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Ken Tapping, April 19, 2017

On 19 April an asteroid will pass close by. At its closest it will be less than five times the distance of the Moon. The asteroid, named 2014 JO25, is about 600 metres across. It will scoot across our northern sky in a few hours, moving at 33.5 km/s. It will be closest to us at 08:24 EDT, 05:24 PDT. However, to see it you’ll need a telescope.

If it were made of basalt, like the Moon, it would have a mass of some 300 million tonnes. This is the biggest object in about 13 years to pass this close. A rough estimate suggests on average we could be hit by something that size every million years or so. Such an event would certainly be a disaster, but it would not be likely to endanger our existence. Smaller objects pass within that distance every week and on average one of them could hit us every 80 years.

The Moon is peppered with craters due to impacts. The Earth has been hit at least as often, but weathering and the continuous recycling of the Earth’s surface due to subduction and the emergence of new land surface have erased most of them. However, there are still conspicuous craters on the Earth’s surface. These cosmic collisions are not unusual; they are just part of the ongoing process of planet building.

The Earth itself was formed through impacts, as dust and progressively larger lumps of material smashed together some 4.6 billion years ago. Some of that material contained ice, which brought us the water to make our oceans. Fortunately most of that primordial “building material” has been used, but there are still pieces of it orbiting the Sun. A piece of this material some 12km across smashed down in the Sudbury area in Ontario about 1.8 billion years ago. The geological disturbance brought a wealth of minerals closer to the surface and concentrated them.

One of the most well-known and dramatic impacts occurred about 64 million years ago. After 180 million years of stability, environmental change and habitat loss was putting many species, such as the dinosaurs and ammonites into a steady decline. Then a 10km diameter asteroid hit the Earth, leading to such a rapid environmental change that 75% of species became extinct, including the dinosaurs and ammonites. In 1908 something entered the atmosphere and exploded over Tunguska, Siberia. Over 2000 square kilometres were flattened, and glasses rattled on shelves in Paris, France. A tiny difference in arrival time could have put that impact in Europe.

Today, our species dominates the Earth. Feeding ourselves and providing for our other needs involves heavily exploiting our planet’s resources. That means we are becoming increasingly vulnerable to any sort of environmental disaster. Can we do anything to reduce the impact risk? This involves two problems: detecting impact threats and then somehow mitigating them.

Small, dark objects on a dark background are hard to see. We usually detect them just in time to watch them sail past. Current radar methods are no better. In principle we can use our observations to assess the possibilities of future collisions. This is rendered difficult by all our data being obtained over a tiny part of the orbit, and the perturbation of that orbit by little tugs by the other planets. This means that unless we can give threatening asteroids a really big “shove”, changing the orbit by more than the uncertainties in our calculations, we might turn a miss into a hit. Unfortunately, as yet we don’t know how to give objects with masses of millions of tonnes a big shove. Blowing them up, as in the movies, would just turn one threat into many. However, the detection and mitigation of cosmic impact threats are getting a lot of attention.

Ken Tapping is an astronomer at the Dominion Radio Astrophysical Observatory, Penticton, BC.

The college meteor camera is already seeing more bright meteors zipping overhead. The Perseid meteor shower started July 17, ends Aug 24 but peaks on Thursday night, August 11 and Friday morning Aug 12. If it’s cloudy Thursday, note that Wednesday night and Friday night will also be very active.

Meteor Flare Over Moon

This year the Earth will cross the centre of the comet debris; so we should get the full show. We should also get three additional early peaks: Jupiter’s gravity has shifted some debris; and we’ll see debris from the 1862 and 1479 comet ejection trails to hit this year. Peak estimates (by Esko Lyytinen and Mikhail Maslov) are 150 to 160 meteors per hour, about three per minute.

There are four peaks in two waves; we’ll miss the first wave since it hits Thursday in daylight; and the last wave which hits in Friday’s morning light. But the whole night should be pretty constant at 100 meteors/hour. Best seeing times in the East Kootenays would be after midnight once the Moon sets (low in Scorpius) and the skies darken; continuing until dawn at 5am. We’ll miss the last wave at 7am. But these peak times are estimates, we can hope they arrive during darkness instead.

 
(Mountain Daylight Savings Time-- minus 1 hr for Pacific)
1.  Thurs Aug 11 at 4:34pm [1862 comet trail]
2.  Aug 11 at 5:24pm [1479 comet trail]
3.  Aug 11 from 6 to 10pm [Jupiter shifts]
4.  Fri Aug 12 from 7 to 9am [Centre of comet orbit].

It takes the Earth a week to pass through all the ice and dust from comet Swift-Tuttle. The shower will gradually taper off and end by Aug 24. The meteors are travelling at a speed of 59 km/s when they enter the Earth’s atmosphere. Their trails will all point to Perseus (if it’s a Perseid). The closer they are, the smaller their trail: and the further away, the longer the trail. Look for their colours—at high speed they ionize the air to a green; then that fades to yellow, orange, red as it slows down. If they disrupt and flare, you may see green/bluish wide streaks that glow afterward for a second or two (mainly it’s water ice, but there may be metals present like copper or cobalt).

Where to look? The composite photo above shows the entire sky, and all the meteors that fell on 11 and 12 Aug 2015 over Cranbrook; taken by our college meteor camera. Perseus is the constellation to the North East (middle left side of the photo). Normally there are fewer meteors seen straight overhead, since there is less volume of atmosphere overhead. There are slightly more meteors seen high to the West around Hercules and above the handle of the big dipper; since the meteor trails are longer there, and the meteors skim lower in a greater volume of atmosphere. That’s where I aim my cameras. (Or where it’s darkest, away from the Moon or city streetlight glow).

Some of the meteors seen will be from the k-Cygnids running from August 6–19. These peak on August 18 at 3 meteors per hour. They show a number of slow falling fireballs moving at 25km/second.

This photo shows a k-Cygnid meteor crossing through Cygnus the Swan as seen during the last Perseid shower of 2015 (it’s tail is short and it points from Cygnus). Photo taken with a Nikon D100, Tamron 28mm f/2.5 lens, 30 second exposure. I outlined Cygnus in yellow against the Milky Way. The bright star Deneb is the tail at top, and Albireo is the beak at bottom. Photo credit: Rick Nowell.

While you’re out stargazing, here is a starmap showing the Perseus region of the sky, looking Northeast late after midnight in August. The Milky Way band (grey in the map) runs through Perseus; who is the Greek hero coming to rescue Andromeda (daughter of Cassiopeia) who is chained to the rocks. Look below the W of Cassiopeia (the Queen of Ethiopia). You should also see the great square of Pegasus, the winged horse to the right. If you have good eyes (or binoculars), you can spot the fuzzy cloud of the Andromeda Galaxy (M31 in the Map) just above Andromeda’s stick-figure knee. (Andromeda’s head is one corner of the square of Pegasus.) The big dipper, little dipper and Polaris are easy to locate to the left. (Starmap generated by Skyglobe software).

Note: to zoom in a picture or map and see the lines, right-click and open in new tab.

The best and most reliable meteor shower of the year are the Geminids at 120 meteors per hour on early Monday December 14. The second best are the Quadrantids at 120/hr on January 4 but these last only for a few hours. The Perseids are better known, since they occur on August 13 when it’s nice and warm out. But they’re actually number three on the list at 100 meteors per hour.

Since the new Moon occurs on Dec 11, the sky will be dark so we should see even the fainter meteors. The peak should occur around 10am in the morning, Dec 14, persisting for 24 hours. But 2am is fine when the shower’s radiant point, Gemini, rises high in the sky to the East. The meteors are the sand, dust and gravel remains of an Apollo asteroid (3200 Phaethon), coming in at medium speeds of 35km/second. (That’s a medium speed for a meteor. Other meteor shower velocities range from 11 to 72 km/s.) The Geminids come in various colours–65% being white, 26% yellow, and the remaining 9% blue, red and green. They’re active from Dec 4 until Thursday Dec 17. Last night I saw a bright yellow tinted fireball zip across Orion crossing a quarter of the Southern sky, leaving a shorter glowing trail along the last third of it’s flight; and another fireball went across Taurus just two minutes later. Last night I saw a bright yellow tinted fireball zip across Orion crossing a quarter of the Southern sky, leaving a shorter glowing trail along the last third of it’s flight; and another fireball went across Taurus just two minutes later.

Which direction is best to look? Where it’s darkest. As you can see in these composite photos from last year, the fireballs scatter all over the sky, radiating out from Gemini to the East. But when you watch the area around Gemini, the streaks there are shorter and slower moving. These fisheye photos show the whole sky as a circle: North is up, South down, East to the left, and West to right.

 

 

 

 

 

 

 

 

 

Geminids during the night of 14 Dec 2014

 

 

 

 

 

 

 

 

 

Geminids during the night of 15 Dec 2014

These photos were taken from Cranbrook, BC with the College of the Rockies meteor cam.

Geminid Meteors Towards North and Big Dipper

Below is a starmap looking East around 11pm on Dec 14. Note Gemini the Twins rising due East, just left of Orion the Hunter. Look for two bright stars, Castor over top of the other, Pollux. Gemini the Twins used to be a benevolent guide for the ancient Sailers. In movies you sometimes hear old sailors exclaim “By Jiminy!”. Sirius is the very bright star along the SouthEastern horizon below Orion. Taurus the Bull is the “>” shape above Orion, with the red eye of Aldebaran. The Pleiades are a small fuzzy patch above that.

Starmap for 14 Dec 2015 Looking East

These pictures are pixelated to fit in this small window–right click and open image in a new tab to zoom in more.