The 2015 Perseids: Weather Prospects, Prognostications and More

The venerable ‘old faithful of meteor showers’ is on tap for this week, as the August Perseids gear up for their yearly performance. Observers are already reporting enhanced rates from this past weekend, and the next few mornings are crucial for catching this sure-fire meteor shower.

First, here’s a quick rundown on prospects for 2015. The peak of the shower as per theoretical modeling conducted by Jérémie Vaubaillon projects a broad early maximum starting around Wednesday, August 12th at 18:39 UT/2:39 PM EDT. This favors northeastern Asia in the early morning hours, as the 1862 dust trail laid down by Comet 109P Swift-Tuttle — the source of the Perseids — passes 80,000 km (20% of the Earth-Moon distance, or about twice the distance to geostationary orbit) from the Earth. This is worth noting, as the last time we encountered this same stream was 2004, when the Perseids treated observers to enhanced rates up towards 200 per hour. Typically, the Perseids exhibit a Zenithal Hourly Rate (ZHR) of 80-100 per hour on most years.

Image credit
The terrestrial situation at the projected peak of the 2015 Perseids. Image credit: NOAA/Dave Dickinson

This translates into a local peak for observers worldwide on the mornings of August 12th and 13th. Comet 109P Swift-Tuttle orbits the Sun once every 120 years, and last reached perihelion in 1992, enhancing the rates of the Perseids throughout the 1990s.

Don’t live in northeast Asia? Don’t despair, as meteor showers such as the Perseids can exhibit broad multiple peaks which may arrive early or late. Mornings pre-dawn are the best time to spy meteors, as the Earth has turned forward into the meteor stream past local midnight, and rushes headlong into the oncoming stream of meteor debris. It’s a metaphor that us Floridians know all too well: the front windshield of the car gets all the bugs!

Perseid radiant
The flight of the Perseid radiant through August. Image credit: Dave Dickinson/Stellarium

Weather prospects — particularly cloud cover, or hopefully, the lack of it — is a factor on every observer’s mind leading up to a successful meteor hunting expedition. Fortunately here in the United States southeast, August mornings are typically clear, until daytime heating gives way to afternoon thunder storms. About 48 hours out, we’re seeing favorable cloud cover prospects for everyone in the CONUS except perhaps the U.S. northeast.

Weather and cloud cover prospects for the mornings of August 12th and August 13th. Image credit: NOAA
Weather and cloud cover prospects for the mornings of August 12th and August 13th. Image credit: NOAA

The Moon is also under 48 hours from New on Wednesday, allowing for dark skies. This is the closest New Moon to the peak of the Perseids we’ve had since 2007, and it won’t be this close again until 2018.

Fun fact: the August Perseids, October Orionids, November Leonids AND the December Geminids are roughly spaced on the calendar in such a way that if the Moon phase is favorable for one shower on a particular year, it’ll nearly always be favorable (and vice versa) on the others as well.

Sky watchers have observed the annual Perseid meteors since antiquity, and the shower is often referred to as ‘The Tears of Saint Lawrence.’ The Romans martyred Saint Lawrence on a hot grid iron on August 10th, 258 AD. The radiant crosses from the constellation Perseus in early August, and sits right on the border of Cassiopeia and Camelopardalis on August 12th at right ascension 3 hours 10’ and declination +50N 50.’ Technically, the shower should have the tongue-twisting moniker of the ‘Camelopardalids’ or perhaps the ‘Cassiopeiaids!’

The last few years have seen respectable activity from the Perseids:

2014- ZHR = 68 (Full Moon year)

2013- ZHR = 110

2012- ZHR = 120

2011- ZHR = 60 (Full Moon year)

2010- ZHR = 90

You can see the light-polluting impact of the nearly Full Moon on the previous years listed above. Light pollution has a drastic effect on the number of Perseids you’ll see. Keep in mind, a ZHR is an ideal rate, assuming the radiant is directly overhead and skies are perfectly dark. Most observers will see significantly less. We like to watch at an angle about 45 degrees from the radiant, to catch meteors in sidelong profile.

Imaging the Perseids is as simple as setting up a DSLR on a tripod as taking long exposures of the sky with a wide angle lens. Be sure to take several test shots to get the combination of f-stop/ISO/and exposure just right for current sky conditions. This year, we’ll be testing a new intervalometer to take automated exposures while we count meteors.

Clouded out? NASA TV will be tracking the Perseids live on Wednesday, August 12th starting at 10PM EDT/02:00 UT:

Remember, you don’t need sophisticated gear to watch the Perseids… just a working set of ‘Mark-1 eyeballs.’ You can even ‘hear’ meteor pings on an FM radio on occasion similar to lightning static if you simply tune to an unused spot on the dial. Sometimes, you’ll even hear a distant radio station come into focus as it’s reflected off of an ionized meteor trail:

And if you’re counting meteors, don’t forget to report ‘em to the International Meteor Organization and tweet ‘em out under hashtag #Meteorwatch.

Good luck and good meteor hunting!

When Good Meteor Showers Go Bad: Prospects for the 2014 Perseids

It’s that time of year again, when the most famous of all meteor showers puts on its best display.

Why are the Perseids such an all ‘round favorite of sky watchers?  Well, while it’s true that other annual meteor showers such as the Quadrantids and Geminids can exceed the Perseids in maximum output, the Perseids do have a few key things going for them. First, the shower happens in mid-August, which finds many northern hemisphere residents camping out under warm, dark skies prior to the start of the new school year. And second, unlike showers such as the elusive Quads which peak over just a few hours, the Perseids enjoy a broad span of enhanced activity, often covering a week or more.

Credit: JPL
The orientation of the orbital path of Comet 109P/Swift-Tuttle and the position of the Earth on August 12th. Credit: JPL-Horizons.

These are all good reasons to start watching for Perseids now. Here’s the low down on the Perseid meteors for 2014:

The History: The Perseids are sometimes referred to as “The Tears of Saint Lawrence,” who was martyred right around the same date on August 10th, 258 A.D. The source of the shower is comet 109P Swift-Tuttle, which  was first identified as such by Schiaparelli in 1866. The comet itself visited the inner solar system again recently in 1992 on its 120 year orbit about the Sun, and rates were enhanced throughout the 1990s.

A 2013 Perseid pierces the plane of the Milky Way.
A 2013 Perseid pierces the plane of the Milky Way. Credit: Stephen Rahn.

Unlike most showers, the Perseids have a very broad peak, and observers and automated networks such as UKMON and NASA’s All Sky Camera sites have already begun to catch activity starting in late July.

Credit: The UK-MON network.
A pair of early 2014 Perseids recently captured by UKMON’s Wilcot station. Credit: The UK-MON network.

In recent years, the rates for the Perseids have been lowering a bit but are still enhanced, with ZHRs at 91(2010), 58(2011), 122(2012), and 109(2013). It’s also worth noting that the Perseids typically exhibit a twin peak maximum within a 24 hour span. The International Meteor Organization maintains an excellent page for quick look data to check out what observers worldwide are currently seeing. The IMO also encourages observers worldwide to submit meteor counts by location. Note that the phase of the Moon was near Full in 2011, with observing circumstances very similar to 2014.

The Prospects for 2014: Unfortunately, the 2014 Perseid meteors have a major strike going against them this year: the Moon will be at waning gibbous during its peak and just two days past Full illumination. This will make for short exposure times and light polluted skies. There are, however, some observational strategies that you can use to combat this: one is to place a large building or hill between yourself and the Moon while you observe — another is to start your morning vigil a few days early, before the Moon reaches Full. The expected Zenithal Hourly Rate for 2014 is predicted to hover around 90 and arrive around 00:15 to 2:00 UT on August 13th favoring Europe, Africa and the Middle East.

Created by Author
The orientation of Earth’s shadow during the projected peak of the Perseids on August 13th at 00:15 Universal Time.  The positions where the Sun, Moon, and radiant of the Perseids are directly overhead are also noted. Created by Author.

The Radiant: It’s strange but true: meteor shower radiants wander slightly across the sky during weeks surrounding peak activity, due mostly to the motion of the Earth around the Sun. Because of this, the radiant of the Perseids is not actually in the constellation Perseus on the date that it peaks! At its maximum, the radiant actually sits juuusst north of the constellation that it’s named for on the border of Camelopardalis and Cassiopeia. This is a great pedantic point to bring up with your friends on your August meteor vigil… they’ll sure be glad that you pointed this out to ’em and hopefully, invite you back for next year’s Perseid watch.

The actual position of the radiant sits at 3 Hours 04’ Right Ascension and +58 degrees north declination.

Credit: Starry Night Education software.
The movement of the radiant of the Perseids. The sky is simulated for latitude 30 degrees north at 2:00 AM local on August 13th. Credit: Starry Night Education software.

Meteor-speak: Don’t know your antihelion from a zenithal hourly rate? We wrote a whole glossary that’ll have you talking meteors like a pro for Adrian West’s outstanding Meteorwatch site a few years back. Just remember, the crucial “ZHR” of a shower that is often quoted is an ideal extrapolated rate… light pollution, the true position of the radiant, observer fatigue and limited field of view all conspire to cause you to see less than this predicted maximum. The universe and its meteor showers are indeed a harsh mistress!

Observing: But don’t let this put you off. As Wayne Gretsky said, “You miss 100% of the shots that you don’t take,” and the same is true with meteor observing: you’re sure to see exactly zero if you don’t observe at all. Some of my most memorable fireball sightings over the years have been Perseids. And remember, the best time to watch for meteors is after local midnight, as the Earth is turned forward into the meteor stream. Remember, the car windshield (Earth) gets the bugs (meteors) moving down the summer highway…

Good luck, and let us know of those tales of Perseid hunting and send those meteor pics in to Universe Today!