Space News & Blog Articles

In this series we are exploring the weird and wonderful world of astronomy jargon! You’ll soon see what we’re talking about this week: luminosity!

Point at a random star on the night sky. Just how bright is that star? Yes, you could measure its brightness, but that’s from your vantage point here on Earth. The brightness that you measure depends on many things that have nothing to do with the star itself. The same star placed further away would appear less bright. The same star but with loads more interstellar dust in front of it would also appear less bright. You are only measuring the brightness in visible light – but the star is also glowing in everything from radio to X-ray.

That’s why astronomers prefer not to use the brightness of a star, but rather its luminosity. Luminosity is, in some sense, the true brightness of an object. It’s a measure of the actual amount of electromagnetic energy emanating from a star. That includes all wavelengths of light, both visible and invisible. It doesn’t matter how much intervening dust there is. It doesn’t matter how far away the star is.

It’s an intrinsic, real property of the star itself. But since we can only measure a limited amount of the radiation coming from a star, calculating the luminosity usually involves modeling the total light output.

By default, the word “luminosity” is short for “bolometric luminosity”, which means the total luminosity across the entire electromagnetic spectrum. But sometimes astronomers might refer to the luminosity in a specific band of wavelengths.

In March of 2019, NASA was directed to develop all the necessary equipment and planning to send astronauts back to the Moon by 2024. This plan, officially named Project Artemis, was part of an agency-wide shakeup designed to ensure that the long-awaited return to the Moon takes place sooner than NASA had originally planned. In accordance with their “Moon to Mars” framework, NASA hoped to assemble the Lunar Gateway first, then land astronauts on the surface by 2028.

Unfortunately, this ambitious proposal has led to all sorts of complications and forced NASA to shift certain priorities. Most recently, NASA’s Office of Inspector General (OIG) submitted a report that indicated that their new Exploration Extravehicular Mobility Units (xEMU) spacesuits will not be ready in time. The resulting delay has prompted Elon Musk to offer the services of SpaceX to expedite the spacesuit’s development and get Artemis back on schedule.

Development of the xEMU spacesuits began in earnest back in 2007 as part of the Constellation Program, the first step in NASA’s ongoing drive to return to the Moon. These efforts came together in 2017 with the birth of the xEMU project, which aimed to create a next-generation spacesuit that could be used in multiple programs. The xEMU spacesuit is similar in design to the Extravehicular Mobility Units (EMUs) that have been in use for 45 years.

These spacesuits are currently used by astronauts aboard the ISS to conduct spacewalks. However, the xEMU design incorporates multiple technological advances that have been made since the Apollo Era that will allow it to accomplish more complex tasks than its predecessors. The new designs emphasize safety, incorporating what the Apollo missions taught us about Moon dust – like how it’s sharp, abrasive, and sticks to everything!

The suits also have a greater range of motion for performing scientific tasks, made possible by a system of bearings on the waist, arms, and legs. The helmets also come with an updated communications system, which replaces the old “snoopy caps” that are known to become sweaty, uncomfortable, and have a single microphone. The new system relies on multiple, embedded microphones inside the upper torso that are voice-activated and much more ergonomic.

Astronomers have an excellent habit of naming large projects after deserving contributors to their field.  From Nancy Grace Roman to Edwin Hubble, some of the biggest missions are named after space exploration pioneers. When ESA and JAXA sat down to figure out a name for their new Mercury probe, they would have come across an important name early in their research – Giuseppe “Bepi” Colombo – the man who helped plan the Mariner 10 Mercury mission.

Giuseppe Colombo was an Italian rocket scientist born in 1920 in Padua.  He studied Mathematics at the University of Pisa and eventually became a Professor of Applied Mechanics at the University of Padua after returning home.

His first major contribution to space exploration was when he noted at a conference on Mariner 10 in 1955 that the spacecraft could make a second and even third pass by Mercury if the orbital mechanics were timed right.  It would require a gravity assist from Venus, but given the probe’s orbital period was roughly twice the planet’s rotational period, it was possible to do so.

After a NASA study confirmed his mechanics, Mariner did, in fact, complete three flybys of Mercury, and one of Venus, with the closest coming in at a mere 327 km from the innermost planet.  This was the first time a spacecraft used an interplanetary gravitational slingshot, a maneuver still commonly used by space probes today, including Colombo’s namesake. It also marked the most data ever gathered up close of Mercury – in fact, “almost everything known until now about the planet Mercury comes from Mariner 10’s orbits during 1974-75, which were inspired by Colombo’s calculations,” according to an ESA biography.

Mercury, the focus of Mariner 10’s mission that Colombo helped plan, seen from the spacecraft.
Credit – NASA

In this series we are exploring the weird and wonderful world of astronomy jargon! You’ll soon have a better way to categorize today’s topic: the Hertzsprung–Russell diagram!

In the early 1900’s astronomy was in a bit of a mess (NB it’s still in a mess, but a completely different one). Astronomers had figured out the trick of spectroscopy, and were beginning some seriously large-scale surveys of our galactic neighborhood.

Those astronomers surveyed all sorts of amazing stars. Giant red ones. Giant blue ones. Small red ones. Medium white ones. The stars they saw had different colors, different temperatures, different specta, and different sizes.

And none of it made any sense.

Why were some stars red and big, while others were blue and big? And what about the small red ones? There needed to be some sort of classification system; some way to organize this giant flood of information. Astronomers had proposed various ideas, like the suggestion that stars start out big and hot and shrink as they age, but that didn’t fit all the data.