Perseid Prospects, Mornings with Mercury and the Lunar X

With the Perseid shower, a great morning apparition of Mercury, and a chance to see craters scratch out an X on the moon, skywatchers have a busy week ahead! 

Perseids are swift meteors that span the range of brightness from the faintest scratches to colorful fireballs, like the one shown here.
Bob King

The waxing gibbous Moon may make a mess of this year's Perseids, but I'll still be out there. Even a full Moon can't kill the year's most anticipated meteor shower. Reduce the numbers, yes, but you're guaranteed to see at least a few. I can't wait to ease into that recliner and watch the sparks fly.

The annual Perseids will peak overnight Monday August 12–13 at the same time a glaring gibbous Moon holds forth in Sagittarius about 10° east of the planet Saturn. During my many years of watching Perseids from a semi-rural location (Bortle 4 sky) ] I've usually seen about 40 meteors per hour during a moonless maximum. With the Moon present this time around that number will be cut in half. Most sources give a zenithal hourly rate of 100 per hour, but this is only under ideal circumstances with the shower's radiant at the zenith and stars visible to magnitude 6.5.

Illustrate the Perseid radiant and lunar presence

The Perseids radiate from the constellation Perseus just beneath the W of Cassiopeia. The map shows the sky at 11 o'clock local time on the night of the peak, when the waxing gibbous Moon will interfere. The higher the radiant, the fewer meteors get cut off by the horizon. That's why the later you stay up, the more meteors you'll see.

2019 will not be kind to either the Perseids or the year's other big shower, the Geminids, when the Moon will be a day past full. Here are a few options for the Perseids. You can go out Monday night the 12th, face away from the Moon so it doesn't further compromise your night vision, and enjoy what comes. The radiant stands some 30° high in the northeastern sky by 11 o'clock, a good time to begin watching. If you have kids, you can go out earlier — there will always be a few to see.

Perseid montage

Gain Lee recorded this montage of bright Perseids over a two-hour period in August 2007 from his heavily light-polluted backyard in Huddersfield, England.
Gain Lee

Or you can rise around moonset (~3:30–4:00 a.m. Tuesday morning) shortly before the start of morning twilight. During this brief interval, the shower radiant will be ideally placed high in the northeastern sky and you may see a nice flurry of activity.

You can also benefit from the fact that the Perseids are active from late July to mid-August and avoid the Moon altogether. The shower will be moderately active on the mornings of the 11th and 12th. The high altitude of the radiant combined with zero moonlight should make for a good show at those times.

Observers will have 1-plus hour of darkness on Monday morning August 12th and two hours on Sunday the 11th. Sunday might be ideal in another way. You can further pad your meteor-time by watching a half-hour into morning twilight.

To maximize these slices of dark sky, find your sunrise time and then back up 1 hour and 40 minutes (latitude 37°–42° N) to account for twilight. That's when you'll see the very first hint of dawn. Observers living between 42°–48°N should subtract 2 hours.

Perseids orbit path August 12–13

Every year in mid-August, Earth collides with particles spread along the orbit of Comet Swift-Tuttle.
Sky & Telescope

Perseids begin life as sand-to-peanut-sized flotsam and jetsam shed by Comet 109P/Swift-Tuttle when it swings near the Sun every 133 years. Earth barrels through this cometary dandruff every late July–early August. Striking the atmosphere around 59 km per second, the particles incandesce while also ionizing the air to create the brief, bright streaks many still call shooting stars. Perseids are swift, white, and often leave glowing trains that persist for a half-second or longer after the meteor disappears. Perseids can appear anywhere in the sky but can be traced backwards to a point in the sky called the radiant, located in western Perseus a short distance below the W of Cassiopeia.

Displaying Mercury's favorable elongation in August

Mercury puts in a great dawn apparition this month, reaching greatest western elongation on August 10th at the Gemini–Cancer border. The planet stands about 7° high 45 minutes before sunrise in the northeastern sky. This view depicts the scene on August 8th when the planet shines at magnitude 0.2. On the morning of the 13th, Mercury, Pollux, and Castor will form a nearly straight line. 

If you choose to observe the shower before dawn, you'll also have the opportunity to see Mercury at the peak of a good morning apparition for skywatchers in the Northern Hemisphere. It shines near –0.5 magnitude on August 13th about 10° below Pollux and Castor in Gemini 45 minutes to an hour before sunrise. Greatest elongation occurs on the 10th when the planet will look like a tiny half-Moon in a telescope. On August 17th Mercury passes slightly less than 1° south of the center of the Beehive Cluster.

Swedish amateur Henrik Adamsson captured this crisp image of the Lunar X on February 22, 2018. The X, a trick of light and shadow involving sunlit crater rims and deeply-shadowed crater interiors, will be at peak display around 10:43 p.m. Central Time, August 7th (3:43 UT August 8th).
Henrik Adamsson

Finally, on Wednesday night, August 7th we'll have the opportunity to see the Lunar X, a happenstance pattern of light in the shape of an X created by low-angled sunlight touching the rims of the adjoining craters Blanchinus, Le Caille, and Purbach. It's also known as Werner X (after a nearby crater) or The Purbach Cross. The X slowly creeps into view as the Sun's first rays touch the craters' rims while their interiors are still steeped in deep shadow.

Lunar X locator

Shadowed craters and their sunlight-touched rims combine to create an alphabetic sight. The map is a simulation of the August 7th Moon at 10:43 p.m. CDT, the time of "max X."
Virtual Moon Atlas

The X is visible around the time of first-quarter Moon every month of the year somewhere on Earth but infrequently from any particular location. If you're hit with cloudy skies or the Moon isn't visible when the X appears, here are several additional times you can look:
* Sept. 6 — 15:47UT (subtract 4 hours for Eastern Daylight-Saving Time, 5 for Central, etc.)
* Oct. 6 — 4:17UT
* Nov. 4 — 17:18UT (DST ends; subtract 5 for Eastern Standard Time, 6 for Central, etc.)
* Dec. 4 — 6:44 UT

Clear and meteor-filled skies!

15 thoughts on “Perseid Prospects, Mornings with Mercury and the Lunar X

  1. Joe StieberJoe Stieber

    I went to my local Green Acres site (in the middle of a large farm field) to look for Mercury this morning, Friday, August 9, 2019. Finally, we had some clear sky along the eastern horizon! As soon as I stepped out of the car, I picked it up at 5:05 am EDT with unaided eyes by following a slightly bent line down from Castor and Pollux. In my 88 mm apo spotting scope, I could make out the thick crescent at 60x (the terminator looked a little concave), despite the poor seeing at the low altitude (about 6.5° at 5:15 am). SkyTools indicates Mercury was 7.7” diameter, 38% illuminated and magnitude +0.2 at the time. Sunrise would be at 6:06 am EDT.

  2. RodRod

    Bob, Joe. I was out early this morning, cool temp near 60F and clear skies here in Maryland. From my stargazing log – “Observed 0450-0530 EDT. Sunrise 0616 EDT. I enjoyed some time sitting in the chair looking at Perseus constellation. One bright, Perseid flashed by, about as bright as Mirfak star. It streaked towards Aldebaran in Taurus. Another fainter Perseid flashed by too near the constellation, about 4th magnitude. This was fun, clear, cool early morning. Starry Night Pro Plus 8 shows these meteors streak at 59 km^-s. Consider a satellite orbits Earth near 8 km^-s. The Perseid radiant near 67 degrees altitude and 25 degrees azimuth when I viewed. I tried calling an owl in from the woods, we were hooting at each other. Bucks are starting to get active, calling now as we move head towards the fall season.”

  3. Joe StieberJoe Stieber

    I was out to the NJ Pines this morning, August 11, after moonset and under a clear sky between 2:45 and 4:15 am EDT, I saw twelve (12) meteors, nine (9) of which were plausible Perseids (they seemed to trail back to the nominal radiant near Perseus’ hat). On the way home, I stopped by my Green Acres site and saw Mercury with unaided eyes again (third morning in a row).

    1. Bob KingBob King Post author

      Hi Joe and Rod,
      Like you guys I’ve been out watching early especially because our forecast looked bad. Got up Aug. 10 for two hours of darkness and caught a superb Perseid fireball.

      1. Jakob

        I was out this morning for an hour ,13 aug 00.00 UT – 1.00 UT and only 2 perseids visible!
        Are they in decline ? Never have I seen this low amount. When was the supposed peak? Went for bed and did not care for Mercury 🙁 Jakob

        1. Bob KingBob King Post author

          Hi Jakob,
          Sorry to hear you saw so few. Certainly moonlight is to blame, but that is an unusually low number. It’s possible you were out in a lull or that the peak was sharper (briefer) this year. Here’s the latest data: The ZHR as of early yesterday evening stood at 48 per hour. That number will change as more observations from later that evening and this morning are added. Another observer from Colorado texted me she saw lots of meteors last night including a couple fireballs. She didn’t give an exact number.

  4. RodRod

    Bob, Joe. Here is another update from my log this morning. I love *Green Acres*, especially as the fall season is approaching (deer season) 🙂 [Observed 0400-0530 EDT. Sunrise at 0617 EDT, the Moon set at 0326 EDT. Morning twilight filling the east sky by 0530 EDT, so I came in. I did observe Mercury from my neighbor’s horse farm, on the road – unaided eye views, beautiful, early morning sky. Four bright Perseids observed, about as bright as Mirfak and one, as bright as Capella. The brightest, streaked through Cassiopeia heading NW away from the radiant. Two others streaked towards Orion, one bright Perseid heading south. Two or three other Perseids were fainter, about 3rd/4th magnitude perhaps. I observed one polar orbiting satellite pass through Cassiopeia in descending node about 2nd magnitude. This was a great, early morning sky view along with Mercury observation. Shortly after 0400 EDT, I could easily see the Double Cluster in Perseus, about 3.8 magnitude and some 5.5 magnitude stars near Mirfak in Perseus constellation. Three or four owls were hooting, these hoots sounded like Great Horn owls, very distinctive. Some bucks were out too calling and making noise as the fall season approaches.]

    The view of Mercury is easy at my location and near the larger horse farm next to me. Later in November this year, weather allowing, I may enjoy the view of Mercury transit across the Sun using my telescope with solar filter. Scheduled for 11-Nov-19. Mercury rose this morning at my location near 0447 EDT and by 0500 or 0505 EDT, high enough to see with unaided eyes above the distant tree line.

  5. Tom-Fleming

    Has there been a study of the impact of Solar Min (or Max) on the burn paths of meteors? Data supports a steeper gradient on the atmospheric density model. This means (or should) meteor paths will be shorter and brighter during Solar Min. The impact on the visual appearance means the brightness will be additionally enhanced due to the measurably shorter slant range to the meteor. Likewise, any shortening of the (apparent) burn path will be offset to some degree by the reduced slant range. Atmospheric modeling has become a good deal more exact in recent years. It would be interesting to see a statistical treatment of Perseids over a solar cycle (though the hypothesis may be lost in a sea of other variables). – Interested in your thoughts.

  6. Jakob

    Hmm, moon 3° above when my observation began and moonset at 00.54 UT. Don’t think our Moon were the issue perhaps high cirrus made things worse. Stars of 5th magnitude were seen in zenit. Another group of 4 observers reported 34 meteors during 2 hours centered on 0 UT 13 aug. Maybe a lull as you said. Jakob

        1. Bob KingBob King Post author

          Well, I don’t know what to say. That was close to the peak time and with a low moon. Let’s wait and see when the final counts come in. For all I know it may have been weaker than normal. We should know soon.

    1. Bob KingBob King Post author

      No problem, Jakob. By the way, if you want to make sure you’re seeing the latest data on the shower, refresh the page when you go to that link. Data is still being compiled by the ZHR has risen to 69/hour.

      1. Jakob

        I have seen the numbers grow and I am still confused. A number of swedish observers also have lesser meteor counts reported compared to IMO. Thanks again Bob 🙂

All comments must follow the Sky & Telescope Terms of Use and will be moderated prior to posting. Please be civil in your comments. Sky & Telescope reserves the right to use the comments we receive, in whole or in part, and to use the commenter’s username, in any medium. See also the Terms of Use and Privacy Policy.


This site uses Akismet to reduce spam. Learn how your comment data is processed.