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Prepare for the Perseids!

by Geoff Chester, USNO Public Affairs | 08 August 2023

by Geoff Chester, USNO Public Affairs | 08 August 2023

The summer Milky Way, imaged 2017 August 21 from Smith's Ferry, Idaho
with a Canon EOS Rebel T2i DSLR; 30-second exposure @ f/4, ISO 6400

The Moon wanes in the morning sky this week as she passes through the rising stars of winter’s bright constellations.  New Moon occurs on the 16th at 1:38 am Eastern Daylight Time.  Night owls and early risers can spot Luna close to the Pleiades star cluster on the morning of the 9th.  On the morning of the 11th she passes just to the south of the star El Nath, the “northern horn” of Taurus, the Bull. 

The annual Perseid meteor shower reaches its peak on the night of the 12th/13th.  This year, the conditions for observing the event are just about ideal as the waning crescent Moon doesn’t rise until after 3:00 am, and her phase will be a very slender crescent.  The Perseids are one of the most reliable of the many annual meteor showers, typically producing some 50 to 75 meteors per hour for an observer at a dark site.  The only other shower that comes close is the December Geminids, but the observing conditions are far more hospitable at this time of the year.

The Perseids have been observed for nearly 2,000 years, with the first records mentioning them in the year 36 CE.  They consist of streams of small particles of ice and dust shed by the comet 109P/Swift-Tuttle, which orbits the Sun with a 133-year period.  It was discovered in July, 1862 by astronomers Lewis Swift in Marathon, New York and Horace P. Tuttle (who later became an astronomer at USNO) at Harvard Observatory.  The comet was a fine naked-eye object during that summer.  In 1866 the Italian astronomer Giovanni Schiaparelli identified it as the source of the Perseid shower.  The shower is active from mid-July through August, but the night of the 12th/13th is when it reaches its peak.  The shower members appear to originate from a point in the sky near the constellation of Perseus, which rises in the northeast during the late evening.  Observing them requires little more than a dark sky, a comfortable chair, and a view of the open sky.  The meteors are very fast, flashing by in mere seconds.  Occasionally a larger particle will produce a bright “fireball” that will leave a short luminous train in its wake for a minute or so.  If you’re clouded out on the first night, the shower will still be at about half the peak strength for a couple of nights before and after the peak time.

While you are out watching the Perseids, spend some time examining the luminous band of the Milky Way, which bisects the sky at local midnight.  With the unaided eye, notice the diffuse glow of the Galaxy’s star clouds.  Also look at the darker voids among those clouds.  In particular, notice the “Great Rift” that splits the Milky Way into two distinct segments.  The rift starts in the middle of the Summer Triangle asterism, and continues down to the southern horizon.  This seeming void is actually a feature of most spiral galaxies, and consists of vast clouds of cold gas and dust that obscure the light of more distant stars.  This dark material contains the building blocks of yet to be formed stars and planets, and sprinkled in the rift are areas where this process is happening.  If you have binoculars, look at some of these brighter knots.  Many of them will start to resolve into star clusters embedded in glowing wisps of glowing gas.  Sweeping the Milky Way with binoculars or a small telescope at low magnification is one of my favorite summer activities, and having a fine meteor shower going on in the background is an added bonus.

Venus passes between the Earth and Sun on the morning of the 13th.  Following this event, the dazzling planet will enter the morning sky, and by the end of the month she will be prominent in the pre-dawn sky. 

Mars continues to barely hang onto his place in the evening sky.  Unfortunately, due to his faintness, he’s not very easy to track down.  He spends his time in the fading glow of evening twilight, setting a bit over an hour after the Sun.  He will linger in the southwestern twilight sky until November, when he finally passes behind the Sun.

Saturn continues to wend his way into the evening sky.  The ringed planet now rises before 9:00 pm local time, and by the late evening you should be able to easily spot his cheerful yellow glow in the southeastern sky.

Jupiter follows Saturn into the evening sky, and this week the giant planet rises well before midnight.  He will be the bright object that you will see in the east if you’re up late watching the Perseids.  He’s still best seen in the pre-dawn sky, crossing the meridian as sunrise begins the new day.


Commander, Naval Meteorology and Oceanography Command | 1100 Balch Blvd. | Stennis Space Center, Mississippi 39529

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