Observing stars in broad daylight: How a multi-lens telescope is changing astronomy

Astronomers at Macquarie University have developed a new technique for observing celestial objects during the day that may enable 24/7 visual monitoring of satellites and significantly improve safety on Earth and in space.

Their technology uses the university’s Huntsman telescope, a unique arrangement of ten parallel camera lenses originally developed for highly sensitive observations of the night sky.

In an article published in Publications of the Astronomical Society of Australia On May 20, researchers will demonstrate Huntsman’s ability to accurately measure stars, satellites and other targets when the sun is high, even though astronomers traditionally only conduct observations at night.

“People have been trying to observe stars and satellites at optical wavelengths during the day for centuries, but it has always been very difficult. Our tests show that the Huntsman telescope can produce remarkable results even in daylight,” says lead author and astrophysics PhD student Sarah Caddy, who was involved in the design and construction of the Huntsman telescope.

Caddy worked with a team of Macquarie PhD students and staff to deploy the Huntsman, which was officially opened at the Siding Springs Observatory in Coonabarabran last year.

The telescope combines an astronomy camera and astromechanical focusing equipment with an array of 10 high-sensitivity 400mm Canon lenses aligned to cover the same patch of sky.

Because the sun blocks out most light from other celestial bodies, astronomers rarely conduct observations during the day. However, Caddy and her colleagues tested special “broadband” filters on a test version of the Huntsman telescope to block most of the daylight while allowing certain wavelengths from celestial bodies to pass through.

This test version, a mini Huntsman single-lens Pathfinder telescope installed in the university’s observatory, allowed the research team to evaluate different settings in a controlled environment without affecting the Huntsman telescope.

Supernova on the way

The Huntsman’s daytime function allows continuous monitoring of certain bright stars that may not be visible at night for months because they are too close to the Sun.

One example is the red supergiant Betelgeuse, a nearby star about 650 light years away in the constellation Orion in our Milky Way.

Betelgeuse is of great interest to astronomers because the star’s brightness decreased significantly from late 2019 to 2020, likely due to a massive ejection of gas and dust.

“Without this daytime mode, we would have no idea whether one of the brightest stars in the sky had gone supernova until several months after its explosive light reached Earth,” says co-author Associate Professor Lee Spitler, head of space projects at Macquarie’s Australian Astronomical Optics (AAO).

“We know that Betelgeuse will explode soon. [in astronomical terms this means anytime between now and millions of years into the future]but not exactly when it will happen.

“For about four months of the year it is only visible during the day because the sun is between Betelgeuse and the Earth at that time.”

Calibration with Betelgeuse

The study confirmed that the Huntsman Project’s daytime photometry data for Betelgeuse agree with observations from observatories around the world and even space telescopes.

“This breakthrough paves the way for continuous long-term studies of stars like Betelgeuse, which experience massive outbursts towards the end of their lives, ejecting enormous amounts of stellar material in the final phase of their cosmic rebirth cycle,” says Spitler.

“Astronomers love when stars in the Milky Way go supernova because they can tell us so much about how elements are formed in the universe.”

Unfortunately, he adds, supernovas are relatively rare in the Milky Way – the last time they occurred was in 1604.

“But when a supernova exploded in a mini-galaxy next to our Milky Way in 1987, it was so useful to astronomers that they were still able to observe the expanding supernova explosion almost 40 years later.”

Avoid collisions

Mastering daylight observation also brings great advantages in the rapidly growing field of space situational awareness (SSA), the careful monitoring of an ever-increasing number of satellites, space debris and other artificial objects in Earth orbit.

More satellites will be launched in the next ten years than in the entire history of human space exploration.

“Given that there are already around 10,000 active satellites orbiting the planet and another 50,000 satellites are scheduled to be launched into low Earth orbit over the next decade, there is a clear need for dedicated day and night telescope networks to continuously detect and track satellites,” says Caddy.

Possible satellite collisions have serious impacts on communications, GPS, weather monitoring and other critical infrastructure.

Satellite photometry is an astronomical technique that uses optical telescopes to study changes in the brightness of celestial objects. It can provide valuable information, including information about the composition, age and condition of orbiting objects.

“By having the ability to observe satellites during the day, we can monitor not only their location but also their orientation. This complements the information we get from radar and other monitoring methods, thus protecting against potential collisions,” says Caddy.

Astro treats

Caddy’s team demonstrated the Huntsman’s potential for other astronomical observations that require day and night coverage, including satellite monitoring.

The team used the Mini-Huntsman over many months to refine their techniques and systematically investigated factors such as optimal exposure times, timing of observations and precise tracking of targets even in atmospheric turbulence.

“Daytime astronomy is an exciting field, and with advances in camera sensors, filters and other technologies, we have made dramatic improvements in the sensitivity and precision achievable under bright skies,” says Caddy.

Spitler adds: “We have refined a method for daylight observation and shown that it can be done with affordable high-end equipment such as Canon lenses.”

The Huntsman is designed so that the ten lenses work in parallel, feeding ten ultra-fast CMOS camera sensors that together can capture thousands of short-exposure images per second.

The connected camera can process images in a flash and manage very large data streams. With the help of a robot controller, it can track and capture fast-moving objects and enables continuous monitoring of the objects around the clock.

“The ability to make accurate observations around the clock breaks long-standing restrictions on the amount of time astronomers are allowed to search the sky,” says Spitler.

“As we enter the next space age, daytime astronomy will become increasingly important.”