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Two astronomers use a pioneering method to suggest that the size of our Sun and the solar radius may be due revision.

Our host star is full of surprises. Studying our Sun is the most essential facet of modern astronomy: not only does Sol provide us with the only example of a star we can study up close, but the energy it provides fuels life on Earth, and the space weather it produces impacts our modern technological civilization.

Now, a new study, titled The Acoustic Size of the Sun suggests that a key parameter in modern astronomy and heliophysics—the diameter of the Sun—may need a slight tweak.

The study out of the University of Tokyo and the Institute of Astronomy at Cambridge was done looking at data from the joint NASA/ESA Solar Heliospheric Observatory (SOHO’s) Michelson Doppler Imager (MDI) imager. The method probes the solar interior via acoustics and a cutting edge field of solar physics known as helioseismology.

Interior of the Sun
A cutaway diagram of the Sun. NASA/ESA/SOHO

‘Hearing’ the Solar Interior

How can you ‘hear’ acoustic waves on the Sun? In 1962, astronomers discovered that patches on the surface of the Sun oscillate, or bubble up and down, like water boiling on a stove top. These create waves that ripple in periodic 5-minute oscillations across the roiling surface of the Sun.

SOHO SDO
A view of the Sun, courtesy of SOHO’s MDI instrument. Credit: NASA

What’s more, astronomers can use what we see happening on the surface of the Sun to model the solar interior, much like terrestrial astronomers use seismic waves traveling through the Earth to model its core. Thanks to helioseismology, we can even ‘see’ what’s going on on the solar farside, and alert observers of massive sunspots before they rotate into view.

Solar Ffarside
Solar farside modeling using helioseismology. Credit: NSF/GONG

The study looked at p-mode waves as they traversed the solar interior. Previous studies relied on less accurate f-mode waves, which are surface waves considerably shorter than the solar radius.

The study defines the solar radius (half the diameter) as 695,780 kilometers… only slightly smaller than the generally accepted radius of 696,000 kilometers obtained by direct optical measurement. This is only smaller by a few hundredths of a percent, or 100-200 kilometers.

SOHO
An artist’s conception of SOHO in space. Credit: ESA/SOHO

The solar radius is a deceptively simple but crucial factor in astronomy. The Sun is a glowing ball of hydrogen and helium plasma without a distinct surface boundary. The photosphere—the glowing visible layer we see shining down on us on a sunny day—is what we generally refer to as the surface of the Sun.

The Solar Radius: A Brief
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Webb Measures the Weather on a Tidally Locked Exoplanet

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Exploring exoplanet atmospheres in more detail was one task that planetary scientists anticipated during the long wait while the James Webb Space Telescope (JWST) was in development. Now, their patience is finally paying off. News about discoveries of exoplanet atmosphere using data from JWST seems to be coming from one research group or another almost every week, and this week is no exception. A paper published in Nature by authors from a few dozen institutions describes the atmospheric differences between the “morning” and “evening” sides of a tidally locked planet for the first time.

First, let’s clarify what the “morning” and “evening” sides mean. Tidally locked planets don’t spin, so one hemisphere constantly faces the planet’s star. As such, there is always a part of the planet where it appears to be “morning,” with the star barely peaking over the horizon. Alternatively, there’s a part of the planet where it seems to be “evening,” where the star is again just barely peaking over the horizon, but it would appear to be setting. 

Typically, on Earth, we would think of the morning side as the star peaking over the eastern side, whereas the evening side would see the star setting into the western sky. However, exoplanets sometimes rotate in the opposite direction from planets in our solar system, so that mental model doesn’t always work for them.

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The JWST light curve for WASP-34b, clearly showing the dip in the star’s brightness as the planet passes in front of it.
Credit – NASA / ESA / CSA / R. Crawford (STScI)

It’s also important not to confuse the “morning” and “evening” sides with the “day” and “night” sides of the planet. On the day side, the full force of the star affects the planet, but on the night side, the star is never seen at all. The temperature differences on such a planet are massive, and cause much more extreme weather than anything we have experience with in our solar system.

That is the case for WASP-39b, one of the most studied exoplanets. It is a “hot Jupiter” and is roughly 1.3 times the size of the largest planet in our solar system, though it only masses in at about the same size as Saturn. It’s 700 light years away and is tidally locked to its star.

Exoplanet hunters have intently studied this exoplanet since its discovery in 2011. It was the target of JWST’s first exoplanet research when it began science operations. Since then, they’ve made several interesting discoveries, and the Nature paper describes a new one—that the “morning” side of WASP-39b is a few hundred degrees cooler than its “evening” side.

Fraser talks exoplanet atmosphere with expert Dr. Joanna Barstow.

This temperature discrepancy is likely due to atmospheric conditions on the planet itself. The paper’s authors believe there is an extremely strong wind on the planet that runs from day to night at thousands of miles an hour. The wind rotates from the day side through the evening side to the night side, then through the morning side back to the day side.

So, essentially, the morning side receives “air” that has been cooled while traveling through the planet’s night side. However, that air is still a blistering 600 C (1,150 F). The temperature on the evening side, though, is hotter at 800 C (1,450 F), much hotter than any conditions found on any planet in our solar system.

Detecting such a temperature difference on an exoplanet hundred of light years away is an impressive technical feat, and the study’s lead author, Néstor Espinoza, credits JWST’s capabilities for enabling it. The telescope watched the planet both while it was traversing in front of its star, but also while it was next to it and emitting its own, admittedly much fainter, light. 

JWST found methane in a different exoplanet atmosphere, as Fraser describes in this video.

They were differentiating between the starlight filtered through the atmosphere of the planet and when there was no filtered starlight coming through allowed the researchers to make temperature estimates. JWST is so sensitive they were also able to split the data into semi-circles to differentiate the”
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Review: Deuter Aircontact Ultra 50+5 and 45+5 SL Backpacks

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Ultralight Backpacks
Deuter Aircontact Ultra 50+5

$250, 55L/3,356 c.i., 2 lbs. 15 oz./1.33kg
Deuter Aircontact Ultra 45+5 SL

$250, 50L/3,051 c.i., 2 lbs. 11 oz./1.21kg

One adjustable size in both models

Aircontact Ultra 50+5: rei.com

Aircontact Ultra 45+5 SL: rei.com

To put Deuter’s updated-for-2024 Aircontact Ultra 50+5 ultralight backpack through the paces, I took it on a pair of quite rugged but also quite different backpacking trips this spring: a three-day hike through southern Utah’s Owl and Fish canyons with a max weight of about 30 pounds in the pack, and six days and about 60 miles backpacking the Grand Canyon’s Gems Route, repeatedly carrying extra water—and starting out with more than 40 pounds inside, including over 10 pounds of water and 11 pounds of food. As I expected, those trips revealed much about the Aircontact Ultra backpacks and why they might appeal to lightweight and ultralight backpackers.

First, I must acknowledge that 40 pounds significantly exceeds Deuter’s recommended max weight for these packs: I knew that but wanted to gauge the Aircontact Ultra’s comfort by exceeding its weight capacity and then seeing when it starts feeling comfortable as my pack weight decreased each day—as I sometimes do with packs in this weight class because, almost inevitably, many backpackers overload ultralight packs at the outset of a trip, or at various points during a long-distance hike, accepting a day or more of compromised comfort for the benefit of having a pack that’s lighter and will be adequately comfortable for most of the trip. I’ve done that countless times.

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Hi, I’m Michael Lanza, creator of The Big Outside. Click here to sign up for my FREE email newsletter. Join The Big Outside to get full access to all of my blog’s stories. Click here for my e-books to classic backpacking trips. Click here to learn how I can help you plan your next trip.

The Deuter Aircontact Ultra 50+5 harness.
” data-image-caption=”The Deuter Aircontact Ultra 50+5 harness.
” data-medium-file=”https://i0.wp.com/tbo-media.sfo2.digitaloceanspaces.com/wp-content/uploads/2024/07/11121334/Deuter-Aircontact-Ultra-505-harness.jpg?fit=200%2C300&ssl=1″ data-large-file=”https://i0.wp.com/tbo-media.sfo2.digitaloceanspaces.com/wp-content/uploads/2024/07/11121334/Deuter-Aircontact-Ultra-505-harness.jpg?fit=683%2C1024&ssl=1″ tabindex=”0″ role=”button” src=”https://i0.wp.com/tbo-media.sfo2.digitaloceanspaces.com/wp-content/uploads/2024/07/11121334/Deuter-Aircontact-Ultra-505-harness-683×1024.jpg?resize=683%2C1024&ssl=1″ alt=”The Deuter Aircontact Ultra 50+5 harness.” class=”wp-image-63988″ style=”aspect-ratio:0.6671875;width:488px;height:auto” srcset=”https://tbo-media.sfo2.digitaloceanspaces.com/wp-content/uploads/2024/07/11121334/Deuter-Aircontact-Ultra-505-harness.jpg 683w, https://tbo-media.sfo2.digitaloceanspaces.com/wp-content/uploads/2024/07/11121334/Deuter-Aircontact-Ultra-505-harness.jpg 200w, https://tbo-media.sfo2.digitaloceanspaces.com/wp-content/uploads/2024/07/11121334/Deuter-Aircontact-Ultra-505-harness.jpg 768w, https://tbo-media.sfo2.digitaloceanspaces.com/wp-content/uploads/2024/07/11121334/Deuter-Aircontact-Ultra-505-harness.jpg 150w, https://tbo-media.sfo2.digitaloceanspaces.com/wp-content/uploads/2024/07/11121334/Deuter-Aircontact-Ultra-505-harness.jpg 800w” sizes=”(max-width: 683px) 100vw, 683px” data-recalc-dims=”1″ />The Deuter Aircontact Ultra 50+5 harness.

In the Grand Canyon, having more than 40 pounds/18.1 kilos in the Aircontact Ultra 50+5 was certainly not “comfortable.” But nor was it all that bad. On that first day, we backpacked about six miles of rough dirt road just to reach the South Bass Trailhead, and then descended the often steep, loose, and rugged South Bass Trail for some 3,400 feet before
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How to Plan Food for a Backpacking Trip

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By Michael Lanza

You’re planning food for a backpacking trip—maybe for yourself or perhaps for your family or a small group of friends—and you have questions about how to do it. How much food do you need? What food should you bring? How complicated or simple do you want to make it? How do your food choices affect how much stove fuel you will need—or do you even need a stove? Drawing on decades of backpacking experience, this article will lay out some general guidelines and detailed advice that will help you plan food for all your backpacking trips.

Over the course of more than three decades and thousands of miles of backpacking all over the United States and around the world—including the 10 years I spent as Northwest Editor of Backpacker magazine and even longer running this blog—I have eaten countless meals in the backcountry and greatly refined my food planning over time.

Tet19 047 Me on Teton Crest Trail copy cropped 35
Hi, I’m Michael Lanza, creator of The Big Outside. Click here to sign up for my FREE email newsletter. Join The Big Outside to get full access to all of my blog’s stories. Click here for my e-books to classic backpacking trips. Click here to learn how I can help you plan your next trip.

A backpacker at a wilderness campsite off the Highline Trail in Wyoming’s Wind River Range.
” data-image-caption=”Our camp below Mount Oeneis and Sky Pilot Peak off the Highline Trail in the Wind River Range.
” data-medium-file=”https://i0.wp.com/tbo-media.sfo2.digitaloceanspaces.com/wp-content/uploads/2023/05/06224928/Wind8-031-Our-camp-below-Mount-Oeneis-and-Sky-Pilot-Peak-off-the-Highline-Trail-CDT-Wind-River-Range-WY..jpg?fit=300%2C200&ssl=1″ data-large-file=”https://i0.wp.com/tbo-media.sfo2.digitaloceanspaces.com/wp-content/uploads/2023/05/06224928/Wind8-031-Our-camp-below-Mount-Oeneis-and-Sky-Pilot-Peak-off-the-Highline-Trail-CDT-Wind-River-Range-WY..jpg?fit=900%2C600&ssl=1″ tabindex=”0″ role=”button” src=”https://i0.wp.com/tbo-media.sfo2.digitaloceanspaces.com/wp-content/uploads/2023/05/06224928/Wind8-031-Our-camp-below-Mount-Oeneis-and-Sky-Pilot-Peak-off-the-Highline-Trail-CDT-Wind-River-Range-WY.-1024×683.jpg?resize=900%2C600&ssl=1″ alt=”A backpacker at a wilderness campsite off the Highline Trail in Wyoming’s Wind River Range.” class=”wp-image-58509″ srcset=”https://tbo-media.sfo2.digitaloceanspaces.com/wp-content/uploads/2023/05/06224928/Wind8-031-Our-camp-below-Mount-Oeneis-and-Sky-Pilot-Peak-off-the-Highline-Trail-CDT-Wind-River-Range-WY..jpg 1024w, https://tbo-media.sfo2.digitaloceanspaces.com/wp-content/uploads/2023/05/06224928/Wind8-031-Our-camp-below-Mount-Oeneis-and-Sky-Pilot-Peak-off-the-Highline-Trail-CDT-Wind-River-Range-WY..jpg 300w, https://tbo-media.sfo2.digitaloceanspaces.com/wp-content/uploads/2023/05/06224928/Wind8-031-Our-camp-below-Mount-Oeneis-and-Sky-Pilot-Peak-off-the-Highline-Trail-CDT-Wind-River-Range-WY..jpg 768w, https://tbo-media.sfo2.digitaloceanspaces.com/wp-content/uploads/2023/05/06224928/Wind8-031-Our-camp-below-Mount-Oeneis-and-Sky-Pilot-Peak-off-the-Highline-Trail-CDT-Wind-River-Range-WY..jpg 150w, https://tbo-media.sfo2.digitaloceanspaces.com/wp-content/uploads/2023/05/06224928/Wind8-031-Our-camp-below-Mount-Oeneis-and-Sky-Pilot-Peak-off-the-Highline-Trail-CDT-Wind-River-Range-WY..jpg 1200w” sizes=”(max-width: 900px) 100vw, 900px” data-recalc-dims=”1″ />Our camp below Mount Oeneis and Sky Pilot Peak off the Highline Trail in the Wind River Range.

I’ll offer this caveat in advance: I’m not someone who feels a great desire to eat “gourmet” style in the backcountry. I certainly want food that tastes good and is satisfying. If you’re not hiking far, it’s easier to carry a little more and spend time preparing special meals. I tend to hike all day, sometimes very long days, so I don’t want to spend much time in food
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