Astrophotography
Astrophotography
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You can follow my photographic adventures on this Instagram feed.
My former backyard in Los Altos Hills, CA (Oct. 2020).
As an astronomer, I am both a professional and an amateur.
While working at Stanford University, I lived in the foothills of the Santa Cruz Mountains, where the light pollution is surprisingly low, at least considering the proximity to Silicon Valley. With the naked eye and only a few seconds of dark adaptation, it was generally possible to see objects like the Lagoon Nebula and the Andromeda Galaxy. (With the naked eye, such objects look like faint smudges, but it's rather wonderful that they are visible at all.) The Milky Way was often visible as a light band running across the sky. On the Bortle scale, it was probably between class 4 and 5.
Unless otherwise indicated, assume that each photograph below was captured in my backyard in Los Altos Hills, CA. Within a 2-hour driving radius, there are some significantly darker sites, but I often found it cumbersome to drag all of my equipment with me.
For astrophotography, I mostly use a Schmidt-Cassegrain telescope with an aperture diameter of 8 in, and I couple to a DSLR camera. Occasionally, I bypass the telescope and use the camera more conventionally with nothing more than a long-focus lens (typically with a focal length of 180 mm but sometimes, for wide-angle shots, 55 mm).
Magnification is less useful in astrophotography than you might initially expect. There are many galaxies and nebulae that are quite large -- in some cases, larger even (in apparent size) than the Moon; but they are very faint. So you often don't need an especially powerful telescope. What is instead necessary is a long photographic exposure, and that is complicated mainly (but not only) by the fact that the Earth rotates, which tends to blur the images. Effectively, we are photographing a moving target. So quite a lot of effort in astrophotography is devoted to keeping up with the rotation and making sure the telescope and camera stay pointed very precisely for several minutes at a time. Typically, I capture exposures of 1-2 minutes each; then I align and stack the best images in post-processing to achieve a much longer effective exposure time.
The game is very different for lunar and planetary photography, for which the targets are bright enough to be able to rely on sub-second exposures. In these cases, however, we demand much finer resolution, and our enemy becomes the distortion created by atmospheric turbulence. A popular technique is lucky imaging, for which the exposures are short but numerous; the images with the least amount of distortion are cherry-picked and then stacked to produce a final image.
Much of my astrophotography occurred during the COVID-19 pandemic. (Did that really happen?) This gallery is perhaps the silver lining of that era for me.
Captured on Jun. 5, 2021 with a 45-minute exposure (18x2.5). The galaxy can be found near the handle of the Big Dipper in the constellation Ursa Major. It lies at a distance of 21 million light years and has nearly twice the diameter of the Milky Way. The spiral arms have been distorted through gravitational interactions with smaller neighboring galaxies.
Captured on Jun. 5, 2021 with a 22.5-minute exposure (9x2.5). This is a star-forming region about 4000 light years away in the constellation Sagittarius. It is bright enough and large enough to be visible with the naked eye from my neighborhood; it appears as a faint, ghostly cloud. The colors emerge only with a long photographic exposure. The red indicates the presence of hot, ionized hydrogen gas. Some of the darker regions consist of dense dust clouds which are opaque and hiding newly born stars.
Captured on Dec. 22, 2020. The mountains in the center of the image are called Montes Alpes (The Alps). The streak rising up toward the left is called the Alpine Valley. These mountains lie on the boundary between Mare Frigoris, the relatively smooth area to the left of center, and Mare Imbrium, the relatively smooth area to the right.
A close-up view of Montes Appeninus, home to the tallest mountain on the Moon, Mons Huygens, which reaches a height of 5.5 km. That would be a respectable peak height on the Earth, but it's even more impressive when you consider that the Moon is nearly 4 times smaller in radius. Whereas Everest reaches a height of 8.8 km, scaling Mons Huygens to an Earth-sized planetary body would produce a summit altitude of 20 km! Mons Huygens is to the lower right of center in a poorly illuminated spot that is difficult to describe in words... In the meantime, the astronauts of Apollo 15 landed in a kind of valley between the second and fifth tallest mountains, which are unfortunately named Mons Hadley (4.5 km) and Mons Hadley Delta (3.9 km), respectively. Mons Hadley is just below the bright white spot to the upper left of center, and Mons Hadley Delta is to the lower right of it across the little valley where the astronauts landed. I have also brought out some color on this image. Notice especially the blue and red regions.
A close-up view of Ptolemaeus, Alphonsus and Arzachel, the three horizontal craters named left to right.
Lunar mountain ranges
Lunar mountain ranges
Captured on Dec. 22, 2020. The mountain range to the lower right is called Montes Appeninus. The smaller range in the center of the image is called the Montes Caucasus. To the lower left from the Caucasus is Montes Alpes. The smooth region at the top of the image and slightly to the right is Mare Serenitatis, below it Mare Imbrium, and to the left Mare Frigoris. I have brought out some of the color. It is not fake, but I have exaggerated it.
Captured on Dec. 22, 2020. The chain of three craters in the center of the image are, from left to right, Ptolemaeus, Alphonsus and Arzachel.
Captured on Dec. 22, 2020. You may notice some coloration, especially blue hues, which indicate the presence of titanium. These colors are real, though I artificially enhanced them in post-processing. Otherwise, you'd just see grey, grey and more grey...
Captured on Dec. 21, 2020 at Byrne Preserve, which is down the street from where I used to live in Los Altos Hills. My backyard had a hill and trees on the western side, which is where the planets would appear, so I couldn't stay there. This was the closest approach of Jupiter and Saturn since 1623. There is no real astrophysical significance to such conjunctions, but it is an intriguing spectacle to see two bright starlike objects so close to each other in the sky. Annoyingly, it was cloudy, and planets, though bright, are small and difficult to photograph. So I decided not to attempt a photo through a telescope. Instead, I just used my largest camera lens and took a conventional photograph. Jupiter is on the left, and Saturn is on the right. If you look closely, you can see that Jupiter forms a line with three smaller starlike specks. The line runs from lower right to upper left. Those little specks are three of the moons of Jupiter.
Captured on Dec. 19, 2020.
Captured on Dec. 18, 2020 with a 32-minute (16x2) effective exposure. This is a complex of several nebulae located just north of the Orion Nebula. The red areas indicate the presence of ionized hydrogen (HII), and the blue areas are reflecting the light from hot, young stars. If you use your imagination, you can see a "running man" in the dark red region near the center of the image.
Captured on Dec. 18, 2020 with a 25-minute effective exposure. This is a region of intense star formation and is relatively nearby at a distance of about 1000 light years. You can see the nebula with the naked eye as a cloudiness around the middle star in the sword of Orion. The colors are too faint to be seen by eye, even with a telescope, but they emerge readily in a long photographic exposure. In post-processing, I adjusted the levels to make both the faint and bright areas visible simultaneously, but this is otherwise what it really looks like.
Captured on Dec. 18, 2020. The quasi-circular dark smooth area is called Mare Crisium. It is actually visible with the naked eye as a small dark spot; the smoothness of the surface was created by lava flows.
Captured on Dec. 18, 2020.
Messier 34 (M34) open cluster
Messier 34 (M34) open cluster
Captured on Dec. 15, 2020 with a 24-minute total exposure. This is a group of relatively young stars that all formed from the same cloud of material.
Captured on Dec. 10, 2020. Orion's belt (three bright stars at left) with the Horsehead Nebula (B33) at bottom (dark red) and Orion's sword (right) defined largely by the Orion Nebula (M42) from a 100x15-second exposure. In fact, Orion's sword consists of several objects. Starting from the left of Orion's sword, there is an open cluster (NGC1981), a medium-sized nebula (NGC1977), a tiny nebula (M43) that is difficult to distinguish in this image, the Great Nebula in Orion (M42) and a smaller nebula (NGC1980). You'll need a star map to be able to distinguish them all.
Captured on Dec. 10, 2020 with a 63x15-second exposure. The Pleiades are easily visible in the winter sky without a telescope. In a long exposure, the blue nebulae emerge, which are dust clouds reflecting the starlight from the Pleiades.
Captured on Dec. 10, 2020 with a 40x15-second exposure (Dec. 10, 2020). There are two small satellite galaxies visible in the image: M32 looks like a bright star to the left of Andromeda's center, and M110 is to the lower right. These two "dwarf galaxies" orbit Andromeda. The image covers a relatively large area.; it would take about ten full Moons to block out the Andromeda Galaxy.
Captured on Nov. 20, 2020 with an 11x2-minute exposure in my backyard (Nov. 20, 2020). On a very clear night, you can just barely make out this galaxy as a faint smudge with the naked eye, which is impressive when you consider that it is nearly three million light years distant.
Captured on Nov. 15, 2020 with an 11x2-minute exposure. It's not an optical illusion: these two clusters in the constellation Perseus are actually near each other, both more than 7000 light years from Earth.
Captured on Oct. 27, 2020. Planets are very difficult to photograph. Although bright, they are small and vulnerable to the turbulence of the Earth's atmosphere. You can just about see an ice cap at the bottom and some surface features.
Captured on Oct. 27, 2020. Mare Humorum is the large smooth area left of center, and Gassendi is the crater on its rim, just above the center of the image.
Captured on Oct. 27, 2020. The elongated crater at left is called Schiller, named not after the poet but after the German astronomer of the early 17th century. (Julius Schiller is known mainly for a star atlas that renamed the constellations after Biblical rather than Greco-Roman pagan figures.) As far as I can tell, the formation of Schiller is not entirely settled, but some people think an asteroid may have impacted at an oblique angle. It also may have broken into pieces before impact and created multiple overlapping craters.
Captured on Oct. 27, 2020. Sinus Iridum, the Bay of Rainbows, is the semi-circle just left of the image center. What happened here is that an impact crater was formed on the rim of the much larger Imbrium Basin, which stretches toward the bottom left. Half of the crater collapsed into the basin, and then the whole thing filled with lava to create the mostly smooth surface we see today.
Captured on Oct. 27, 2020 with lucky-image stacking of frames from an 85-second video. You are looking at Copernicus crater near the center and Tycho on the right.
Captured on Oct. 19, 2020 with a 4x2-minute exposure.
Captured on Oct. 17, 2020 with a 6x1-minute exposure. This is a region of the constellation Cygnus. The very bright star in the center is called Sadr. The surrounding nebulae are actually thousands of light years behind it.
Captured on Oct. 17, 2020 with a 6x1-minute exposure. The nebula is so-named because it vaguely resembles the continent if you orient north to the right. The redness indicates that this is a cloud of ionized hydrogen (HII). The region of sky shown in this image is quite large. You could comfortably fit ten full Moons in this area. Despite its size, the North America Nebula is notoriously difficult to see by eye, even with a telescope, but it shows up pretty quickly in a photographic exposure. The very bright star at bottom center is Deneb. The lower left portion of the nebula is sometimes referred to as the Pelican Nebula; don't ask me why.
Captured on Oct. 13, 2020 with a 3-minute exposure. You are looking at gas that was blown off of a dying star. The colors are real.
Captured on Aug. 12, 2020 with a 180-second exposure. This is one of the largest globular clusters in the sky and was discovered by Edmund Halley (of comet fame) in 1714.
Captured on Aug. 12, 2020 with a 240-second exposure. Although the object was discovered in 1773 by Charles Messier, who gives his name to the M in, e.g., M51, the spiral structure was not resolved until 1845 by Lord Rosse. It was the first object recognized to have the spiral structure we now associate with many (but not all) galaxies. At that time, though, no one knew what a galaxy was. They called these objects "spiral nebulae" until as recently as the 1920s. The smaller splotch to the right is a dwarf galaxy (NGC 5195) that is interacting with the Whirlpool Galaxy.
Captured on Aug. 12, 2020 with a 240-second exposure. This is a star-forming region. The three columns rising toward the upper left are sometimes called the Pillars of Creation, and you can find amazing images of them from the Hubble Space Telescope. The red color is real and indicates the presence of hydrogen (H-alpha line). When viewed directly by eye through a telescope, the Eagle Nebula is impressively unimpressive. You just barely see a faint cloudiness and no color at all. The structure and color emerge only in long-exposure photographs.
Captured on Aug. 10, 2020 with a 90-second exposure. This is an open cluster in the constellation Scutum. It gets its name from the V-shape that is supposedly reminiscent of a flock of flying ducks.
Captured on Aug. 7, 2020 with a 210-second exposure. This is a star-forming region in the constellation Sagittarius. It's quite large. On a dark night, you can see it with the naked eye as a faint little cloud. Your eyes aren't sensitive enough to detect the colors, but a camera will easily bring them out in an exposure of about 30 seconds. The colors are real. The only significant post-processing is a dehaze to remove background sky glow.
Captured on Aug. 7, 2020 with a 90-second exposure. Unfortunately, M22 doesn't have a cute name and is only referred to by its catalog number. It's in the constellation Sagittarius, which is prominent in the southern sky at this time of year. There are lots of globular clusters in that part of the sky, because it's where the center of the Milky Way Galaxy is.
Captured on Jul. 22, 2020. In the late days of this comet's appearance, it turned greenish. I caught it between some tree branches just before it set.
Captured on Jul. 18, 2020 with a 1-minute exposure. The name "trifid" is supposed to mean that it is divided into three parts, because the red cloud is very roughly cut in three by the dark veins.
Captured on Jul. 14, 2020 from Byrne Preserve, which was near my house in Los Altos Hills and allowed for an unobscured view of the comet after sunset but before it descended below the horizon. I brought only a camera, since I didn't want to deal with the hassle of all the telescope equipment. Serendipitously, the comet was in the same direction as San Francisco, which comes out quite clearly even when magnified only with a camera lens rather than a telescope. You can see the financial district and the Bay Bridge in the lower right of the image. I played a lot of games in post-processing to bring out both the faint comet and the bright city lights, so the result is somewhat surreal.
Captured on Jul. 10, 2020. I woke up at 3:30 AM to photograph the comet NEOWISE (C/2020 F3) from my front porch in Los Altos Hills, CA. The Moon was at third quarter, which created quite a lot of sky glow. I fumbled around for a while with a tripod that had one unreliable leg that kept occasionally collapsing. Then I was amusingly confused by the fact that I was looking through the camera eyepiece over the top of my glasses, which I don't normally wear for any activities other than brushing my teeth. So I didn't quite catch the comet until maybe 30 minutes after it rose. I took this photo with a 180-mm lens and an exposure time of 2 s. You can see a hint of a bifurcation in the tail.
Captured on Jul. 1, 2020. Gassendi crater is in the middle with Mare Humorum (the smooth area) on the left. Gassendi is about 100 km in diameter. This image was made by stacking the best frames from a one-minute video. For stacking, I use freeware called AutoStakkert!. Then I sharpen the image in Photoshop. The idea is to take many images through video and then filter the majority of them, since they are mostly ruined by atmospheric turbulence. You take the remaining few that are decently sharp, align them and then stack them. The stacked image is better than any individual frame of the video. You can start to resolve rilles inside Gassendi as well as some tinier craters.
Captured on Jul. 1, 2020. Sinus Iridum is the semi-circle on the edge of Mare Imbrium, the smooth area on the left. This image was made by stacking the best frames from a ~1-minute video.
Captured Jun. 30, 2020. This photo is a stack of 11 targeting a crater called Clavius, which is the one near the image center with an arc of five craters inside it. When I captured these images, I was less interested in Clavius than in the techniques required to create photographs with finer angular resolution. I took 11 images and then stacked them to sharpen the image a bit and to average away atmospheric turbulence.
Captured on Jun. 28, 2020. This is a double star that appears as a single star with the naked eye. The colors only become apparent when the two are resolved and separated, and the colors are real. Stars are bright, so you don't need much exposure time for a photo like this. Through a telescope, the stars look basically like this (but with some adorable twinkling).
Captured on Jun. 26, 2020 with a 30-second exposure. This is a globular cluster in the constellation Serpens.
Captured on Aug. 31, 2019 at Pinnacles National Park. At Pinnacles, the sky is much darker than in my neighborhood in Los Altos Hills; Pinnacles probably ranks between class 2 and 3 on the Bortle scale. There is only a very faint sky glow from distant urbanized areas. This photo was taken with a 10-sec. exposure, and it brings out some of the red colors. The Milky Way appears colorless to us (because it's generally quite faint), but much of the structure shown in this photo can be discerned at Pinnacles with the naked eye.
Captured Jul. 13, 2019 at Montebello Open Space Preserve. I used to have an after-hours permit for Montebello, which is located just 20 minutes uphill from my former house in Los Altos Hills. The sky is a little darker and less turbulent up there. This lunar photograph is approximately centered on the crater Tycho (just below the center of the image), which is a relative new arrival and whose ejecta can be seen as radial streaks covering a large area on the lunar surface. The colors have been enhanced in order to better discern surface features. The Moon is actually close to perfectly grey.
Captured Jul. 10, 2019. Photographing planets is difficult, simply because they are small. They are bright, which is helpful, but we demand much finer resolution than for deep-sky objects like galaxies and nebulae. Seeing features by eye through a telescope is actually quite easy when it comes to bright planets like Jupiter. Looking through the telescope, you can easily see the bands and the Great Red Spot. While you're looking, however, the turbulence in the air is perturbing the image. Your brain is sophisticated enough to filter away those disturbances, but most cameras, unfortunately, are not.
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