Tuesday, November 22, 2011


Fireballs in the Sky - 
Geminids Meteor Shower on Dec 14th, 2011



Star gazers can soon witness another sky theatre spectacle in the mesmerizing night skies - the Geminids Meteor Shower, peaking on 13th/14th Dec. This is one of the best meteor showers of the year and never disappoints observers. Unfortunately the peak of the shower this year falls 3 days after the Full Moon and that will hamper the observations. Geminids peak on 14th December 2011 at 16:35 UT or 10:05 IST

The source of the Geminids shower is asteroid 3200 Phaethon. There's a cloud of dust trailing the asteroid and the Earth plows through it every year in mid-December. Bits of dust traveling  at 80,000 mph hit our atmosphere and turn into glowing meteors.The Geminids got its name because its radiant position, from which it appears to originate, lies in the constellation Gemini.


Observe and Photograph the Geminids:
SPACE has the following handouts and suggestions to ensure that each one of you can go out and observe this wonderful spectacle (Though Moon will be a deterrent) .

SPACE suggests that students, amateur astronomers and the public go out on Dec 14th morning to a dark site away from lights and observe this nightsky spectacle. Details about timing and observing suggestions can be found listed below.

Meteor Showers provide a wonderful photographic opportunity. Another post in this blog  provides details on techniques and suggestions by SPACE to employ for meteor photography.



Record and Report:
We would like all observers to become Citizen Scientists and record their results and report it to IMO (International Meteor Organization). Details can be found in the attachment, as well as on the IMO website, listed below. Each citizen scientist who reports their observations will have the privilege to have their names and results listed on the IMO website.

SPACE has been observing Geminids for past few years and reported successfully to IMO. This can be found on the blog listed below.


Geminids Details:
Maxima - 14th December 2011 at 16:35 UT or 10:05 IST
ZHR (Zenith Hourly Rate) - around 120.
The best time to watch the activity near the peak in India is on 13th December night/early morning on 14th.

Relevant Websites:
SPACE astrophotography of Geminids:
https://picasaweb.google.com/109156850798846600382/GEMINIDS2010

https://picasaweb.google.com/109156850798846600382/Geminids2009


IMO website reporting location:
http://www.imo.net/visual/major/observation

Enjoy the last meteor shower of the Year.

Monday, November 21, 2011


Shoot the Geminids

Photographing meteors such as the Geminids is possible using a Single Lens Reflex (SLR) camera. The camera must have a "T" (time) or "B" (bulb) setting for taking time exposures. You will also need a cable release, a tripod or a very stable surface to place the camera on, for best results. The camera will need a lens that is between "fisheye" and 50mm. Lenses larger than 50mm may capture too small a field of view. This article is written for the film camera but can be used as it is for digital SLRs.


Here is what you will need to do.

Set up your photography equipment in an area that is shaded from any stray lights that may interfere. This is absolutely necessary!

Set the camera on a tripod or some other surface that is very stable. Make sure the focal ratio is set to the lowest possible setting. This means that the aperture of the camera is "wide open". Make sure the camera is set to "B" or "T" for time exposure. Set the focus to infinity.

Aim the camera at the area of the sky that you intend to photograph. Once positioned properly, make sure the tripod is locked down to prevent its "head" from moving under the weight of the camera. If you do not have a tripod, use things to prop the camera up in a way so that it is stable and so that you can still look thru the view finder.

Depress the cable release button and lock it in place. Allow the camera to take a picture for anywhere from 15 to 30 seconds, maybe more. Once the desired time has elapsed, release the cable release lock which will end the exposure. While taking the picture, do not move the camera at all.

The length of time that you should expose the film can be a tricky thing. Light pollution will shorten the amount of time that an exposure can be made before the file reaches it's "Sky Fog Limit" or is effectively overexposed. Experimenting with the length of time an exposure is well worth the effort!

The speed and grain size of the film is an important consideration. Generally speaking, ASA 400 film is "fast" enough for these purposes. Fine grained film such as ASA 100 will give you sharper images than ASA 400 but the pictures would be much darker. With low light levels, "fast" film is highly desired. ASA 800 will expose quicker than ASA 400 but will be grainier. Kodak Gold and Fuji Film's of ASA 400 or ASA 800 should suffice.

The "F" stop or "focal ratio" setting is very important. As mentioned above, you want the camera to be "wide open" or set to lowest focal ratio setting. The reason is that the film will be able to gather more light if the aperture is wider. Your pictures will capture more fainter meteors at a lower focal ratio than at a higher focal ratio. If your camera produces fuzzy results and it is indeed correctly focused, close the aperture down one stop.

Go out on a clear night and test your setup! On a clear night prior to the Geminid meteor shower, set your camera up and take a few pictures. This will help you determine what works best for your camera and how the film reacts to the night sky in your area. Try a few exposures of 15 seconds, 30 seconds, 1 minute, 2 minutes, 3 minutes and 4 minutes using the lowest focal ratio, and record the frame number and exposure time on a scratch pad. Repeat the process with the focal ratio backed off one stop. When you get the film developed, you'll be able to compare the results with your notes and determine what works best for your camera and sky conditions. What you will see are called "star trails". Every star in the photo will appear to be "trailed" for all photos over 20-30 seconds in duration. This is OK though as many meteor photographers do use this method. You would need an "equatorial" mount with a tracking motor to eliminate this effect. Knowing how your camera records light before the main event is essential!

Warn the film developer that your pictures may be very dim! When getting your photographs developed, it is a good idea to make sure they know your photographs are dim and to the untrained eye, may appear to be of nothing at all. If the developer uses normal processing, you should at least get some kind of results. The important thing is that they print them! It is a better idea to have them developed locally, where you can discuss what's on the film prior to processing it.

Some Geminids are exceedingly bright and may possibly overexpose or ruin a time exposure. If a very bright fireball crosses the camera's field of view, end the exposure shortly thereafter. Know where your camera is pointing! Sometimes, a bright meteor will leave a "train" or trail. These make very interesting photographs as the trails become twisted and contorted by winds high in the upper atmosphere.

Framing your picture with natural landscapes will help to make it more interesting and will provide the viewer with a better perspective of the event. Trees, cactus, rock formations and distant mountains are all good objects to try this on. A wide field photograph of meteors while looking across a very still lake or pond may make for astounding poster quality shots, especially if the water surface is very still and reflects the meteor well. If you have a lake or pond nearby, give this a try. It may actually be possible if the meteor counts are high and if they are bright. Although the moon will significantly interfere with meteor observing and photography this year, it may provide a bit of foreground illumination to the setting.

Enjoy the show and Good Luck!

Sunday, November 13, 2011

How to shoot the Leonids Meteor Shower
18th Nov, 2011

Photographing meteors such as the Leonids is possible using a Single Lens Reflex (SLR) camera. The camera must have a "T" (time) or "B" (bulb) setting for taking time exposures. You will also need a cable release, a tripod or a very stable surface to place the camera on, for best results. The camera will need a lens that is between "fisheye" and 50mm. Lenses larger than 50mm may capture too small a field of view. This article is written for the film camera but can be used as it is for digital SLRs.


Here is what you will need to do.

Set up your photography equipment in an area that is shaded from any stray lights that may interfere. This is absolutely necessary!

Set the camera on a tripod or some other surface that is very stable. Make sure the focal ratio is set to the lowest possible setting. This means that the aperture of the camera is "wide open". Make sure the camera is set to "B" or "T" for time exposure. Set the focus to infinity.

Aim the camera at the area of the sky that you intend to photograph. Once positioned properly, make sure the tripod is locked down to prevent its "head" from moving under the weight of the camera. If you do not have a tripod, use things to prop the camera up in a way so that it is stable and so that you can still look thru the view finder.

Depress the cable release button and lock it in place. Allow the camera to take a picture for anywhere from 15 to 30 seconds, maybe more. Once the desired time has elapsed, release the cable release lock which will end the exposure. While taking the picture, do not move the camera at all.

The length of time that you should expose the film can be a tricky thing. Light pollution will shorten the amount of time that an exposure can be made before the file reaches it's "Sky Fog Limit" or is effectively overexposed. Experimenting with the length of time an exposure is well worth the effort!

The speed and grain size of the film is an important consideration. Generally speaking, ASA 400 film is "fast" enough for these purposes. Fine grained film such as ASA 100 will give you sharper images than ASA 400 but the pictures would be much darker. With low light levels, "fast" film is highly desired. ASA 800 will expose quicker than ASA 400 but will be grainier. Kodak Gold and Fuji Film's of ASA 400 or ASA 800 should suffice.

The "F" stop or "focal ratio" setting is very important. As mentioned above, you want the camera to be "wide open" or set to lowest focal ratio setting. The reason is that the film will be able to gather more light if the aperture is wider. Your pictures will capture more fainter meteors at a lower focal ratio than at a higher focal ratio. If your camera produces fuzzy results and it is indeed correctly focused, close the aperture down one stop.

Go out on a clear night and test your setup! On a clear night prior to the Geminid meteor shower, set your camera up and take a few pictures. This will help you determine what works best for your camera and how the film reacts to the night sky in your area. Try a few exposures of 15 seconds, 30 seconds, 1 minute, 2 minutes, 3 minutes and 4 minutes using the lowest focal ratio, and record the frame number and exposure time on a scratch pad. Repeat the process with the focal ratio backed off one stop. When you get the film developed, you'll be able to compare the results with your notes and determine what works best for your camera and sky conditions. What you will see are called "star trails". Every star in the photo will appear to be "trailed" for all photos over 20-30 seconds in duration. This is OK though as many meteor photographers do use this method. You would need an "equatorial" mount with a tracking motor to eliminate this effect. Knowing how your camera records light before the main event is essential!

Warn the film developer that your pictures may be very dim! When getting your photographs developed, it is a good idea to make sure they know your photographs are dim and to the untrained eye, may appear to be of nothing at all. If the developer uses normal processing, you should at least get some kind of results. The important thing is that they print them! It is a better idea to have them developed locally, where you can discuss what's on the film prior to processing it.

Some Leonids are exceedingly bright and may possibly overexpose or ruin a time exposure. If a very bright fireball crosses the camera's field of view, end the exposure shortly thereafter. Know where your camera is pointing! Sometimes, a bright meteor will leave a "train" or trail. These make very interesting photographs as the trails become twisted and contorted by winds high in the upper atmosphere.

Framing your picture with natural landscapes will help to make it more interesting and will provide the viewer with a better perspective of the event. Trees, cactus, rock formations and distant mountains are all good objects to try this on. A wide field photograph of meteors while looking across a very still lake or pond may make for astounding poster quality shots, especially if the water surface is very still and reflects the meteor well. If you have a lake or pond nearby, give this a try. It may actually be possible if the meteor counts are high and if they are bright. Although the moon will significantly interfere with meteor observing and photography this year, it may provide a bit of foreground illumination to the setting.

Enjoy the show and Good Luck!

Fire from the skies - Leonids Meteor Shower


Fire from the skies
Leonids Meteor Shower
18th Nov, 2011

Come November and all amateur astronomers around the world start looking up to the skies for an event which we call the “leonids meteor shower”. One can see trains of shooting stars coming from a particular area in the sky at an amazing rate. Only Geminids shower can rival this event. You all must have seen a shooting star whizzing past in the skies. This phenomenon can be seen almost any day of the year but a shower of shooting star is something that happens only few times. Leonids is one of these and the most prominent one.

Leonids are a prolific meteor shower associated with the comet Tempel-Tuttle. The meteor shower is visible every year around November 17 when the Earth moves through the Leonid meteor stream. The stream comprises solid particles, known as meteoroids, ejected by the comet as it passes by the Sun. It’s like truck carrying garbage littering the road with it while it moves. A typical particle is no bigger than fine dust, and rapidly vaporizes emitting a streak of light as it hits Earth's atmosphere at tremendous speed (71 km/s).  As the entire meteor streaks are parallel, because of effect of perspective they appear to originate from a single point in the sky (just like railway tracks appear to meet at some distance) and as a result Leonids get their name from the location of their radiant in the constellation Leo. The Leonids are famous because their meteor showers, or storms, can be among the most spectacular. In most years the rate at which meteors are likely to be seen is not great; however, years of highly elevated rates tend to follow a 33 year cycle, associated with the 33 year orbit of Comet Tempel-Tuttle. Storms in peak years featured thousands of meteors per hour; notable events were observed in 1698, 1799, 1832, 1833, 1866, 1966, 1999, 2001 and 2002. During a strong storm in dark viewing conditions the sky can appear to be "raining stars".

More information about the Leonids:

Most visible Leonids are between 1 mm and 1 cm in diameter. For example, a Leonid meteor barely visible with the naked eye in a dark sky, is caused by a meteoroid of 0.5 mm in diameter and weights only 0.00006 gram.

Just before they enter the Earth's atmosphere, Leonid meteoroids travel at 71 kilometers per second, or 213 times as fast as speed of sound.

Source of light - When meteoroids enter the Earth's atmosphere, they collide with air molecules. Those collisions sputter away the outer layers of the particle, creating a vapor of sodium, iron and magnesium atoms. Electrons are knocked into larger orbits from the nucleus of the atoms. When the electrons fall back to their rest positions, light is emitted. This is the same process as in gas discharge lamps.

Sounds - Meteors do not normally cause audible sounds. Hence, they will pass by unnoticed if not seen. A sonic boom is sometimes heard for very bright Leonid meteors, called fireballs

Leonid meteor shower date and timings:

It can be seen from Nov 14 till Nov 21. The peak usually occurs around 17 November This time its spread over 2 days. This year Moon will mar the observations but still its worth observing. Details are given below:

In 2011 usual Leonid return is expected with overall maximum ZHR up to 15. However, there is a possibility of three local peaks, two of which will be caused by interaction with trails and the third is the background one.



19:58 UT on 16 November (01:28 IST 17th November)

The first local peak will be caused by 1800 trail. Its own ZHR is 4-5, and adding to the background activity this should give ZHR ~10 around 19:58 UT on 16 November (01:28 IST 17th November).

The encountering parts of 1800 trail have low meteor brightness around this submaximum time and possibility of higher activity on radio. Then some decrease in activity is expected with local minimum of ZHR=7 around 3:24 UT on 17 November.



3:34 UT on 18 November 2011 (09:04 IST on 18th November)
The next maximum will be the background one. By IMO's data, it occurs at 3:34 UT on 18 November 2011 (09:04 IST on 18th November). We expect that its intensity will be not high, with ZHR of ~10.Then some minor decrease in activity to ZHR=9 is possible around 17:56 UT 18 November (23:26 IST November 18th). Though such weak variations in activity could hardly be detected by visual observations, so between second and third peaks activity will likely sustain at ZHR=9-10.



23:25 UT on 18 November (04:55 IST 19th November)

Finally, the third and most intensive among non-prominent Leonids 2011 peaks will be an enhancement from 1567 trail. It is expected to occur around 23:25 UT on 18 November (04:55 IST 19th November), and ZHR for a short period should reach 15. This peak will be notably sharper that previous two, significant changes in meteor brightness are not expected.






Observing Meteors Visually 

Taken from BAA blog

Naked eye observation of meteors is one of the easiest and most pleasant forms of work open to the amateur astronomer. Even a beginner can make useful observations, and it is a good way to learn the constellations. Meteor work is excellent for clubs and societies with little or no equipment; essentially only the human eye is needed.

A meteor during the peak of the 2009 Leonid Meteor Shower. The photograph shows the meteor, afterglow, and wake as distinct components
The notes below assume that a single observer is on watch, though most of what is said is relevant to group observation. Organisation of a meteor watch by a group of observers is more complex, though potentially productive of much more useful data (see Group Gbserving below)
The first requirement for the observer is to find a good dark site. Rural residents are favoured here. Urban lights, smog and haze have a major, adverse, impact on meteor rates. Hence, even if you have to drive some miles to get to a good site, it will be well worth the trouble to have darker skies.

What equipment should I use?

1. Norton’s 2000.0 Star Atlas or similar star maps.
2. Report sheets (will be made available to you during the meteor observation).
3. Timepiece – accurate to better than 30 seconds. 
4. Dim red torch – to enable you to note down data, but retain the dark adaptation of your eyes.
5. Several pens or pencils. These have a habit of breaking or getting mislaid in the dark, so have plenty of back-ups!
6. Clothing. Bring plenty of this; even on a summer night it can get chilly, and it is better to have too much clothing than too little. One advantage of a house back-garden site is that one can retreat indoors to warm up if necessary. A hat reduces loss of body heat from the head.
7. Food and drink. Refreshments should be available to be taken during breaks. Alcoholic beverages should, of course, be avoided!

Observer requirements

are rather more stringent
1. Patience. This is the prime requirement. The observer may face long intervals between meteors, or waiting for clouds to pass. Eagerly-awaited shower maxima often appear to turn out cloudy, and observations may have to wait for another year. Remember, however, that observations are required on all possible nights during a shower – so don’t just restrict watches to maximum night. One advantage of group watches is that the company helps to pass cloudy intervals.
2. Alertness. You must always be alert, otherwise the fainter meteors, which generally make the bulk of the bag, will be missed. If you are tired, or cold, or find your attention wandering, you should stop observing, at least for a while, since your results will not be reliable.
3. Honesty. All observers have different eyesight, and perception for meteors. An observer must not be disappointed to see fewer meteors than a colleague. Meteor work is not a competition, and conscious or unconscious ‘doctoring’ of observations is worse than useless, and indeed misleading.

Observing

Having covered the instrumental and personal requirements, we can get down to what is required from the observations. Before going outside to observe, find the radiant co-ordinates for the shower(s) active on the night in question, in this case it would be in perseus.
It is important to note that the radiant position the night of peak activity only. In accordance with theory, radiants generally move among the stars at a rate of about 1 degree per day. So, for a night other than maximum, the radiant will have RA and Dec different from the values mentioned.
Plot this position in Norton’s, and draw a circle of 8 degrees diameter centred on this position. The enclosed area is taken as the radiant for the night in question. Examine this area carefully indoors, until you are confident that you will recognise the area in the sky when you actually begin to observe.
Once outdoors, use the time that you spend getting dark adapted to record your name, address, and observing site (including latitude and longitude), and date on the report sheet. Note the sky conditions, mentioning whether any cloud, moonlight, fog or mist is present. Once you are fully dark-adapted, estimate the magnitude, to the nearest 0.25 mag, of the faintest star you can see in the area of sky being watched (not the zenith). Some observers prefer to estimate this limiting magnitude using the North Polar Sequence.
Now you are ready to begin the watch. Write down the start time of the watch in UT to the nearest minute. All times used in this type of work are required in Universal Time, which is 5.5 hours + IST. 
Of course, because astronomers work exclusively at night, the date changes at midnight, halfway through the observing period. To prevent confusion and ambiguity as to exactly which night the observations are carried out, one must record the Double-Date on the report form – for example, 30-31 October.
Some observers, once they get past midnight, use the 24-hour clock beyond the figure 24 so that, for example, 2 am becomes 2600 UT. This is quite acceptable. So long as your record of date and time is unambiguous, do what you find most convenient.
As the name implies, a meteor watch involves concentrating on the sky and noting details of any meteors seen. Solo observers should watch the sky 50 degrees above the horizon, and 30-40 degrees to one side of the shower radiant expected to be active on the night in question; most meteors should be seen here.
As each meteor appears, not whether it was a shower member or a random sporadic, estimate how bright it was, and give its time of appearance to the nearest minute in UT.
To ascertain whether a meteor belonged to a given shower, or was a sporadic, mentally project its path in the sky backwards. If the projected path intersects the 8-degree radiant circle, the meteor is a shower member. Otherwise it is a sporadic. Those with paths tangential to the radiant should be considered as possible shower members. If a stick, or piece of string is held up against the meteor path when the event is seen, this will give you time to collect your thoughts after the meteor has vanished. Estimation of the magnitudes of shower and sporadic meteors may be omitted by those observers wishing only to carry out counts. The others should estimate meteor magnitudes by comparison with nearby stars. It will be adequate to estimate to the nearest whole magnitude. Do not forget that there is a mag. 0 between -1 and +1. Estimation of meteor magnitude is largely subjective, since the meteor is rarely present long enough to enable very accurate visual photometry; it is a remembered impression that is compared with the stars. For bright meteors, errors in magnitude estimation are much larger, due to the lack of suitable comparison standards. Useful tips for bright meteor estimation: Full Moon is mag. -12.5; Venus is -4.4 at its brightest; Jupiter about -2.2. Large scatter in the magnitude estimates of fireballs can hardly be avoided. The list here offers some further suitable comparisons for fainter meteors:
Magnitude Object(s)
-4 Venus
-2 Jupiter
-1 Sirius
0 Capella, Rigel, Arcturus
+1 Regulus, Spica, Pollux
+2 Belt stars of Orion, Beta Aurigae, Gamma Geminorum,
Pointers of Plough, Polaris, Denebola, Alphard
+3 Delta Ursae Majoris, Gamma and Delta Leonis, Epsilon Geminorum
+4 Eta Persei, Delta Aurigae, Rho Leonis
+5 Faintest meteors generally visible to naked eye
Note the time of appearance of the meteor, having made due allowance for the time spent thinking about magnitude and type, and writing these down, perhaps 15-30 seconds.
Then, and only then, you may make any notes about the meteor itself. For example, did it explode? Did it have an intense colour? Did it have a long-duration persistent train?
As this is the first time we have mentioned meteor trains, a few words about them would not go amiss. Many observers, especially beginners, are confused by the difference between meteor trails and persistent trains. A night-time meteor train appears as a faint nebulous streak of light left behind, along the track of a meteor, but AFTER the meteor itself has extinguished. Do not mistake it for the actual moving streak of a fast meteor – this is the trail. Momentary meteor trains are generally likened in appearance to the vapour wake of a jet aircraft, and are only left by about a quarter of all meteors. Meteor trains lasting more than a few seconds are quite rare. Statistically, one must observe about 600 meteors to observe a train of 10 seconds’ duration or more!
Each meteor seen during the watch should be treated similarly; practice makes perfect, and you should soon be able to get down the data quickly and efficiently. Abbreviations such as “S” for sporadic, or “P” for Perseid, and writing the minutes instead of minutes and hour, will help you to cope with the sudden rushes of meteors that sometimes occur. As long as you get all the data down, and you can understand your symbols at a later date, you can use any symbols you like. Many experienced observers, to reduce “dead time” spent looking away from the sky, note meteor details in such a shorthand, for later, neat transcription to the Section’s report forms.
At the end of the watch, note the time to the nearest minute. Then you can stop, or have a break and start another watch later. Ideally, watches should last for an hour, or multiples of an hour, at a time. Monitor the sky conditions during each watch, as these may change.