December Solstice Brings Winter, Summer Seasons

In meteorology, Earth’s winter season for the Northern Hemisphere and summer season for the Southern Hemisphere began on Dec. 1, 2021. However, the December solstice brings in the astronomical winter and summer seasons, respectively, for the two hemispheres of our planet. This will happen on Dec. 21 at 15:59 UTC, which is 9:59 a.m. CST in the United States.

Summer solstice explanation
During the solstices, Earth reaches a point where its tilt is at the greatest angle to the plane of its orbit, causing one hemisphere to receive more daylight than the other. Credits: NASA/Genna Duberstein

Solstices come twice a year. For the Northern Hemisphere, the summer (June) solstice occurs around June 20-21, and the winter (December) solstice happens around Dec. 21-22. At the solstice, the Sun’s path appears farthest north or south, depending on which half of the planet you’re on. Seasons change on Earth because the planet is slightly tilted on its axis as it travels around the Sun.

Earth’s axis may be imagined as an imaginary pole going right through the center of our planet from “top” to “bottom.” Earth spins around this pole, making one complete turn each day. That is why we have day and night.

Earth's seasons
Click to view larger. Credit: NASA/Space Place

Although the tilt of the Earth as compared to the plane of its orbit around the Sun is more or less constant (23.5˚), at the December solstice, the Northern Hemisphere receives the most indirect sunlight, causing cooler temperatures. The Southern Hemisphere receives the most direct sunlight, causing warmer temperatures, so it is summer there.  At the June solstice, this effect reverses and the Northern Hemisphere receives the most direct sunlight, causing warmer temperatures, and the Southern Hemisphere receives the most indirect sunlight, causing cooler temperatures.

The December solstice brings the shortest day and longest night of the year for locations in the northern half of the globe, like the U.S., while the southern half of the globe is experiencing its longest day and shortest night. Therefore, all locations north of the equator see daylight shorter than 12 hours and all locations south see daylight longer than 12 hours.

After the winter solstice in the Northern Hemisphere, the days will get longer and the nights shorter until the summer solstice on June 21, 2022, when things reverse.  The March equinox on March 20, 2022, will mark the beginning of the astronomical spring season and the September equinox on September 22, 2022, will mark the beginning of astronomical fall.

The ancient cultures knew that the Sun’s path across the sky, length of daylight, and location of the sunrise and sunset all shifted in a regular way throughout the year. Additionally, people built monuments, like Stonehenge in England and the Torreon in Machu Picchu, Peru, to follow the Sun’s annual progress and predict its movements.

Today, we have even more information about the universe, and we celebrate the solstice as an astronomical event caused by Earth’s tilt on its axis and its motion in orbit around the Sun.

No matter where you are on Earth’s globe – this is your time to celebrate this seasonal change!

by Lance D. Davis  

Geminid Meteor Shower: NASA to Livestream Annual Highlight of December Skies

Every December we have a chance to see one of our favorite meteor showers – the Geminids. The shower is currently active until Dec. 17 and will peak on the night of Dec. 13 into the morning of Dec. 14, making those hours the best time for viewing the meteor shower.

Geminids
All meteors appear to come from the same place in the sky, which is called the radiant. The Geminids appear to radiate from a point in the constellation Gemini, hence the name “Geminids.” The graphic shows the radiants of 388 meteors with speeds of 35 km/s observed by the NASA Fireball Network in December 2020. All the radiants are in Gemini, which means they belong to the Geminid shower. Credit: NASA

The Geminids are caused by debris from a celestial object known as 3200 Phaethon, whose origin is the subject of some debate. Some astronomers consider it to be an extinct comet, based on observations showing some small amount of material leaving Phaethon’s surface. Others argue that it has to be an asteroid because of its orbit and its similarity to the main-belt asteroid Pallas.

Whatever the nature of Phaethon, observations show that the Geminids are denser than meteors belonging to other showers, enabling them to get as low as 29 miles above Earth’s surface before burning up. Meteors belonging to other showers, like the Perseids, burn up much higher.

The Geminids can be seen by most of the world. Yet, it is best viewed by observers in the Northern Hemisphere. As you enter the Southern Hemisphere and move towards the South Pole, the altitude of the Geminid radiant – the celestial point in the sky where the Geminid meteors appear to originate – gets lower and lower above the horizon. Thus, observers in these locations see fewer Geminids than their northern counterparts.

Besides the weather, the phase of the Moon is a major factor in determining whether a meteor shower will have good rates during any given year. This is because the moonlight “washes out” the fainter meteors, resulting in sky watchers seeing the fewer bright ones. This year, the Moon will be almost 80% full at the peak of the Geminids, which isn’t ideal for our highly regarded meteor shower. Nevertheless, that bright Moon is expected to set around 2:00 a.m. wherever you are located, leaving a couple of hours for meteor watching until twilight.

“Rich in green-colored fireballs, the Geminids are the only shower I will brave cold December nights to see,” said Bill Cooke, lead for NASA’s Meteoroid Environment Office, located at Marshall Space Flight Center in Huntsville, Alabama.

NASA will broadcast a live stream of the shower’s peak Dec. 13-14 via a meteor camera at NASA’s Marshall Space Flight Center in Huntsville, Alabama, (if our weather cooperates!), starting at 8 p.m. CST on the NASA Meteor Watch Facebook page.

Meteor videos recorded by the All Sky Fireball Network are also available each morning to identify Geminids in these videos – just look for events labeled “GEM.”

Learn more about the Geminids below:


Why are they called the Geminids?

All meteors associated with a shower have similar orbits, and they all appear to come from the same place in the sky, which is called the radiant. The Geminids appear to radiate from a point in the constellation Gemini, hence the name “Geminids.”

How fast are Geminids?

Geminids travel 78,000 mph (35 km/s). This is over 1000 times faster than a cheetah, about 250 times faster than the swiftest car in the world, and over 40 times faster than a speeding bullet!

How to observe the Geminids?

If it’s not cloudy, get away from bright lights, lie on your back, and look up. Remember to let your eyes get adjusted to the dark – you’ll see more meteors that way. Keep in mind, this adjustment can take approximately 30 minutes. Don’t look at your cell phone screen, as it will ruin your night vision!

Meteors can generally be seen all over the sky. Avoid watching the radiant because meteors close to it have very short trails and are easily missed. When you see a meteor, try to trace it backwards. If you end up in the constellation Gemini, there’s a good chance you’ve seen a Geminid.

Observing in a city with lots of light pollution will make it difficult to see Geminids. You may only see a handful during the night in that case.

When is the best time to observe Geminids?

The best night to see the shower is Dec. 13/14. Sky watchers in the Northern Hemisphere can go out in the late evening hours on Dec. 13 to see some Geminids, but with moonlight and radiant low in the sky, you may not see many meteors.

Best rates will be seen when the radiant is highest in the sky around 2:00 a.m. local time, including the Southern Hemisphere, on Dec. 14. The Moon will set around the same time. Therefore, observing from moonset until twilight on Dec. 14 should yield the most meteors.

You can still see Geminids on other nights, before or after Dec. 13-14, but the rates will be much lower. The last Geminids can be seen Dec. 17.

How many Geminids can observers expect to see Dec. 13/14?

Realistically, the predicated rate for observers in the northern hemisphere is closer to 30-40 meteors per hour. Observers in the Southern Hemisphere will see fewer Geminids than those in the northern hemisphere – perhaps 25% of rates in the Northern Hemisphere.


Although this year’s conditions are not the best for viewing the Geminid meteor shower, it will still be a good show to catch in our night skies.

And, if you want to know what else is in the sky for December, check out the video below from Jet Propulsion Laboratory’s monthly “What’s Up” video series:

Happy viewing stargazers!

by Lance D. Davis

Experience NASA’s Journey to LCRD Launch

LAUNCH UPDATE:  NASA’s Laser Communications Relay Demonstration (LCRD) is now scheduled to lift off Tuesday, Dec. 7 at 3:04 a.m. CST (4:04 a.m. EST) aboard United Launch Alliance’s Atlas V rocket. Get more details here.


Have you ever witnessed one of NASA’s launches? It’s definitely a sight to see when a rocket takes to the sky, soaring beyond our atmosphere into space.

If you haven’t, you’ll have another chance soon with the Laser Communications Relay Demonstration (LCRD), which will continue NASA’s exploration of laser communications to support future missions to the Moon and throughout our solar system.

Illustration of NASA’s Laser Communication Relay Demonstration
Illustration of NASA’s Laser Communication Relay Demonstration communicating over laser links.
Credits: NASA’s Goddard Space Flight Center

LCRD is scheduled to launch Dec. 5 aboard an Atlas V551 rocket from Cape Canveral Space Force Station in Florida with a two-hour launch window that opens at 3:04 a.m. CST (4:04 a.m. EST).

Live coverage of the launch begins on NASA Live at 2:30 a.m. CST (3:30 a.m. EST), with countdown commentary on NASA Television, the NASA app, and NASA social media.

Register as an LCRD virtual guest to experience NASA’s journey to the LCRD launch. Along with participating online in the launch, you’ll also gain access to curated launch resources, mission information, interaction opportunities, and schedule updates. Following launch, virtual guests will receive a stamp for their virtual guest passport!

Like technology demonstrations that have come before it, LCRD is a giant step towards making operational laser, or optical, communications a reality.

But just how much data can NASA transmit at once with laser communications? To give you an idea, sending a high-resolution map of Mars would take around nine weeks with spacecraft’s current onboard radio systems, but as little as nine days with laser communications. That kind of data rate is much more appealing for future human exploration and science missions.

With the mission operating for at least two years, LCRD will start off “talking” with ground stations in California and Hawaii to test the invisible, near-infrared lasers. Engineers will beam data to and from the satellite – located more than 22,000 miles above Earth – to study and enhance the technology’s performance for an operational mission. LCRD will also help NASA update how astronauts communicate to and from space.

As NASA goes back to the Moon, laser communications can empower sustainable communications and help us prepare for a human presence on Mars.

Get the full LCRD experience below:

The Mission:

For Fun:

For Students: 

Watch, Engage on Social Media:

Developed and led by Goodard Space Flight Center in Greenbelt, Maryland, LCRD is funded by the Technology Demonstration Missions program, located at Marshall Space Flight Center in Huntsville, Alabama, which is part of the Space Technology Mission Directorate at NASA Headquarters in Washington. Additionally, it’s funded by the Space Communications and Navigation program, also at NASA Headquarters.

Learn more about LCRD.

by Lance D. Davis