Watch live @ 3 pm ET: NASA’s ‘Great Conjunction’ guide to the Saturn-Jupiter ‘Christmas Star’, ,

NASA will broadcast a NASA Science Live episode at 3 p.m. EST (1900 GMT) to offer a detailed guide on how to see the “Great Conjunction” of Jupiter and Saturn on Dec. 21. The event, a rare meeting of the planets, has been billed as a “Christmas Star” celestial sight.

Saturn and Jupiter will be at their closest in the night sky for the first time since 1623 on Dec. 21, but their last pairing was not visible to most observers on Earth. The event next week will be the first visible to most areas since 1226, nearly 800 years ago.

Video: ‘Great conjunction’ of Jupiter and Saturn is closest since 1623
Related: Get ready for the ‘Great Conjunction’ of Jupiter and Saturn

Skywatchers are in for an end-of-year treat. What has become known popularly as the “Christmas Star” is an especially vibrant planetary conjunction easily visible in the evening sky over the next two weeks as the bright planets Jupiter and Saturn come together, culminating on the night of Dec. 21.

In 1610, Italian astronomer Galileo Galilei pointed his telescope to the night sky, discovering the four moons of Jupiter – Io, Europa, Ganymede, and Callisto. In that same year, Galileo also discovered a strange oval surrounding Saturn, which later observations determined to be its rings. These discoveries changed how people understood the far reaches of our solar system.

Thirteen years later, in 1623, the solar system’s two giant planets, Jupiter and Saturn, traveled together across the sky. Jupiter caught up to and passed Saturn, in an astronomical event known as a “Great Conjunction.”

“You can imagine the solar system to be a racetrack, with each of the planets as a runner in their own lane and the Earth toward the center of the stadium,” said Henry Throop, astronomer in the Planetary Science Division at NASA Headquarters in Washington. “From our vantage point, we’ll be able to be to see Jupiter on the inside lane, approaching Saturn all month and finally overtaking it on December 21.”

The planets regularly appear to pass each other in the solar system, with the positions of Jupiter and Saturn being aligned in the sky about once every 20 years.

What makes this year’s spectacle so rare, then? It’s been nearly 400 years since the planets passed this close to each other in the sky, and nearly 800 years since the alignment of Saturn and Jupiter occurred at night, as it will for 2020, allowing nearly everyone around the world to witness this “great conjunction.”

The closest alignment will appear just a tenth of a degree apart and last for a few days. On the 21st, they will appear so close that a pinkie finger at arm’s length will easily cover both planets in the sky. The planets will be easy to see with the unaided eye by looking toward the southwest just after sunset.

From our vantage point on Earth the huge gas giants will appear very close together, but they will remain hundreds of millions of miles apart in space. And while the conjunction is happening on the same day as the winter solstice, the timing is merely a coincidence, based on the orbits of the planets and the tilt of the Earth.

“Conjunctions like this could happen on any day of the year, depending on where the planets are in their orbits,” said Throop. “The date of the conjunction is determined by the positions of Jupiter, Saturn, and the Earth in their paths around the Sun, while the date of the solstice is determined by the tilt of Earth’s axis. The solstice is the longest night of the year, so this rare coincidence will give people a great chance to go outside and see the solar system.”

Want to learn when and where to look up? Join Throop as he talks about the “Great Conjunction” on #NASAScience Live Thursday, Dec. 17. Submit your questions by using #askNASA. The NASA Science Live episode will air live at 3 p.m. EST Thursday on NASA Television and the agency’s website, along with the NASA Facebook, YouTube, and Periscope channels.

For those who would like to see this phenomenon for themselves, here’s what to do:

Find a spot with an unobstructed view of the sky, such as a field or park. Jupiter and Saturn are bright, so they can be seen even from most cities.

An hour after sunset, look to the southwestern sky. Jupiter will look like a bright star and be easily visible. Saturn will be slightly fainter and will appear slightly above and to the left of Jupiter until December 21, when Jupiter will overtake it and they will reverse positions in the sky.

The planets can be seen with the unaided eye, but if you have binoculars or a small telescope, you may be able to see Jupiter’s four large moons orbiting the giant planet.

Each night, the two planets will appear closer low in the southwest in the hour after sunset as illustrated in the below graphic:

Learn these tips and trick on how to photograph planets:
https://solarsystem.nasa.gov/news/1615/how-to-photograph-the-conjunction-of-saturn-and-jupiter/

Night Sky Network:
https://nightsky.jpl.nasa.gov/

Visitors to Both Jupiter and Saturn:
https://nightsky.jpl.nasa.gov/news-display.cfm?News_ID=931

Want to learn more about planetary conjunctions? Take a look at some of these resources:
https://blogs.nasa.gov/Watch_the_Skies/2015/06/30/jupiter-and-venus-conjunction/
https://youtu.be/sofRYcfaqy0

Read these skywatching Tips from NASA:
https://solarsystem.nasa.gov/whats-up-skywatching-tips-from-nasa/

Update for 11:10 am ET: SpaceX has called off today’s launch attempt for the NROL-108 spy satellite due to higher than expected pressures in the Falcon 9 rocket’s upper stage. The next launch attempt will be Friday, Dec. 18, at 9 a.m. EST (1400 GMT). There is a 3-hour launch window for the mission.

A SpaceX Falcon 9 rocket will launch a classified payload for the U.S. National Reconnaissance Office on Thursday (Dec.17).

The mission, designated NROL-108, will lift off from Cape Canaveral Space Force Station in Florida, in a 3-hour launch window that opens at 9:45 a.m. EST (1445 GMT).

You can watch the launch live in the window above, courtesy of SpaceX, or tune in via the company’s website. The live broadcast will begin approximately 15 minutes before liftoff.

Read more: SpaceX will launch a spy satellite for the National Reconnaissance Office Thursday. Watch it live!

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A SpaceX Falcon 9 rocket stands ready to launch the NROL-108 mission for the U.S. National Reconnaissance Office. The mission is scheduled to launch from Cape Canaveral Space Force Station in Florida on Dec. 16, 2020. (Image credit: SpaceX)

SpaceX is targeting Thursday, December 17 for launch of the NROL-108 mission, which will launch from Launch Complex 39A (LC-39A) at Kennedy Space Center, Florida. The three-hour launch window opens at 9:00 a.m. EST, or 14:00 UTC, and a backup launch opportunity is available on Friday, December 18 with a three-hour launch window opening at 9:00 a.m. EST, or 14:00 UTC.

Falcon 9’s first stage booster previously supported launch of SpaceX’s 19th and 20th cargo resupply missions to the International Space Station, a Starlink mission, and the SAOCOM 1B mission. Following stage separation, SpaceX will land Falcon 9’s first stage on Landing Zone 1 at Cape Canaveral Space Force Station in Florida.

You can watch the launch webcast live starting about 15 minutes before liftoff.

Find out what the astronauts and cosmonauts aboard the International Space Station are up to by tuning in to the “ISS Live” broadcast. Hear conversations between the crew and mission controllers on Earth and watch them work inside the U.S. segment of the orbiting laboratory. When the crew is off duty, you can enjoy live views of Earth from Space. You can watch and listen in the window below, courtesy of NASA.

“Live video from the International Space Station includes internal views when the crew is on-duty and Earth views at other times. The video is accompanied by audio of conversations between the crew and Mission Control. This video is only available when the space station is in contact with the ground. During ‘loss of signal’ periods, viewers will see a blue screen.

“Since the station orbits the Earth once every 90 minutes, it experiences a sunrise or a sunset about every 45 minutes. When the station is in darkness, external camera video may appear black, but can sometimes provide spectacular views of lightning or city lights below.”

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