Star Gazer’s Guide {Dec. 10-16}

Here are this week’s best astronomical events that you can view right from your backyard. Below is a grouping of reflection nebulae in Orion–NGC 1977, NGC 1975, and NGC 1973. These beautiful features are often overlooked in favor of the brighter stellar nursery of the Orion Nebula, but are stunning in their own right. Their characteristic blue color is an artifact of the interstellar dust reflecting the light from young, hot stars, and the redder regions are faint emissions from hydrogen atoms. More information here if you are interested! As for events this week, you won’t want to miss the Geminid meteor shower. It’s expected to be one of the best meteor showers of the year. Happy exploring!

“All my life through, the new sights of nature made me rejoice like a child.” –Marie Curie

Reflection Nebula


You can use the star chart provided here. And for any terms or units you may be unfamiliar with, I’ve provided a glossary at the end of the guide for your convenience. All events were calculated based on Boulder, CO (latitude 40⁰ N), but should provide good approximations for most cities near the same latitude. If you would like, you can change your location on the linked sites for each event. Let me know if you have any questions. I’d love to know what you see this week!


Thursday 12/10

17:00 MST          New Moon

A New Moon occurs when the Moon passes between the Earth and the Sun, such that its lighted side is facing directly away from the Earth (sun-side). While the New Moon can be seen during a more rare solar eclipse, most months the Moon passes just above or below the Sun as seen from the Earth. The New Moon rises and sets with the Sun, and this is why we are unable to see the New Moon–it is hidden in the glare of the Sun during the day.  More information here.

17:31 MST          ISS Passing

The ISS will make a visible pass (magnitude -1.4) starting at 10⁰ elevation in the WNW and moving NNE, reaching a highest elevation of 22⁰. More information here.

22:27 MST          204P/LINEAR-NEAT at Perihelion

Comet 204P/LINEAR-NEAT will make its closets approach to the Sun at a distance of 1.93 AU. From Boulder, it will be visible from 22:27 MST (24⁰ above Eastern horizon) to 06:02 MST (48⁰ above Western horizon). It will reach its highest point in the sky at 03:19, 67⁰ above the Southern horizon. More information here.


Friday 12/11

05:39 MST          Iridium Flare (Iridium 45)

The Iridium 45 satellite will cause an iridium flare of magnitude -2.6 to -8.1 that will be seen as a bright flash across the sky. The flare will begin at an elevation of 48⁰ in the NNW. More information here.

17:00 MST          Moon at Perihelion

The Moon will reach its closest point in its orbit to the Sun, at a distance of 0.9821 AU. The Moon will lie between the Sun and the Earth at this time. For comparison, the Earth will be at a distance of 0.9846 AU from the Sun. More information here.


Saturday 12/12

17:18 MST          Iridium Flare (Iridium 45)

The Iridium 45 satellite will cause an iridium flare of magnitude -2.0 to -6.5 that will be seen as a bright flash across the sky. The flare will begin at an elevation of 25⁰ in the SSW. More information here.


Sunday 12/13

17:12 MST          Iridium Flare (Iridium 32)

The Iridium 32 satellite will cause an iridium flare of magnitude -2.0 to -6.6 that will be seen as a bright flash across the sky. The flare will begin at an elevation of 25⁰ in the SSW. More information here.


Monday 12/14

24:00 MST          Geminid Meteor Shower

The Geminid meteor shower will reach its peak activity tonight. Shooting stars associated with the shower should be visible from December 7th through 16th. The maximum rate of visible meteors is expected to reach 100 per hour; however, this zenithal hourly rate is dependent on many factors, such as sky conditions, light pollution at the observer’s location, and altitude of the meteor shower’s radiant in the sky. The Moon will be 3 days old at the peak, and so will present minimal interference. At midnight, the shower’s radiant will appear 75⁰ below the SE horizon from Boulder, with the meteors traveling directly outward from this point. In order to see the most meteors possible, it is best to look at any dark patch of sky 90⁰ around the radiant, rather than at the radiant itself. This is because the meteors will typically appear brightest at these locations. It is so named the Geminid meteor shower because of its radiant’s location with the constellation Gemini. More information here.


Tuesday 12/15

20:00 MST          NGC 1981 well placed

The open star cluster NGC 1981 will be well placed for observation in Orion’s sword. It should be visible for latitude between 65⁰N and 74⁰ S, reaching its highest point in the sky around midnight local time. In Boulder, NGC 1981 will become visible around 20:00 MST when it rises 18⁰ above the Eastern horizon. It will reach its highest point in the Boulder sky around 00:05 MST, 45⁰ above the Southern horizon. It will become inaccessible around 04:06 MST when it sinks above the SW horizon. The star cluster will be too faint to see easily with the naked eye, but is visible through binoculars or a small telescope. More information here.


Wednesday 12/16

17:03 MST          Iridium Flare (Iridium 30)

The Iridium 30 satellite will cause an iridium flare of magnitude -4.2 to -6.2 that will be seen as a bright flash across the sky. The flare will begin at an elevation of 22⁰ in the SSW. More information here.



Apogee: The point in the orbit farthest away from the Earth.

Apehelion: The point in the orbit farthest away from the Sun.

Arcminute: An angular measurement, defined as 1/60 of one degree. Denoted by ‘. (approx. 1 inch at a distance of 100 yards, the Moon is approx 31’)

Arcsecond: An angular measurement, defined as 1/60 of an arcminute. Denoted by “. (approx. dime at a distance of 1 mile )

A great resource for understanding and approximating angular measurements in the night sky, here. The Moon is approx 1/2⁰. Your outstretched hand is approx 20⁰, with each finger approx 1⁰. Your closed outstretched palm is approx 10⁰.

AU: Astronomical Unit, Defined as the distance between the Sun and Earth.

Conjunction: An alignment of two celestial bodies such that they present the least angular separation as viewed from Earth.

Elongation: The angle between the Sun and a planet, with Earth as the reference point. The greatest elongation of a planet occurs when this separation angle is at its largest. More information here.

Iridium Flare: Iridium fares occur when sunlight is reflected off the antenna (of one of the 66 active telecommunication sats in LEO, known as the Iridium constellation) directly down at Earth. This reflection causes an illuminated spot on the surface of the Earth. To an observer on the ground, the event appears to be a bright flash, or flare in the sky, which lasts for a few seconds.

ISS: International Space Station. More information here.

Magnitude: A logarithmic measure of the brightness of an object. Brighter objects have a lower (more negative) magnitude. More information here.

Opposition: When a celestial body is opposite the Sun in the sky.

Perigee: The point in the orbit closet to the Earth.

Perihelion: The point in the orbit closest to the Sun.

Radiant: The point in the sky where meteors of a meteor shower appear to originate.


Time Conversions from MST

Eastern Daylight Time, EST = MST + 2:00

Central Daylight Time, CST = MST + 1:00

Mountain Daylight Time, MST

Pacific Daylight Time, PST = MST – 1:00

Alaska Daylight Time, AKST = MST – 2:00

The standard for astronomical times is UTC if you happen to come across it, where MST = UTC – 6:00.


Sources used here, here, and here.

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