Tuesday, August 10, 2010

Observing Meteors Visually


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.

Saturday, August 7, 2010

Observation trip for persieds meteor shower

Come August and we have one of the best annual celestial fireworks shows – Persieds Meteor Shower.  Right now the earth is passing through fragments and dust trails created by the comet swift tuttle and this means the perseids meteor shower has started and will be getting stronger each day until its peak on 12th August 2010. Only bad weather and clouds can deprive us from this wonderful display of fireworks from the skies.  The persieds Meteor showers of August is one of the most famous Astronomical Summer time events. Some call the persieds "old Reliable" because every year it seems to deliver an extraordinary exhibit in the August skies. Lets pack our bags and spend a night under the stars far away from city light.
Also see the article about the persieds in the file sections.
astronomicans (amateur wing of SPACE) HAS decided to go for observation, following are the details about the observation.
Overnight observation of Persieds Meteor Shower 2010
Date: 12th August 2010
Day: Thursday
Venue: Sakaras, SPACE’s new observation Site (120km from from SPACE office)
astronomical Data for the site:
Sunset                                                                                                 19:01pm
Astronomical twilight ends                                   20:28pm
Astronomical twilight begins                                              04:25am
Assembly point:                                                              SPACE office
Reporting time:                                                               2:30 pm
Departure for site:                                                          3:30 pm
Departure for SPACE office from the site:          6:00 am (13 aug)
Arrival at SPACE office:                                               9:30 am
Cost:                                                                                      ` 600 (approx)
The cost includes the logistics at the site and the transportation which will depend on number of participants and will be either cab or bus. Food is not included in the cost.
So what are you waiting for pick up bags and cameras, and chase the meteor shower!!
Kindly confirm it before 9th August 2010 with Ms Shikha at 9212669953

Perseids Meteor Shower



Fire from the skies (in monsoon!!!!)
Perseids Meteor Shower
Night of August 12th, 2010


Seeing a shooting star in the sky makes one feel that a star has died, but is it really so. Death of a star results in one of the biggest celestial shows in the universe and definitely a shooting star is not that. The words “shooting star” it self is a misnomer. We all know that when a small particle of space dust enters earth atmosphere, it burns up while travelling towards Earth and result is a streak of light in the skies. It has nothing to with star death. Sometimes the particle is so big that part of it burns in the atmosphere and the rest falls on earth as it happened last few years in certain parts of India.



The show
Perseids can be seen from July 15th –August 25th. Most of these nights one can see few meteors from the shower. Night of August 12 is the peak of the Perseids meteor shower. timing of the mean or ‘traditional’ broad maximum will vary between August 12, 18h30m UT to August 13, 07h00m UT, while the shorter, enhanced will be between August 12, 09h30m to August 13, 13h30m UT. When Perseus rises in the northeast. This is the time to look for Perseid Earthgrazers--meteors that approach from the horizon and skim the atmosphere overhead like a stone skipping the surface of a pond. Earthgrazers are long, slow and colourful; they are among the most beautiful of meteors. An hour of watching may show only a few of these--"at most"--but seeing even one makes the long night worthwhile. The thin, crescent moon will be out of the way early, setting the stage for a potentially spectacular show. For best viewing, look to the northeast after midnight. Other things which will spoil the show will be monsoon clouds.

How to observe the meteor shower?
Don’t expect hundreds of meteors in the skies at one time. Perseids meteor shower usually have ZHR of around 100-120 meteors. Now what is this term ZHR? Official figures for meteor numbers are given as the ZHR or Zenithal Hourly Rate. This is the number of meteors you could expect to see given perfect conditions if the radiant (the point from where all the meteors seem to be coming) was directly overhead - i.e. at the zenith. Obviously, if the radiant is on the horizon, you can't see half the sky around the radiant, so you will only see half the number of meteors. Again, if half the sky is cloudy, you will only see half the number of meteors. Hence, for a ZHR of 110 (about what you can expect for the Perseids shower), you might only see two-thirds or half because the radiant isn't directly above your head. So expect to see around a meteor per 2 minutes !!

The first and last rule of meteor observing is look up. If you do not look up, you will not see any meteors, because by the time someone else has seen it, it will be gone before you look in that direction. Rules for meteor observing are generally the same as for all astronomy observations. The exception to that rule is that you should be looking up at all times. You can employ an easy chair for this purpose, but the best way is to get a sleeping bag and find a dry, comfortable spot to lie down on.

For observation make sure that you have the widest area of sky visible possible. Try to get away from light pollution. If you can see the Milky Way, it will be dark enough to see meteors. Typically, meteors will be about the same brightness as Venus or Jupiter down to the brightness of medium-brightness stars).

Depending on your location and disposition, insect repellent like odomos gel might be advisable as well. On the whole, just use common sense and try to enjoy yourself. Meteors can provide some of the more spectacular sights in the sky, so stop reading about it and get out there!