Uranus
Reaching the Outer Realm of the Planets
Photography of the solar system’s most remote planets, Uranus and Neptune, is difficult, far tougher than for any of the others that orbit closer to the Sun. While each is a relatively large world compared to the Earth, they receive considerably less concentrated sunlight owing to their great distances. Just how far away are we talking here?? As of the date of capture for the image below, Uranus was 157 light-minutes from us. By comparison, the Moon is about 1.5 light seconds away. To put this into perspective, if the Moon was represented by a point one foot away, Uranus would be over one nautical mile (1 nm = 6076 feet) distant.
The scale of the accompanying image gives an indication of the challenges involved. In angular width (~6.5 arc-minutes), we are seeing a dimension about 1/5 that of the Moon. The disc of Uranus, heavily overexposed here, is only 3.7 arc-seconds across. In other words you could place 105 discs of Uranus across the breadth of this view.
The techinques used for photographing Uranus aren’t the same as for the other “Gas Giants,” Jupiter or even Saturn. Those objects appear telescopically large and bright enough to respond well to shortish exposure times which can help capture those moments of good seeing that can be fleeting on many nights. But for Uranus, and to an even greater degree Neptune, that strategy will not work since exposures must necessarily be longer to compensate for these dimmer targets. Hence steady skies are a must.
This is especially true if hoping to capture cloud band details (versus just the bands), which is possible. Filtering out short wavelengths of light, those most prone to image degradation caused by poorer seeing, is an effective approach. Astrophotographers that have enjoyed some success recommend transmission filters that only pass wavelengths greater than 685 nanometers – the infrared and beyond.
Armed with the modern tools of CMOS cameras, software, and, of course, the Carroll telescope, the imaging of Uranus is a worthy test that SRO is well-suited to take on. On nights of very good seeing, for which the region is noted, the optic can gather enough light to keep even filtered exposures relatively fast while maintaining adequate control over noise levels in the resulting frames. So long as the proper filtration is used and the astronomer focuses accurately (a challenge in the infrared), the outcomes could help produce useful science on world that may be glimpsed more often than you think, but not critically so because its demands are beyond the means of most observers. Who wants to try??
Uranus and Four of Its Twenty Eight Moons
Sara Martin and Pam Sable
When imaging a distant planet like Uranus, you have to make a choice - detect the moons, or try to resolve the planet. Here, it's all about those faintish moons...
The brightest is Titania, at magnitude 13.7, which should be within reach of the Carroll's 6-inch guide telescope. Even the faintest - Umbriel, a full magnitude dimmer - might be glimpsed in the "six," under ideal conditions based on magnitude alone. The problem here is Uranus itself, "blindingly" bright in contrast to its attendants, making them difficult to spot, especially those orbiting closest to it.
A curiosity of Uranus is somewhat evident here, and would be more so if you could observe for an extended period of time. These moons would appear to circle the planet versus sway back and forth in front of and behind it as the moons of Jupiter and Saturn do within their systems. This is due to Uranus' extreme axial tilt - around 90 degrees, the largest of the eight planets in the solar system. It is thought to be the result of either a large collision or, as a recent theory suggests, the dynamics of "losing" a relatively large moon in the distant past. Regardless, this oddity leads to extremely long "seasons" at the poles which last for decades. Summers there have no setting sun and winters never see it.
The identification of objects in this view was made much, much easier by automated efforts. The image was
uploaded to a "plate-solving" server which identifies candidate stars and positionally matches them to stellar astrometric data compiled in massive catalogs, two of which are represented here.
Stars with the designation 'HD' come from the legacy compilations honoring American amateur astronomer Dr. Henry Draper, these completed about 100 years ago. The two in this image are about as faint as any in that catalog. The GAIA entries have been tabulated by a space-based astrometic survey telescope operated by the ESA - the European Space Agency.
GAIA, which is an acronym for Global Astrometric Interferometer for Astrophysics, is no longer accurate because the original intent to use interferometry was scrapped in favor of traditional optical methods. The name was retained for continuity.
The plate-solver wasn't fooled by the transient positioning of the Uranus system in Capricornus, but neither could it identify the planet or its companions. The moons were sleuthed using highly accurate astronomy software...on a cell phone. Try explaining that to Dr. Draper!
Uranus and Four of Its Twenty Eight Moons
Sara Martin and Pam Sable
When imaging a distant planet like Uranus, you have to make a choice - detect the moons, or try to resolve the planet. Here, it's all about those faintish moons...
The brightest is Titania, at magnitude 13.7, which should be within reach of the Carroll's 6-inch guide telescope. Even the faintest - Umbriel, a full magnitude dimmer - might be glimpsed in the "six," under ideal conditions based on magnitude alone. The problem here is Uranus itself, "blindingly" bright in contrast to its attendants, making them difficult to spot, especially those orbiting closest to it.
A curiosity of Uranus is somewhat evident here, and would be more so if you could observe for an extended period of time. These moons would appear to circle the planet versus sway back and forth in front of and behind it as the moons of Jupiter and Saturn do within their systems. This is due to Uranus' extreme axial tilt - around 90 degrees, the largest of the eight planets in the solar system. It is thought to be the result of either a large collision or, as a recent theory suggests, the dynamics of "losing" a relatively large moon in the distant past. Regardless, this oddity leads to extremely long "seasons" at the poles which last for decades. Summers there have no setting sun and winters never see it.
The identification of objects in this view was made much, much easier by automated efforts. The image was
uploaded to a "plate-solving" server which identifies candidate stars and positionally matches them to stellar astrometric data compiled in massive catalogs, two of which are represented here.
Stars with the designation 'HD' come from the legacy compilations honoring American amateur astronomer Dr. Henry Draper, these completed about 100 years ago. The two in this image are about as faint as any in that catalog. The GAIA entries have been tabulated by a space-based astrometic survey telescope operated by the ESA - the European Space Agency.
GAIA, which is an acronym for Global Astrometric Interferometer for Astrophysics, is no longer accurate because the original intent to use interferometry was scrapped in favor of traditional optical methods. The name was retained for continuity.
The plate-solver wasn't fooled by the transient positioning of the Uranus system in Capricornus, but neither could it identify the planet or its companions. The moons were sleuthed using highly accurate astronomy software...on a cell phone. Try explaining that to Dr. Draper!