Want to Watch History Burn? Check Out a Meteor Shower!

 

By JoEllen McBride, PhD

 

Fireballs streaking across the sky. Falling or shooting stars catching your eye. Meteors have fascinated humans as long as we’ve kept records. Depending on the time of year, on a clear night, you can see anywhere from 2 to 16 meteors enter our atmosphere and burn up right before your eyes. If you really want a performance, you should look up during one of the many meteor showers that happen throughout the year. These shows can provide anywhere from 10 to 100 meteors an hour! But what exactly is burning up to create these cosmic showers?

 

To answer this question we need to go back in time to the formation of our solar system. Our galaxy is full of dust particles and gas. If these tiny particles get close enough they’ll be gravitationally attracted and forced to hang out together. The bigger a blob of gas and dust gets, the more gas and dust it can attract from its surroundings. As more and more particles start occupying the same space, they collide with each other causing the blob to heat up. At a high enough temperature the ball of now hot gas can fuse Hydrogen and other elements which sustains the burning orb. Our Sun formed just like this, about 5 billion years ago.

 

Any remaining gas and dust orbiting our newly created Sun coalesced into the eight planets and numerous dwarf planets and asteroids we know of today. Even though the major planets have done a pretty good job clearing out their orbits of large debris, many tiny particles and clumps of pristine dust remain and slowly orbit closer and closer to the Sun. If these 4.5 billion year old relics cross Earth’s path, our planet smashes into them and they burn up in our atmosphere. These account for many of the meteors that whiz through our atmosphere unexpectedly.

 

The predictable meteor showers, on the other hand, are a product of the gravitational influence of the larger gas giant planets. These behemoths forced many of the smaller bodies that dared to cross them out into the furthest reaches of our solar system. Instead of being kicked out of the solar system completely, a few are still gravitationally bound to the Sun in orbits that take them from out beyond the Kuiper belt to the realm of the inner planets. As these periodic visitors approach our central star, their surfaces warm, melting ice that held together clumps of ancient dust. The closer the body gets to the Sun, the more ice melts– leaving behind a trail of particulates. We humans see the destruction of these icy balls as beautiful comets that grace our night skies periodically. But the trail of dust remains long after the comet heads back to edge of our solar system.

 

The dusty remains of our cometary visitors slowly orbit the Sun along the comet’s path. There are a few well-known dust lanes that our planet plows into annually. Some of these showers produce exciting downpours with over a hundred meteors an hour and others barely produce a drip. April begins the meteor shower season and the major events for 2017 are listed below.

Shower Dates

Peak Times

(UT)

Moon Phase At Peak Progenitor
Range Peak
Lyrid (N) Apr 16-25 Aprl 22 12:00 Crescent Thatcher 1861 I
Eta Aquarid (S) Apr 19-May 28 May 6 2:00 Gibbous 1P/Halley
Delta Aquarid (S) Jul 21-Aug 23 Jul 30 6:00 First Quarter 96P/Machholz
Perseid (N) Jul 17-Aug 24 Aug 12/13 14:00/2:30 Third Quarter 109P/Swift-Tuttle
Orionid Oct 2-Nov 7 Oct 21 6:00 First Quarter 1P/Halley
Taurids Sep 7-Nov 19

Nov 10/11

Nov 4/5

12:00

Crescent

Full

2P/Encke
Leonid Nov Nov 17 17:00 New 55P/Tempel-Tuttle
Geminid Dec 4-16 Dec 14 6:30 Crescent 3200 Phaethon*
Quadrantid (N) Dec 26-Jan 10 Jan 3 14:00 Full 2003 EH1

S= best viewed from Southern Hemisphere locations

N= best viewed from Northern Hemisphere locations

*This is an asteroid with a weird orbit that takes it very close to the Sun!

 

Here is a list of things you can do to ensure the best meteor viewing experience.

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  • Check the weather. If it’s going to be completely overcast your meteor shower is ruined.
  • Is the Moon up? Is it more than a crescent? If the answer to both of these is yes you will have a more difficult time seeing meteors. The big, bright ones will still shine through but those are rare.
  • When trying to catch a meteor shower, make sure the constellation the shower will radiate from is actually up that night. Hint: Meteor showers are named after the constellation they appear to radiate from.
  • You need the darkest skies possible. So get away from cities and towns. The International Dark Sky Association has a dark sky place finder you can use. Your best bet is to find an empty field far from man-made light pollution.
  • Make sure trees and buildings aren’t obscuring your view.
  • It takes about 30 minutes for your eyes to completely adjust to the darkness. If you have a flashlight, cover it with red photography gel to help keep your eyes adjusted.
  • Ditch the cell phone. Cell phones ruin your night vision. Every time you look at your screen your eyes have to readapt to the dark when you look back up at the sky. There are apps you can download that dim your screen (iPhone, Android) but your eyes will still need time to adjust to the darkness if you glance at your phone. Also looking away almost guarantees the biggest meteor will streak by at just that moment.
  • Dress comfortably. In the fall and winter, wear warm clothes and have hot chocolate and coffee on hand. In the spring and summer, some cool beverages will enhance your experience. Make sure you have blankets to lay on or comfortable chairs so you can keep your eyes on the skies.

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Follow these guidelines and you’ll have the best chance of watching 4.5 billion years of history burn up before your very eyes.

A Short History of Fast Radio Bursts

 

By JoEllen McBride, PhD

Humans have gazed at the stars since the beginning of recorded history. Astronomy was the first scientific field our distant ancestors recorded information about. Even now, after thousands of years of study, we’re still discovering new things about the cosmos.

Fast radio bursts (FRBs) are the most recent astronomical mystery. These short-lived, powerful signals from space occur at frequencies you can pick up with a ham radio. But don’t brush the dust off your amateur radio enthusiast kit just yet. Although they are powerful, they do not occur frequently and happen incredibly fast. Which is exactly why astronomers only recently noticed them. The first FRB was discovered in 2007 from data taken in 2001. The majority of FRBs are found in old data. Their short duration meant astronomers overlooked them as background signals but closer inspection revealed a property unique to radio signals originating from outside our galaxy.

 

Signal or Noise?

Radio signals are light waves with very long wavelengths and low frequencies. Visible light (the wavelengths of light that bounce off objects, hit our eyes and allow us to see) happens on wavelengths that are a few hundred times smaller than the thickness of your hair. The wavelength of radio waves can be anywhere from a centimeter to kilometers long. The longer the wavelength, the lower the frequency  and more the signal is delayed by free-floating space particles. This is because space is not a perfect vacuum. There is dust, atoms, electrons and all kinds of small particles floating around out there. As light travels through space, it can be slowed down by these loitering particulates. Larger distances mean more chances for the light to interact with particles and these interactions are strongest at the lowest frequencies where radio waves happen.

Radio signals from within our own galaxy are close enough that they are not really affected by this delay. But sources far outside of the Milky Way have very large distances to travel so by the time the signal reaches our telescopes, it has interacted with many particles. This produces a streak or a ‘whistle’ where the higher radio frequencies in the signal reach our telescopes first and the lower ones arrive shortly afterwards.

When astronomers started noticing these whistles at unexpected frequencies, they no longer believed they were background noise but signals from the far reaches of space. They needed another piece to the puzzle though to determine exactly what was causing these interstellar calls.

 

It Takes Two to Find a FRB

The signals discovered in previous data appeared to be one-and-done events, which meant they could not be observed again with a bigger telescope to get a more precise location. Without a precise position on the sky, astronomers couldn’t tell where the signals were coming from, so had no idea what was producing them. What astronomers needed was a signal detected by two different telescopes at the same time. One telescope to broadly search for the signal and a second, much larger telescope to accurately determine its location. So they began to meticulously watch the sky for new FRBs. The first real-time observation of an FRB was in May of 2014. Although it was observed by only one telescope so its precise location was unknown, it gave astronomers a way to detect future ‘live’ bursts. In May and June of 2015 a search by another team of astronomers yielded the first ever repeating FRB.

The Arecibo radio telescope (yes the one from Goldeneye) detected the first signals then they requested follow-up observations from the Very Large Array to more precisely pin-down the location. Once they had a location, yet another team of astronomers could take pictures at visible frequencies to see what was lurking in that region of space. They found a teeny tiny galaxy, known as a dwarf galaxy, at a distance of 3 billion light years from Earth. This galaxy is full of the cold gas necessary to create new stars which means many stars are being born and the huge, bright ones are living quickly and dying.

 

Who or What is Calling Us?

Where the FRBs are coming from is important because it allows astronomers to pick between the two plausible theories for what causes FRBs. The energy produced by these bursts is impressive, so the most likely culprits take us into the realm of the small and massive: supermassive black holes (SMBH) and neutron stars. One idea suggests that FRBs could be the result of stars or gas falling into the SMBH at the center of every galaxy. If this were the case, we would expect the FRBs to occur in the central regions of a galaxy, not near the edges. Neutron stars, on the other hand, are formed after the death of massive stars. These stars are typically 10 to 30 times more massive than our Sun, so do not live for long. Astronomers expect a galaxy creating lots of new stars to also create lots of neutron stars as the most massive stars die first. Star formation can occur anywhere in a galaxy but is most commonly observed in the outer regions.

This repeat FRB is located pretty far from the center of a galaxy going through a period of intense star birth so this lends credence to neutron stars being the source. Of course, we are looking at a single data point here. There is no reason to suspect that there is a single cause for FRBs. We need more real-time observations of FRBs so we can figure out where they are located and whether or not they always come from dwarf galaxies. FRB searches have been added to three radio frequency surveys, known as CHIME, UTMOST and HIRAX, that will detect and locate these powerful signals with great precision.

It looks like we can continue to look forward to another few millennia of cosmic discoveries.

The Oldest Stars are the Poorest

 

By Knicole Colon

A recent letter published in Nature by Keller et al.  presented a star that is composed of an extremely small amount of metals, making it possibly one of the oldest stars in the universe.  Such stars as this one (known technically as SMSSJ031300.36-670839.3, but let’s call it the “senior citizen” for simplicity) are called “metal-poor,” where the term “metal” refers to any element that is heavier than helium (at least in astronomy).  This discovery is groundbreaking because only a handful of extremely metal-poor stars were previously known, and the senior citizen is significantly more metal-poor than those other stars.

The authors first identified this star as having a particularly low amount of metals based on measurements of its apparent brightness taken at different wavelengths of light.  These measurements tell you the color of the star, and there are empirical relations that can be used to extract a star’s properties based on its color.  For a more robust determination of a star’s properties, astronomers turn to spectroscopy.  With spectroscopy, it is possible to identify absorption lines caused by different elements present in a star.  Keller et al. acquired spectra from two different telescopes and found that the senior citizen’s spectrum had very few absorption features that would be caused by heavy metals.  Furthermore, the authors compared spectra of the senior citizen to spectra of two other extremely metal-poor stars that also have similar temperatures and surface gravities as the senior citizen.  They found that where some spectral features due to elements like nickel and iron exist in the other two metal-poor stars, in the senior citizen’s spectra you simply see nothing.  Stars tend to have very complicated spectra because they are composed of many different elements, so to find a star with very few spectral features is remarkable.

If we backtrack for a minute, we have to ask how such metal-poor stars are formed in the first place, and why that means they are old.  It is believed that the very first generation of stars evolved, generated metals as heavy as iron in their cores, then died and spread their metal-rich ashes throughout the universe.  However, assuming that metal-poor stars are formed from gas that is not metal-rich, that gas must not have been enriched by that first generation of stars.  That suggests that metal-poor stars are quite old – not necessarily first generation stars themselves, but old enough that perhaps they formed in areas where the metal-rich leftovers from the first stars to die had not yet reached.

Keller et al. offer a new theory as to why this star is so metal-poor.  The authors theorize that in the early universe, a single low-energy supernova (i.e. the explosive death of one of the first stars ever formed) enriched the gas from which the metal-poor stars formed.  Their theory also includes the formation of a black hole after the supernova event, which served to trap the heaviest metals that had formed in the core of the star.  Correspondingly, lighter elements like carbon would have been successfully ejected into space by the supernova explosion and would then have enriched the gas from which new stars would form.  This theory is surprising because, as mentioned above, it has been the general belief that the first stars that ever formed in the universe were extremely massive and would go out with a very-high-energy bang, enriching the gas around them with lots of metals (regardless of whether a black hole was formed or not).  Therefore, while the discovery of such a metal-poor star is certainly one for the record books, the exact origin of such a star is still a mystery.

Spend Valentine’s Day Under the Stars

 

By Knicole Colon

What’s more romantic than spending a night with that special someone under the stars?  If you really want to romance someone, you could tell them the story behind some of the constellations.  Cassiopeia is a “W”-shaped constellation that is easily recognizable in the northern night sky.  It was named after a queen in Greek mythology, who was extremely vain and constantly bragged about how beautiful she and her daughter, Andromeda, were.  As a punishment for her boasting, she was placed in the sky to cling to her throne for the rest of time.  While you’re with your honey and telling them this story, be sure to say how much more beautiful or handsome they are than Cassiopeia.  That should win you some brownie points for sure.

Andromeda, Cassiopeia’s daughter, also has a constellation named after her.  The constellation is located in the sky right next to Cassiopeia.  There’s also a galaxy named after her that is visible with binoculars or a small telescope (though it just looks like a faint smudge, it really is an entire galaxy containing billions of stars!).  In mythology, Andromeda was bound to a rock as prey for a huge sea monster that had been sent to attack her kingdom.  Poseidon, god of the sea, had sent the monster as punishment for the queen’s boasting.  Luckily, Andromeda ended up being saved by (and then marrying) Perseus, a hero in Greek mythology.

Cassiopeia. Credit: Chaouki (Flickr).
Cassiopeia. Credit: Chaouki (Flickr).

Perseus also has a constellation named after him that is located right next to Andromeda and Cassiopeia.  He killed the dangerous creature Medusa and used her head to turn the sea monster to stone, thereby saving Andromeda and making it pretty clear that he deserved permanent recognition in the sky.  It’s probably a good idea for you to assure your loved one that you would gladly save them if they were ever in peril of being eaten by a sea monster.

The movie Clash of the Titans (both the original 1981 version and the recent remake) is one famous version of the story of Cassiopeia, Andromeda, and Perseus.  So, if it happens to be cloudy on Valentine’s Day, you still have the option of watching the movie and proudly declaring that you know a little something about the constellations that are named for characters in the movie.