Starship Asterisk*

Rocket Streak and Star Trails

Explanation: Fixed to a tripod and looking east across the Kennedy Space Center's Turn Basin, a camera captured these star trails as a series of short exposures over a three hour period on the evening of January 23rd. Positioned just a few miles from Space Launch Complex 41 at Cape Canaveral Air Force Station, it also captured a spectacular night launch of an Atlas V rocket carrying NASA's Tracking and Data Relay Satellite TDRS-L. Creating the trails, the apparent motion of the stars through the sky is just a reflection of the daily rotation of planet Earth on its axis. But that rotation is also the reason the rocket streak follows a path arcing east across the Atlantic. Launching toward the east, in the direction of Earth's rotation, adds the rotation velocity to the rocket and reduces the fuel needed to reach orbit. A little ironically, TDRS-L is destined for a geostationary orbit. From there, 36,000 kilometers or so above the equator, its orbital period will match Earth's rotation and the satellite will hang motionless in planet Earth's sky.

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That's a beauty. The rocket just seems to touch the equator as it fades from view.

Edit: the star trails look closer to two hours long.

I always enjoy going back to Canaveral even though it's only through a spectacular photo'. Your last line should have the word "apparently" before "motionless". I assert the satellite will have considerable inertial velocity.

Are geostationary satellites always facing with one side toward Earth? I imagine them that way, but I guess it would depend on the satellite's purpose. If they are always facing one direction is it by tidal locking or do they have to maintain attitude with thrusters?

I understand some satellites take advantage of tidal locking:
http://en.wikipedia.org/wiki/Gravity-gr ... bilization

"And it's OUT OF THE BALL PARK!!!l....HOME RUN...in the top of the Fifth Inning...."

Interesting shot...

:---[===] *

What are the other streaks? There is one from bottom middle moving up and to the right, and another (the same one?) from there to the right. An airplane would have more 'arc-ish' movement? Satellite(s)?
To me it also looks like the right side stars are arcing toward the south too.
Maybe I'm just having a bad morning.....

It is a fantastic picture.

Geosynchronous satellites use a combination of thrusters and reaction wheels to keep one side pointed toward the earth. Gravity-gradient stabilization only works in low earth orbit; the gradient is too weak at geosynch even for the largest (current) satellites,

George wrote:What are the other streaks? There is one from bottom middle moving up and to the right, and another (the same one?) from there to the right. An airplane would have more 'arc-ish' movement? Satellite(s)?
To me it also looks like the right side stars are arcing toward the south too.
Maybe I'm just having a bad morning.....

It is a fantastic picture.

This picture shows some of the Southern hemisphere stars as well as some of the Northern hemisphere. The Northern stars appear to rotate about the North Pole, and the Southern stars appear to rotate about the South Pole.

Doesn't anyone proofread these? I'm always finding typos, such as this one:

it's orbital period

I'm happy to offer my copy-editing services if you are hiring .

kingernie wrote:I always enjoy going back to Canaveral even though it's only through a spectacular photo'. Your last line should have the word "apparently" before "motionless". I assert the satellite will have considerable inertial velocity.

The caption doesn't say it will be motionless. It says it will hang motionless in the sky. That is perfectly correct, without modification.

geckzilla wrote:Are geostationary satellites always facing with one side toward Earth? I imagine them that way, but I guess it would depend on the satellite's purpose. If they are always facing one direction is it by tidal locking or do they have to maintain attitude with thrusters?

They don't need to face Earth, or maintain a fixed orientation. But most do, simply because most have purposes that require it, such as communications relays or some sort of Earth imaging. Some are steerable- that is, they use reaction wheels or some other technology to modify where they are pointing, as opposed to pointing instruments themselves.

Chris Peterson wrote:

geckzilla wrote:
Are geostationary satellites always facing with one side toward Earth? I imagine them that way, but I guess it would depend on the satellite's purpose. If they are always facing one direction is it by tidal locking or do they have to maintain attitude with thrusters?

They don't need to face Earth, or maintain a fixed orientation. But most do, simply because most have purposes that require it, such as communications relays or some sort of Earth imaging. Some are steerable- that is, they use reaction wheels or some other technology to modify where they are pointing, as opposed to pointing instruments themselves.

Some space observatories are at least geosynchronous
...perhaps in order to regularly download data to the same ground station:

http://en.wikipedia.org/wiki/Infrared_Space_Observatory wrote:
<<The Infrared Space Observatory (ISO) was a space telescope for infrared light designed and operated by the European Space Agency (ESA), in cooperation with ISAS (part of JAXA as of 2003) and NASA. The ISO was designed to study infrared light at wavelengths of 2.5 to 240 micrometres. The Euro 480.1 million ISO was launched on 17 November 1995 from the ELA-2 launch pad at the Guiana Space Centre near Kourou in French Guiana. The launch vehicle, an Ariane 44P rocket, placed ISO successfully into a highly elliptical geocentric orbit, completing one revolution around the Earth every 24 hours.>>

I really like that effect where the northerly stars appear to draw circles around one point and the southerly stars appear to draw circles around another point. Is there some image (perhaps a previous APOD) that shows this the best it can be shown? Would you want to stand at the equator to take such an image?

MarkBour wrote:I really like that effect where the northerly stars appear to draw circles around one point and the southerly stars appear to draw circles around another point. Is there some image (perhaps a previous APOD) that shows this the best it can be shown? Would you want to stand at the equator to take such an image?

There have been a number of APOD star trail images that capture this effect (including a very extreme example). Use the search feature on the APOD page and you can find more.

The only advantage to taking such an image from the equator is that the trails will be symmetric with respect to the horizon, which might be aesthetically interesting. But otherwise, the effect looks the same regardless of your latitude.

Still don't see a response to the "What the other streaks are?" Meteors?

Spitfire Freehouse wrote:Still don't see a response to the "What the other streaks are?" Meteors?

Airplanes. Meteors are short streaks. Planes sweep across the entire sky and blink their lights on and off. Satellites don't blink as far as I know. They do more of a shimmering thing if the sunlight glints a certain way off them. Sometimes Iridium satellites flash in a way which resembles a meteor streak.

geckzilla wrote:

Spitfire Freehouse wrote:Still don't see a response to the "What the other streaks are?" Meteors?

Airplanes. Meteors are short streaks. Planes sweep across the entire sky and blink their lights on and off. Satellites don't blink as far as I know. They do more of a shimmering thing if the sunlight glints a certain way off them. Sometimes Iridium satellites flash in a way which resembles a meteor streak.

Yes, they're certainly airplanes. A few satellites do "blink" though. These are objects that are rotating or tumbling and and show a periodic variation in brightness- sometimes enough to look like they're blinking.


Source

Yes everyone they are airplanes, I had no intention of spending more time in post to analyze every shot to remove the aircraft streaks. Actually, if you look towards the NE horizon (left) you'll also notice some odd red & green trails - that's from the USAF Pave Hawks of the 920th Rescue Wing from local Patrick AFB clearing the range for the launch.

- Mike Killian

Chris Peterson wrote:

MarkBour wrote:I really like that effect where the northerly stars appear to draw circles around one point and the southerly stars appear to draw circles around another point. Is there some image (perhaps a previous APOD) that shows this the best it can be shown? Would you want to stand at the equator to take such an image?

There have been a number of APOD star trail images that capture this effect (including a very extreme example). Use the search feature on the APOD page and you can find more.

The only advantage to taking such an image from the equator is that the trails will be symmetric with respect to the horizon, which might be aesthetically interesting. But otherwise, the effect looks the same regardless of your latitude.

You can also determine the latitude of the photographer by the angle the equatorial star trails make with the horizon. Looking eastward from the Earth's equator, the stars appear to rise vertically. From the N. Hemisphere, they appear to rise with a southward component, and from the S. Hemisphere they appear to rise with a northward component. The angle the equatorial star trails make with the horizon is 90 degrees minus your latitude.

Attached is a panoramic simulation of what the sky will look like early this evening from the equator, it is a stereographic projection showing the celestial sphere's grid coordinates of Right Ascension and Declination. Note that from the equator, the North and South celestial poles coincide with the North and South cardinal points on the horizon. The stars trails all follow lines of constant Declination (angle from celestial equator), which are indicated on the grid by the concentric arcs about each pole (skewed slightly because of the projection method).

Nitpicker wrote:You can also determine the latitude of the photographer by the angle the equatorial star trails make with the horizon.

However, unless the intersection of the equator and the horizon is on the optical axis of the camera, determining the actual angle can be tricky. You need to understand the optical properties of the lens.

Chris Peterson wrote:

Nitpicker wrote:You can also determine the latitude of the photographer by the angle the equatorial star trails make with the horizon.

However, unless the intersection of the equator and the horizon is on the optical axis of the camera, determining the actual angle can be tricky. You need to understand the optical properties of the lens.

True, I wouldn't bet the farm on this method. Merely for amusement, I just dusted off my old protractor and got an answer for this APOD, about four degrees closer to the equator than Cape Canaveral, or ~500km too far South, but still closer than Cuba.

What a great shot/compilation.

There two other lines of light which I didn't see referenced. They are both linear, which is interesting as the other light trails are curved, and seem to converge at a point directly above and halfway up the rocket's trajectory. Because they are straight, they have to be stationary with respect to the camera position. In short, what are they? Any thoughts? I am missing the obvious?

Rob ME wrote:There two other lines of light which I didn't see referenced. They are both linear, which is interesting as the other light trails are curved, and seem to converge at a point directly above and halfway up the rocket's trajectory. Because they are straight, they have to be stationary with respect to the camera position. In short, what are they? Any thoughts? I am missing the obvious?

Those are the airplane tracks under previous discussion. Not sure why you think then represent stationary objects. If that were the case, they'd be seen as points.

Chris Peterson wrote:

Rob ME wrote:There two other lines of light which I didn't see referenced. They are both linear, which is interesting as the other light trails are curved, and seem to converge at a point directly above and halfway up the rocket's trajectory. Because they are straight, they have to be stationary with respect to the camera position. In short, what are they? Any thoughts? I am missing the obvious?

Those are the airplane tracks under previous discussion. Not sure why you think then represent stationary objects. If that were the case, they'd be seen as points.

Chris, Those are not airplane traces, they can't be. 1st of all, the photo-compilation took place over 3 hours, an airplane would not still be in sight in that time. 2nd, they are perfectly straight - an airplane would trace a curved line that would cross a portion of the photo, not end/originate from a single point. 3rd they start at the horizon and continue straight at what would have to be an exceedingly high trajectory, ending at a single point in the middle of the sky. Not airplanes, can't be. There is what appears to be an airplane taking off just above the horizon on the left hand side - very different from what we see with those 2 lines . I guess it must be meteors. I thought it might be laser beacon or something associated with the launch so my reference to stationary was not a stationary object but a stationery source.