Will the Perseid shower be visible from {insert your location}?


I am asked this question over and over again, and it’s a good one. Everyone knows that you have to be in the right place to observe solar eclipses and other astronomical goings-on, so why should meteor showers be any different?

You do have to be in the right part of the planet to view meteor outbursts or storms, because the trails of comet debris are so narrow (hundreds of thousands of miles) that it only takes a few hours for the Earth to pass through the stream. A few hours is not enough time for the Earth to do a complete rotation (which takes 24 hours), so only those people located in areas where it is night and where the radiant is visible will be able to see the outburst or storm. These dramatic events require the viewers to be in the right ranges of both latitude AND longitude.

This is not true for normal meteor showers, like this year’s Perseids. The main stream of particles extends for millions of miles along Earth’s orbit, requiring days for it to cross. All we need is one day to take the longitude out of the visibility calculations, because then the entire planet will experience night while the shower is still going on. That’s the good news.

The kicker is that we not only have to have darkness, but also the radiant — in this case, located in the constellation of Perseus — has to be visible, i.e. above the horizon. The elevation of the radiant depends in part on latitude of the observer, and one can derive — or look up, in this age of Google — a relatively simple equation that gives the maximum elevation of the radiant:

maximum elevation = 90 – |dec -lat|

where dec is the declination of the radiant and lat is latitude of the observer (all in degrees). The vertical lines before dec and after lat mean to take the absolute value of dec — lat.  In order to see meteors from the shower, the maximum elevation must be 0 or greater (preferably more than 15 degrees). In the case of the Perseids, dec = 58 deg, so it is easy to calculate the maximum elevation for various latitudes:

 

We see that everyone in the northern hemisphere has a shot at seeing Perseids (weather permitting), but folks south of -32 degrees latitude get the shaft.

 

On the world map above, the red shaded area is the region where the Perseids will not be visible. If you live south of Brazil, at the very southern tip of Africa, or southern Austrailia, you need to take a road trip to the North if you wish to see Perseids. If you want see decent numbers, it will be a long ride, as you need to trek to somewhere above  -17 degrees latitude.

So will I see Perseids? You can find out on your own — look up your latitude (remember, Google is your friend), use the equation above, stick in 58 degrees for the dec, and calculate the maximum elevation. If it is above 15 degrees, you are good.

Remember to get away from city lights. A dark sky is important.

Enjoy the show!

How low can they go?


Real-life meteor showers are not like what you see in movies — there are no flaming rocks barreling out of the sky blasting holes in buildings, or sending cars hurling many yards through the air. Most meteor showers are caused by debris left behind by comets, icy particles mixed with dust and organics that stand no chance of surviving their kamikaze death dives through Earth’s atmosphere. The meteors that actually do make it through, becoming meteorites when they strike ground, are very, very few in number and originate from asteroids (and much more rarely, Mars and the Moon). There are only a handful of recorded falls each year.

So how low can a Perseid get? The NASA all-sky cameras can provide the answer, at least for the bigger Perseids (inch or so across); the smaller particles burn up higher. Our two station camera network can determine the trajectory of a meteor through triangulation, and tell us the start height of the meteor (the location where it is first seen) and its end height (the location where it disappears or “burns up”). Both cameras observed 80 Perseids last year and 24 so far this year, which gives us enough data to tackle the problem.

We start out by taking the end heights of the Perseids and throwing them into 1 mile wide altitude bins. This results in the following graph:

 

Looking at the plot, it is apparent that most large Perseids burn up at about 56 miles (90 km) altitude. Some ablate as high as 65 miles (104 km), whereas others may get as low as 47 miles (76 km) altitude. We see none getting down to 45 miles or lower, which gives this old ground dweller a warm fuzzy feeling — I can enjoy the shower, secure in the knowledge that the meteors are going poof way up there.

It turns out that our friends the Perseids don’t get very low at all, ending their interplanetary journeys at least 46 miles above our heads.