and the first day of fall (autumnal equinox) in the southern hemisphere




  1. EarthSky.org
  2. PAGASA Astronomical Diary — March 2011
  3. Philippine Celestial Events for 2011 (by PAS)
  4. SeaSky.org
  5. Wikipedia Encyclopedia