Newsletter Archive

Perseids!

July 21, 2021


Greetings sky-watchers,

It's time to mark your calendars and get ready for a night of meteor-watching! If you've been ignoring the lesser meteor showers (like I have) and saving up your meteor-watching time for a really impressive show, then get ready, because the best meteor show of the year (by most accounts) is coming up in August. We also have some pretty sunset planets and a couple of planetary oppositions in the near future.

And one other quick announcement before I forget: I'm getting ready to start teaching live classes on Outschool. Come and visit!

The Annual Perseid Meteor Shower

There are perhaps one to two dozen annual meteor showers, depending on how you count. But many of them barely exceed the background activity of everynight meteors. On any given night, if you watch carefully in good conditions, you can expect to see an average of perhaps one meteor per hour, shooting randomly across the sky. We call these lost and lonely travellers "sporadic" meteors. Sometimes you might see, let's say, four in one hour ... but was that a "shower", or just four sporadic meteors that happened to come along within the same hour? With some meteor showers, it can be hard to tell, because there are so few of them. With the better meteor showers, you should expect to see dozens per hour. With the upcoming Perseid meteor shower, if you're lucky, you might see as many as one hundred per hour.

With some meteor showers, the meteors themselves are not very impressive either. They are just pinpoints of light. Like earth satellites, they look just like stars, except they move. But sometimes a meteor might expand into a bright "fireball", or it might leave a "persistent train" — a glowing tail that lasts in the sky for a second or two. The appearance of fireballs and trains is somewhat random, but not completely so. Certain annual meteor showers are known to have a much higher percentage — they usually put on a much better show — than the others. The Perseid shower is one of the annual meteor showers with frequent fireballs and trails.

There are a couple of impressive meteor showers that happen annually in late fall and early winter. But who wants to lie on the cold ground and watch their breath condense for an hour in the middle of the night in the middle of winter? The Perseids are the only really impressive meteor shower that happens in the summer (in the northern hemisphere), when the nights are much more comfortable and welcoming to meteor-watchers.

Some of the annual meteor showers don't last very long. Sometimes they happen in a brief flurry lasting only a few hours. The "peak" of activity for the Perseid shower lasts for several days, so if you miss it one night, you can try the next. The entire shower lasts almost a month, and has actually started already, so you can begin to watch tonight if you want to. (But the rates probably won't be very impressive until we reach the "peak" nights in a couple of weeks.)

For all of these reasons, the Perseid shower is often considered the "best" of the year. Furthermore, sometimes an annual meteor shower will coincide with a full or nearly full moon, which makes the faint wispy meteors more difficult or even impossible to see, and cuts the number of visible meteors by half or more. The upcoming 2021 Perseid meteor shower coincides with a waxing crescent moon, which means that the moon will set not long after the sun, and after that we will have a night of completely moon-free viewing.

So if you want to make your kids get up in the middle of the night, go outdoors, and look up for an hour, the upcoming Perseid shower is your best opportunity to impress them with the beauty of a spectacular meteor shower. You'll probably even enjoy it yourself.

The Perseid Peak will take place from August 11th to the 13th, and the most impressive viewing will probably be before dawn on those mornings. The rates normally improve as the night goes on, and are highest before dawn, but you can probably see a few meteors in the evenings as well (if you live in the northern hemisphere). Last year I completely forgot about the Perseids, but coincidentally I just happened to be outdoors in the evening trying to take pictures of stars in the middle of August. I remember seeing an impressive meteor that evening, I traced it backwards to Perseus, and I suddenly realized that I had seen a Perseid meteor without even trying.

As you may remember, one of the characteristics of a meteor shower is that all of the meteors belonging to that shower do not fly in random directions, but are organized. They all seem to emanate from the same point in space, as if we were flying through a cloud towards that point in space, and watching the debris in the cloud streak past us. The constellation marking that place in the sky from which the meteors seem to come is known as the "radiant" of that shower, because the meteors seem to radiate from that point in the sky, and we use each shower's radiant to give the shower its name. The radiant of the Perseid meteor shower naturally lies in the constellation of Perseus. In August, Perseus is close to the northeastern horizon for much of the night (if you live in the northern hemisphere) meaning that all of the Perseid meteors will fly very roughly from the northeast across the sky towards the southwest. Your best view will be overhead, where the sky is clearest, but you may also want to keep your eyes open for "earthgrazers" that skim horizontally along the eastern and northern horizons, especially early in the evening when the radiant is very low. I've never seen one myself, but these "earthgrazers" apparently tend to be especially long, slow, and colorful, for some reason.

If you live in the southern hemisphere, you should still be able to see Perseids, but they might not be quite as frequent, and they won't fill your sky. Perseus will lie far below your northern horizon until well after midnight, so you may be able to see some meteors rising up from your northern horizon, but not before midnight.

As always, try to find as dark a place as possible, and give your eyes time to adjust to the dark. You'll see more meteors that way. If you live in a city, you won't see 100 per hour, but the Perseids are bright enough that you should still be able to see many per hour (depending on your exact circumstances).

Facing northeast at about 2AM in mid-August

There are actually a couple of additional meteor showers going on already as we speak, but they are both minor, especially if you live in the northern hemisphere. The moon is also nearly full, which makes these showers quite negligible (for me, at least). The Capricornids (which peak around July 29) and the delta Aquarids (which peak around July 30) both have meteor rates that aren't much above the normal, everynight sporadic meteors. The Capricornids are often fairly bright, according to reports, so if you live in the southern hemisphere and you are an avid meteor hunter, you may want to look up the details for that one. And if you can wait a couple hundred years, you'll be in for a treat — the earth's orbit is expected to slowly wobble into a denser part of the dust stream that causes the Capricornids, making this shower even stronger than any current meteor shower.

Plenty of Planets

Last winter, Mercury, Venus, Jupiter, and Saturn were all hibernating near the sun, and were nowhere to be found in the night sky. Only Mars was visible, dimly decorating the evening canopy. In late August, the situation will be nearly reversed. Mars is sinking into the sunset, approaching the farthest and faintest point of its synodic cycle, while the other planets are starting to show off. Soon, instead of a paucity of planets, we will have planets aplenty.

You might still be able to find Mars over the sunsets, but I doubt it. It is growing ever fainter and ever closer to the sun, and is hard to pick out of the sunset glow. It will pass the sun (it will reach "conjunction") at the end of September, after which it will become a morning planet. On the other hand, Venus is climbing ever higher and ever brighter over the sunset, and will soon be joined by Mercury. Mercury is passing the sun at the moment, and will rapidly climb over the sunset throughout August. (Mercury will reach "greatest elongation" on September 13th, and will reach a slightly higher peak than normal, so that might be another good opportunity to go Mercury-hunting.)

Unfortunately, the "planet highway" (i.e. the zodiac) is tilted very far to the left as it extends upwards from the sunset at present. This means that even though Venus is growing quite far from the sun, it is still pretty close to the horizon. As of right now, it becomes visible maybe 20 minutes after sunset, and sets around an hour after sunset, so you still need good timing and a clutter-free horizon to see it. (This is one case where southern hemisphere viewers have the advantage. The sunset zodiac stands up much straighter right now in the southern hemisphere.) However, Venus will continue to climb, and the zodiac will straighten up a bit, and Venus will become the glorious "Evening Star" through all of September, October, and November. (It will then fall rapidly out of the sky in December.) If you look for it, see if you can identify Leo chasing the sun into the sunset. Venus is currently right next to Regulus, the period at the bottom of the "backwards question mark", or the "Sickle of Leo".

The August new moon will happen on the 8th, and for a few days after that, the lovely crescent moon will join the sunset scene. That might be a good time to become a sunset-watcher. Mercury will probably still be too low and dim to see except under exceptional circumstances, but even without Mercury, the combination of Venus and a crescent moon over a sunset can be remarkably beautiful. I highly recommend it.

Perhaps you remember the opposition of Mars last October? Mars reached the "full moon position" on the opposite side of the sky (and the opposite side of the earth) from the sun, and it became for awhile the ruler of the night. Jupiter and Saturn will reach this position in mid-August: Saturn on the 11th, and Jupiter on the 19th. In mid-August, these two planets will rise in the east as the sun sets in the west, and set in the west as the sun rises in the east. They will also brighten a tiny bit, but you probably won't notice it. They won't surge in brightness nearly so much as temperamental Mars did. Nevertheless, Jupiter is quite bright anyway, and it will soon look down upon the nighttime earth like a full moon, taking its turn as the ruler of the night.

That's it for now. Happy Sky-Watching!