12/03/2018 – Ephemeris – Comet Wirtanen should be bright enough for the naked eye or binoculars this month

Ephemeris for Monday, December 3rd. The Sun will rise at 8:02. It’ll be up for 9 hours and 1 minute, setting at 5:03. The Moon, half way from last quarter to new, will rise at 4:56 tomorrow morning.

Beside Comet Machholz-Fujikawa-Iwamoto which I talked about last Thursday and should be at peak brightness about now in the western twilit sky, we have another comet, this one Comet 46P/Wirtanen is brightening in the east in the evening. Wirtanen is a member of the Jupiter family of comets, whose 5.44 year orbit of the Sun takes it from just outside the Earth’s orbit to just inside Jupiter’s orbit. This time around it will come as close as 7.1 million miles of the Earth. As of Thanksgiving the comet was 100 times brighter than its nominal expected brightness. I don’t know if it will stay that way. It has a history of outbursts. If it keeps it up Wirtanen could be as bright as the Pleiades stars when it passes them on the 16th.

The times given are for the Traverse City/Interlochen area of Michigan. They may be different for your location.

Addendum

The path of Comet 46P/Wirtanen from November 21, 2018, to January 1, 2019. The labels are month, date, and expected magnitude. Click on the image to enlarge. Created using Cartes du Ciel (Sky Charts).

Check back every Wednesday at least where Comet Wirtanen will be past of the planet report.  I’ll be covering the comet on other days throughout the month.  Also check  Seiichi Yoshida’s Weekly Information about Bright Comets: http://www.aerith.net/comet/weekly/current.html

11/28/2018 – Ephemeris – Bright planets and comets tonight

Ephemeris for Wednesday, November 28th. The Sun will rise at 7:56. It’ll be up for 9 hours and 8 minutes, setting at 5:04. The Moon, 1 day before last quarter, will rise at 11:05 this evening.

Let’s look at the bright planets for tonight. Two of them are visible in the evening sky. Saturn will be briefly visible very low in the southwestern sky and from about 6 p.m. and will set at 7:10 p.m. Mars will be in the south as the skies darken tonight. Mars will be due south at 6:52 p.m., and it will set at 12:17 a.m. Mars is moving eastward, crossing the constellation of Aquarius this month. It’s currently about midway through Aquarius, moving eastward and northward, so its setting time won’t change much over this month. Venus, our brilliant morning star, will rise at 4:33 a.m. in the east southeast. The blue-white star Spica is still to the right and a bit above it. There are two comets entering our sky. More on that tomorrow.

The times given are for the Traverse City/Interlochen area of Michigan. They may be different for your location.

Addenda

Planets and the Moon

Mars, and Saturn seen at 6 p.m. tonight November 28, 2018. Created using Stellarium.

Venus and the Moon in the morning sky at 7 a.m. November 29, 2018. Note the bluish star Spica to the right of it. Created using Stellarium.

The waning gibbous Moon as it should appear tomorrow morning in binoculars. Created using Stellarium.

Telescopic view of Venus tomorrow morning November 29, 2018. Created using Stellarium.

Planets, two comets and the Moon at sunset and sunrise of a single night starting with sunset on the right on November 28, 2018. The night ends on the left with sunrise on the 29th. Click on the image to enlarge. Created using my LookingUp program.

Bright comets

Comet C/2018 V1 (Machholz-Fijikawa-Iwamoto) in twilight starting tonight November 28, 2018. The comet won’t climb that deramatically at 6 p.m. on the rest of the nights because the stars in the field will set 4 minutes earlier each successive evening. The latest magnitude estimate of the comet on December 1 is 5.2, two magnitudes brighter than shown here. Created using Cartes du Ciel (Sky Charts).

Comet 46P/Wirtanen positions for the next week. Positions are marked with month-date and magnitude. The latest magnitude prediction for December 1st is 4.6, 5.1 magnitudes brighter than shown here. The comet may make magnitude 3 by mid-December. Star field position is for 9 p.m. on the 28th. Click on the image to enlarge. Created using Cartes du Ciel (Sky Charts).

11/25/2018 – Ephemeris Extra – Comet 46P/Wirtanen may be naked eye in December

he path of Comet 46P/Wirtanen from November 21, 2018, to January 1, 2019. The labels are month, date, and expected magnitude. On November 22nd it was observed to be magnitude 5.5, about 5 magnitudes brighter than the predictions on the chart.  Click on image to enlarge. Created using Cartes du Ciel (Sky Charts).

Comet 46P/Wirtanen will be well placed in the evening sky for observation. Though a small comet, it has a history of being active, which is not disappointing us now. It will be closest to the Earth on December16^th at 7.1 million miles (11.4 million km). 

On December 16^th the comet will be closest to the Pleiades. On the 23^rd it will appear close to the bright star Capella. After that it will become circumpolar.

Comet Wirtanen is a small short period comet of 5.44 years.  It’s orbit doesn’t come as close to the Sun as the Earth.  It’s closest to the Sun, called perihelion it which it reaches December 12th is about 98 million miles (158 million km).  The orbit extends out to nearly Jupiter’s orbit.

Checkout photos and animations of this and other comets in http://www.spaceweather.com/’s Realtime Comet Gallery.

Also check out Seiichi Yoshida’s website and his weekly information about Bright Comets: http://www.aerith.net/comet/weekly/current.html.

Here is a black on white chart that I created for our society’s newsletter of the positions of the comet when it passes the Pleiades.  The positions are for 9 p.m. EST (01:00 UT on next date) on the displayed dates. Created with Cartes du Ciel (Sky Charts).

A note about comet magnitudes

Comet magnitudes are always devilishly hard to estimate. A comet always appears dimmer than its magnitude suggests because one is comparing the brightness of a diffuse object with the point source of a star. One either has to reduce the size of the comet to almost a point or defocus the star to the size of the comet to make the comparison if it doesn’t have a tail.

A point about magnitudes. They’re like golf scores. The lower the number, the brighter the object, and the better the golf score. Blame the ancient Greek astronomer Hipparchus, who ranked star brightness from first magnitude for the brightest stars to sixth magnitude for the dimmest stars visible to the naked eye. Modern astronomers put a mathematical basis for the system saying that a magnitude difference of 5 equals a brightness difference of 100. So each magnitude step equals the 5^th root of 100 or 2.512. So a 5^thmagnitude star is about two and a half times brighter than a 6^thmagnitude star, and so on.