Plants

When it comes to sex, most plants have the best of both worlds: Their sex organs - their flowers - are both male and female. The few species that segregate the sexes have long baffled scientists, because a single-sex plant tends to reproduce less successfully than a plant with flowers of both sexes.

Now, two University of Arizona researchers have discovered a new pathway for the evolution of single-gender plants, which they report in this week's issue of Science [Sept. 29 issue]. Doctoral candidate Jill Miller and her advisor, ecology and evolutionary biology Professor D. Larry Venable, found that single-sex plants of the species they examined have more than the usual two sets of chromosomes.

While studying the evolutionary history of wolfberries, spiny shrubs in the potato/tomato family (Lycium), Miller noticed something unusual. All three North American species that had segregated sexes were also "polyploids," with either four or eight sets of chromosomes instead of the usual two sets.

Sensing that this association of polyploidy with separate sexes was not a coincidence, Miller began digging deeper into the connection, looking for the possible involvement of self-fertilization. "People have studied the evolution of separate sexes in plants for a long time and described a lot of different pathways, but nobody's ever made the explicit connection and tried to look for this particular pathway," noted Miller.

Despite the presence of both male and female flowers, most plants cannot mate with themselves because self-incompatibility is built into their genes. This arrangement can be seen as a genetic taboo against inbreeding. Although some plants can get away with self-fertilization, in other plants it leads to "inbreeding depression," harmful effects that come from being too inbred.

This is where polyploidy comes in. The presence of more than two sets of chromosomes can disrupt the genetic taboo preventing self-fertilization. A self-incompatible plant thus evolves the ability to reproduce on its own - but not necessarily for its own good. Self-fertilization can still cause inbreeding depression in such plants.

Under these conditions, an individual plant that produced single-sex flowers would have an evolutionary advantage. It could never self-fertilize and so it would never suffer from inbreeding depression. The plant would be fit for long-term survival and the single-sex mutation could become the prevailing lifestyle in certain plant populations.

The three polyploid species of wolfberries studied by Miller and Venable are all single-sex plants, while their nearest relatives are hermaphrodites. The researchers speculate that a polyploid event and consequent breakdown of self-incompatibility led to the evolution of separate sexes in this branch of the family tree. Although the male flowers in the single-sex species appear to share both genders, in actuality they only function as males. But technically these species have one more stepping stone to true gender separation.

Miller and Venable suspect this scenario occurred independently in a South African lineage of the same family, Lycium. The South African plants are further along in the process, having evolved separate-sex flowers that don't even pretend to serve both functions. The researchers also have uncovered strong evidence that the same evolutionary tactic occurred at least 20 times in other plants.

"It looks like it might be relatively common," Miller said. "If it is relatively common, that makes it sort of amazing that nobody yet has described it."

Polyploidy does not always lead to the evolution of separate sexes because there are other possible strategies for avoiding inbreeding depression. In most cases, the newly self-compatible plants are able to survive inbreeding depression and eventually purge their genes of harmful mutations.

An alternate pathway would be for the plant to develop flowers where the male and female parts are not active at the same time, reducing the possibility of self-fertilization. But the results of Miller and Venable's research suggest that the link between polyploidy and inbreeding depression may be the key to a common, and previously unsuspected, pathway to the evolution of separate sexes in plants.

Suicidal planet seems on death spiral into star`

By SETH BORENSTEIN, AP Science Writer – Wed Aug 26, 1:00 pm ET

WASHINGTON – Astronomers have found what appears to be a gigantic suicidal planet.

The odd, fiery planet is so close to its star and so large that it is triggering tremendous plasma tides on the star. Those powerful tides are in turn warping the planet's zippy less-than-a-day orbit around its star.

The result: an ever-closer tango of death, with the planet eventually spiraling into the star.

It's a slow death. The planet WASP-18b has maybe a million years to live, said planet discoverer Coel Hellier, a professor of astrophysics at the Keele University in England. Hellier's report on the suicidal planet is in Thursday's issue of the journal Nature.

"It's causing its own destruction by creating these tides," Hellier said.

The star is called WASP-18 and the planet is WASP-18b because of the Wide Angle Search for Planets team that found them.

The planet circles a star that is in the constellation Phoenix and is about 325 light-years away from Earth, which means it is in our galactic neighborhood. A light-year is about 5.8 trillion miles.

The planet is 1.9 million miles from its star, 1/50th of the distance between Earth and the sun, our star. And because of that the temperature is about 3,800 degrees.

Its size — 10 times bigger than Jupiter — and its proximity to its star make it likely to die, Hellier said.

Think of how the distant moon pulls Earth's oceans to form twice-daily tides. The effect the odd planet has on its star is thousands of times stronger, Hellier said. The star's tidal bulge of plasma may extend hundreds of miles, he said.

Like most planets outside our solar system, this planet was not seen directly by a telescope. Astronomers found it by seeing dips in light from the star every time the planet came between the star and Earth.

So far astronomers have found more than 370 planets outside the solar system. This one is "yet another weird one in the exoplanet menagerie," said planet specialist Alan Boss of the Carnegie Institution of Washington.

It's so unusual to find a suicidal planet that University of Maryland astronomer Douglas Hamilton questioned whether there was another explanation. While it is likely that this is a suicidal planet, Hamilton said it is also possible that some basic physics calculations that all astronomers rely on could be dead wrong.

The answer will become apparent in less than a decade if the planet seems to be further in a death spiral, he said.

SNE Sea-Buckthorn Capsule

SeaBuckthorn : Nature's Anti-oxidant

In recent years people have discovered the many potential benefits of antioxidants in the diet, and the pharmaceutical industry has raced to synthesize more and more powerful varieties of them. But in chasing new discoveries we have forgotten a time-honored natural source of antioxidants: Seabuckthorn

Seabuckthorn , a hardy plant which grows in dry soil, which had very healthful and even miraculous herbal properties. It sounded rather exotic, but it seemed to thrive. It certainly lived up to its name - it had thorns enough to deter even the most thick-skinned buck. They looked pretty on the bush, oval-shaped and a bright orange colour. They didn't have much flavour, and they weren't even particularly sweet.It seems that it was already known in Ancient Greek times. It is also called "Sallow Thorn", presumably from the berries which can stain the skin yellow (they have been used to make pigments and dyes). Seabuckthorn's Latin name is Hippophae rhamnoides L., translated to mean "giving light to a horse" (hippos - horse, phaos - light); refer- , to its reputed power of curing blindness in horses (- well, who am I to argue). It is native to Europe and some northern regions of Asia, but is cultivated elsewhere too. What is the secret? Seabuckthorn berries have a unique composition, combining a cocktail of components usually only found separately. The content of vitamin C, vitamin E and carotenoids reads like the label on a pack of multi-vitamin pills. The vitamin C content is among the highest for any plant (4th after rose-hips, hot chili pepper and sweet red pepper), while for vitamin E it takes 2- nd place around the other "champions" are all nuts and seeds with a high fat content. Seabuckthorn berries also have a high content of b-carotene (see Tables 1 and 2). The beta-carotene content is what gives the berries their colour, which can vary from yellow to red depending on the variety. All of these components are classified as natural anti-oxidants, which form a vital part of the body's defense system.

Wonder-working berriesDespite the wide area where Seabuckthorn grows, few people in Europe or America make use of its medicinal properties. But in some countries like Tibet, China, Russia and Ukraine, Seabuckthorn oil is a popular home-made ointment for minor cuts, sunburn, and skin irritation; and its curative properties have been confirmed by scientific research. If you are able to harvest some Seabuckthorn berries, you can try preparing the oil yourself. Why do we need anti-oxidants?Smoking, drinking alcohol, exposure to environmental pollutants, and also exposure to ultraviolet light or nuclear radiation can all trigger the production of "free radicals" on the skin's surface, or inside the body. Free radicals are very simple compounds of oxygen, in which the innocent molecule has acquired an extra electron. Free radicals are very reactive particles and they aggressively attack all the surrounding molecules within the cell. The attacked molecules are oxidized, becoming structurally damaged and even making them toxic for the body. Vitamins with antioxidant properties form a natural line of defense against free radicals; they "catch" free radicals and neutralize them. These anti-oxidant vitamins, all present in Seabuckthorn oil, are vitamin A (derived from -carotene), vitamin C (ascorbic acid) and vitamin E (-tocopherol).

For busy peopleFor those of us not lucky enough to have a Seabuckthorn bush, or with no time to prepare the oil ourselves, fortunately it is available in ready-prepared form; as a liquid for use on the skin, or as capsules for internal use. The finished product is more often blended with an oil such as sunflower oil, olive oil and almond oil. Also on the market you can find a very concentrated extract (not blended), used by manufacturers of cosmetics and other products. Seabuckthorn oil standardized using carotenoids (not less than 170mg% and maximum 300-420mg%) and sum of tocoferols (not less than 110mg%).The purity is very important; not every product is of a good standard. But one high-quality product I have found in Eastern Europe are the Rhamno-Fitt Seabuckthorn oil capsules produced by Biogal Rt. in Hungary. It does not contain any preservatives or chemical stabilizers. Each capsule contains 300mg of pure (not blended) Seabuckthorn oil, and provides 500 mcg of beta-carotene (1/6 of daily requirement) and 300 mcg of vitamin E (1/3 of daily requirement). The suggested dosage is 3 capsules per day.

Rhamno-Fitt capsules for a healthy body and healthy skinFor a healthy bodily systemInfection prophylaxis:reinforces the body's defensesRhamno-Fitt capsules is very rich source of vitamins and minerals, especially in vitamins A, C, E and beta-carotenes, flavanoids, and other bioactive compounds. Rhamno-Fitt capsules increases the capability of the body's immune-system and can prevent vitamin A deficiency in the body. Also has an antibacterial action; inhibits the growth of staphylococci and other bacteria. These effects are especially valuable at the end of a long winter, in the treatment of colds, febrile conditions, exhaustion, also during periods of convalescence.Promotes healthy arteriesRetards the development of atherosclerosis and cardiac disorders. Rhamno-Fitt capsules are also a fairly good source of essential unsaturated fatty acids, that is important for regulation of prostaglandin synthesis. Prostaglandins regulates blood pressure and water-salt balance. Their role was emphasized in many scientific researches. Each Rhamno-Fitt capsule contains 35-60% of Palmitoleic acid, 5-35% butyric oil acid and 0-15% linoleic acid. So high content of essential fatty acids is fairly uncommon for a fruit. Usually oils, animals fats and fish oils have these acids.Anti-Cancer activityAnti-tumor activity of Seabuckthorn was demonstrated in many scientific works. Just mention one of them. Chinese scientists Li Y and Liu H from Shanxi Medical College, Taiyuan, China published an article (IARC Sci. Publ. 1991; 105, 568-70) in which three group of rats were fed a diet containing carcinogens: First group (control) drunk a tap-water, second group drunk water with Vitamin C and the third group drunk water together with Seabuckthorn juice. The result were intrigues. The average life span of rats in a group given Seabuckthorn juice was 270 days, when given ascorbic acid - 220 days and in control group only 195 days. Moreover microscopic examinations of the liver (main target of carcinogens) showed that Seabuckthorn juice can prevent tumor production more effectively comparing with ascorbic acid solutions and pure water. Regenerative effectsThese were discovered during experiments on patients with skin defects. Promotes recovery from colitis, healing of erosion of the cervix, of stomach and duodenal ulcers, and of burns affecting the mucous membranes. Also speeds recovery from external wounds and sores, e.g. bedsores.For healthy skin - a valuable external nutrient and ointmentAs a skin nutritive and restorativeSuch anti-oxsidants like vitamin E and beta-corotene effectively combat wrinkles, dryness, and other symptoms of aging or of a neglected skin. That is why Rhamno-Fitt capsules delays the aging process externally and enternally. As a healing ointmentThe oil can be used as an ointment to promote healing of burns (including sunburn), eczema, radiation injury ulcers and small cuts or abrasions. This healing effect is due to the beta-carotene (provitamin-A) that is in Seabuckthorn oil. The oil should be applied to the skin after washing and drying, and left for at least 20 minutes before removal. For best results, apply in the evening and leave overnight. However, remember that it will probably leave a temporary slight yellow-orange stain - so try and apply evenly!Other applications of SeabuckthornFirstly in food industry in the production of juices with tonic effect, syrups and concentrates. The fresh berries are astringent and it is being investigated as a food that is capable of reducing the incidence of cancer and also as a means of halting or reversing the growth of cancers. As a natural vitamin C additive and aroma for fruit and vegetables preserves. As ingredient in sauces and in the production of confectionary and aromas. Seabuckthorn also used in pharmaceutical and cosmetic industries.

Protease (a digestive enzyme)

A protease is any enzyme that conducts proteolysis, that is, begins protein catabolism by hydrolysis of the peptide bonds that link amino acids together in the polypeptide chain, which form a molecule of protein. In other words, proteases break down proteins.


Classification


Standard

Proteases are currently[update] classified into six groups:
Serine proteases
Threonine proteases
Cysteine proteases
Aspartate proteases
Metalloproteases
Glutamic acid proteases
The threonine and glutamic acid proteases were not described until 1995 and 2004, respectively. The mechanism used to cleave a peptide bond involves making an amino acid residue that has the cysteine and threonine (peptidases) or a water molecule (aspartic acid, metallo- and glutamic acid peptidases) nucleophilic so that it can attack the peptide carboxyl group. One way to make a nucleophile is by a catalytic triad, where a histidine residue is used to activate serine, cysteine, or threonine as a nucleophile.

By optimal pH


Alternatively, proteases may be classified by the optimal pH in which they are active:
Acid proteases
Neutral proteases, notably involved in type 1 hypersensitivity. Here, it is released by mast cells and causes activation of complement and kinins.[1] This group includes the calpains.
Basic proteases

Occurrence

Proteases occur naturally in all organisms. These enzymes are involved in a multitude of physiological reactions from simple digestion of food proteins to highly-regulated cascades (e.g., the blood-clotting cascade, the complement system, apoptosis pathways, and the invertebrate prophenoloxidase-activating cascade). Peptidases can either break specific peptide bonds (limited proteolysis), depending on the amino acid sequence of a protein, or break down a complete peptide to amino acids (unlimited proteolysis). The activity can be a destructive change, abolishing a protein's function or digesting it to its principal components; it can be an activation of a function, or it can be a signal in a signaling pathway.
Bacteria also secrete proteases to hydrolyse (digest) the peptide bonds in proteins and therefore break the proteins down into their constituent monomers.
A secreted bacterial protease may also act as an exotoxin, and be an example of a virulence factor in bacterial pathogenesis. Bacterial exotoxic proteases destroy extracellular structures. Protease enzymes are also used extensively in the bread industry in bread improver.
Proteases, also known as proteinases or proteolytic enzymes, are a large group of enzymes. Proteases belong to the class of enzymes known as hydrolases, which catalyse the reaction of hydrolysis of various bonds with the participation of a water molecule.
Proteases are involved in digesting long protein chains into short fragments, splitting the peptide bonds that link amino acid residues. Some of them can detach the terminal amino acids from the protein chain (exopeptidases, such as aminopeptidases, carboxypeptidase www A); the others attack internal peptide bonds of a protein (endopeptidases, such as trypsin, chymotrypsin, pepsin, papain, elastase).
Proteases are divided into four major groups according to the character of their catalytic active site and conditions of action: serine proteinases, cysteine (thiol) proteinases, aspartic proteinases, and metalloproteinases. Attachment of a protease to a certain group depends on the structure of catalytic site and the amino acid (as one of the constituents) essential for its activity.
Proteases are used throughout an organism for various metabolic processes. Acid proteases secreted into the stomach (such as pepsin) and serine proteases present in duodenum (trypsin and chymotrypsin) enable us to digest the protein in food; proteases present in blood serum (thrombin, plasmin, Hageman factor, etc.) play important role in blood-clotting, as well as lysis of the clots, and the correct action of the immune system. Other proteases are present in leukocytes (elastase, cathepsin G) and play several different roles in metabolic control. Proteases determine the lifetime of other proteins playing important physiological role like hormones, antibodies, or other enzymes -- this is one of the fastest "switching on" and "switching off" regulatory mechanisms in the physiology of an organism. By complex cooperative action the proteases may proceed as cascade reactions, which result in rapid and efficient amplification of an organism's response to a physiological signal.
Proteases are part of many laundry detergents.

Lipase Enzyme & Lipolysis, Important To Breakdown Fats!

The lipase enzyme is a naturally occurring enzyme found in the stomach and pancreatic juice, which is also found within fats in the foods that we eat. Lipase enzyme digests fats and lipids, helping to maintain correct gall bladder function. As such, these constitute any of the fat-splitting or lipolytic enzymes, all of which cleave a fatty acid residue from the glycerol residue in a neutral fat or a phospholipid. The lipase enzyme controls the amount of fat being synthesized and that which is burned in the body, reducing adipose tissue (fat stores). The lipase enzyme belongs to the esterases family of proteins. The lipase enzyme is found widely distributed in the plant world (beans and legumes), as well as in molds, bacteria, milk and milk products, and in animal tissues, especially in the pancreas. In sufficient quantities of lipase enzyme production, lipase can help use fat-stores to be burned as fuel. Indeed, lipase is a rate-determining enzyme, which not only activates the burning of stored body fats but also effectively inhibits fatty acid synthesis, or fat storage! Hormone-Sensitive Triacyclglycerol Lipase, as it is also known, actually stimulates lipolysis in fat tissues, safely raising blood fatty acid levels, which ultimately activates the beta-oxidation pathway in other tissues, such as liver and muscle. In the liver, lipolysis leads to the production of ketone bodies that are secreted into the bloodstream for use as an alternative fuel to glucose by peripheral tissues. Lipase enzymes contain sulfhydryl groups (SH) and are activated by substances that keep SH groups in the reduced state, such as, ascorbic acid or Vitamin C and L-Glutathione and L-Cysteine. The lipase enzyme is rather unique in that it selectively helps in the breakdown of fats but without damaging the fat-soluble vitamins or unsaturated omega-3, 6 fatty acids like Gamma-Linolenic Acid (GLA), Docosahexaenoic Acid (DHA), and Eicosapentaenoic Acid (EPA). Try Växa's homeopathic medicinal, Digestin, which contains the powerful digestive lipase enzymes and other important enzymes: Amylase, Protease, Cellulase, Lactase, Sucrase, Maltase, plus 30 additional ingredients, such as Marshmallow Root, Papain, Papaya Leaf and much more! Digestin is doctor-formulated, natural homeopathic medicinal with no side effects and has helped countless people with digestive problems and can help you as well.

Amylase (a digestive enzyme)

An amylase is an enzyme that breaks starch down into sugar. Amylase is present in human saliva, where it begins the chemical process of digestion. Foods that contain much starch but little sugar, such as rice and potato, taste slightly sweet as they are chewed because amylase turns some of their starch into sugar in the mouth. The pancreas also makes amylase (alpha amylase) to hydrolyse dietary starch into di- and trisaccharides which are converted by other enzymes to glucose to supply the body with energy. Plants and some bacteria also produce amylase. As diastase, amylase was the first enzyme to be discovered and isolated (by Anselme Payen in 1833).[citation needed] Specific amylase proteins are designated by different Greek letters. All amylases are glycoside hydrolases and act on α-1,4-glycosidic bonds

Classification

α-Amylase

Main article: alpha-Amylase
(EC 3.2.1.1 ) (CAS# 9014-71-5) (alternate names: 1,4-α-D-glucan glucanohydrolase; glycogenase) The α-amylases are calcium metalloenzymes, completely unable to function in the absence of calcium. By acting at random locations along the starch chain, α-amylase breaks down long-chain carbohydrates, ultimately yielding maltotriose and maltose from amylose, or maltose, glucose and "limit dextrin" from amylopectin. Because it can act anywhere on the substrate, α-amylase tends to be faster-acting than β-amylase. In animals, it is a major digestive enzyme and its optimum pH is 6.7-7.0. [1]
In human physiology, both the salivary and pancreatic amylases are α-Amylases. They are discussed in much more detail at alpha-Amylase.
Also found in plants (barley) , fungi (ascomycetes and basidiomycetes) and bacteria (Bacillus).

β-Amylase

(EC 3.2.1.2 ) (alternate names: 1,4-α-D-glucan maltohydrolase; glycogenase; saccharogen amylase) Another form of amylase, β-amylase is also synthesized by bacteria, fungi, and plants. Working from the non-reducing end, β-amylase catalyzes the hydrolysis of the second α-1,4 glycosidic bond, cleaving off two glucose units (maltose) at a time. During the ripening of fruit, β-amylase breaks starch into sugar, resulting in the sweet flavor of ripe fruit. Both are present in seeds; β-amylase is present prior to germination, whereas α-amylase and proteases appear once germination has begun. Cereal grain amylase is key to the production of malt. Many microbes also produce amylase to degrade extracellular starches. Animal tissues do not contain β-amylase, although it may be present in microrganisms contained within the digestive tract.

γ-Amylase

(EC 3.2.1.3 ) (alternative names: Glucan 1,4-α-glucosidase; amyloglucosidase; Exo-1,4-α-glucosidase; glucoamylase; lysosomal α-glucosidase; 1,4-α-D-glucan glucohydrolase) In addition to cleaving the last α(1-4)glycosidic linkages at the nonreducing end of amylose and amylopectin, yielding glucose, γ-amylase will cleave α(1-6) glycosidic linkages. Unlike the other forms of amylase, γ-amylase is most efficient in acidic environments and has an optimum pH of 3.

Uses

Amylase enzymes are used extensively in bread making to break down complex sugars such as starch (found in flour) into simple sugars. Yeast then feeds on these simple sugars and converts it into the waste products of alcohol and CO2. This imparts flavour and causes the bread to rise. While Amylase enzymes are found naturally in yeast cells, it takes time for the yeast to produce enough of these enzymes to break down significant quantities of starch in the bread. This is the reason for long fermented doughs such as sour dough. Modern bread making techniques have included amylase enzymes (often in the form of malted barley) into bread improver thereby making the bread making process faster and more practical for commercial use.[2]
When used as a food additive Amylase has E number E1100, and may be derived from pig pancreas or mould mushroom.
Bacilliary amylase is also used in detergents to dissolve starches from fabrics.
Workers in factories that work with amylase for any of the above uses are at increased risk of occupational asthma. 5-9% of bakers have a positive skin test, and a fourth to a third of bakers with breathing problems are hypersensitive to amylase. [3]
An inhibitor of alpha-amylase called phaseolamin has been tested as a potential diet aid. [4]
Blood serum amylase may be measured for purposes of medical diagnosis. A normal concentration is in the range 21-101 U/L. A higher than normal concentration may reflect one of several medical conditions, including acute inflammation of the pancreas, macroamylasemia, perforated peptic ulcer, and mumps. Amylase may be measured in other body fluids, including urine and peritoneal fluid.

History

In 1831 Erhard Friedrich Leuchs (1800-1837) described the diastatic action of salivary ptyalin (amylase) on starch.[5] The modern history of enzymes began in 1833 when French chemists described the isolation of an amylase complex from germinating barley and named it diastase.[6] In 1862 Danielewski separated pancreatic amylase from trypsin.[7]

Strong Meteor Shower Expected Tonight

The annual Perseid meteor shower is expected to put on a good show this week for those willing to get up in the wee hours of the morning and wait patiently for the shooting stars.
In North America, the best time to watch will be between midnight to 5 a.m. on Wednesday, Aug. 12, but late Tuesday night and also Wednesday night could prove fruitful, weather permitting.
The Perseids are always reliable, and sometimes rather spectacular. The only things that puts a damper on the August show are bad weather or bright moonlight. Unfortunately this week, as the Perseids reach their peak Tuesday and Wednesday nights, the moon will be high in the sky, outshining the fainter meteors.
Still, skywatchers around the globe will have a good chance of spotting the brighter meteors. Some already are enjoying the show.
Already underway
The Perseids are bits of debris from Comet Swift-Tuttle, which has laid down several streams of debris, each in a slightly different location, over the centuries as it orbits the sun. Every August, Earth passes through these debris streams, which spread out over time.
"They are typically fast, bright and occasionally leave persistent trains," says Joe Rao, SPACE.com's Skywatching Columnist. "And every once in a while, a Perseid fireball will blaze forth, bright enough to be quite spectacular and more than capable to attract attention even in bright moonlight."
Low numbers of Perseids, including some bright fireballs, have already been reported as Earth began entering the stream in late July. Seasoned observers have counted up to 25 per hour already, or nearly one every two minutes.
Most meteors are no bigger than a pea. They vaporize as they enter Earth's atmosphere, creating bright streaks across the sky.
The Perseids appear to emanate from the constellation Perseus, which rises high in the sky around midnight and is nearly overhead by dawn. Like most meteor showers, the hours between midnight and daybreak are typically the best time to watch, because that's when the side of Earth you are on is rotating into the direction of Earth's travels through space, so meteors are "scooped up" by the atmosphere at higher rates, much like a car's windshield ends the lives of more bugs than does the rear bumper.
Astronomers expect up to 200 meteors per hour in short bursts of up to 15 minutes or so. But many of the fainter meteors will simply not be visible due to moonlight, and rates will go down even more for those in urban areas. More likely a typical observer under reasonably dark skies might hope to see a meteor every couple minutes when the bursts come, and fewer during lulls.
When to watch
The best time to watch is between midnight and dawn Wednesday. Forecasters say the best stretch could come between 4 a.m. and 5 a.m. ET (1-2 a.m. PT), which would be after daybreak in Europe. Some Perseids might be visible late Tuesday night, and Wednesday night into Thursday morning could prove worthwhile, too.
Meteor forecasting is still in its infancy, however, so the best bet for anyone truly hungry to spot shooting stars is to get in as much observing time as possible from around 11 p.m. Tuesday night until dawn Wednesday, and if you miss that show, try the same time frame Wednesday evening into Thursday morning.
Meteors should be visible in the pre-dawn hours, weather permitting, all around the Northern Hemisphere.
"Earth passes through the densest part of the debris stream sometime on Aug. 12," said Bill Cooke of NASA's Meteoroid Environment Office. "Then, you could see dozens of meteors per hour."
Viewing tips
The best location is far from city and suburban lights. Ideally, find a structure, mountain or tree to block the moon. Then scan as much of the sky as possible. The meteors can appear anywhere, heading in any direction. If you trace their paths backward, they'll all point to the constellation Perseus.
People in locations where any chill might occur should dress warmer than they think necessary to allow for prolonged viewing.
Seasoned skywatchers advise using a blanket or lounge chair for comfort, so you can lie back and look up for long periods. Allow at least 15 minutes for your eyes to fully adjust to the darkness. Then expect meteors to be sporadic: You might see two in a row, or several minutes could go by between shooting stars.
Avid meteor watchers might want to try scanning the northeastern horizon from 9 p.m. to 11 p.m. local time (your local time, wherever you are) for Perseids that graze the horizon.
"Earthgrazers are meteors that approach from the horizon and skim the atmosphere overhead like a stone skipping across the surface of a pond," Cooke explained. "They are long, slow and colorful – among the most beautiful of meteors." He notes that an hour of watching may net only a few of these at most, but seeing even one can make the whole night worthwhile.