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the COSMOS

Star Gazer’s Guide {Oct. 15-21}

Here are this week’s best astronomical events that you can view right from your backyard. Happy exploring!

Don’t tell me that man doesn’t belong out there. Man belongs wherever he wants to go–and he’ll do plenty well when he gets there. — Werner von Braun

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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 10/15

05:49 MDT        Iridium Flare (Iridium 80)

The Iridium 85 satellite will cause an iridium flare of magnitude -4.7 that will be seen as a bright streak across the sky. The flare will begin at an elevation of 40⁰ in the South. More information here.

19:06 MDT        Iridium Flare (Iridium 62)

The Iridium 62 satellite will cause an iridium flare of magnitude -8.0 that will be seen as a bright streak across the sky. The flare will begin at an elevation of 49⁰ in the South. More information here.

13:39 MDT         136108 Haumea at Solar Conjunction

Haumea is one of the fastest rotating large objects in our system, and is classified as a dwarf planet. Haumea will appear very close to the Sun, as it passes around the far side of the solar system from Earth. Haumea will be separated from the Sun by only 27⁰, making it unobservable for several weeks as it will be lost in the Sun’s glare. More information here. Note: This is not an observable event. I included it here simply because I found it interesting. (See below, Eris Opposition on Friday 10/16 as well.)

14:12 MDT         Moon at Perihelion

The Moon will reach its closest point in its orbit to the Sun, at a distance of 0.9949 AU. The Moon will lie between the Sun and the Earth at this time. For comparison, the Earth will be at a distance of 0.9971 AU from the Sun. More information here.

 

Friday 10/16

05:40 MDT         Mercury at Greatest Elongation West

Mercury will be at its greatest separation from the Sun. However, it will be difficult to observe with an elevation of just 13⁰ above the horizon. Mercury will be visible in the dawn sky, rising at 05:40 MDT and fading from view as dawn breaks around 06:66 MDT. It’s magnitude will be -2.6.  More information here.

05:43 MDT        Iridium Flare (Iridium 81)

The Iridium 81 satellite will cause an iridium flare of magnitude -4.6 that will be seen as a bright streak across the sky. The flare will begin at an elevation of 40⁰ in the South. More information here.

06:58 MDT         136199 Eris at Opposition

Eris is a dwarf planet and the 9th largest body in our solar system (bigger than even Pluto!). Eris will be visible for much of the night, placed within the constellation Cetus. In Boulder, Eris will become visible around 21:28 MDT (24⁰ above SE horizon), will reach its highest peak around 01:05 (46⁰ above Southern horizon) and become un-observable by 04:39 MDT when it drops below the SW horizon. Eris, discovered in 2005, was actually the celestial object which forced astronomers to legitimately discuss the definition of planet. Prior to this, there were no strict guidelines for planet classification. This ultimately led to Pluto being demoted from its planet status, to dwarf planet status. Quite an interesting story! When Eris is directly opposite the Sun (at opposition), it is actually at its closest approach to Earth. This is why it appears at its brightest and largest today. At opposition, Eris lies at a distance of 95.33 AU and will reach a peak brightness of magnitude 18.6. However, because it is still so distant from the Earth, it will look very much like a star. More information on the event here. Note: This event will not be observable. The limit of the human eye is around 6.5 magnitude. I’ve included it here because I found it interesting.

18:36 MDT         Moon-Saturn Conjuction

The Moon and Saturn will be very close, passing within 2⁰54’ of each other. The Moon will have a magnitude of -10.2 in the constellation Scorpius, while Saturn will have a magnitude of 1.2 in the constellation Libra. From Boulder, the pair will be difficult to see because of its low elevation of no more than 15⁰. They will become visible around 18:36 MDT as the dusk sky fades, setting 2 hours after the Sun at 20:19 MDT. More information here.

 

Saturday 10/17

03:52 MDT         Jupiter-Mars Conjuction

Jupiter and Mars will be very close, passing within 0⁰22’ of each other.  Jupiter will have a magnitude of -1.8, while Mars will have a magnitude of 1.5. Both will be located in the constellation Leo. From Boulder, the pair will be visible in the dawn sky with a rise time of 03:52 MDT and will remain visible until dawn breaks at 06:56 MDT. More information here.

 

Sunday 10/18

19:36 MDT         ISS Passing

The ISS will make a visible pass (magnitude -1.9) starting at 10⁰ elevation in the NNW and moving NNE. More information here.

 

Monday 10/19

18:43 MDT         ISS Passing

The ISS will make a visible pass (magnitude -1.4) starting at 10⁰ elevation in the NNW and moving ENE. More information here.

20:19 MDT         ISS Passing

The ISS will make a visible pass (magnitude -1.4) starting at 10⁰ elevation in the NW and moving NW. More information here.

 

Tuesday 10/20

05:28 MDT        Iridium Flare (Iridium 41)

The Iridium 41 satellite will cause an iridium flare of magnitude -1.9 that will be seen as a bright streak across the sky. The flare will begin at an elevation of 36⁰ in the SSW. More information here.

14:33 MDT         Moon at First Quarter

The Moon will be at first quarter tonight. The different Moon phases occur because of our changing perspective as the Moon orbits the Earth. The phases cycle every 29.5 days–from new moon, to first quarter, to full moon, to last quarter, and then finally to new moon again. The half phase is ideal for observing the craters and mountains on the Moon’s surface. More information here.

19:27 MDT         ISS Passing

The ISS will make a visible pass (magnitude -2.9) starting at 10⁰ elevation in the NW and moving ENE. More information here.

 

Wednesday 10/21

20:11 MDT         ISS Passing

The ISS will make a visible pass (magnitude -1.8) starting at 10⁰ elevation in the WNW and moving WSW. More information here.

24:00 MDT         Orionid Meteor Shower

The Orionid meteor shower will reach its peak activity tonight. Shooting stars associated with the shower should be visible from October 16th through October 30th. The maximum rate of visible meteors is expected to reach 25 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. Note in particular that the moon will present significant interference in the early evening sky. At midnight, the shower’s radiant will appear 20⁰ above the eastern horizon, 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 Orionid meteor shower because of its radiant’s location with the constellation Orion. More information here.

 

Glossary

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 MDT

Eastern Daylight Time, EDT = MDT + 2:00

Central Daylight Time, CDT = MDT + 1:00

Mountain Daylight Time, MDT

Pacific Daylight Time, PDT = MDT – 1:00

Alaska Daylight Time, AKDT = MDT – 2:00

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

 

Sources used here, here, and here.

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