Events for March 2013

The following table gives the date and time of important astronomical events for March 2013. The time of each event is given in Greenwich Mean Time or GMT (a.k.a. Universal Time or UT). To convert GMT to Eastern Standard Time (EST) just subtract 5 hours. To convert GMT to other time zones, visit Time Zones. Some of the astronomical terms used in the calendar are explained in Definitions.

 Date    GMT   Astronomical Events for March 2013
------  -----  --------------------------------------------
        (h:m)
Mar 01  06:56  Spica 0.1°N of Moon
Mar 02  15:21  Saturn 3.3°N of Moon
Mar 03  02:30  Moon at Ascending Node 
Mar 04  12:11  Antares 6.4°S of Moon
Mar 04  13     Mercury at Inferior Conjunction 
Mar 04  21:53  LAST QUARTER MOON 
Mar 05  10     Comet Panstarrs at Perigee: 1.0969 AU
Mar 05  23:20  Moon at Perigee: 369954 km
Mar 10  04     Comet Panstarrs at Perihelion: 0.3015 AU
Mar 11  19:51  NEW MOON 
Mar 16  06:15  Moon at Descending Node 
Mar 18  01:16  Jupiter 1.5°N of Moon
Mar 18  01:24  Jupiter 5.0°N of Aldebaran
Mar 18  02:56  Aldebaran 3.5°S of Moon
Mar 19  03:13  Moon at Apogee: 404262 km
Mar 19  17:27  FIRST QUARTER MOON 
Mar 20  11:02  Vernal Equinox 
Mar 24  19:17  Regulus 5.8°N of Moon
Mar 27  09:27  FULL MOON 
Mar 28  14:29  Spica 0.0°N of Moon
Mar 28  17     Venus at Superior Conjunction 
Mar 29  00     Uranus in Conjunction with Sun 
Mar 29  20:18  Saturn 3.3°N of Moon
Mar 30  05:55  Moon at Ascending Node 
Mar 31  03:55  Moon at Perigee: 367494 km
Mar 31  22     Mercury at Greatest Elongation: 27.8°W

As the events above transpire, I will post photographs of some of them at Recent Images.

Astronomical events calendars for complete years and for five time zones are available through the links below.

Time Zones Calendars of Astronomical Events
Greenwich Mean Time 2012 2013 2014 2015 2016 2017 2018 2019 2020
Eastern Standard Time 2012 2013 2014 2015 2016 2017 2018 2019 2020
Central Standard Time 2012 2013 2014 2015 2016 2017 2018 2019 2020
Mountain Standard Time 2012 2013 2014 2015 2016 2017 2018 2019 2020
Pacific Standard Time 2012 2013 2014 2015 2016 2017 2018 2019 2020

For additional years and time zones, see Calendars of Astronomical Events.

The sky events tables were all generated by a computer program I wrote (with THINK Pascal running on a Macintosh G4) using Astronomical Algorithms (Jean Meeus).

Fred Espenak


Near-Earth Asteroid 2012 DA14

A few months ago, I blogged about the minor planet Toutatis which passed within 4.3 million miles (6.9 million kilometers) of Earth on December 12, 2012. This is about 18 times the distance to the Moon, and is considered a close approach relative to the scale of the Solar System. But this pales in comparison to a minor planet called 2012 DA14, which was discovered last year (February 23, 2012), just seven days after passing 1.6 million miles (2.6 million km) from Earth.

The near-Earth asteroid 2012 DA14 passed 17,200 miles (27,700 km) from the surface of Earth on February 15, 2013. Six hours after its closest approach, 2012 DA14 was imaged from Bifrost Astronomical Observatory. Photo copyright 2013 by Fred Espenak.

The near-Earth asteroid 2012 DA14 passed 17,200 miles (27,700 km) from the surface of Earth on February 15, 2013. Six hours after its closest approach, 2012 DA14 was imaged from Bifrost Astronomical Observatory. Photo copyright 2013 by Fred Espenak.

With a diameter of about 50 meters (160 ft), 2012 DA14 is truly a near-Earth asteroid. This year’s flyby (February 15, 2013) brought the asteroid even closer as it passed 17,200 miles (27,700 km) from the surface of Earth. This is well inside the orbits of geosynchronous satellites which travel at distances of about 22,200 miles (35,800 km) from Earth’s surface.

At its closest, 2012 DA14 was above the Eastern Hemisphere and not visible from the USA. About 7 hours later, the asteroid was above the horizon in Arizona, and I was able to image it from Bifrost Observatory. By that time (03:30 UT on Feb 16), 2012 DA14 was quickly receding from Earth at a distance of 120,300 miles (193,700 km). It was now 100x fainter at magnitude 12.3 (compared to magnitude 7.4 at nearest approach).

Nevertheless, 2012 DA14 was still moving rapidly across the sky making it a challenge to image. Even in the short 15 second exposures I used, the asteroid left long trails. Below is a time-lapse animation made from a series of images acquired with a 12″ ASA astrograph.

Time-Lapse of Near-Earth Asteroid 2012 DA14 from Fred Espenak on Vimeo.

This is a record close approach for a known object of any size. Asteroids this large actually hit the Earth about once every 1000 years. The effects of such a direct hit could completely level an unfortunate city in its path, or produce a devastating tsunami in the case of an ocean hit. Astronomers have only recently received funding to discover and track potentially dangerous asteroids, but most of these objects are faint and hard to detect unless they are already close to Earth. More funding is needed to catalog all near-Earth asteroids as soon as possible.

Sixty-five million years ago, a much larger 10-kilometer size asteroid collided with Earth, resulting in the extinction of 75% or more of all species on Earth including the dinosaurs (see: Chicxulub crater and Cretaceous–Paleogene extinction event). Perhaps someday, we will have all of these threats identified and will have a defense system in place to destroy or deflect such objects. But for the time being, such schemes remain the grist of Hollywood movies, and planet Earth (and mankind) remains at risk.

Fred Espenak

Comet Panstarrs or Bust

2013 holds the promise of not 1 but 2 bright comets! Comet ISON will be best visible in November and December 2013 (see: Comet ISON Discoverd). The second comet is named Panstarrs (C/2011 L4) and it will grace the evening sky in March.

A computer simulation illustrates the appearance of Comet Panstarrs on 4 evenings during March 2013. Visit Comet Panstarrs Viewing Charts to see individual charts for every day from March 5 through March 25.

A computer simulation illustrates the appearance of Comet Panstarrs on 4 evenings during March 2013. Visit Comet Panstarrs Viewing Charts to see individual charts for every day from March 5 through March 25.

Comet Panstarrs was discovered in June 2011 by the Panoramic Survey Telescope and Rapid Response System (PannSTARRS) in Hawaii. Since then, the comet has slowly grown brighter as it approaches the inner Solar System. Between June 2011 and May 2012, its apparent magnitude increased from 19 (extremely faint) to 13.5 (visible in large amateur telescopes). By August, it was magnitude 11.5.

Comet Panstarrs will be closest to Earth on March 05 (distance of 1.09 astronomical units) and it reaches perihelion (closest point to the Sun) 5 days later on March 10. It is during this period that Panstarrs is at its brightest, but just how bright will it be?

From one analysis of 35 measurements made between between February and October 2012, the comet’s brightening trend indicates that it should reach a maximum magnitude of -1 (as bright as Sirius, the brightest star in the sky) and should be visible in a dark sky a week later near magnitude +1 with a 10° to 20° long tail. This would place it in the exclusive category of brightest comets seen in the past 100 years. But predicting the brightness of comets is fraught with uncertainty. To understand why, we need to known something about the physical nature of comets.

Comet Hale–Bopp was one of the most spectacular and widely observed comets of the 20th century. Learn more about this remarkable object and view additional images at the Comet Hale-Bopp Photo Gallery. Photo copyright 1997 by Fred Espenak.

Comet Hale–Bopp was one of the most spectacle and widely observed comets of the 20th century. Learn more about this remarkable object and view additional images at the Comet Hale-Bopp Photo Gallery. Photo copyright 1997 by Fred Espenak.

The nucleus of a comet is a solid body typically several kilometers in diameter. It is composed of a mixture of frozen gasses (water, carbon dioxide, ammonia, carbon monoxide, methane, etc.) and dust – this is known as the dirty snowball model. The exact proportions of the gasses and dust, and the structure of these components, varies from comet to comet.

As a comet approaches the Sun, solar radiation slowly vaporizes the outer layers of the nucleus, spewing gas and dust particles into space. This expanding cloud of material forms an enormous bubble around the nucleus called the coma, which can be over a million kilometers in diameter. Solar radiation pushes against the coma and forces dust particles to stream away from the Sun to produce the dust tail. The solar wind – a continuous stream of electrically charged particles from the Sun – interacts with cometary gas to produce ions (electrically charged atoms). The ions also stream away from the comet in the direction opposite the Sun to form the ion tail. Both of these tails are visible in telescopes, and – if the comet is especially bright – to the naked eye. The tail of a bright comet may be over 100 million kilometers long!

Predicting the future brightness of a comet is a notoriously difficult business because it depends on the exact size, structure and composition of the nucleus as well as how rapidly it rotates. This information is essentially unknown, so brightness estimates are largely based on a comet’s past behavior during the previous months. But just like the stock market, “past performance is no guarantee of future results”. This is especially true since the comet heats up more rapidly as it gets increasingly closer to the Sun.

Hailed as the Great Comet of 1996, Comet Hyakutake made one of the closest passes to Earth of any comet in the past two centuries. Its immense tail stretched nearly half way across the sky. For additional images and more information, see the Comet Hyakutake Photo Gallery. Photo copyright 1996 by Fred Espenak.

Hailed as the Great Comet of 1996, Comet Hyakutake made one of the closest passes to Earth of any comet in the past two centuries. Its immense tail stretched nearly half way across the sky. For additional images and more information, see the Comet Hyakutake Photo Gallery. Photo copyright 1996 by Fred Espenak.

Comet Panstarrs has a slightly hyperbolic orbit suggesting it is a new comet from the outer Oort Cloud and making its first encounter with the Sun. In the past, comets with similar orbits have shown rapid brightening as they approach the Sun, thereby promising spectacularly bright apparitions as they pass perihelion. Unfortunately, the growing brightness of these comets quickly tapers off as a thin veneer of fresh volatiles surrounding the nucleus evaporates into space. This is exactly what happened to the over-hyped Comet Kohoutek in 1973.

Comet Panstarrs’ observed rate of brightening has slowed in December and January, leading to a new projected maximum brightness of magnitude +3 (as bright as the stars in the “Big Dipper”) instead of magnitude -1. This would still make Panstarrs visible to the naked eye, but not nearly as impressive.

So which brightness prediction is correct? It’s still anyone’s guess given the capricious nature of comets. Just make sure you watch the evening sky shortly after sunset throughout mid-March.

Fred Espenak

Animation of Comet Panstarrs Visibility during March 2013 from Fred Espenak on Vimeo.