As we transition from summer to fall, two of the most photogenic planets, Jupiter and Saturn, have passed the point of closest approach (opposition) to the Earth for the year. Yet, they still make great targets for planetary astrophotography, especially since they are now high in the sky soon after sunset. As another bonus, photographing these planets does not require traveling to a dark sky site. This kind of astrophotography can be done from our backyards.
Saturn’s rings make it a favorite of astronomers, but Jupiter’s larger apparent size (due to its larger actual size and closer orbit), easily visible cloud bands and cloud swirls, and four bright moons make a more dynamic target for astrophotographers.
On rare occasions, these planets actually come close enough to be photographed together (a conjunction), as they did in late 2020. The composite shot below shows the two planets passing each other (from our viewpoint) over a few days, providing a convenient size comparison. The moons of Jupiter can also be seen in various positions around Jupiter. Our Moon was added to the composite as another size reference. It was not close to the pair during this conjunction.
The photo below is a single shot showing Jupiter and Saturn at their closest approach on December 21, 2020.
The photos above are examples of what can be done with a standard camera equipment (Nikon D850 + 2x teleconverter) coupled to a moderate-sized refractor (mine is a Japanese Borg 100ED, a 100mm diameter, f/6.4). The lower photo was shot with a Canon RP mirror-less camera coupled to the same telescope.
Shooting for Maximum Detail
When trying to shoot detailed shots of the planets, in many respects, planetary astrophotography is very different from most other types of astrophotography. Instead of taking longer and longer exposures, planetary astrophotographers try to take short (video rate) exposures and stack hundreds or thousands together to beat the natural distortions of our atmosphere. High magnification is also used compared to most other types of astrophotography.
To meet these goals, specialized equipment is necessary: a telescope to provide the high magnification is needed to start. Typically, this is a telescope which utilizes mirrors, which are less expensive in large sizes than a refractor. Amateur equipment typically goes up to 14-inch diameter (35 cm) reflecting telescopes. Refractors generally become impractical and too expensive beyond 6-inch (15 cm) diameters.
On the back end, a modern camera capable of shooting video (even a cell phone) can be used, but the tradeoff is loss of detail and dynamic range due to the 8-bit format and compression used in consumer cameras. The best solution is to use an astronomical “video” camera that features high dynamic range, lossless “raw” recording, and fast data transfer, usually to a computer via USB 3. A wide range of popular cameras are made by manufacturers QHY and ZWO in China.
Along with the specialized cameras specialized (but fortunately free) software is used to capture bursts of video. More specialized (and free) software is used to sort, align, and stack the captured frames. To sharpen and remove noise from the resulting stacked image, yet another free program is used to extract the highest possible detail from the image.
- Firecapture:records video bursts to a computer
- Autostakkert: sorts, aligns, and stacks frames
- Registax: wavelet-based sharpening
As mentioned earlier, planetary astrophotography generally requires taking high-speed but short bursts of frames, unlike deep sky astrophotography, which may take frames of a single target throughout multiple nights. The reason for this is that many of the planets are rotating so rapidly that stacking a long burst of frames will smear the final image.
Using Firecapture’s versatile capabilities also makes it easy to schedule regular bursts of frames, process each burst, and then assemble the resulting stacked frames into a time-lapse animation. Jupiter’s easily visible details and moons make the best target for this. In the example below, Jupiter’s moon Io is crossing Jupiter while casting a shadow on Jupiter. In the meantime, on the other side of Jupiter, the Great Red Spot (a permanent storm feature) comes into view.
Regular astrophotography of Jupiter can also yield some rare results. Recently an amateur astronomer was lucky enough to record a flash of light against the disk of Jupiter. This was probably a large meteor, estimated at 20 meters across, exploding in Jupiter’s atmosphere.
In some cases, longer bursts of frames need to be stacked as often amateur astronomers opt to use monochrome cameras with separate red, green, and blue filters for the highest resolution. In this case, three bursts of frames need to be taken sequentially, during which time planetary rotation can be unacceptable. In this case, another specialized program (Winjupos), will map the frames to a 3D model of the planet and stack the frames after “derotating” them to line them up properly.
Other Planetary Targets
Another favorite of planetary astrophotographers is Mars. At the closest approach, many surface details such as dark areas and polar caps are visible, but the instances of close approach (opposition) only occur about every 26 months. The next Mars opposition will be in December 2022. At the moment, Mars is on the far side of the sun relative to the Earth. However, later this year, Mars will become visible in the morning sky. It will be small but will be growing in apparent size as we approach opposition.
The remaining planets (Mercury, Venus, Uranus, and Neptune) have little or no features which show up in typical amateur telescopes, but photographing them all for your “collection” is a nice challenge. The family portrait below shows the planets as photographed over a marathon all-night (sunset to sunrise) session in July 2018.
Back in 2018, the planets were lined up in the sky as shown in the 180-degree panoramic shot below. At the time the panorama was made, Mercury had already set, and Uranus and Neptune had not yet come up in the East.
One thing to note in the planetary family portrait above is that Mars was close to opposition, so it appears very large compared to the other planets. Mercury and Venus show partial illumination phases at various times, appearing “full” when smallest. The range of apparent sizes (in arcseconds) of the planetary disks are:
- Mercury: 4.5” - 13.0”
- Venus: 9.5” - 66.0”
- Mars: 3.4” - 25.1”
- Jupiter: 29.8” - 50.1”
- Saturn: 14.9” - 20.7”
- Uranus: 3.3” - 4.0”
- Neptun: 2.1” - 2.3”
For reference, the Moon and Sun are about ½ degree (1,800 arcseconds) in size.
Planetary Combo Opportunities
Because the planets are always moving against the sky and relative to each other, other photo opportunities to watch for are conjunctions (close apparent approaches to two or more objects) or even occultations (eclipses) of planets by the Moon. Jupiter and its moons also provide photo ops at certain times when the moons are occulted by Jupiter or pass in front of Jupiter, often also casting shadows on Jupiter.
In any case, if you’re looking for challenges in astrophotography, check out the planets.