I have noticed an increased number of reported sightings of bright lights in the night sky lately, some appearing, then disappearing only to appear
again and some with brief flashes.
I thought it might be a good idea to post this information regarding the ISS and how to spot it as well as many other satellites and orbiting objects.
I saw my first iridium flare (61) last week and had I not known what it was I would have been calling mufon.
And please don't get me wrong. I am not fishing for explanations or trying to debunk anyone's sighting. However, it is always a good idea to rule
out the obvious first.
Spot the Space Station
If you're out watching the twilight sky in the time frame from 45 to 90 minutes before sunrise, or 45 to 90 minutes after sunset, you'll might see a
few "moving stars." They are most likely artificial satellites.
The brightest of all is the International Space Station, and this month provides some great opportunities to see it from just about anywhere.
Satellites are seen at night because they are illuminated at high altitudes by reflected sunlight and can be seen against a dark sky. A satellite
entering the Earth's shadow immediately vanishes from view and pursues an unseen path until it again emerges into full sunlight. There are nearly
10,000 satellites now in orbit around Earth,
The ISS can briefly flare:
Nominally, its visual magnitude from the ground can make it appear as bright as the planets Jupiter and Venus, although in recent days some
observers have seen the ISS briefly "flare" to dazzling brilliance, thanks to sunlight glinting off one of its many solar panels. In fact, some have
even been able to glimpse the ISS while the sun was just above the horizon!
Type I and Type II passes:
Moreover, because the ISS revolves around the Earth in an orbit that is inclined 51.6 degrees to the equator, there are two types of passes that
are visible.
In the first case (we'll call it a "Type I" pass), the ISS initially appears over toward the southwestern part of the sky and then sweeps over
toward the northeast. About seven or eight hours later, it becomes possible to see a second type of pass (we'll call it "Type II"), but this time
with the ISS initially appearing over toward the northwestern part of the sky and sweeping over toward the southeast.
Great viewing:
And between roughly July 17 through 24, thanks to the shortness of the nights, North Americans will get a chance to see the ISS undergoing a
series of Type I passes after sunset in the evening sky, and then see it again the following morning before sunrise, undergoing a series of Type II
passes.
For some locations, there may be as many as six chances to see the ISS during a single night! For much of North America and Europe, the "prime
viewing period" for both evening and morning passes will run roughly from about July 17 through 21. After July 21, the window of opportunity for the
Type II morning passes will close and only Type I evening passes will be possible, lingering into the early part of August.
Viewing Tips:
Some passes are superior to others. If the ISS is not predicted to get much higher than 20 degrees above your local horizon, odds are that it will
not get much brighter than a moderately bright star (10 degrees is roughly equal to the width of your fist held at arm's length). In addition, with
such low passes, the ISS will likely be visible for only a minute or two. Conversely, those passes that are higher in the sky — especially those
above 45 degrees — will last longer and will be noticeably brighter.
The very best viewing circumstances are those that take the ISS on a high arc across the sky about 45 to 60 minutes after sunset, or 45 to 60 minutes
before sunrise. In such cases, you'll have it in your sky upwards to four or five minutes; it will likely get very bright — perhaps even briefly
"flare" in brilliance — and there will be little or no chance of it encountering the Earth's shadow.
For the upcoming series of evening and morning passes, take note of the fact that, for those occurring in the evening, the ISS will usually start out
rather dim, then tend to grow in brightness as it moves across the sky. In contrast, for the morning passes, the ISS will already be quite bright when
it first appears and will tend to fade somewhat toward the end of its predicted pass. This is due to the change in the angle of sunlight hitting the
vehicle.
Lastly, remember that in certain cases, the ISS will either quickly disappear when it slips into the Earth's shadow (during evening passes) or quite
suddenly appear when it slips out of the Earth's shadow (during morning passes). This becomes increasingly more likely for those predicted passes
that take place more than 90 minutes after sunset or more than 90 minutes before sunrise.
Link to article
How can you tell what you saw? This is one of my favorite sites. The Heavens Above site can pinpoint from your location passes of anything from the
Hubble to the ISS to amatuer radio satellites to iridium flares and will even forcast the object's trajectory, duration and magnitude. Here are a few
links worth checking out if you have a sighting and your not sure what it is.
Heavens Above
Nasa J-Pass
Nasa's SkyWatch
So, I'll say it again, I am not trying to debunk anyone's sighting, but if your going to be out star-gazing/ufo hunting, you might want to arm
yourself with this information first.
Rush
