Early next Monday morning (April 5) at 6:21:22 a.m. Eastern Time, the Space Shuttle Discovery is scheduled to be launched on mission STS-131 to the International Space Station. If the flight comes off on time, it will take place 46-minutes before sunrise at the launch site at Cape Canaveral, Florida. Along much of the United States Eastern Seaboard, it will be morning twilight . . . a most unusual circumstance for the launch of space shuttle. Only five out of the 130 previous shuttle flights have taken place just before sunrise on Florida's "Space Coast" and this will be the very first morning twilight launch to take a northeast trajectory parallel the East Coast.
The question one might ask at this point is, "Will Shuttle Discovery be visible locally from the Greater New York Area soon after it leaves Pad 39A in Florida?" To answer this question, I revisited a similar shuttle launch which took place back in 1991.
On September 12 of that year, shuttle Discovery was launched on mission STS-48, in order to place UARS (Upper Atmospheric Research Satellite) into orbit. Liftoff came at 7:11 p.m. Eastern Time. In Florida this was 20-minutes before sunset, while it was exactly the moment of sunset in New York. Eight minutes later, the shuttle came up over the southern horizon as seen from here in the Metropolitan Area. It streaked rapidly on a relatively low trajectory above the horizon, appearing to equal or even rival the planet Venus in brightness. At the moment of MECO (Main Engine Cut Off), ground observers could see a "puff" of vapor emanating from the shuttle and immediately afterward, looking at the shuttle with binoculars revealed two objects: the shuttle orbiter and the orange external fuel tank which had just been jettisoned over the Atlantic. It only lasted about a minute, but it was all very exciting to watch.
Now . . . we may have another chance to see something similar in our early morning sky next Monday.
The 1991 shuttle launch was during the evening hours. When the shuttle appeared over New York it was eight minutes after local sunset and the Sun was 1.7-degrees below the horizon.
On Monday morning, assuming an on-time liftoff at 6:21:22 a.m., prospective shuttle watchers should start to concentrate on the south-southeast horizon at 6:28:30 a.m. EDT. The Sun will be 2.3-degrees below the horizon, so twilight conditions will be quite similar to September 1991. Sunrise will come about five minutes later.
Shuttle Discovery will appear to rapidly streak eastward, and will appear about 7.5-degrees above the southeast horizon at the scheduled moment of MECO (6:29:43 a.m.). I expect Discovery to appear between magnitude -2 to -4 or somewhere between the brightness of the planets Jupiter and Venus. Since the amount of reflected sunlight will be diminishing as the shuttle races across the sky toward the east, it might appear to rapidly fade from view around the time of MECO. While the shuttle should initially be readily visible to the unaided eye, binoculars will certainly aid in keeping the shuttle in view for a longer interval of time.
Good Luck and clear skies!