OBSERVING THE AURORA IN NEW YORK
------------------------------
John Pazmino
NYSkies Astronomy Inc
nyskies@nyskies.org
www.nyskies.org
2003 May 25 initial
2017 February 22 current
Introduction
----------
Altho the northern lights, the aurora, is infrequent over New York
City, it does appear often enough that you should be versed in its
appearance and behavior. I deal here solely with the visual aspects of
the aurora, leaving out the geophysics and theory. I also miss out
radio and magnetic methods of observing the northern lights, but I do
touch on photographing it.
New York is not considered a favored place for the aurora because
it is far from the geomagnetic north pole, about 51 degrees north
geomagnetic latitude, and its skies are not truly dark. They are
slicked with luminous graffiti. Never the less the City experienced
substantial aurorae roughly once a decade and minor ones every couple
years.
The frequency of aurora tracks the overall solar activity. It is
far less during sunspot minimum, yet showing up when unusual solar
storms break out.
The keys to a successful sighting of the northern lights from the
City are preparation and lots of luck.
By the way, you know that 'aurora borealis' means 'northern dawn',
if from nothing but blind rote. Do you know where this term came
from? Galileo coined it first in 1619!
Aurora oval
---------
When aurora are sparked on Earth by the influx of protons and
electrons from the Sun, the lights concentrate around a rough circle
centered on the geomagnetic north pole. The pole is displaced from the
geographic pole in the general direction of New York. We are more
likely to see the aurora than our geographic latitude, 41 degrees
north, indicates. Banking off of the geomagnetic pole, we are at 51
degrees north.
Compared to European and Asian sites of similar geographic
latitude, New York is actually the more favored to experience the
northern lights. On the other hand, the US Midwest is a tad closer to
the geomagnetic pole and the its countryside has far darker skies.
Aurorae are more common and easier to notice there than in the City.
Altho the aurora oval is the concentration of lights when they
occur, the density of the lights varies widely around the oval. There
may be a strong display at certain points of the oval and none at
others. That's why we may miss an aurora when the oval is over the
city when other places along it get a show. Or vice versa.
The oval is the southern boundary for aurorae. While strongest
along the circle, aurorae play within it. Hence, if the aurora oval is
south of the City we may get a weaker, but still satisfying, display.
Size of the oval
--------------
The aurora oval varies in size according as the strength of the
geomagnetic storm producing it. The greater the storm, the farther out
from the geomagnetic pole is the oval. The storm strength is given by
a figure of merit called the Kp (kay-pee) index, which is given in
aurora predictions and alerts.
Kp is one of many parameters for monitoring the interaction of the
Earth's magnetic field with the solar wind, but it's the simplest
single measure of aurora prospects. 'Kp' is the German initials for
'planetarische Kennziffer', 'planetary index' in English. It is a
combined global measure of geomagnetic disturbance collected from a
battery of geomagnetic stations in high north and south latitudes.
Each computes for 3-hour intervals thruout the day an index, K,
for itself. If there were such a station near New York, it would be
better to track its K index rather than go by the global one. But
there isn't.
Along the City's longitude meridian the aurora oval lies at
approximately the locations below.
------------------------
Kp approximate location
-- --------------------
5 St Lawrence River, Montreal QC
6 southern Adirondacks, Albany NY
7 smack over New York City, northern New Jersey, Long Island
8 southern Chesapeakw Bay
9 North Carolina
------------------
Thus, a Kp greater than 6 gives New York a sporting chance of viewing
the aurora. Because Kp is a quasilog number, it takes a massively
severe disturbance to push it from 5 thru 9, making aurorae only an
occasional apparition over the City.
The Kp index is one of the factors cited in aurora alerts and
predictions. You can get these predictions by email, cell or pager
signal, websites, or maillists. I assume here that you got or can get
these bulletins.
Tracking aurora activity
----------------------
It is impossible at present to confidently forecast an aurora over
a given location. The best is to stipulate the chances of getting an
aurora based on various trends in geophysical parameters, such as the
Kp index and size of the aurora oval. Even then, you may miss a
display because it fell on your location in daytime or ell on a remote
longitude.
US NOAA maintains a 'Space weather prediction center' in Boulder,
Colorado, to track geophysical parameters. It makes NO predictions or
forecasts for aurorae. It does issue alerts when solar-terrestrial
interaction heats up. It has a web 'Enthusiasts Dashboard' that
displays twenty or so panels of data. These charts, maps, graphs track
many items up thru the previous couple hours. The link is
www.swpc.noaa.gov/communities/space-weather-enthusiasts
Please know that a web can be rearranged at will without notice
and this link may break. If so, try a search for 'NOAA' + 'enthusiasts
dashboard'. Clicking on a data panel enlarges it for easier reading,
saving, printing. Clicking the large panel returns to the home page.
Letterpress on other pages at NOAA explain the items but you still
must apply your astronomy smarts to plan an aurora watch or answer to
an alert.
It is wise to keep an eye on the sky when ever outdoors during a
period of likely aurora, even if none is expected for your location.
Make the deliberate task of learning the normal and usual sky glows
from terrestrial sources. You really don't want to miss an aurora
because you failed to distinguish it from an ordinary hotspot of
luminous graffiti you should have known about.
In the old days
-------------
Modern forecasts for aurora are based on satellite monitoring of
the Sun. The birds collect solar wind and radiation that never reaches
the ground and is not modulated by the atmosphere. Satellites in high
orbit or at a Lagrange point gather solar particles and radiation
before Earth's magnetic field distorts them.
The information is processed by several centers for geophysics and
then sent out to the astronomy world within minutes or hours.
Before the space age, we relied on the casual but unknown
correlation between sunspots and other visible photosphere events and
the later eruption of aurorae. From experience we figured that from
the appearance of a large sunspot it would take two to four days for
the electrons and protons to reach Earth.
The prediction was iffy because we could not follow the solar flow
on its way to Earth, We could not know if the flux was even aimed to
Earth at all. There were many false alarms. No aurora showed up after
we witnessed what we felt was a sure source for them.
We were with annoying frequency blindsided by aurorae for which we
had no previous warning. There were no major sunspot groups or flares.
International Geophysical Year
----------------------------
In 1957-1958 for the first time ever, humankind mounted a
coordinated all-points study of Earth and her interaction with the Sun
and outer space. It ran for 18 months to bracket the sunspot maximum
of 1957. Among the prime disciplines of the IGY was the northern --
and southern -- lights.
The space age didn't yet start at the start of the IGY. The first
birds orbited by the Soviet Union and United States later were very
crude and of short life. By rockets and balloons we did capture some
of the solar particles and measured the fluctuations in the Earth's
magnetic field.
IGY recruited home astronomers to monitor aurorae. It issued
booklets and charts to aid in collecting data about the display in a
consistent and uniform manner. I myself got started in astronomy
largely thru participation in this, and other, IGY project,
Our current paradigma of aurora theory, including the discovery of
the aurora oval, derives directly from the IGY work.
Season and hour
-------------
In New York the best season for aurora is from October thru March.
These are the months of long nights, standard time, and somewhat more
clearer darker skies. Note that these are terrestrial factors. An
aurora can strike the City at any time of the year as governed by the
jivings from the Sun.
The summer months, with brief nights and daylight savings time are
the lousiest for aurora watching in the City. More over, the air is
typicly laden with moisture and haze that scatter luminous graffiti
and smother auroral light
The prime hours within a night is the four hours centered on local
[standard time] midnight. However, aurora can start in twilight -- it
could even be in progress at nightfall -- and can last for many hours
right thru dawn. If you possibly can, check the sky repeatedly on a
night of an alert at, say, half hour intervals. Once well past
midnight with no aurora, you may safely go to bed. Aurorae almost
never start after midnight.
You can have two aurora sites. One at or near your home for the
initial checking. This can be a north-facing window or terrace. The
other site, with more of the ideal parameters, is used when there is
really strong chance of an aurora erupting soon.
Observing site
------------
I assume you are within the City. It is most unlikely you will
travel to a remote darksky site for an aurora alert. The leadtime is
almost always too short. Aggravating your state of mind is the
elevated anxiety while traveling to the darksky sire with aurora
playing over your car or bus.
Examine your normal starviewing site; it may or may not be
adaptable for aurora watching. For sure, when ever you are at your
starviewing site, take the moment every so often during an alert to
scan the sky for aurora. At least, you are outdoors and engaged in
astronomy, even if the very location is deficient for proper study of
the northern lights.
The ideal site has an open sky to the north quadrant and zenith,
shielding from nearby ground light, and personal safety. The latter is
important because you may be at the site for an hour or more waiting
for the aurora to hit and then remain on site for some hour or more
watching the display.
The horizon from northwest thru northeast should be free of high
skyline. Certainly the average skyline better be less than 20 degree
altitude over this zone in order to see low-lying arcs and glows.
The north quadrant should have the least luminous graffiti, but
you'll probably use the place of opportunity regardless of the
distribution of luminous graffiti on the sky. Just know that the less
there is, the better is the view of aurora.
Because you'll skip and dance around to take in the show over your
head, watch out for ice, rocks, pipes, curbs, and other walking
hazards of the night. Deliberately move several meters away from your
telescope, car, chairs, ground cloths.
It helps if there are amenities to hand, like restrooms and
shelter from wind.
Candidate aurora viewing stations are building rooftops, interior
field or elevated hill of a park, and a north-facing shoreline.
Sky conditions
-------------
Like for other diffuse and faint celestial targets, an aurora from
the City demands a actually clear night. Any noticeable haze or thin
cloud, specially if lighted from ground sources, will cut down your
chances of seeing the northern lights. On the other hand, aurora can
be appreciated under the nominal clear night conditions of Manhattan,
now in the first decade of the 21st century having transparency of 4th
to 4-1/2 magnitude.
During an aurora alert, don't be discouraged by a deficient sky. As
long as it is not opaque and stars are discernible, do scan for
northern lights. Take care that cloud and haze may accentuate luminous
graffiti in an unfamiliar way. You could be misled to claim an aurora
sighting. Such a night you normally pass up for ordinary stargazing.
For a possible outbreak of northern lights you take what ever quality
of night that's out there.
Twilight and moonlight
--------------------
A northern lights display can begin in daylight and reveal itself
at nightfall. As twilight fades you notice sections of the sky that
aren't darkening normally. from New York the aurora, according to
extant records, is in its north glow stage at nightfall. I have no
record of a massive display in progress when the sky gets dark.
Depending on the level of the aurora alert, you may start your
vigil in mid twilight. Otherwise, wait until full night after nautical
twilight for the City.
Moonlight will slaughter the weaker aurora, but you may have no
choice but to tough it out during a watch at large Moon. Be careful of
thin cloud lighted by the Moon; they can look like aurora patches. If
feasible, confine your aurora hunting to small Moon, from a few days
before to a few days after new Moon. Once the Moon nears the quarter
phase, her light on top of the City's own night lighting, will raise
the barrier against seeing the northern lights perhaps just too much.
In more northern parts of the world a strong display can be
discerned in full daylight. This never happened in New York!
Winter clothing
------------
As for protection against weather, being that you'll be viewing
mostly in the frostbite season, take the same cautions and advice as
for regular starviewing. On the other hand, unlike for meteor
watching, you'll be moving about and generating internal body warmth.
This may let you get away with one less layer of clothing to improve
dexterity and agility.
I note here, like for regular observing, you must protect the
feet, head, and hands. There are the usual tricks of packing shoes
with rubber slabs (cut up an old mouse pad) as insulation from the
ground, wrapping a scarf under your hat, using flip-finger gloves.
When the wind picks up, do retreat into shelter as long as you can
still observe the aurora or major sections of it. You may be too busy
to think of drink or food, but it can't hurt to pack some goodies,
just in case. Like for all observing, taking in substances that impair
or deteriorate your senses is really no good.
Terrestrial lights
----------------
You absolutely must be familiar with the normal and occasional
insults on the sky from earthly sources of illumination. In New York
there are many ways to fake an aurora by ordinary and not so ordinary
outdoor lighting. This means that at your aurora station you should
make note of these normal glows and patches and plot them on a skydome
chart for future reference.
Bear in mind that the size and brightness of luminous graffiti
varies with moisture and haze. On a very clean night it may be small
and weak. On a humid hazy night it may swell and brighten. Be wisely
about temporary illuminations from stadia, dance clubs, street fairs,
store openings. They can cause glows and beams easily mistaken for
aurora.
There are two really common mistaken aurorae, one peculiar to the
winter months. First is searchlights. From afar they could mimic the
rays or beams of northern lights! The giveaway is that they oscillate
about a point on the horizon and not well below it, as a real aurora
ray would. Also, if you are seeing the spot of the beam on clouds,
looking like a glowing aurora patch, you really can't be seeing aurora
because of these very clouds.
The other is weird. If you look over a highway, carpark, truck
stop, where cars are moving about and the air be filled with ice fog,
you may see shafts or columns of light sliding back and forth. They
can look quite like rays of an aurora. They are just the headlights of
cars reflected off of the ice in the ground layer of air.
The litmus test is that the beams are vertical and parallel and
they slide across each other. Real aurora rays converge (or radiate if
you think of them as shooting upwards) and they just about never
criss-cross over themselfs.
Other effects of the City that can fool you are construction
welding or torching, emergency flashing or rotating lamps, sparks from
railroad catenary or third rail. The very source may be hidden from
view by structure or skyline, leaving only the illuminations in the
sky to fool you. In some cases you should have anticipated the lights,
like knowing about the railline, or you may be caught by surprise,
like police action in the next 'hood.
Auroral forms
-----------
It's ludicrous to describe only in words the varied shapes and
sizes of display. Check the image gallery of astroclub websites for
examples of what an aurora can look like. Study pictures in observing
and aurora books and in magazine articles about northern lights,
Understand that usually the pictures are for a specially bright
and extensive aurora of the sort you may not encounter soon. The
pictures may look blurred and smeared because the aurora moved about
in the sky during the exposure. The colors may be exaggerated due to
the erratic reaction of film chemicals to the aurora's brightline
emission spectrum.
Illustrations and pictures
------------------------
Articles, books, webs often have illustrations and pictures of
northern lights. Those painted or drawn try hard to capture the forms
and structures of the aurora at a given moment, or as a general
overview of the display. They present the arcs, rays, patches, glows,
in a realistic scene, according as the skill of the artist.
photographic illustrations can be horribly misleading if captured
on film. Since so much aurora litterature dates from the 20th
century,, before the diffusion of electronic imaging among aurora
scientists, the pictures required many seconds to a minute of
exposure. In that time the formations can shift across the sky,
blurring their impression on film. The pictures can show blobs,
smears, spots of color that hardly resemble the scene in the sky.
Newer observers can be sent astray during an aurora watch. They
may pass over real formations in the sky. There was no way out of this
situation except if the author cautioned the reader in the text or
picture caption.
At the turn of the 21st century a sweeping conversion of imaging
began from chemical to digital medium. By about 2010 this wholesale
migration of photography was nearing completion.very new litterature,
with digital images for illustrations, could present a more fair
impression of aurora formations. That's because the electronic sensor
in the camera is an order or more efficient in converting photons into
image impression than film ever was. The much shorter exposure reduce
the blurring and smearing from the auroral movement in the sky.
And a digital image is manipulable by image editing software to
add labels and remove distracting parts of the landscape. Judicious
use of image editing can clarify and highlight aurora features in the
pictures.
Glow
--
The most common aurora seen in New York is the glow. This is a
swelling of brightness in the north quadrant along the horizon and
extending up to several tens of degree altitude. Typicly it appears
rapidly, as if some cosmic lamp were gradually turned up, and then
stays quietly for many minutes to an hour. After then, it gently fades
away, leaving a clear sky. When bright it can silhouette clouds in
front of it; this is one way to tell it's aurora and not ground-based
lighting.
The extent is quite varied among displays. A mild glow can mimic
the lightcap of a distant conflagration. A substantial glow can fill
the whole north quadrant up to the zenith..
The glow and usually other features of the aurora are symmetrical
about the north point. Even so, a particular display may be centered a
ways off of north, with a trend in the City for northeast.
Arcs and bands
------------
An arc is a bland single-color arch spanning northwest to
northeast and culminating in the north at some tens of degree altitude.
The bottom edge is well defined while the upper edge is diffuse. It's a
few degrees broad. Probably the sky below the arc is darker than that
above, but the arc may be topped by a faint glow not noticed at first.
If the arc is folded or kinked, it's called a band. It looks like
a loose rope or dress/skirt hem. It, like the arc, has a sharp lower
and diffuse upper margin and a single color thruout.
Rays
--
Sprouting from the arc or band may be spikes, pickets, darts,
beams. These are more or less evenly spaced but their color may
graduate from top to bottom. In the quiet form, the rays stay put,
except for brightening or dimming as a unit.
Sometimes the rays appear with no arc or band. The spring from a
convergence point below the north horizon. This is a perspective
effect; the arc or band is too far away beyond the Earth's curve.
Physicly the rays align with the local magnetic lines of force, more
or less vertical, as parallel features. Perspective makes them diverge
or converge in the sky.
I can't think of an instance of an isolated ray, with both ends in
clear sky. A ray is rooted at one end on an arc/band, the horizon, or
a corona.
Patches
-----
A patch is a luminous blotch or spot on the sky detached from the
horizon. Unlike the glow, a giant patch overlapping the north horizon,
a patch may sit any where in the sky. It is several degrees across and
resembles a high power view of a deepsky nebula, a diffuse yet smooth
glowball. Patches seem from New York to be red most of the time, altho
they can be of any other color. One peculiarity is that when there are
several patches in the display, they tend to share a single color.
Corona
----
A corona is one of the two most fantastic aspects of a major
aurora. It is a patch high in the south from which rays emanate out in
all directions, sometimes right down to the horizons. In a well
developed form the coronal patch has a central hole devoid of
luminous material. The corona may start as a small red nebula which
then shoots its rays out toward the horizons.
The corona is at the geomagnetic zenith, the upper vanishing point
for the magnetic lines of force cutting thru the ground. Or, it's the
point where the upper end of a freely suspended vertical magnetic
compass points. For New York this is about 70 degrees up in the south.
The convergence of rays in the corona is the perspective view of
parallel lines, similar to the effect of a meteor shower.
Curtain or drape
--------------
If the northern arc or band sprouts enough rays, they close up
into a striped sheet reaching toward the zenith to look amazingly like
a cosmic curtain. At this stage in the display, the curtain may whip
and flutter as if bluffetted by wind! In the ultimate form, the rays
of the curtain continue over the zenith to a corona.
In general the band/arc and rays have different colors, but there
seems to be no normal combination for New York.
The arrival of a curtain or corona marks the grandest extent of
the display. Such have been seen in full form only a few times from
the City in the whole 20th century.
Colors
----
Aurorae shine by excitation of nitrogen and oxygen in the upper
air. The three major spectral lines emitted are red at wavelength
630nm; green, 558nm; blue/violet, 427nm. If you apply to the display a
simple spectroscope or even just a transmission grating, you'll see
the picket-fence structure in the aurora spectrum.
Where two auroral features overlap, the resulting color is the
additive mix of the separate ones. Thus merging red and green parts of
the display will cause a yellow hue.
The red, green, and blue spectral emissions are by chance near the
central wavelengths of the photography tricolor bands! It can be a
potential useful tool to have to hand a set of these filters. They are
obtainable from photography or lithography sources. By inspecting the
suspect aurora thru them you could distinguish it from ground-based
lights.
The colors you get in photographs will not match those seen by
eye. Film is made to capture a continuous spectrum of light, typicly
sunlight. This is indicated by the color temperature rating of the
film. Daylight film is rated for 5700K or so, the temperature of a
blackbody radiating a solar spectrum of light.
When presented with light of specific discrete wavelengths, such
as neon lights at a carnival, the film goes nuts. You do get very
pretty colors but not those you recall seeing in real life.
Black aurora
----------
By far the creepiest color of aurora I ever saw is BLACK. Yes,
there is such a thing!! In an otherwise luminous display there may be
some places on the sky where the aurora avoids. It's as if there was a
'grease spot' there where the aurora 'ink' can't stick. Other
descriptions are a foreground opaque patch blocking aurora behind it,
or a hole torn out of skydome.
The aurora circulates around this black (actually an absence of
luminosity with clear sky within it) to slide 'around' or 'behind' it!
In the three instances I saw such a phaenomenon, the black spot
stayed put all thru the display; it did not partake of the agitations
of other features. On one occasion the black spot wavered in size
slowly but otherwise did not move about. In all cases, this spot ws in
the northern quadrant of the sky but not at all symmetrical with the
other parts of the display.
Brightness
--------
Aurora in the City have to be mighty brilliant to attract your
attention. Satellite monitoring of the aurora oval shows that New York
should see several aurora a year in times of active Sun. Most of them
are weak, about as bright as the Milky Way. given that the Milky Way
is a rare treat in New York, a weak aurora will be routinely missed.
A brighter display is about equal to ground-lighted clouds or
haze. At this level of brilliance, the aurora could attract public
attention for being reflection from a large conflagration or other
earthly calamity.
The most brilliant of aurorae seen from the City allowed papers
and charts to be read by them! Under such a display the entire
populance could be sent panicking into the streets.
With clues from color, kinetics, evolution, and so on, you may
recognize an aurora of the lesser brilliance, before it is dismissed
for funny cloud. Once and again, you simply have to be intimately
versed in the luminous behavior of your own sky.
When you are in a foreign part of the City, with no fluency about
the native sky, you may miss or disregard a true aurora. Heartbreaking
agony is what you'll be in when your fellow astronomers later report
about the display which you were ignorant of over your head!
Pulsating and flaming
-------------------
Any aurora feature can pulsate, throb and beat in brilliance in a
timescale of seconds, like a discoteque lamp. This seems, at least for
displays in the City, to be done almost only by features of a red
color. Such an action can be awesome, even frightening! Red suggests
blood, war, danger, evil. The pulsing reminds you of a heart. What
cosmic fate awaits you!?
Flaming is seen mostly in the rays. Waves or beads of light sweep
along the ray like a chaser light. All the rays may flame in
synchronism or they may so their thing out of step.
Texture
-----
On the whole aurora features are smooth bland luminous areas. Once
in a while, specially for glows and large patches, there may be
texture within them. These are variously described as mottling, weave,
pebbling, dimpling. The feature has a rough surface, like that of
stucco, cloth, brick.
Kinetics
------
Aurora features partake in motion, sometimes rather violently.
Glows and patches are the calmer quieter forms of northern light,
while the rays and curtain are the most agitated. The motion resembles
that of lightweight objects blown about in wind, like tree branches,
flags, smoke. It is this rapid movement that causes so many aurora
photographs to look blurred and fuzzy while the skyline is sharply
imaged. Aurora pictures are usually of a many second exposure, during
which the can be substantial motion of the display.
When chronicling a display use the horizontal frame to describe
motions, not celestial based on RA & dec. It's just a LOT easier to do
it this way.
Evolution
-------
No two aurorae are the same. There is no standard script for them
to follow. An aurora may consist of just a calm stable glow. Or it may
explode into an orgy of gyrating shapes and colors all over the sky.
Altho you can sense that something gross will happen any second, it's
impossible to foretell just what to expect.
The forms arrive by resolving out of the dark sky as a swelling of
brightness. The leave by waning in luminance. Some features come by
growing from nothing to some large area and then go by contracting
back to nothing size.
Patches have a tendency to align along an arc, roughly with a
declination parallel as they come and go. In a strong display the
patches may grow in number until they merge into a continuous band.
This band later may fragment back into patches, which then one by one
fade away.
Sounds
----
It is generally accepted that aurora do not produce ordinary
acoustic sounds. The air where they live is far too thin for that.
Never the less reliable accounts abound of noises heard during
aurorae.
The sound is variously described as a fireplace flame, frying pan
cooking, crinkling cellophane, distant train whistle, aeolian tones,
snaps and pops.
It may be that you are picking up electromagnetic induction in the
ear, where the vibrations of the eardrum are converted into electric
signals for the brain to interpret. You may have heard such sounds
near electric machines or power lines.
I hazard that with the perpetual ambient noise in the City any
sound caused by aurora will be completely submerged. But do listen
carefully and try to discern if a new noise is in the air not present
before or after the aurora.
I suppose that if you witness northern lights from a remote empty
quiet site with fresh snow on the ground (to absorb and stifle local
noise) and you keep real still, there is the chance to listen up for
any celestial sounds.
I have no knowledge of anyone successfully audiotaping aurora
noise to confirm what was heard by ear. I may suggest that if the
aurora noise is an electromagnetic effect, the recorder will pick it
up and impress it on tape like static. However, the recorded noise may
may not faithfully replicate the acoustic sensation of auroral sounds.
Documenting the display
---------------------
Do not try to make a faithful drawing of the aurora on the spot.
Time is precious and the display may be too kinetic for you to capture
on paper all of its details. In the stead, make schematic notes and
plots on a prepared chart.
Have a supply of allsky starmaps with the brighter stars plotted
at half hour intervals thru the night of your watch. Leave off all
labels and grids. Stars to second or third magnitude are enough for
viewing northern lights in the City. Mark the compass points around
the horizon.
Know for sure the compass points in your skyline at your viewing
site! Do this by day against landmarks.
In the field it's best to leave off of instruments for angle
measures. They can be distracting to operate and hard to read in the
dark. Go by the the fist-&-clock method of taking altitudes and
azimuth. The closed fist at arm length is quite ten degrees. For the
clock in azimuth, twelve is north; three, east; six, south; nine,
west.
Have a clock (for telling time) with large or lighted numbers; set
this with a reliable time source to within a minute.
Have pens, felttips, notepad with you.
As the aurora develops, take alt-azimuth readings of the
boundaries, extremities, and edges of the features and note the time.
Then plot them on the sky chart. You can also bank off of the stars
for fixing points of the display. It's not critical to scale off the
distances on the chart; be sure to litterally write in the
measurements. From these you can later make a clean scaled plot
indoors.
If the display starts running away from you, drop the chart and
scribble in the notepad. Use any abbreves and symbols you want. Firm
up these notes soonest you get back indoors. Memory erodes very
quickly over the ensuing days.
When you take pictures, note the time of the exposure and the
center of the camera field. You'll be astounded how difficult it is a
week later, when the film comes back, to decipher your images! Digital
images are no less tough to figure out if they are uploaded even only
a few hours later.
Notifying others
--------------
It can be immensely frustrating to witness an aurora and know that
other astronomers around you may be missing it! However I advise
AGAINST quitting your watch to call your fellows. It's better to
capture a continuous record of the display than to lose large parts of
it due to absence in search of other observers.
If you got in hand mobile comms (cellphone, radio email, pager
ringup), then, yes, sound the alarm to your fellow astronomers. You
continue to monitor the display with only momentary diversion to
operate your piece. Have with you the addresses of these folk when you
do aurora observing.
Photography
---------
Starting in about 2000 and essentially complete by 2010
photography shifted from film to digital imaging. Also picture-taking
functions were built into many small electronic devices besides
'cameras'. Any person, not just an astronomer, can take excellent
aurora pictures with gadgets like computer tablets, netbooks, watches,
cell-phones, even some hats!, without a dedicated camera.
With the extremely sensitive and efficient sensor inside a digital
imaging module e, only a couple seconds of exposure can capture good
northern light picture.s.
The exposure may be adequate just by shooting the aurora in the
device's automatic mode. Else, manually set the exposure to, say, 4 to
8 seconds.
An imaging module may be built to shoot in 'color' mode, often
with no other option. If so, this is one less parameter to worry
about. Else deliberately set the device to in color, not black-&-white
or other monochrome.
You have to prop up the device to aim at the sky and use the timed
shutter. The aiming is easier from the the live-view panel. The much
smaller and lighter mass of most electronic gadgets compared to
traditional film cameras makes it simpler to support the scene with
handy props. A regular tripod is not a necessity like for film
cameras. There is no need for strong zoom. Aurora features have no
minute texture or internal structure. Shoot with a wide field and try
to include some landscape for scale.
In preparation for picture-taking at night with no lighting,
practice operating your imaging gadget entirely by feel. Be careful
about hanging memory cards and batteries in the dark.
Virtually all electronic devices, cameras and others with picture-
taking module, run off of batteries. You must have a stock of fresh
batteries. This is specially the case for aurora seen under cold air.
It is tempting to examine the image on the viewing screen after
each shot. This is a gross mistake. Yes, inspect the first one or two
pictures to be sure there was no blunder in setting the device. Then
after, concentrate of the show above you. The aurora can be kinetic
and evolving, requiring your attention on the sky at all times. Just
take pictures and worry about the images after the display winds down.
Triangulation
-----------
Northern lights populate the atmosphere from 90-100 kilometers up
to 200-300 kilometers. From places in the City a few kilometers apart
it should be feasible to do triangulation on a display. It seems
simple to do with photographs and some play on a calculette.
It in fact is disgustingly tough. The main problem is that you can
never be sure the two stations are sighting the same exact point in
the display. With the motion and evolution of a display, the stations
may bank off of entirely different spots, rendering any calculations
ridiculously wrong.
You could try preplanned photographs of a certain constellation at
certain times. Within the picture pairs you may find some definite
identity of some spot for your triangulation.
Conclusion
--------
Northern light displays from New York City are rare and can be
easily missed within the overall sky luminance. Never the less, you
can see the brighter shows from even the center of Manhattan IF you
are prepared and are sky-wisely. Mind the auroral alerts, exercise
your eyes and mind on the normal behavior of your sky, Have aurora
tools to hand, and hang loose.