David Dickinson is an Earth science teacher, freelance science writer, retired USAF veteran & backyard astronomer. He currently writes and ponders the universe as he travels the world with his wife.
An artist's conception of asteroid 3 Juno. Credit: David Aguilar, Harvard-Smithsonian Center for Astrophysics.
Not all oppositions are created equal. This week’s sky target offers a good case in point, as asteroid 3 Juno reaches its most favorable viewing position for the decade. Continue reading “Catching Asteroid 3 Juno at Its Best”
Comet 46P Wirtanen in Cetus from September, 2018. Image credit and copyright: Hisayoshi Kato.
One. More. Comet. Though the next great ‘Comet of the Century’ has yet to make its appearance in 2018, we’ve had a steady stream of binocular comets this year, including Comets C/2017 S3 PanSTARRS, 38P Stephan-Oterma, and 21P Giacobini-Zinner.
Poster for The Most Unknown. Credit: Science Sandbox.
What are the big questions in modern science? All too often, the public perception of science seems to be that we know all that there is to know, and the modern game in science is to simply fill in the gaps in our knowledge.
Nothing could be further from the truth. We recently came across a fascinating documentary that not only looks at some of the big questions today in multi-interdisciplinary science, but has scientists ask and interview other scientists.
We’re talking about The Most Unknown, directed by Peabody-award winning filmmaker Ian Cheney (director of The City Dark and The Search for General Tso) and advised by filmmaker Werner Herzog (known for The Wrath of God and Grizzly Man). The film takes nine scientists for diverse disciplines such as biology and astronomy and catches them all pushing the boundaries of their respective fields into the unknown. What emerges is a fascinating look at the state of modern science, and a glimpse at where things are headed.
An amazing view. The Barnard loop through Orion (right) Comet 21P Giacobini-Zinner (lower left) and Comet 38P Stephan-Oterma (upper left, see enlargement below). Image credit and copyright: Hisayoshi Kato.
Neptune, as seen by Voyager 2 in 1989. The deep blue color applied helped enhance the view of features in the atmosphere. Image Credit: NASA/JPL
Have you seen the outer ice giant planets for yourself?
This week is a good time to check the most difficult of the major planets off of your life list, as Neptune reaches opposition for 2018 on Friday, September 7th at at ~18:00 Universal Time (UT)/2:00 PM EDT. And while it may not look like much more than a gray-blue dot at the eyepiece, the outermost ice giant world has a fascinating tale to tell. Continue reading “Exploring the Ice Giants: Neptune and Uranus at Opposition for 2018”
The Sun in hydrogen alpha from August 25th, 2018, showing enigmatic sunspot AR 2720. Image credit and copyright: Damien Weatherly.
A precursor to the start of Solar Cycle 25? The Sun in hydrogen alpha from August 25th, 2018, showing enigmatic sunspot AR 2720. Image credit and copyright: Damien Weatherly.
What’s up with the Sun? As we’ve said previous, what the Sun isn’t doing is the big news of 2018 in solar astronomy. Now, the Sun sent us another curveball this past weekend, with the strange tale of growing sunspot AR 2720.
A view along the solar system, using Cosmic Watch.
A view along the Solar System, using Cosmic Watch.
Watching the heavens on a nightly, or even casual basis? The web and modern technology has certainly altered the landscape of modern astronomy, (mostly) for the better. Once, we all huddled around cardboard planispheres, illuminated by red flashlights; now, it’s now a common sight to see illuminated smartphone apps accompanying telescopes at star parties, all waving skyward with virtual planetarium programs guiding users around the night sky.
Comet 21P/Giacobini-Zinner from August 14th. Image credit and copyright: Rolando Ligustri.
Comet 21/P Giacobini-Zinner from August 14th. Image credit and copyright: Rolando Ligustri.
A periodic comet may put on a fine show for northern hemisphere viewers over the next few months.
Comet 21/P Giacobini-Zinner is currently a fine binocular comet, shining at +8th magnitude as it cruises across the constellation Cassiopeia. This places it above the horizon for the entire night for observers north of the equator in August, transiting the local meridian at dawn. And unlike most comets that get lost in the Sun’s glare (like the current situation with C/2017 S3 PanSTARRS), we’ll be able to track Comet 21/P Giacobini-Zinner right through perihelion on September 10th.
The orbit of comet 21P, showing the comet’s position at closest approach. Credit: NASA-JPL.
This is because the comet is on a short period, 6.6 year orbit around the Sun that takes it from an aphelion of 6 Astronomical Units (AU) exterior to Jupiter’s orbit, to a perihelion of 1.038 AU, just 3.3 million miles (5.2 million kilometers) exterior to Earth’s orbit. The 2018 apparition sees the comet pass 0.392 AU (36.5 million miles/58.3 million kilometers) from the Earth on September 11th.
This is the closest passage of the comet near Earth since September 14th, 1946, and won’t be topped until the perihelion passage of September 18th, 2058. Its next cycle of passes to Earth closer than 0.1 AU aren’t until next century in the years 2119 and 2195, respectively.
Comet 21/P from August 10th. Image credit and copyright: John Purvis.
Discovered by astronomer Michel Giacobini at the Côte d’Azur Observatory in Nice, France on the night of December 20th, 1900 as it was crossing the constellation Aquarius, the 21st periodic comet was recovered two orbits later by Ernest Zinner on October 23rd, 1913 as it passed a series of variable stars near Beta Scuti.
Though the comet generally tops out at +8th magnitude, it has been known to undergo periodic outbursts near perihelion, bringing it up about 3 magnitudes (about 16 times) in brightness. This occurred most notably in 1946.
The light curve for Comet 21/P. The black dots represent actual observations and magnitude observations. Credit: Seiichi Yoshida’sWeekly Information on Bright Comets.
Comet 21/P Giacobini-Zinner is also the source of the Draconid (sometimes referred to as the Giacobinid) meteors, radiating from the constellation Draco the Dragon on and around October 7th and 8th. Feeble on most years, this shower can produce surprises, such as occurred in 1998, 2005 and most recently in 2011, when a Draconid outburst topped a zenithal hourly rate of 400 meteors per hour, flirting with ‘meteor storm’ status. And while we’re not expecting a meteor storm to accompany the 2018 perihelion passage of Comet 21/P Giacobini-Zinner, you just never know… it’s always worth keeping an eye out on early October mornings for the “Tears of the Dragon,” just in case. Note that the Moon reaches New phase on October 9th, just a few days after the meteor shower’s expected annual peak, a fine time to watch for any unheralded Draconid outbursts.
Prospects for Comet 21P
The comet is visible from the northern hemisphere through the remainder of August and all through September as it glides across Auriga, Taurus and Gemini and visits several well known celestial sights. In fact, it actually transits in front of several deep sky objects, including Messier 37 (Sept 10th), and Messier 35 (Sept 15th).
Comet 21P passes in front of open cluster Messier 35 on September 15th. Credit: Starry Night.
The comet will be moving at about two degrees per day when it’s nearest to the Earth, on and around September 11th.
We begin to lose the comet, as it heads southward in late October. Still, the comet is over 50 degrees above the eastern horizon at dawn come October 1st as seen from latitude 30 degrees north, having maintained a similar elevation throughout most of September. Not bad at all.
Here are some upcoming dates with destiny for Comet 21/P Giacobini-Zinner:
August 19: Crosses into the constellation Camelopardalis.
August 29: Crosses into the constellation Perseus.
August 30th: Crosses into the constellation Auriga.
The celestial path of Comet 21P from August 16th through September 15th. Credit: Starry Night.
September 2: Passes one degree from the bright star Capella.
Sept 7-8: Grouped 2 degrees from the open clusters M36 and M38.
Sept 10: Photo-Op: Skirts very near the open cluster M37. Also reaches perihelion on this date, at magnitude +7.
Sept 11: Passes closest to the Earth, at 0.392 AU distant.
Sept 13: Nicks the corner of the constellation Taurus.
Sept 14th : Enters the constellation Gemini.
Sept 15th: Photo-Op: crosses in front of the open cluster M35.
Sept 16: Crosses the ecliptic southward and near the +3.3 magnitude star Propus (Eta Geminorum).
Sept 17: Crosses into Orion.
Sept 21: Crosses into Gemini.
Sept 23: Crosses into Monoceros.
Sept 24: Passes near the Christmas Tree Cluster, NGC 2264.
The celestial path of Comet 21P from September 15th through October 15th. Image credit: Starry Night.
Oct 1: Crosses the galactic plane and the celestial equator southward.
Oct 7: Crosses in front of the open cluster M50.
Oct 10: Crosses into Canis Major.
Oct 31st: Passes near the bright star Aludra and may drop below +10th magnitude.
Binoculars are your best friend when you’re looking for comets brighter than +10th magnitude. With a generous field of view, binoculars allow you to sweep a suspect area until the faint fuzzball of a comet snaps into view. I like to ‘ambush’ a comet as it passes near a bright star, and a good time to spot comet 21/P Giacobini-Zinner is coming right up on September 2nd when it passes less than one degree from the bright +0.1 magnitude star Capella.
Don’t miss this year’s fine apparition of Comet 21/P Giacobini-Zinner, coming to a night sky near you.
