Astrophotography in San Francisco

From the Space Tourism Guide:

Can You See the Milky Way in the Bay Area? Unfortunately, it is very difficult to see the Milky Way in San Francisco. Between the foggy weather and the light pollution from 7 million people, you can imagine that the faint light of our galaxy is lost to view.

But C. Roy Yokingco argues:

Some people say the Milky Way cannot be photographed within 50 miles of a major metropolitan area. Well, this photo of the Milky Way was captured 12 linear miles south of downtown San Francisco, California.

Be sure to click through to see the photo.

Quora tells us:

Light pollution is not usually an obstacle because you can always subtract out the pollution digitally! […] Light pollution is not blocking the light of galaxy–it is merely being added to the light of the galaxy.

Light pollution does limit the length of time that you can expose a single frame. The greater the light pollution, the shorter the time before you saturate the camera (i.e., fill the frame with all white). Obviously, you can’t retrieve an image from a frame that is fully white.

The poster went on to recommend using multiple exposures to work around that limit, but didn’t expand on how to combine them effectively. The poster also didn’t expand on how to subtract out the pollution.

Filtering light pollution

Sky and Telescope magazine suggests removing light pollution by setting a custom levels black point in your image editor of choice.

The PureNight filter claims to solve some of the frustrations of light pollution from ever reaching your sensor:

PureNight is made of a special type of glass called didymium glass. PureNight mounts in front of your camera lens with a standard square filter holder (sold separately).

PureNight greatly reduces transmission of yellow and orange light in the 575nm to 600nm wavelengths, the same wavelength of light that is emitted by high pressure sodium vapor lamps. Sodium vapor lamps are most commonly used on street lights and industrial lighting fixtures and so they are one of the most prevalent sources of light pollution for astrophotography.

There are other filters, of course, and B&H Photo tested nine of them.

Where in SF to look

The Space Tourism Guide offers this list of places to go stargazing around the SF Bay, including this mention of Twin Peaks:

Twin Peaks is hit or miss for stargazing: you might get lucky and be above enough light pollution for good straight-up views, or Karl the Fog may roll in and obscure everything. Even if it’s not clear enough for stars, you’ll still have amazing views of all of San Francisco.

More generally, they advise:

If you’re in San Francisco and want to see as much of the night sky as possible, try and get to the Pacific Coast, where large parks, beaches, and open land help make this possible.

The guide names a number of other places to gaze upon the stars, as well as this advice about when to go looking:

While some of the best night sky views for San Francisco should be in the summer months, the weather rarely cooperates. Most of the summer, the upper part of the Bay Area is blanketed in the famous fog; the lower part of the Bay (San Jose) is swelteringly hot.

San Francisco is known for having an ‘Indian summer’ with great weather in September and October. Therefore, the best time of year to go stargazing in San Francisco is in late August to early October. If the skies are clear, there are great celestial objects to look for, including the Draconids Meteor Shower. In particular, if you’re seeking a view of the Milky Way, September is the best chance you’ll have.


The Quora post above offers this tip for estimating light pollution and star visibility:

One heuristic for measuring light pollution is to count the number of stars that you can see with the naked eye in the Little Dipper (excluding Polaris). The number of stars that you can see is roughly equivalent to the faintest magnitude visible in your skies.

Previously here at MaisonBisson: notes on observing the milky way, which features this photo CC-BY-ND by Lukas Schlagenhauf. The photo, also used atop this post, wasn’t taken in SF, but in the Swiss Alps surrounded by similarly heavy light pollution at lower elevations.