This post discusses the expected meteor activity and lunar conditions for the upcoming week. It is focused on North American latitudes but may be used in all locations. Sky charts displaying current radiant positions are provided for early evening hours, mid-night, and the hour prior to dawn. European readers may wish to use the charts in the same article at www.imo.net for better accuracy.
Meteor Activity Outlooks for observers in the southern hemisphere are available upon request at: lunro.imo.usa@cox.net
Clear Skies!
Robert Lunsford
ALPO Meteors Section Coordinator
Location of the Ursid (URS) radiant on December 21/22, looking slightly east (right) of due north.
The Ursid meteor shower is the least observed of the major annual showers. In the northern hemisphere December nights are cold and often cloudy. Another hindrance is the fact that it peaks just before the Christmas holiday when many people are busy with holiday festivities. This shower is completely invisible from the southern hemisphere as the radiant lies too far north to be seen from south of the equator this time of year.
The Ursids are active from December 18-23 with a sharp maximum on December 22nd. Activity is normally low away from maximum with rates less than 1 shower member per hour. At maximum activity this source normally adds 5-10 medium velocity meteors to the 15 or so that are normally seen each morning hour from dark sky sites. This year though, the earth passes close to several past trails of debris that closely follow the orbit of comet 8P/Tuttle. This could enhance the Ursid activity seen this year. See the list of encounters in chronological order below listing the year of the debris trail, the expected time of maximum activity and the expected activity:
815 debris trail, December 22, 03h − 22h UT Expected activity: High
719 & 733 debris trails, December 22, 03h15m − 03h40m UT Expected activity: Low
filament, December 22, 05h27m UT Expected activity: Low
829 debris trail, December 22, 06h10m UT Expected activity: High
801 debris trail, December 22, 17h31m UT Expected activity: Low
These predictions are no guarantee of exceptional activity as the timing is easier to predict than the density of the dust trails. The moon will be near its first quarter phase and half illuminated. Therefore it will set near midnight local standard time for most locations. The most favorable time appears to be near 6:10 Universal Time on December 22nd, when the Earth encounters the trail of debris from the trail created in the year 829. This timing favors western Europe all the way to the west coast of North America, basically wherever it is night at that time. Those in western North America will have to deal with moonlight while the moon will have set for all the other locations to the east. The northern polar and sub-polar regions are also favored as the radiant remains high in the sky at all times.
At maximum, the Ursid radiant lies just west of the fairly bright (2nd magnitude) star known as Kochab (beta Ursae Minoris). To those not familiar with star names, this area lies adjacent to the bowl of the “Little Dipper” as shown in the star chart. This area of the sky lies lowest in the northern sky near 20:00 (8pm) local standard time. This is the worst time to view the Ursids as most of the activity will occur beyond your line of sight, below the northern horizon. As the night progresses the Ursid radiant will slowly rise higher into the sky and is best placed during the last dark hour before dawn. To best view this activity it is suggested that you face toward the northern half of the sky. It doesn’t have to be directly at the radiant, but it’s a good idea to have the radiant within your field of view to help with shower association. Don’t look straight up as this is the worst place to look for meteors. Lower you view so that none of the horizon blocks your view. About half way up in the sky is suggested for most observers.
Despite the bitter cold, try to view for at least an hour. Meteor activity is notoriously variable and if you view for only a short time, it may occur during a lull in activity. Viewing for at least an hour ensures you will see several peaks and valleys of activity. Serious observers can contribute to our knowledge of the Ursids by providing data on each meteor they see. The time and magnitude of each meteor are most important. Additional information such as color, velocity, and persistent train phenomena can also be recorded. Note that not every meteor will be an Ursid. There are several minor showers also active during this period adding a few meteors to the hourly total. There are also upwards of 10 random meteors appearing each hour to add to your count. Therefore shower association of each meteor must be included.
Observers are encouraged to share their meteor observations with the International Meteor Organization as soon as possible after the session by filling out an online visual form. If you happen to be observing at a time of high meteor activity be sure to use smaller time periods within your session so that no period has excess of 20 meteors.
If you have never viewed this shower, be sure to check it out this year!
December 18, 2020
This post discusses the expected meteor activity and lunar conditions for the upcoming week. It is focused on North American latitudes but may be used in all locations. Sky charts displaying current radiant positions are provided for early evening hours, mid-night, and the hour prior to dawn. European readers may wish to use the charts in the same article at www.imo.net for better accuracy.
Meteor Activity Outlooks for observers in the southern hemisphere are available upon request at: lunro.imo.usa@cox.net
Clear Skies!
Robert Lunsford
ALPO Meteors Section Coordinator
December 11, 2020
This post discusses the expected meteor activity and lunar conditions for the upcoming week. It is focused on North American latitudes but may be used in all locations. Sky charts displaying current radiant positions are provided for early evening hours, mid-night, and the hour prior to dawn. European readers may wish to use the charts in the same article at www.imo.net for better accuracy.
Year in and year out the Geminids are currently the most dependable meteor shower. Unfortunately, they are active in December when temperatures are often cold and skies cloudy in the northern hemisphere. Then is this display worth viewing this year? Most certainly! So it may be chilly out, but if you bundle up and step outside over the next week, you’ll be able to enjoy one of the most active meteor showers of the year!
The Geminids are often bright and intensely colored. Due to their medium-slow velocity, persistent trains are not usually seen. These meteors are also seen in the southern hemisphere, but only during the middle of the night and at a reduced rate.
Unlike most other meteor showers, the Geminids are not associated with a comet but with an asteroid. 3200 Phaethon is an asteroid with an orbit that brings it closer to the Sun than any other named asteroid (though there are numerous unnamed asteroids with smaller perihelia*). For this reason, it was named after the Greek myth of Phaëthon, son of the sun god Helios. Even though 3200 Phaethon is classified as an asteroid, it often acts like a comet by ejecting dust when it nears the sun. The Earth is near the orbit of 3200 Phaethon during the first three weeks of December. It comes closest to the core of the orbit on December 14th each year. This is the date most Geminid meteors are encountered and seen. When the Earth is near the edge of the orbital debris of the asteroid, little activity is seen.
* The perihelia is the point in a solar orbit where the orbiting body is closest to the sun.
So when and where do I look?
The Geminids are expected to be active between December 1st and 22nd this year. The highest rates are expected to occur on the night of December 13/14, when rates can exceed one per minute from dark sky sites. The early portion of the Geminid activity will be difficult to observe due to the waning gibbous moon. The moon will not reach its last quarter phase until December 7th. On that date the half-illuminated moon will lie above the horizon from midnight onward. One can still view Geminid activity during the evening hours but rates will be low due to the fact that the maximum is a week away and that the radiant lies low in the east during the early evening hours. During December 7-14, the moon will rise approximately 45 minutes later with each passing night. This will allow you to watch later in the night with each passing day. By December 12, the moon will be a non-factor as it will be a slender crescent and will not rise until the start of dawn. If your weather appears to be overcast on the peak night, the two nights prior and the one night after the peak will also produce impressive activity.
Position of the Geminids Radiant on Dec 13th, 22:00 UTC
The prime hours to watch Geminid activity are between 11pm and 4am local standard time. During these hours the radiant of the Geminid meteors will lie highest above the horizon. The radiant lies in the constellation of Gemini near the bright star known as Castor (alpha Geminorum). The radiant is not the actual source of the meteors. This artificial point in the sky, as well as the stars of Gemini, happen to lie in the background while the stream of Geminid meteors enter the atmosphere, seemingly from the radiant in the constellation of Gemini. The radiant point and the constellation of Gemini serves as a useful guide to identifying Geminids as not all meteors seen in December are Geminids. There are several other minor showers radiating from the constellations of Orion, Monoceros, Hydra, and Leo Minor, to name a few. There are also random meteors that appear from all over the sky. These meteors once belonged to their own meteor shower, but time has dispersed them to the point that a connection with other meteors is now impossible. On the night of maximum activity, the Geminids will provide over 90 percent of the meteor activity during the night. As you move away from the peak night this percentage falls drastically.
Geminid meteors can appear in any part of the sky. You do not have to face the constellation of Gemini to see them. It does help to have the radiant somewhere within your field of view. This will help in the identification of each meteor. Geminid meteors will shoot outward from the radiant while others will have random paths and speeds. Geminid meteors will appear slowest and shortest near the radiant. This is due to foreshortening as the meteors seen close to the radiant are moving in a direction toward you. Geminid meteors will appear fastest and longest at a point 90 degrees away from the radiant. Beyond 90 degrees distant from the radiant, the meteors will begin to slow and become shorter again.
During the early evening hours, I like to face eastward and watch Geminid earthgrazers shoot from the northeastern horizon. When viewed at this time and position, the Geminid meteoroids (meteors still in outer space) can only graze the upper portions of the atmosphere. Due to the lower density of air molecules at this altitude, the meteors take longer to disintegrate and thus create long streaks in the sky. Most of these long streaks appear low in the north or south, but if you are lucky you will witness some that shoot high overhead.
As the night progresses, the Geminid radiant rises higher into the eastern sky. Their duration and length will become noticeably shorter as they can now penetrate deeper into the atmosphere. This should not cause concern as these meteors still disintegrate while still many miles high in the atmosphere. While the individual meteors may become less impressive, there will now be many more of them as you can now see the meteors that were once shooting downward, below the horizon. For the remainder of the night the Geminids will produce an occasional colorful fireball, which is a meteor brighter than all the objects in the sky except the sun and moon. You may think that fireballs are created by very large meteoroids. Actually, fireballs can be produced by object as small as golf balls. When you consider the average meteor is produced by meteoroids the size of small pebble, then a golf ball is large compared to them. Geminid fireballs are notable for their intense color. Many of these are brilliant green, as well as yellow and orange.
During the peak hours of the Geminid display I like to face due south and have the radiant drift westward through my field of view. This also allows me to monitor the minor showers that are active in the same region of the sky. If I have enough energy to view until dawn, I tend to shift my view more westward to keep the radiant within my field of view.
Don’t go outside and stand to try and view the Geminid activity. Your neck will quickly stiffen and you will soon tire. I suggest using a comfortable lounge chair that allows you to look half-way up in the sky comfortably. Bring plenty of blankets to keep warm. Those who wish to contribute meteor counts should watch for at least one hour. The reason for this is that meteoroids are distributed randomly in outer space. When quoted hourly rates are 60, this does not mean you will see one meteor every minute. There will be 5 to 10 minute periods when little activity is evident. There will also be periods of similar length when there will be continuous activity of 3-4 meteors per minute. There are several “peaks” and “valleys” of meteor activity each hour so if you only watch for a short time, you may find yourself viewing during one of the lulls of activity.
This post discusses the expected meteor activity and lunar conditions for the upcoming week. It is focused on North American latitudes but may be used in all locations. Sky charts displaying current radiant positions are provided for early evening hours, mid-night, and the hour prior to dawn. European readers may wish to use the charts in the same article at www.imo.net for better accuracy.
