Editor's note: The live webcast above is provided by the Griffith Observatory in Los Angeles, California.
Jupiter and Saturn will align in the night sky today (Dec. 21) in an event astronomers call the "great conjunction," and you can watch it online with webcasts from The Virtual Telescope Project, Slooh and more.
Tonight's great conjunction — also nicknamed the "Christmas Star" — marks the closest apparent encounter of Jupiter and Saturn in nearly 400 years. The two planets will be closest to each other in the sky tonight, which is also winter solstice, and may be viewed as one point of light, appearing only a tenth of a degree apart. They will remain in close alignment for a few days and will be easily visible to the naked eye when looking toward the southwest just after sunset.
You can watch the winter solstice great conjunction webcasts live here throughout the day.
A conjunction occurs when planets appear incredibly close to one another in the sky because they line up with Earth in their respective orbits. While Jupiter and Saturn align about once every 20 years, this year's conjunction marks the first time since 1623 that the two gas giants have passed this close to one another in our sky — and nearly 800 years since skywatchers were able to witness the event at night. The planetary alignment has also been called a "Christmas star," since it falls on the first day of winter in the Northern Hemisphere and only a few days before Christmas.
Great conjunction 2020: NASA tips to see Jupiter & Saturn as a 'Christmas Star'
To get a closer view of tonight's great conjunction of Jupiter and Saturn and to learn about the science and history of the spectacular celestial event, tune into these free webcasts today from observatories around the world.
The Virtual Telescope Project
The Virtual Telescope Project, an online observatory founded by astrophysicist Gianluca Masi of the Bellatrix Astronomical Observatory, will stream live views of the great conjunction from Ceccano, Italy. The webcast will also celebrate the winter solstice.
"After 400 years, the giant planets Jupiter and Saturn are ready to amaze us with an exceptionally close conjunction. While they apparently meet up there every 20 years, next 21 Dec. they will be at their closest since 1623. Something so rare and unique that you cannot miss it. This will happen on the day marking the 2020 Winter Solstice!" Masi said in a statement. "The Virtual Telescope Project is ready to bring this one-in-a-lifetime experience to you, online, so that you can join live from the comfort of your home."
The Virtual Telescope Project webcast will begin at 10:30 a.m. EST (1530 GMT). You can watch the event directly via the Virtual Telescope Project.
The online observatory Slooh will host another live webcast of the great conjunction, starting at 2 p.m. EST (1900 GMT). You can watch the event live here on Space.com, courtesy of Slooh, or directly via Slooh's YouTube channel.
Slooh astronomers Paul Cox, Bob Berman and Mike Shaw will host the webcast and discuss the planetary alignment while showing live views from Slooh's telescopes at the Institute of Astrophysics of the Canary Islands and in Chile.
"We'll discuss why this 'great conjunction' is the best in our lifetimes and how you can view and photograph it from your backyard!" Slooh said in a statement. "And we'll investigate whether a similar conjunction was the event witnessed as the Christmas Star — the Star of Bethlehem."
Slooh members will also be able to participate in a special Moments Quest, which is a gamified experience using Slooh's online telescopes to learn more about the conjunction and capture images of the event remotely.
Lowell Observatory in Flagstaff, Arizona, will also host a webcast today to celebrate the great conjunction with commentary from astronomers and educators at the observatory, along with evening telescope views of the event. You can watch the webcast online directly via Lowell Observatory or on their YouTube channel starting at 7:00 p.m. EST (0000 GMT on Dec. 22).
"For most Great Conjunctions, Jupiter and Saturn are separated by about 1 degree, which is the width of two full moons in the sky," according to a statement from Lowell Observatory. "This year, they will be separated by just one-tenth of a degree, which is one-fifth the size of the full moon. A Great Conjunction happens every 20 years, but the last time Jupiter and Saturn were this close was the year 1623."
Vanderbilt Dyer Observatory
The Vanderbilt Dyer Observatory at Vanderbilt University in Brentwood, Tennessee, is also offering a live webcast of the great conjunction, hosted by Billy Teets, acting director and outreach astronomer at the observatory.
"During the past month, Jupiter and Saturn have appeared as bright 'stars' in the southwestern sky and have been drawing noticeably closer together each night," according to a statement from the Dyer Observatory. "On Dec. 21, the two will appear closer together in our sky (an event known as a conjunction) than they have in nearly four centuries, making them simultaneously visible in a telescope. The next extraordinarily close conjunction of the two giant planets won't occur for another 60 years."
The Dyer Observatory webcast will start at 6 p.m. EST (2300 GMT). Teets will discuss the phenomenon and how the planetary alignment works. You can watch the webcast live, via the observatory's YouTube channel.
University of Exeter
The Astrophysics Group at the University of Exeter and Exeter Science Centre in England offered a livestream view of Jupiter and Saturn on Sunday (Dec. 20) from 11:15 a.m. to 1:15 p.m. EST (1615 - 1815 GMT). You can rewatch the event on the University of Exeter's Physics and Astronomy Department's YouTube channel.
The University of Exeter also offers tips for skywatchers to witness the event live. Professor Matthew Bate, head of the Astrophysics Group, explains the great conjunction, including when and how to watch Jupiter and Saturn converge, in a video on the department's YouTube channel. Bate also describes what viewers can expect to see with the naked eye, using binoculars or through a telescope.
Editor's note: If you capture an amazing view of the great conjunction of Dec. 21 and would like to share it with Space.com for a story or gallery, send images and comments in to firstname.lastname@example.org.
Follow Samantha Mathewson @Sam_Ashley13. Follow us on Twitter @Spacedotcom and on Facebook.