The Sky This Week
U.S. Naval Observatory's Weekly Blog

A Comet Collision?

by Geoff Chester, USNO Public Affairs
24 May 2022

Messier 101, spiral galaxy in Ursa Major, imaged 2022 March 26 from Mollusk, Virginia
with an Explore Scientific AR102 10.2-cm (4-inch) f/6.5 refractor and a ZWO ASI183MC CMOS imager.

The Moon’s slender waning crescent greets early morning skywatchers this week, wending her way past the rising bright planets as morning twilight gathers.  New Moon occurs on the 30th at 7:30 am Eastern Daylight Time.  Look for Luna close to the planets Mars and Jupiter before dawn on the 25th.  She then brackets the bright dazzle of Venus on the 26th and 27th.  She will return to the evening sky with the start of the new month.

The May observing campaign for the citizen-science Globe at Night program continues this week, with the constellation of Boötes, the Herdsman serving as the target star pattern for your observations.  Many of us will be headed out of town for the upcoming holiday weekend, so it will be a perfect opportunity to look at the constellation from a place other than your back yard.  Hopefully you will be visiting someplace with darker skies than what we find near big cities, and you will be able to see more than the brightest stars in the constellation.  The brightest star in Boötes is Arcturus, which glows with a distinctive tint that classical observers of the 19th Century described as “topaz”.  The brightest star in the northern hemisphere of the sky, its dazzle is only fleeting on the cosmic time-scale.  It has the largest proper motion across the sky of any of the first-magnitude stars except for Alpha Centauri, a property first measured by astronomer Edmund Halley in 1718.  It is currently passing the solar system at a distance of just under 37 light years.  It will be closest to us in about 4,000 years, then it will start to retreat into the depths of the Milky Way.  In about half a million years it will no longer be visible without a telescope.

There is another good reason to keep an eye on this part of the sky.  On the night of the 30th/31st, Earth will possibly plow into a cloud of debris shed by the obscure periodic comet 73P Schwassmann-Wachmann 3, which has been undergoing a dramatic breakup since 1995.  While the largest of the comet’s 66 known fragments won’t reach the vicinity of Earth until August, some astronomers think that a large “puff” of dust from the initial 1995 fragmentation will produce a short but intense burst of meteors between Arcturus and the end of the “handle” of the Big Dipper that night.  Should the shower actually occur, astronomers predict that the peak of activity will occur between 12:45 and 1:15 am EDT on the 31st, when the radiant point will be high in the west for observers along the East Coast.  The times will be an hour earlier for each time zone west of the Eastern time zone and the radiant will be well-placed for most of the nation except the Pacific coast, Alaska, and Hawai’i.  As with any event involving comets and meteor showers, predictions are very dicey at best, and there is more likelihood that we won’t see anything at all, but there will be no moonlight to interfere and the hours aren’t too bad, which is good enough odds for me.  If (and that’s a big “IF”) predictions pan out, we might see several hundred “shooting stars” in half an hour!

The absence of the Moon and a long holiday weekend mean that it is also a great time to dust off the telescope and go exploring for distant galaxies.  The area of the sky bounded by the Big Dipper and the bright stars Regulus, Arcturus, and Spica is the location of the north rotational pole of our Milky Way galaxy, which affords us a glimpse into very deep space.  Under dark skies a good six-inch telescope will reveal dozens of misty swatches of light, each representing the combined light of hundreds of billions of stars located tens of millions of light years away.  That’s what I call a real weekend getaway!

Much closer to home, four of the five “naked eye” planets in the solar system parade across the early morning sky.  Golden Saturn is first above the horizon, rising at around 1:30 am local time among the dim stars of Capricornus.  Ruddy Mars and bright Jupiter arrive at around 3:00 am.  The pair are joined by the waning crescent Moon before dawn on the 25th.  Mars passes close to the giant planet on the mornings of the 28th through the 30th.  Dazzling Venus is the last to rise, but you should have no trouble finding her in the gathering morning twilight.  She will remain in the morning sky for the rest of the year, while the others will wander into the evening sky later in the summer.
 
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