Astrophotography Blog: May 2014

Wednesday, May 28, 2014

Removing Light pollution Astrophotography Urban Astronomy

The moon and the stars no longer come to the farm. The farmer has exchanged his birthright in them for the wattage of his all-night sun. His children will never know the blessed dark of night.

— Leslie Peltier in his autobiography

Urban night skies are rarely dark. Streetlights, billboards, and city glow create a thick orange haze that hides the stars and washes out the beauty of the night sky. Yet even from light-polluted locations, it’s possible to recover the natural tones of the night sky — with the right technique and patience.

Golden Bridge, Los Angeles – Before and After

Even in one of the brightest cities on Earth, the hidden beauty of the night sky can still be revealed. This composite image of the Golden Bridge in Los Angeles shows two worlds in one frame — the left half captures the harsh glow of urban light pollution, while the right half reveals what the same scene looks like after careful digital correction.

Split image of Golden Bridge in Los Angeles showing before-and-after light pollution removal — left side with heavy orange glow, right side with clear starry sky.

Light pollution Astrophotography Urban Astronomy

The difference is striking. On the left, the orange sky glow typical of large cities drowns out all but the brightest stars. On the right, subtle gradient removal and color correction bring back the natural depth of the night sky. No Milky Way is visible here — just the quiet, real sky above Los Angeles as it would appear without the interference of artificial light.

Photoshop Processing Steps for Light Pollution Removal

The following steps describe exactly how I processed the Golden Bridge image to reduce light pollution and restore the natural night sky appearance. This simple method can be repeated for other urban nightscapes.

Step1: Select the Layers panel and then duplicate the layer

Step 2: Filter -> Noise -> Median… (about 50 px)
Step 3: Filter-> Blue -> Gaussian Blue… (about 30px)
Step 4: Select original layer
Step 5: Image -> Apply image (Blending: Subtract; Offset: 40)
Step 6: Delete the duplicate layer

In this photo, the digital cleanup was done using gradient-removal layers in Photoshop and subtle color balance adjustments. The goal wasn’t to create an unrealistic night sky, but to recover the true dynamic range that excessive lighting had hidden. The restored image shows a faint trace of the starry night rising over the bridge — a reminder that the night is never completely lost to light.

See also for example video in my other post: Comet 103P/Hartley 2 from New York City

Note, that Astronomy Tools has more sophisticated methods to remove light pollution, or you can do some variations of such methods (it depends from size of you original image). You also can apply it only for part of original image.

The other way to remove light pollution is using multiple images, see for example my other post: M42 Orion Nebula using iOptron SkyTracker in NYC

Why Light Pollution Happens

Light pollution occurs when artificial lights scatter in the atmosphere and overpower natural celestial light. Sodium and LED streetlights create broad orange or blue glows that spread for tens of kilometers, reducing contrast in photos and drowning out faint stars. For astrophotographers, it’s the biggest obstacle between the camera and the universe.

Preserving the Night Sky

As urban areas expand, the number of places with truly dark skies continues to shrink. Each successful image that recovers the stars from behind the glow is not just an artistic act — it’s also a message about preservation. Protecting our night environment helps both wildlife and human curiosity. After all, the sky is our oldest map of time.

Final Thoughts

Removing light pollution is part art, part science, and part patience. Whether working from a city balcony or a remote desert, every photographer can uncover the universe hidden behind the glow. The Golden Bridge image proves that even in the heart of Los Angeles, the stars are still there — waiting to be revealed.

Friday, May 23, 2014

Golden Gate Bridge Astrophotography California San Francisco

Golden Gate Bridge - Astrophotography, May 2014

Golden Gate Bridge astrophotography under night sky, long-exposure image with reduced light pollution, San Francisco urban nightscape

Golden Gate Bridge Astrophotography California San Francisco

Golden Gate Bridge at night San Francisco California

Tuesday, May 13, 2014

Astronomy Green Laser Pointer

An astronomy green laser pointer is a very useful tool for pointing out stars and constellations during night sky lectures and public stargazing events. Unlike a normal flashlight, the beam of a green laser becomes visible in the atmosphere and appears as a bright line extending into the sky.

This makes it easy for astronomers and astrophotographers to show exactly where a star, planet, or constellation is located. During group observations it helps beginners quickly identify objects such as the Big Dipper, Cassiopeia, or Polaris.

The green wavelength (~532 nm) is especially effective because the human eye is most sensitive to green light. For this reason green laser pointers are widely used in astronomy education, planetarium demonstrations, and astrophotography tutorials.

Most astronomy laser pointers used for stargazing are low-power green lasers (typically around 5 mW). This level is bright enough for the beam to be visible in the night sky while still being suitable for educational demonstrations when used responsibly. Many amateur astronomers use simple handheld laser pointers powered by AAA batteries during public observing sessions.

Below are several examples of green laser pointers used for astronomy. The photos show both the handheld laser pointer device and the visible green beam used to point at stars and constellations during stargazing and astrophotography sessions.

Astronomy green laser pointer pointing to the Big Dipper constellation

Astronomy green laser pointer pointing to the Big Dipper (Ursa Major)

In the first image the green laser beam is pointing toward the Big Dipper (Ursa Major), one of the easiest constellations to recognize in the northern sky.

Green laser beam reflected from backyard astronomy observing table

Green laser beam reflected from my backyard astronomy observing table

In this photo the green laser beam is reflected from the astronomy table in my backyard observing setup. This is the table where I usually keep my laptop, batteries, and other equipment during astrophotography sessions.

The following photos show the green laser pointer itself placed on the observing table. These images were taken during daytime so the details of the handheld astronomy laser pointer can be seen more clearly.

Green laser pointer on astronomy observing table photographed during daytime

Green laser pointer on the astronomy observing table photographed during daytime to show the device used for stargazing

Close-up of handheld green laser pointer used for astronomy photographed in daylight

Close-up daytime view of a handheld green laser pointer used for astronomy observations

Green laser pointer astrophotography pointing to Cassiopeia constellation Canon 60Da

Laser Pointer astrophotography Canon 60Da Cassiopeia constellation

In my case I use a simple handheld green laser pointer powered by AAA batteries. It is an inexpensive device (about $15) but works very well for astronomy demonstrations and small stargazing groups.

Safety note: Green laser pointers should always be used responsibly. Never point a laser toward aircraft, vehicles, or people. Many astronomy clubs use low-power lasers (typically 5 mW or less) and only activate them briefly when explaining constellations during stargazing events.

A green laser pointer is one of the most useful tools for teaching and exploring the night sky. During public stargazing events it helps observers quickly identify stars and constellations by visually tracing patterns in the sky. Used responsibly, a green astronomy laser pointer becomes an excellent aid for learning how to locate familiar objects such as the Big Dipper, Cassiopeia, and the North Star (Polaris), and it can also be helpful during astrophotography sessions when explaining the structure of the night sky.

If you use a green laser pointer during stargazing or astronomy observations, feel free to share your experience or tips in the comments below.