Archive for the ‘Comets’ Category
A classic summer astronomical standby may be in trouble this year, but that shouldn’t stop you from looking. That’s right, we’re talking about the Perseids, that “old faithful” of meteor showers which sees northern hemisphere residents getting bundled up to camp out under the summer stars every mid-August.
Some of our earliest astronomical memories come from watching this very shower under the dark northern Maine skies of our 1970’s childhood… yes, the Perseids are public crowd-pleaser and even an occasional Yahoo-trending fave that can even knock the likes of Brittany & friends down to the number 2 slot for a 12 hour period… so, what’s this news of the Perseids being “troubled?” They haven’t been threatened by irate pop stars, have they?
Unfortunately, this year’s menace is a more inviolate force; the Full Moon. Yes, this year’s Perseid meteor shower peaks the morning of August 13th, mere hours before the Moon reaches Full status on the same day at 14:57EDT/18:57UTC. Instead of the usual respectable zenithal hourly rate (ZHR) of around 100 meteors per hour, observers can only expect to see a paltry few of the very brightest fireballs…
But all is not lost. With a little planning, a few factors can work in YOUR favor this year. Keep in mind that the Perseids have a very broad peak, and the radiant near the head of the constellation Perseus lies above the horizon all night for observers north of 32° latitude. Plus, this month’s Full Moon (known as a Sturgeon Moon) has a southerly declination of about -11° degrees; your best bet for catching Perseids this year may lie with watching several mornings prior, in the window of time between the setting of the waxing gibbous Moon and the beginning of local twilight… and yes, you CAN still watch a meteor shower during a Full Moon and see an occasional Perseid.
Generally speaking, the farther north in latitude you are located, the more likely you’ll be able to take advantage of these twin factors. Finding as dark a site as possible and putting something physically between yourself and the bright Moon is the key. A building or a hill makes an excellent “Moon-block.” Perseids are swift movers with an atmospheric entry velocity of about 61 km/sec.
The meteors are tiny grain-like debris shed by the comet Swift-Tuttle, and the shower occurs as the Earth intersects the path of the comet every mid-August. The Perseids are also famously known as the “Tears of Saint Lawrence” who was martyred on August 10th, and are probably the most well known of all meteor showers because of their annual dependability and their timely occurrence with the northern hemisphere summer vacation and holiday season.
Historic ZHR rates have always hovered around 60, but the past several years have seen an enhanced ZHR of +100. This shower is also infamous for sparking “Meteor Shower of the Millennium!” headlines annually, Although I have yet to see the same occur this year… a shower that MAY be a contender for said headline is the Giacobinids (or do you say Draconid?) meteors in early October 2011, an obscure shower that may dazzle this year… more on this to come in October.
Wonder what that the above graphic has to do with anything astronomical? You are looking at what is known as a nomogram, a graphical device that is a neat way to show interrelationships between factors. (Hey, how do you spend your weekend?) The graphic above was adapted from a nomogram featured in the November 2002 issue of Sky & Telescope; it shows the interrelationship between the two biggest factors that affect the zenithal hourly rate; namely, the radiant’s elevation above the horizon, and the limiting magnitude of your sky. (For a way “math-y-ier” dissertation on nomograms and the ZHR, click here).
This device will be your indispensible friend and secret weapon as you plot your meteor observing adventures for this or any shower. The ZHR is a theoretical limit; it assumes that you have absolutely perfect skies with a radiant directly overhead and an unwavering 360°degree view. Unrealistic, right? Well, it’s something to strive for. As you can see after playing around with the graphic a bit, the biggest killer of how many meteors you’ll see is how dark a sky you are under.
Even when the Perseid radiant is half way (45° degrees) in altitude towards the zenith, a limiting magnitude of +4 (as is typical around a Full Moon) means you’ll see roughly 10% of the zenithal hourly rate, i.e. 6-10 meteors per hour instead of 60-100. Yes, light pollution, both natural and manmade, is a real meteor shower buzz-kill. And keep in mind, other factors can conspire to lower that rate even further, such as obstructions on the horizon and the fact that a sole observer can only cover a limited swath of the sky visually. Still, the sight of a well placed fireball can be unforgettable and just plain pure magic to witness.
Out there somewhere in our solar system is a 26 kilometre wide comet, a chunk of dirty ice on a 130 year orbit of the Sun. This giant cosmic snowball was thought to have been born in the Oort Cloud, a vast spherical region of icy objects nearly 6 trillion miles from the Sun, almost a light year. With a total mass of roughly 40 times that of Earth, the Oort Cloud is so far out that the Sun’s gravity is weak but the gravity of nearby stars can have an effect, nudging these remote icy chunks out of position and sending them on a long journey towards the inner solar system. One of these mysterious icy travellers is called Comet Swift-Tuttle, much larger than the object thought to have spoiled the party for the dinosaurs, and the largest known chunk of space stuff to make repeated passes near the Earth. Although you can breath a sigh of relief, as it poses no degree of threat for at least a few thousand years, so we get to see its associated meteor shower without that bothersome mass extinction. Comet Swift-Tuttle, which last made its closest approach to Earth in 1992, is the particular comet in question that we’re interested in for August as it produces the Perseid meteor shower.
As this comet makes its way around the solar system it leaves a trail of dusty material in its wake. Every August as the Earth passes through this debris stream we get to see probably the most reliable and best meteor showers of the year. The fine grains zip through the atmosphere at 130,000 miles per hour, at a rate of up to 90 to 100 an hour. As with anything in astronomy it’s always best to view a meteor shower from a darker location, and hopefully with the bright Moon out of the way.
OK, so here’s where your view of the August 2011 Perseids may be taken down a slight notch as compared to other years. The Moon normally gives cracking views in your binoculars or telescope, but our old friend Lunar is nobody’s friend when it comes to meteor showers as its light can wash out all but the brighter of those spectacular shooting stars. This year we have a full Moon unfortunately on the two nights of the shower’s peak. This peak time is during the pre dawn hours of Friday the 12th and Saturday the 13th of August…so that’ll be the 11th beyond midnight, and the 12th beyond midnight. You have more chance of seeing meteors in the small hours as Earth faces into the shower during this time, resulting in the chance of seeing more and faster meteors. The Perseid meteor shower actually starts from the end of July and goes up until late August, but peaks on the mornings of the 12th and 13th of August. So keep your eyes peeled for Perseids in the weeks either side of the peak too. You’ll see the the Perseids seeming to radiate from, you’ve guessed it…the constellation Perseus. Although you can actually catch them streaking across any part of the sky, they’ll just seem to be coming from the direction of that constellation. Look to the north-east after dark and you’ll see Perseus rising, it then moves higher to the east before dawn. Even though the Moon will be in the sky during the peak, don’t let that dissuade you as it’s still well worth getting outside…don’t miss it.
The great thing about meteor showers is that the only equipment needed is your eyeballs, so everyone can join in. Get some friends and make a night of it, and the best thing about the Perseids is they conveniently come at the best time of the year when it’s nice and warm (hopefully). Meteor watching requires a lot of patience, but if you sit back, relax and put some time in you should be rewarded. There’s actually another night sky attraction to admire while you’re waiting for shooting stars, and that’s the solar system’s heavyweight Jupiter. The gas giant starts rising from the east shortly before midnight on the dates of the meteor shower peak. Check it out naked eye, but if you happen to have some binoculars with you grab a quick peek at the stormy planet blazing brightly at magnitude -2.36, and get a look at those moons. Don’t get too distracted though as you’ll want to keep an eye out for Comet Swift- Tuttle’s fireworks.
Don’t forget to get involved with Meteorwatch on Twitter…tweet your location and how many meteors you observe, and see your results on the Meteormap. Good luck !
Article by John Brady of Astronomy Central
I am often asked or hear about bright fireballs in the sky, often reported by non astronomy minded people, so when you ask where was it and what direction it was travelling etc, you get very sketchy information back like: It was over my house and headed towards town, I think?
Only if you have many sightings of the same fireball can you interpolate where it was and what direction etc it was travelling? Things are going to be made a lot easier if you live in some parts of the United States.
NASA is building a network of "Meteor Cameras" in a few of States in the US called the "All-sky Fireball Network". This is a network of cameras set up by the NASA Meteoroid Environment Office (MEO) with the goal of observing meteors brighter than the planet Venus, which are called fireballs. The collected data will be used by the MEO in constructing models of the meteoroid environment, which are important to spacecraft designers.
The Network will eventually consist of up to 15 overlapping cameras in north Alabama, northwest Georgia, and southern Tennessee, placed on public buildings and schools. The network will use sensitive black and white cameras which are able to see the whole of the sky (All Sky).
Because the cameras have overlapping fields of view, more than one camera can see the same meteor at the same time, helping in getting data about its trajectory and with clever data collection software, ascertain if the meteor came from a comet or an asteroid.
NASA’s All-sky Fireball Network uses ASGARD (All Sky and Guided Automatic Realtime Detection). ASGARD not only handles all the data processing (which is considerable) it also automatically pushes the results to the web. See the results here: http://fireballs.ndc.nasa.gov
Originally posted on Sky and Telescope by by Kelly Beatty, October 6, 2010
Everyone enjoys a great meteor shower, those special times each year when a profusion of shooting stars zip across the sky. So here's a head's up: all of you should circle October 8th on next year's calendar.
This is the yearly date when Earth plows through a tenuous band of space dust created by Comet Giacobini-Zinner along its orbit. Ordinarily, the Draconid shower (formerly called the Giacobinids) puts on a so-so celestial show, delivering about 20 meteors per hour if you can view them under a moonless, pitch-black sky. That's hardly worth staying up for: after all, from a similarly clear, dark site you'll see six or seven random ("sporadic") meteors per hour.
However, this shower has a Jekyll-and-Hyde personality. In 1933 and 1946 the Draconids dazzled skywatchers with astounding meteor "storms" — delivering shooting stars at rates that briefly topped 10,000 per hour! — because Earth crossed through a particularly dense ribbon of debris shed by the comet in 1900. The shower hasn't put on that kind of performance in the years since, though in 2005 it surged unexpectedly to double or triple the usual rate.
If celestial prognosticators are right, we're in for a treat next year, when Draconid rates could top 600 per hour — that's 10 per minute — under ideal viewing conditions. That surge is in the cards because we'll likely clip the stream of particles ejected in 1900. Odds are that it's still largely intact, even though the comet's 6½-year-long orbit periodically puts it in Jupiter's disruptive vicinity.
At a meeting of planetary scientists now under way in Pasadena, California, meteor dynamicist Jérémie Vaubaillon (IMCEE, France) put forth predictions that he'd calculated with colleagues Mikiya Sato and Jun-ichi Watanabe (NAOJ, Japan). If they're right, next October 8th Earth crosses some cometary debris shed by Comet G-Z between 1873 and 1894, peaking at perhaps 60 meteors per hour centered at 17:09 Universal Time, followed at 19:57 UT by a much stronger, 600-per-hour pulse from the 1900 stream.
The rate is very uncertain, Vaubaillon admits, because there's no way to know whether those earlier streams are still densely packed or have been spread thin. Meteor observing wasn't as rigorous back then as it is now. But next year's results should help disentangle which streams are still contributing to the overall rates.
Other meteor specialists are also struggling to come up with firm rates. In 2008 Sato and Watanabe independently estimated a maximum of 500 per hour (at 20:36 UT), whereas NASA researchers Danielle Moser and William Cooke have offered a more optimistic 800 per hour (at 19:11).
These times favor observers in Europe, but don't rush out to book a plane just yet. First, the Draconid shower tends to produce many faint meteors that'll be obliterated by a nearly full Moon that night.
Second, because the shower's radiant is way up near the head of Draco (declination +54°), the best observing sites would likewise be geographically north. But there's a reason that so few people book vacations to Scandinavia in October: "Weather in Northern Europe is not very pretty," notes Canadian meteorologist Jay Anderson. "October can be very nice, but usually it is the time when the winter cloudiness begins to encroach on the daily weather."
Instead, Anderson's cloud-cover map (at right) suggests that the northernmost "good weather" spot is in the Greek Islands. "Santorini — a favorite place of mine — has clear/few/scattered cloud cover 74% of the time. I know where I'd go."
With the Quadrantids meteor shower that has just past yielding around 100 meteors per hour in near-perfect New Moon conditions, which showers of the next two years will give us as good a display?
There are a few regular, dependable showers that can be relied on to put on a good show year after year, given a good Moon phases, so let’s concentrate on those:
The Lyrids peak this year on April 21/22, only three days after the Full Moon, making conditions far from ideal. The ZHR is around 20, but under bright Moon conditions this will be much reduced, so that from the UK you might only see a few Lyrids per hour.
The Perseids peak on 12/13 August 2011 coincides exactly with a Full Moon, making this shower pretty much a write-off in 2011.
The Orionids peak occurs on 21/22 October 2011 just after the last quarter Moon, with the Moon rising a little after midnight, just as the meteor shower radiant is gaining height. Again, far from ideal.
The Leonids peak on 17/18 November occurs during a last quarter Moon, which unfortunately is smack bang in the direction of Leo, and so will obscure many of the Leonids in 2011
The Geminids peak on 13/14 December 2011 will likewise be completely obscured by an almost-full Moon in Gemini.
The Quadrantids peak on 3/4 January 2012 will feature a waxing gibbous Moon which won’t set until 0400.
The Lyrids peak on 21/22 April 2012 is the first major shower peak in 15 months where the Moon is absent, meaning that you should get good views of this shower which has a ZHR of only around 20.
The Perseids peak of 12/13 August 2012 will feature a thin waning crescent moon that’s visible in the sky from midnight, obscuring some of the Perseids.
The Orionids peak on 21/22 October 2012 is pretty much Moon-free from around 2330, as the Moon sets.
The Leonids peak on 17/18 November 2012 will also be Moon free from early evening, and so presents an opportunity to see a few Leonids.
Rounding off this two year run of poor Moon conditions for meteor showers, we end with the Geminids on 13/14 December, coinciding wonderfully with a New Moon on 13 December, meaning conditions will be near perfect.
Looking Northeast at about 10 PM. (Photo by Author).
This year, believe the hype; this month’s Geminid meteor shower is a sure bet. This shower is one of the few dependable ‘old faithful’ meteor showers of the year. Peaking on the night of December 13th-14th, this year’s apparition sees a well placed northern radiant rising high in the northeast as the first quarter Moon sets about midnite local. The Geminid stream radiates from very near the bright star Castor in the zodiac constellation Gemini the Twins and typically produces up to 100 to 120 meteors per hour. If you are placed in mid-northern latitudes, you may see some activity shortly after sunset, but the real meteoritic action will begin after midnite. Think of a car driving at night in a snowstorm, not a stretch in the depths of the northern hemisphere winter. Looking forward into your high beams you get the cool vintage “Star Trek” effect, as you and your vehicle plow headlong into the stream of snowflakes. Think of the flakes as meteors and the car as the Earth; we face headlong into the meteor stream after midnight, and hence see more flashing meteor trains. The Geminids present several swift movers and fireballs, and the darker skies you have access to, the more you’ll see. Be sure to dress warm (it is winter out there!) and make a point to count and record your observations. Meteor shower observing is one of the few remaining scientific endeavors that remains low tech. Also, don’t forget to participate in the #meteorwatch via Twitter! This shower has a broad peak, and will be active the week of December 12th until the 18th, when the solstice-centered Ursids become active. In fact, there are some indications that the Geminids have been increasing in activity over the past decade, and certainly there’s a lot of material out there. The predicted peak centers on 5:00 AM UTC, just past midnite Tuesday morning from the US East Coast. And if that weren’t enough, it’s one of the last meteor showers with the Moon placed below the horizon until 2012; only the Quadrantids and Giacobinids have the same favorable geometry in 2011. Good luck, and be sure not to miss this unique meteor shower!
The astro-term for this week is the Yarkovsky Effect. The parent body that produces the Geminids, 3200 Phaethon, harbors somewhat of a mystery. Discovered in 1983, this space rock has been identified as the source of the Geminid meteor stream.NASA researchers estimate a massive amount of material exists, more than 100 times that of the average meteor stream. Unlike most streams that emanate from comets, however, 3200 Phaethon is an asteroid. Or is it an inactive comet? The mystery deepens, as the color of this strange rock is very similar to another asteroid, Pallas. 3200 Phaeton’s path sees it passing within Mercury’s orbit every 1.4 years, which brings it well within the realm of the Yarkovsky effect. This is the tiny bit of momentum imparted on a rotating body as it re-radiates photons absorbed from the Sun. On large bodies the effect may be negligible, but on tiny asteroids it can produce major changes in orbit over time. In fact, employing the Yarkovsky Effect by changing the reflectivity of an Earth-crossing asteroid is one way of possibly deflecting a lethal space rock. Is 3200 Phaethon a dormant comet or the remnant of an asteroid belt break up? This is one worldlet that definitely begs future exploration.
The final meteor shower of 2010 is the Geminids, the peak of which falls on the night of the 13/14 December 2010. The Geminids is described by the IMO as “one of the finest, and probably the most reliable, of the major annual showers presently observable”, and this year’s shower is set to put on a good show. (You can read the IMO’s rather technical summary of the 2010 Geminids here: http://www.imo.net/calendar/2010#gem)
The predicted Zenith Hourly Rate (see my previous post about ZHR and what it actually means here) is around 120. Although the peak is predicted to occur around 1100 on 14 December, it should happen some time between 1840 on 13 December and 1600 on 14 December 2010. The best time for the peak to occur for stargazers in the UK would be between 0030 and 0600 on 14 December, after the Moon sets but before twilight begins.
The radiant for this shower is actually quite favourable, and if you wait till the Moon sets at around 0030 on 14 December then the only light pollution limiting your view will be man-made. If you observe before the Moon sets then you will lose a few of the fainter Geminids in its glow, but it’s only a first quarter moon, and so will only really have an impact if you’re observing from very dark skies.
Let’s use the equation relating ZHR to actual observations of meteors to work out how many you might see:
Actual Hourly Rate = (ZHR x sin(h))/((1/(1-k)) x 2^(6.5-m)) where
h = the height of the radiant above the horizon
k = fraction of the sky covered in cloud
m = limiting magnitude
In the case of the 2010 Geminids, if observed from the UK, h = 45 degrees. Let’s assume you have clear skies (haha) with k = 0.
The number of Geminids you can expect to see from a variety of observing sites is as follows:
For very light polluted sites, such as city centres m = 3, and therefore you can expect to see only around 8 meteors per hour.
In suburban skies near a city or town centre m = 4, and you’ll see around 15 meteors per hour.
In rural skies where m = 5, you’ll see 30 meteors per hour.
Under very dark skies, where m = 6.5 (i.e. where there is no or negligible effect of light pollution, like in Galloway Forest Dark Sky Park) you’ll see up to 85 meteors per hour, once the Moon sets. A first quarter moon will impose a limiting magnitude, even at a very dark site, of around 6, in which case you’ll see a slightly reduced 60 meteors per hour.
Remember, all of these numbers assume perfectly clear skies. If half your sky is cloudy, cut these numbers in half!
How many Geminid meteors will I see?
|Where are you observing from?||Limiting magnitude||Number of Geminids per hour|
|A very light polluted city centre||3||7 or 8|
|Dark Sky Site||6.5||85 (after the Moon sets at 0030)|
If you fancy a good view of this spectacular meteor shower, then head to Galloway Forest Dark Sky Park, where we have an evening of talks and meteorwatching planned, weather permitting!
Originally posted on and full credit Universe Today
Are you ready to walk into the lion’s cage? Then break out your favorite skywatching gear because the 2010 Leonid meteor shower is underway…
In the pre-dawn hours on the mornings of November 17 and November 18, the offspring of Comet Temple/Tuttle will be flashing through our atmosphere and just taunting you to test your meteor watching skills against bright skies. Although the phat Moon will greatly interfere with fainter meteor trails, don’t let that stop you from enjoying your monring coffee with the sparkling “cubs” that will be shooting out from the constellation of Leo.
Where? For all observers the constellation of Leo is along the ecliptic plane and will be near its peak height during best viewing times. When? Because of the Moon, just a couple of hours before local dawn is the best time to watch. Why? Read on!
Although it has been a couple of years since Temple/Tuttle was at perihelion, don’t forget that meteor showers are wonderfully unpredictable and the Leonids are sure to please with fall rate of around 20 (average) per hour. Who knows what surprises it may bring! Each time the comet swings around our Sun it loses some of its material in the debris trail. Of course, we all know that is the source of a meteor shower, but what we don’t know is just how much debris was shed and where it may lay.
As our Earth passes through the dusty matter, it may encounter a place where the comet let loose with a large amount of its payload – or it may pass through an area where the “comet stuff” is thin. We might even pass through an area which produces an exciting “meteor storm” like the Leonids produced in 1883! For those in the know, the Leonid meteor shower also made a rather incredible appearance in 1866 and 1867 – dumping up to 1000 (not a typo, folks) shooting stars recorded even with a Moon present! It erupted again in 1966 and in 1998 and produced 3000 (yep. 3000!) video recorded meteors during the years of 2001 and 2002. But remember, human eyes may only be able to detect just a few…
And I ain’t lion!
Photo Courtesy of Stardate.org, Texas University
Earth is entering a broad stream of debris from Halley's Comet, and this is causing the annual Orionid meteor shower. "The best time to look is during the hours before dawn on Thursday, Oct. 21st, and again on Friday, Oct 22nd," advises Bill Cooke of NASA's Meteoroid Environment Office. "Unfortunately, we have a bright Moon this year. Even so, I'd expect some bright Orionids to shine through the moonlight." An all-sky camera at the University of Western Ontario recorded this early Orionid fireball on Oct. 18th:
Orionid meteors stream from the elbow of Orion the Hunter: sky map. Because the shower's radiant point is close to the celestial equator, sky watchers in both hemispheres can enjoy the show. Moonlit meteor rates will probably be around a dozen per hour.
Radar rates could be much higher. The US Air Force Space Surveillance Radar in Texas is scanning the skies for satellites, space junk, and meteoroids. When an Orionid passes overhead–ping!–there is an echo. Moonlight does not interfere with this method of meteor observing, so it's perfect for this year's Orionids. Tune into Spaceweather Radio for live echoes.
Originally posted on www.spaceweather.com