Jupiter And The Sun Cross Paths Today

A short-lived halo created by ice crystals in a layer of cirrostratus clouds yesterday afternoon. Photo: Bob King

A sweet halo circled the sun yesterday along with some very curvy altocumulus clouds. The display was brief, but I thought you’d enjoy seeing a photo.

Another solar event happens today – Jupiter is in superior conjunction with the sun.

A conjunction occurs when two celestial bodies line up close together in the sky. If you’ve seen the moon and bright planet paired together one above the other, you’ve witnessed a conjunction. ‘Superior’ refers to planets that lie beyond Earth’s orbit. During superior conjunction, the sun is always in the foreground and planet in the distance background. Although they appear near one another in the photo, Jupiter is almost six times farther away than the sun.

The sun slowly passes to the left or east of the giant planet Jupiter today as seen in these photos taken by the coronagraph on the space-based Solar and Heliospheric Observatory (SOHO). In just a few hours time, you can see that Jupiter "moves" from slightly west of the sun in the evening sky (left) to slightly right of the sun and into the morning sky. Credit: NASA/ESA

Jupiter is less than one degree (two full moon widths) directly below the sun today. You can’t see the planet because it’s completely lost in the glare of the sun, but SOHO’s coronagraph, which uses a mask to block the sun’s disk so scientists can study the sun’s corona or outer atmosphere, shows the planet very well. SOHO orbits between the sun and Earth around a stable zone called L1 Lagrangian point. From this unique vantage point, scientists can observe the sun 24/7.

Jupiter has spent the past many months as an evening planet. Conjunction is the time a planet transitions from the evening sky into the morning sky. For a brief time it’s lined up with the sun, but hour by hour is slowly appears to swing west of the sun, reappearing to the naked eye in morning twilight a couple weeks later.

I emphasize the word ‘appears’, because the planet’s not actually doing the moving. It’s the sun. Because the sun is much closer to us than an outer planet like Jupiter, it appears to move faster in the sky, passing the planet by.

The sun with its family of planets goes around the center of the galaxy at 150 miles per second, completing an orbit in 225 million years. This interval is called a cosmic year. The solar system is inclined relative to the plane of the galaxy. Sun and orbits exaggerated for clarity. Illustration: NASA with my additions

Of course, the sun itself only appears to be moving past Jupiter. The real culprit is the Earth. Our orbital journey around the sun at 18.5 miles per second makes the sun appear to move at a stately pace through the sky over the four seasons. The reality is that the sun, in its kingly location at the center of the solar system, is basically sitting still with all the planets going around it. Now if enlarge our view, the sun – along with its family of planets, asteroids and comets – is traveling around the center of the galaxy at 150 miles per second.

Arctic sea ice photographed from the air on March 26. Credit: NASA imagesIf you’d like to follow Jupiter’s progress over the next few days, click HERE to see the most recent SOHO images.

Yesterday a great photo of Arctic sea ice arrived in my e-mail made with a high-resolution digital camera mounted on NASA’s P-3B Earth science aircraft. It was taken on March 26, when the plane flew just 1,500 feet over the ice, and shows large plates of snow-covered ice separated by dark ‘leads’ of open water. Right away I was reminded of Jupiter’s moon Europa, which is similarly covered in ice and bears a remarkable resemblance to the picture.

Europa's bizarre-looking surface is covered in fractured sheets of thick ice. Credit: NASA

The temperature at Europa is wee bit colder – only around 250 below – with a surface comprised of cracked plates of ice. As with the Arctic ice, if you look closely, you can see how the pieces fit like in almost puzzle-like fashion.

Look for the moon below the Seven Sisters (Pleiades) star cluster tonight. The Hyades are right next door. Created with Stellarium

There are no open ‘leads’ of water we know of on airless Europa (it’s too cold), but it’s clear that currents or motions beneath the surface worked to break and move vast sections of its icy crust. Indeed, astronomers are virtually certain the little moon harbors an ocean of liquid water in its interior.

I’d feel bad if I didn’t leave you with something you might be able to see with you own two eyes from your home or apartment tonight. That’s why it’s good news the moon is headed for the Pleiades this evening. Once you’ve got the scene, a further glance will take you to the Hyades star cluster. So easy.

3 Responses

  1. Loved the article – the Jupiter conjunction got me thinking about the lack of communication that can occur when our space probes are on a system that goes into conjunction (such as Mars, in January). I realized sadly that there are no probes currently orbiting Jupiter – but checked in on Juno, which is still on schedule for a launch later this summer (Aug. 5, to be precise!).


    1. astrobob

      Because Jupiter’s an outer planet, it can’t pass between us and the sun. It looks like it might be in front of the sun but it’s way out behind it.

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