Text, photos, sketches by Herb Johnson, NJAA, Dec 1999 - Mar 2000
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On December 3rd 1999 I read an email message from Sky and Telescope magazine that a nova
had been found in the constellation of Aquila which was rapidly approaching
a visible magnitude. Novae are stars
that are suddenly very bright for days and then dim over many days. "Visible" means a
magnitude or brightness above about 6th magnitude: the scale is brighter for lower values,
so 5th magnitude would be barely visible. I decided to try to photograph it to see if I
could record the change. The photo shown here is my
best photo of the event, and I describe below not only how I photographed it, but how
I was able to find the right part of the sky, and how I identified which star is the nova.
The Sky and Tel message gave the coordinates of the then 6th magnitude object on Dec 2nd as: RA 19h 23m 05.38s, Dec. +4d 57' 20.1". Translation: Right ascension of 19 hours 23 minutes, declination of plus 4 degrees 57 minutes. Right ascension is the location around the 24-hour circle on the celestial equator, which starts at 0 hours near Cepheus. Declination is the angular location above or below the celestial equator, where plus 90 degrees locates the North Star (Polaris).
I found the constellation in my field sky chart, the Meade Seasonal Starchart and planisphere;
photocopied the section of that page, and marked the location of the nova on the copy (Chart 1).
Aquila contains the bright (1st magnitude) star Altair and is located "above" or north of
the popular southern constellation Sagittarius. The trick in finding constellations is to
note the pattern of brighter stars in the constellation and the relationship of that
constellation to others in the sky. Also, to know approximately where the constellation will
be in the course of the evening, as the rotation of the Earth makes the sky appear to set
in the West and rise in the East. A planisphere can be set for time and date to show the
visible sky. It indicated that Aquila was only going to be above the horizon for a few
hours after sunset. I would probably need about an hour's darkness to see or photograph
stars of 5th and 6th magnitude.
I also photocopied the area of the nova from a deeper sky atlas, Uranometria (section 251) and marked the nova's location as well as the location of the brighter stars nearby (Chart 2). I made sure I could identify those same stars in my field chart: both charts had Greek letters or numbers to designate several bright stars in the constellation. I would need to know these stars and their arrangements from both charts in order to star hop my way to the nova.
In the copy of the Uranometria chart, the bright stars from the field chart are identified
with arrows. The location of the nova is identified from the arrows at the edges of the
chart: they point to a common location that I marked with an X.
On December 6th I set up my equipment around sunset. As it got dark I spotted the star Altair f rom its orientation relative to other bright stars, I used my binoculars to look below Altair and I could see the 3rd magnitude stars that made up the rest of the constellation. With some study and the darkening sky I thought I could see a star where the nova should be: but there ere many stars in that area of 5th magnitude or so!
To photograph the nova, I simply used the most sensitive film on hand - 800 speed Kodak Max - and used a range of exposures from half a minute to 90 seconds using a stopwatch. To aim the camera, I judged the distance below Altair to the nova area, aimed the lens of my Nikon FG SLR camera so that Altair was on top, and set the zoom to cover both Altair and the area of the nova (about 30 mm focal length, f/3.5) I used a tripod of course and a "bulb" or remote shutter control to minimize any vibration.
I also took some photos a few days later, on the 9th. Some days later, I developed the photos I exposed and they came out surprisingly well! The short exposures had the least startrailing, or streaking of stars due to motion of the sky (Earth) during exposure and at first inspection showed stars to probably 5th magnitude. The longer exposures were too streaked. Unfortunately, there was no obvious change between the photos of the 6th the 9th. So I would have to see if the nova was literally a "new star" (that's the literal meaning of nova) by comparing the photos to my sky charts. I'd work with my Dec 9th photo of about a minute's exposure.
First, I put a piece of paper over my photo and marked the brightest stars.
I knew that Altair was on top and the brightest in the field. By carefully comparing the
stars of similar brightness in the photo and their orientation, with stars of similar
magnitude from my field chart, I could identify the portion of the constellation in the
photograph. Fortunately this included the area of the nova! I drew the constellation lines
and produced the sketch #1 shown here.
Then, I located and traced the dimmer stars from the photograph onto a copy of that sketch (sketch 2) and started to identify the dimmer stars, including those of 5th magnitude that would hopefully include the nova. This was about as dim as the photograph could show by eye.
It took a few hours to identify patterns and groups of brighter stars that were designated
parts of the constallation (see arrows in Chart 2) and then dimmer stars and their patterns
(circled areas 1 and 2 in Chart 2 and Sketch 2). This procedure works best with a few
stars at a time, and you have to be able to "see" these patterns at different scales.
This is a skill much like finding these same patterns in the sky from sky charts, to find
unfamiliar objects from familiar locations; that is called star-hopping.
Finally, after a few re-sketches, I was reasonably confident that I found the area near the nova. Sure enough, there was a red star of about 5th magnitude in my photo that was not in my skychart! I've made a closeup of the photo, the nova is centered in the four crosshairs. To find this section in the full photo, note the arrangements of dim stars near the bright star in the closeup marked "d". This star is Aquila delta, which is also identified in the two sketches, as a bright star centered between the left and right sides of the photo, and 3/4's of the way down from the top of the photo.
A few weeks later, I brought the photos and sketches to the NJAA Research meeting.
Rod McCrea, who had been observing the nova as well, immediately spotted the nova from
the photos without looking at my sketches - the very same object! Rod and my colleagues
were pleased enough with my photos and work that I though I'd share them with the rest of
the membership, and so I assembled this presentation.
I'd welcome any questions: contact me or see my work on this Web site.
Copyright © 2000 Herb Johnson
Most recent revision Mar 14 2000