The southern predawn sky has been interesting to watch over the last several weeks; each morning, everything in the southern sky has moved slightly towards the west – except Mars. Mars continues its retrograde motion – causing it to move west but at a much slower pace. The distance between Mars and Saturn will continue to grow well into the summer.
Southern predawn sky, Apr. 17, 2018. Credit: Stellarium / Bob Trembley.A thin crescent Moon joins Venus is low in the western sky near sunset for the next couple days.
Venus and the Moon in the western sky shortly after sunset, Apr. 17, 2018. Credit: Stellarium / Bob Trembley.
The Moon
The Moon Apr. 17-23, 2018 2018. Visualizations by Ernie WrightThe Moon is a waxing crescent visible in the western sky at dusk. The Moon will be at first quarter on April 23rd, making it a great observing target this weekend.
The Sun
The Sun has been spot-free for 2 days. There is a coronal hole at the Sun’s south pole, and a large oddly-shaped coronal hole along the equator. There is also a lot of coronal loop activity just north of the equatorial hole. SpaceWeather.com says: “G1-class geomagnetic storms and polar auroras are possible when the solar wind arrives on April 19-20. Sky watchers between 50o and 60o N latitude should also be alert for STEVE, an aurora-like phenomenon which tends to appear in that latitude range during springtime geomagnetic storms.”
The solar wind speed is 294 km/sec, with a density of 3.0 protons/cm3.
The Sun’s chromosphere had a large persistent prominence over the last couple days – see the 4:00 o’clock region in the video below.
You can create your own time-lapse movies of the Sun here: AIA/HMI Browse Data.
You can browse all the SDO images of the Sun from 2010 to the present here: Browse SDO archive.
Asteroids
Upcoming Earth-asteroid encounters:
Note the asteroid highlighted in red at the top of the list below – this one was a surprise to everyone! Asteroid 2018 GE3 flew by the Earth at half the distance to the Moon, only a day after it was discovered! Space.com has an article stating that the asteroid was 3.6 times the size of 1908 Tunguska impactor!
| Asteroid |
Date(UT)
|
Miss Distance
|
Velocity (km/s)
|
Diameter (m)
|
| 2018 GE3 |
2018-Apr-15
|
0.5 LD
|
29.6
|
63
|
| 2018 GC2 |
2018-Apr-17
|
9 LD
|
4.9
|
15
|
| 2018 GP4 |
2018-Apr-17
|
11.4 LD
|
9.3
|
18
|
| 2018 GK4 |
2018-Apr-17
|
5.9 LD
|
10.8
|
20
|
| 2018 GS3 |
2018-Apr-20
|
8.5 LD
|
19.8
|
22
|
| 2016 JP |
2018-Apr-20
|
12 LD
|
12.7
|
214
|
| 2018 GR1 |
2018-Apr-21
|
18.2 LD
|
16.3
|
52
|
| 2018 GG4 |
2018-Apr-23
|
9.8 LD
|
14.9
|
19
|
| 2012 XL16 |
2018-Apr-23
|
15.8 LD
|
6.1
|
28
|
| 2018 GH |
2018-Apr-25
|
14.6 LD
|
10.7
|
89
|
| 2018 GB2 |
2018-Apr-27
|
17.2 LD
|
14.6
|
94
|
| 2013 US3 |
2018-Apr-29
|
10.1 LD
|
7.7
|
214
|
| 2018 GO4 |
2018-Apr-29
|
11.8 LD
|
8.6
|
45
|
| 2018 GY1 |
2018-Apr-29
|
13.2 LD
|
16.7
|
135
|
| 2018 FV4 |
2018-Apr-29
|
17.7 LD
|
6.5
|
58
|
| 2002 JR100 |
2018-Apr-29
|
10.8 LD
|
7.7
|
49
|
| 1999 FN19 |
2018-May-07
|
9.7 LD
|
5.7
|
118
|
| 2016 JQ5 |
2018-May-08
|
6.3 LD
|
10.4
|
9
|
| 388945 |
2018-May-09
|
6.5 LD
|
9
|
295
|
| 2018 GR2 |
2018-May-11
|
13.4 LD
|
9.8
|
109
|
| 1999 LK1 |
2018-May-15
|
13.3 LD
|
10
|
141
|
| 2018 GL1 |
2018-May-18
|
14.3 LD
|
5.2
|
66
|
| 68347 |
2018-May-29
|
9.5 LD
|
13.3
|
389
|
| 2013 LE7 |
2018-May-31
|
17.8 LD
|
1.7
|
12
|
| 2018 EJ4 |
2018-Jun-10
|
5.6 LD
|
6.2
|
195
|
| 2015 DP155 |
2018-Jun-11
|
9 LD
|
4.4
|
170
|
Notes: LD means “Lunar Distance.” 1 LD = 384,401 km, the distance between Earth and the Moon. Table from SpaceWeather.com
Near-Earth objects discovered this month: 81, this year: 568, all time: 18119. As of April 17, 2018 there are 1907 known potentially hazardous asteroids.
Meteor Showers
The Lyrids Meteor shower runs from April 16-25, peaking April 21-22. Best viewing time is after midnight. Meteors will appear to originate from the area shown in the image below.
Lyrids Meteor Shower Radiant. Credit: StellariumFireballs
On Apr 16, 2018, the NASA All Sky Fireball Network reported 6 fireballs. That number will likely increase with the onset of the Lyrids meteor shower.
In this diagram of the inner solar system, all of the fireball orbits intersect at a single point–Earth.The Solar System
This is the position of the planets in the solar system:
Position of the planets in the inner solar system, Apr. 17, 2018. Credit: NASA Eyes on the Solar System / Bob Trembley.
Position of the planets in the solar system, Apr. 17, 2018 – alternate view. Credit: NASA Eyes on the Solar System / Bob Trembley.I was playing with NASA’s Eyes on the Solar System while writing this post, and turned on constellations for the first time. It’s pretty cool to be able to point to the constellation Sagittarius and say that the New Horizons probe is there.
Position of the New Horizons spacecraft in Sagittarius, with constellations shown. Credit: NASA Eyes on the Solar System / Bob Trembley.Continuing to play, I ended up at Neptune’s tiny moon Nereid. Nereid has a highly elliptical orbit, and takes 360 (Earth) days to complete one orbit of Neptune. I wondered how Neptune would look from Nereid at farthest and closest approaches:
Apps used for this post:
Stellarium: a free open source planetarium app for PC/MAC/Linux. It’s a great tool for planning observing sessions.
NASA Eyes on the Solar System: an immersive 3D solar system and space mission simulator – free for the PC /MAC. I maintain the unofficial NASA Eyes Facebook page.
