Events for April 2013

The following table gives the date and time of important astronomical events for April 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 April 2013
------  -----  --------------------------------------------
        (h:m)
Apr 03  04:37  LAST QUARTER MOON 
Apr 10  09:35  NEW MOON 
Apr 12  12:12  Moon at Descending Node 
Apr 14  10:51  Aldebaran 3.4°S of Moon
Apr 14  18:23  Jupiter 2.1°N of Moon
Apr 15  22:21  Moon at Apogee: 404865 km
Apr 18  00     Mars in Conjunction with Sun 
Apr 18  12:31  FIRST QUARTER MOON 
Apr 21  04:44  Regulus 5.9°N of Moon
Apr 22  11     Lyrid Meteor Shower
Apr 25  00:10  Spica 0.0°N of Moon
Apr 25  19:57  FULL MOON 
Apr 25  20:09  Partial Lunar Eclipse; mag=0.014
Apr 26  02:28  Saturn 3.5°N of Moon
Apr 26  14:07  Moon at Ascending Node 
Apr 27  19:48  Moon at Perigee: 362268 km
Apr 28  08     Saturn at Opposition 

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


Comet Panstarrs from Granite Gap

Tonight (March 14), we returned to Granite Gap – the location where we first saw Comet Panstarrs on March 10 (Got Panstarrs?). It’s hard to believe it was just 5 nights ago. Since then, we’ve observed and photographed Panstarrs every night (March 11: Comet Panstarrs – The Movie, March 12: Comet Panstarrs Meets the Moon, and March 13: Comet Panstarrs From Antelope Pass).

It seemed appropriate that we bring our Chicago friends Greg and Vicki Buchwald to Granite Gap for their first view of Panstarrs. They were not disappointed. Because the comet is getting little higher each evening, it’s further away from the interfering glow of twilight. Consequently, Panstarrs is easier to see with the naked eye, and the tail appears longer with greater structure than on previous nights. I estimate the tail appeared 1° long to the naked eye, but photography revealed a tail twice as long.

We spotted Panstarrs in binoculars at 7:00 pm, about 50 minutes after sunset. Greg and I both set up cameras and tripods to image Panstarrs while the ladies viewed the comet through binoculars. I used a Nikon D7000 and Nikkor 300mm f/2.8 lens to shoot another time-lapse sequence of the comet setting. I picked this fast lens so that I could take relatively short exposures of the comet since I didn’t bring a tracking mount. My previous movies were shot with a wider angle lens (e.g., Comet Panstarrs – The Movie), but I wanted a higher magnification movie of Panstarrs tonight.

On the evening of March 14, 2013, Comet PanSTARRS was captured in a time lapse sequence as it set over the Chiricahua Mountains in Arizona. Nikon D7000 and Nikkor 300mm f/2.8 lens, 3 seconds at f/2.8, ISO 1000. Comet PanSTARRS From Granite Gap copyright 2013 by Fred Espenak on Vimeo.

The resulting movie shows hints to the ion tail (to the right of the dust tail) for the first time. If you haven’t had a chance to see Comet Panstarrs yet, the next few days will be your best opportunity before the Moon gets too bright. So get out there!

Fred Espenak

Comet PanSTARRS From Antelope Pass

After last night’s frantic chase of Comet Panstarrs and the Moon, Pat and I decided to take a more leisurely trip or tonight’s view the comet.

We traveled into New Mexico via Route 9 to Antelope Pass in Hidalgo County. This location put us high above the San Simon Valley with a clear view to the west of Arizona’s Chiricahua Mountains. We parked just off the road which immediately piqued the attention of a Border Patrol agent. When I explained to him that we were going to photograph the comet, he said “What comet?”. I guess we all have our own priorities as he headed down the road, no longer interested in us.

We spotted Panstarrs in binoculars at 6:58 pm, about 45 minutes after sunset. Pat decided to forego photography, opting instead to just watch tonight. Meanwhile, I busily set up two tripods and cameras. The Nikon D300 and Nikkor 18-200 VR zoom would be used to make another time-lapse sequence of the comet setting (see: Comet Panstarrs – The Movie). The Nikon D7000 was attached to my Nikkor 300mm f/2.8 “monster lens”. I chose this fast lens so that I could take relatively short exposures of the comet since I didn’t bring a tracking mount.

Comet PanSTARRS appears above the Chiricahua Mountains in Arizona shortly before setting on the evening of March 13, 2013. Nikon D7000 and Nikkor 300mm AF f/2.8 lens, 2 seconds at f/2.8, ISO 1000. Photo copyright 2013 by Fred Espenak.

Comet PanSTARRS appears above the Chiricahua Mountains in Arizona shortly before setting on the evening of March 13, 2013. Nikon D7000 and Nikkor 300mm AF zoom lens, 2 seconds at f/2.8, ISO 1000. Photo copyright 2013 by Fred Espenak.

The trickiest thing about shooting a comet-setting image sequence is choosing a middle-of-the-road exposure. The sky brightness changes enormously during the 18 minutes of the time-lapse sequence, so you need an exposure the won’t grossly overexpose the first exposures nor underexpose the last ones. From the previous night’s shooting, I chose 4 seconds at f/5.6 and ISO 1600. I started the sequence at 7:12 pm and ran though comet-set at 7:28 pm. During that period, two cars drove past us on Route 9 – each time ruining 3-4 exposures in the time-sequence which were later removed when making the final movie.

The resulting movie appears below. Overall, comet Panstarrs has been getting a little higher each night, allowing us views later in evening twilight. This means better views of the dust tail, and it’s also getting easier to see the comet with the naked eye.

Tomorrow, our Chicago friends Greg and Vicki Buchwald arrive for a visit and will get their very first view of Comet Panstarrs. I can’t wait to see their reactions. (See the Comet Panstarrs Viewing Charts for a preview of the comet’s appearance each night through March 25)

Fred Espenak

On the evening of March 13, 2013, Comet PanSTARRS was captured in a time lapse sequence as it set over the Chiricahua Mountains in Arizona. Nikon D300 and Nikkor 18-200 VR zoom lens, 4 seconds at f/5.6, ISO 1600. Comet PanSTARRS From Antelope Pass copyright 2013 by Fred Espenak on Vimeo.

Comet Panstarrs Meets the Moon

Comet PanSTARRS appears in conjunction with the crescent Moon on the evening of March 12, 2013. This image was taken from San Simon, AZ using a Nikon D7000 and Nikkor 80-400 VR zoom lens (2 seconds, F/5.3, ISO 1000). Photo copyright 2013 by Fred Espenak

Comet PanSTARRS appears in conjunction with the crescent Moon on the evening of March 12, 2013.
This image was taken from San Simon, AZ using a Nikon D7000 and Nikkor 80-400 VR zoom lens (2 seconds, F/5.3, ISO 1000). Photo copyright 2013 by Fred Espenak

On March 12, sky watchers enjoyed an extra treat as Comet Panstarrs was joined by the crescent Moon only 1 and 1/2 days past its New phase. The pair were only separated by 4° and appeared low in the west during evening twilight.

After my success shooting a long image sequence of the comet the previous night and subsequently converting the sequence into a video (Comet Panstarrs – The Movie), I was determined to try it again tonight.

Pat and I, along with astrophotographer buddy Joe Morris drove up to San Simon, AZ where we enjoyed a great view the previous night. My plan was to shoot the comet and Moon setting behind the most recognizable features of the Dos Cabezas Mountains. We arrived at one possible location about 10 minutes after sunset and quickly set up our tripods and cameras. As we waited for the glare of evening twilight to fade, we searched for the crescent Moon in binoculars. About 25 minutes after sunset, Joe picked out the razor thin crescent. I quickly took note of the Moon’s position and realized that it would set far to the north of my desired mountain composition. “Everybody back in the car! We’re moving south!” I shouted. Joe fired back with “You’ve got to be kidding!”, but Pat reassured him I was dead serious.

So back into the car went the cameras, tripods and people. I drove south and stopped several times to evaluate the Moon’s position, each time estimating where it would set. I finally found a location I liked – out came the cameras, tripods and people once again.

Within 10 minutes, we were all lined up along the side of the road and happily shooting the celestial spectacle of comet and crescent Moon. Because of the Moon’s young age, it was brightly illuminated in Earthshine (sunlight reflected off of Earth which illuminates the “dark” part of the Moon). Fortunately, the Moon did not overpower the fainter comet. Indeed, I found it easier to spot Panstarrs with the naked eye than on previous nights. I suspect this was due to the comet’s higher altitude tonight, allowing us to view it later in a darker sky.

Comet PanSTARRS and the crescent Moon appear above the Dos Cabezas Mountains, Arizona shortly before setting. Photo copyright 2013 by Fred Espenak

Comet PanSTARRS and the crescent Moon appear above the Dos Cabezas Mountains, Arizona shortly before setting. Photo copyright 2013 by Fred Espenak

We watched in awe as Panstarrs and the Moon set on opposite sides of the tallest mountain peak in the Dos Cabezas. Time to pack up, drive home, download and process images! (see the finished result below)

Fred Espenak

On the evening of March 12, 2013, Comet PanSTARRS and the crescent Moon were captured in a time lapse sequence as they set over the Dos Cabezas Mountains in Arizona. Nikon D300 and Nikkor 18-200 VR zoom lens. Comet PanSTARRS and the Moon copyright 2013 by Fred Espenak on Vimeo.

Comet Panstarrs – The Movie

After successfully finding and imaging Comet Panstarrs last night (Got Panstarrs?), I decided to try something different. My goal was to shoot a long time series which could later be processed and assembled into a movie showing the comet in time-lapse as it set.

While considering this project, Pat suggested that we try a different location where we could gets a clearer shot of the horizon. So we drove 25 miles north from Portal to San Simon, AZ where we enjoyed a lovely view of the Dos Cabezas Mountains to the west.

Arriving 20 minutes after sunset, I quickly set up my equipment: a Nikon D90 and Nikkor 18-200 VR zoom lens for the image sequence, and a Nikon D7000 and Nikkor 80-400 VR zoom lens for still shots. By the time I was ready, it was now dark enough to search for Panstarrs. Pat spotted it first at 6:55 pm. Panstarrs seemed a bit brighter than last night (March 10), but perhaps that was because it was a few degrees higher and not quit as deeply immersed in the glow of twilight. We enjoyed views of the comet in binoculars for several minutes before I “went to work.”

One of the still shots from the image sequence shows Comet PanSTARRS above the Dos Cabezas Mountains on the evening of March 11, 2013. It was taken from San Simon, AZ using a Nikon D90 and Nikkor 18-200 VR zoom lens at 200mm. Photo copyright 2013 by Fred Espenak

ne of the still shots from the image sequence shows Comet PanSTARRS above the Dos Cabezas Mountains on the evening of March 11, 2013. It was taken from San Simon, AZ using a Nikon D90 and Nikkor 18-200 VR zoom lens at 200mm. Photo copyright 2013 by Fred Espenak

A remote cable release timer allowed me to automatically shoot an image of Panstarrs and the Dos Cabezas Mountains every 3 seconds. I used the other camera with the 80-400 zoom to shoot occasional stills as the comet slowly set. By 7:20 pm, the show was over. We packed up and headed home to download and begin processing the images.

The assembled Panstarrs movie appears below. Tomorrow, the crescent Moon joins the comet for a not-to-be-missed conjunction!

Fred Espenak

On the evening of March 11, 2013, Comet PanSTARRS was captured in a time lapse sequence as it set over the Dos Cabezas Mountains. Comet PanSTARRS – The Movie copyright 2013 by Fred Espenak on Vimeo.

Got Panstarrs?

My first attempt to view Comet Panstarrs was on March 6. While the telescopes in Bifrost Observatory are well suited to imaging the comet, the observatory lies near the eastern foothills of the Chiricahua’s so the western horizon is blocked by mountains towering 12° or more into the sky. Because of this, I traveled a short distance into New Mexico to search for the comet from a location 10 miles northeast of Rodeo, NM. Although the distant Chiricahua’s appeared much smaller there, I was unsuccessful in finding Panstarrs due to the bright twilight sky and the comet’s low altitude.

The following days brought clouds and rain as a low pressure system passed through Arizona. The next opportunity to search for Panstarrs occurred this evening (Sunday, March 10). The comet passed through perihelion earlier in the day and was several degrees higher in the sky than it was on March 6.

Comet Panstarrs first shows itself in bright twilight about 45 minutes after sunset on March 10. This image was captured from Granite Gap, NM using a Nikon D7000 and a Nikkor 18-200 VR lens. Photo copyright 2013 by Fred Espenak

Comet Panstarrs first shows itself in bright twilight about 45 minutes after sunset on March 10. This image was captured from Granite Gap, NM using a Nikon D7000 and a Nikkor 18-200 VR lens. Photo copyright 2013 by Fred Espenak

This time, Pat and I drove out to Granite Gap, NM where I began searching about 30 minutes after sunset. As the bright glow of evening twilight gradually subsided, I picked out the comet around 7 pm (40 minutes after sunset) while using a pair of 8×40 binoculars. Once I knew the comet’s location, I could just make it out with the naked eye. But it was NOT easy.

Quickly setting up a tripod, I photographed Panstarrs for the next 10 minutes using a Nikon D7000 and a Nikkor 18-200 VR lens. The strong twilight prevented seeing any more than about 1/4° of the comet’s dust tail. Nevertheless, it was a thrilling sight after all the anticipation. The comet set behind the distant Chiricahua Mountains around 7:13 pm.

The weather forecast for the next week is looking very promising and I plan to continue imaging the comet as it climbs higher each evening. See the Comet Panstarrs Viewing Charts for a preview of the comet’s appearance each night through March 25.

Fred Espenak

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 Ready-Or-Not

Anticipation is building as Comet Panstarrs heads for perihelion on March 10. Will it live up to all the “comet hype” to become a spectacular comet like Hale-Bopp or Hyakutake (see: Comet Panstarrs or Bust)?

Current predictions and its recent performance suggest that Panstarrs will fall short of being a truly great comet. Nevertheless, it should still become a memorable object to see especially from a dark-sky location.

Southern Hemisphere observers tracking the comet during the last week of February have reported that Panstarrs is visible to the naked eye and displays a prominent dust tail 1.5° long. According to comet expert John Bortle, he expects “a peak brightness of about (magnitude) +2.2 on or about March 10th, with a slow fading thereafter taking the comet to about magnitude +5.0 by month’s end.” He goes on say that Panstarrs “… should exhibit a fairly broad, strongly curving dust tail between 5 and 15 degrees in extent.” For more of Bortle’s comments, see Sky & Telescope: Panstarrs Update.

German astronomer Uwe Pilz has made some simulations of Panstarrs’ predicted dust tail during March. It will curve up and to the left for Northern Hemisphere observers looking west about 40 minutes after sunset. Using Pilz’ simulations and a bit of artistic license, I have created a Photoshop image of what Comet Panstarrs may look like. The dust tail is broad and curves to the left while the ion tail is narrow and points straight up.

A Photoshop rendition of Comet Panstarrs is based on predictions that the comet will exhibit a broad dust tail curving up and to the left of the nucleus as seen about 40 minutes after sunset on March 15. Diagram copyright 2013 by Fred Espenak.

A Photoshop rendition of Comet Panstarrs is based on predictions that the comet will exhibit a broad dust tail curving up and to the left of the nucleus as seen about 40 minutes after sunset on March 15. Diagram copyright 2013 by Fred Espenak.

Keep in mind that the relative brightnesses of the two tails are only a guess. The gas tail will probably be much fainter and may only be visible though binoculars or photographically with time exposures.

There is cautious optimism that Comet Panstarrs will remain a naked eye comet with a visible dust tail during early evenings from mid to late March. A dark sky with a low western horizon will be essential for the best views of the comet in order to follow it as the glow of evening twilight fades.

Visit Comet Panstarrs Viewing Charts to see individual sky charts for every day from March 5 through March 25.

Fred Espenak